Crystals

15 pages, 5258 KiB

Open AccessArticle

Supramolecular Assemblies in Pb(II) Complexes with Hydrazido-Based Ligands

by Ghodrat Mahmoudi, Saikat Kumar Seth, Fedor I. Zubkov, Elena López-Torres, Alessia Bacchi, Vladimir Stilinović and Antonio Frontera

Crystals 2019, 9(6), 323; https://doi.org/10.3390/cryst9060323 - 25 Jun 2019

Cited by 15 | Viewed by 4520

Abstract

Herein, we describe the synthesis and single crystal X-ray diffraction characterization of several Pb(II) complexes using Schiff base hydrazido-based ligands and different counterions (NO₃⁻, I⁻ and ClO₄). In the three complexes reported in this work, the lead(II) [...] Read more.

Herein, we describe the synthesis and single crystal X-ray diffraction characterization of several Pb(II) complexes using Schiff base hydrazido-based ligands and different counterions (NO₃⁻, I⁻ and ClO₄). In the three complexes reported in this work, the lead(II) metal exhibits a high coordination number (n > 8) and thus it is apparently not involved in tetrel bonding interactions. Moreover, the aromatic ligands participate in noncovalent interactions that play an important role in the formation of several supramolecular assemblies in the solid state of the three Pb(II) complexes. These assemblies have been analyzed by means of Hirshfeld surface analysis and DFT calculations. Full article

(This article belongs to the Special Issue Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds)

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11 pages, 1461 KiB

Open AccessArticle

Field-Independent Features in the Magnetization and Specific Heat of Sm₃Co₄Ge₁₃

by Harikrishnan S. Nair, K. Ramesh Kumar, Baidyanath Sahu, Sindisiwe P. Xhakaza, Pramita Mishra, Debkanta Samal, Sarit K. Ghosh, Biju R. Sekhar and André M. Strydom

Crystals 2019, 9(6), 322; https://doi.org/10.3390/cryst9060322 - 25 Jun 2019

Cited by 2 | Viewed by 3587

Abstract

The cubic intermetallic compound Sm

_{3}

Co

_{4}

Ge

_{13}

(space group

P m \bar{3} n

) possesses a cage-like structure composed of Ge and displays an antiferromagnetic transition at

T_{N} \approx

6 K in magnetization,

M (T)

, [...] Read more.

The cubic intermetallic compound Sm

_{3}

Co

_{4}

Ge

_{13}

(space group

P m \bar{3} n

) possesses a cage-like structure composed of Ge and displays an antiferromagnetic transition at

T_{N} \approx

6 K in magnetization,

M (T)

, specific heat,

C_{p} (T)

and in thermal conductivity,

κ (T)

. The magnetic transition at

T_{N}

is observed to be robust against applied magnetic fields up to 9 T. From the analysis of specific heat, a Sommerfeld coefficient

γ

= 80(2) mJ/mol-Sm K

^{2}

is estimated. The magnetic entropy released at

T_{N}

is estimated as lower than that of a doublet, R ln(2). A positive Seebeck coefficient is observed for the thermopower,

S (T)

. Photoemission spectroscopy reveals distinct electronic character of the near-

E_{F}

valence band states arising out of Co(

3 d

)-Sm(

4 f

) hybridization and Sm(

4 f

) electron correlation. The unusual field-independent features in magnetization, specific heat and electrical transport is an indication of the significant correlation between f and d wave functions. Full article

(This article belongs to the Special Issue Magnetic Field-induced Phase Transition)

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14 pages, 2318 KiB

Open AccessArticle

Ice Crystal Coarsening in Ice Cream during Cooling: A Comparison of Theory and Experiment

by Jingyi Mo, Robert D. Groot, Graham McCartney, Enyu Guo, Julian Bent, Gerard van Dalen, Peter Schuetz, Peter Rockett and Peter D. Lee

Crystals 2019, 9(6), 321; https://doi.org/10.3390/cryst9060321 - 25 Jun 2019

Cited by 12 | Viewed by 5804

Abstract

Ice cream is a complex multi-phase structure and its perceived quality is closely related to the small size of ice crystals in the product. Understanding the quantitative coarsening behaviour of ice crystals will help manufacturers optimise ice cream formulations and processing. Using synchrotron [...] Read more.

Ice cream is a complex multi-phase structure and its perceived quality is closely related to the small size of ice crystals in the product. Understanding the quantitative coarsening behaviour of ice crystals will help manufacturers optimise ice cream formulations and processing. Using synchrotron X-ray tomography, we measured the time-dependent coarsening (Ostwald ripening) of ice crystals in ice cream during cooling at 0.05 °C/min. The results show ice crystal coarsening is highly temperature dependent, being rapid from ca. −6 to −12 °C but significantly slower at lower temperatures. We developed a numerical model, based on established coarsening theory, to calculate the relationship between crystal diameter, cooling rate and the weight fraction of sucrose in solution. The ice crystal diameters predicted by the model are found to agree well with the measured values if matrix diffusion is assumed to be slowed by a factor of 1.2 due to the presence of stabilizers or high molecular weight sugars in the ice cream formulation. Full article

(This article belongs to the Special Issue Ice Crystals)

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11 pages, 2899 KiB

Open AccessArticle

Simulation-Based Development of a New Cylindrical-Cavity Microwave-Plasma Reactor for Diamond-Film Synthesis

by Qijun Wang, Gai Wu, Sheng Liu, Zhiyin Gan, Bo Yang and Junheng Pan

Crystals 2019, 9(6), 320; https://doi.org/10.3390/cryst9060320 - 24 Jun 2019

Cited by 17 | Viewed by 7102

Abstract

A 2.45 GHz microwave-plasma chemical-vapor deposition (MPCVD) reactor was designed and built in-house by collaborating with Guangdong TrueOne Semiconductor Technology Co., Ltd. A cylindrical cavity was designed as the deposition chamber and a circumferential coaxial-mode transformer located at the top of the cavity [...] Read more.

A 2.45 GHz microwave-plasma chemical-vapor deposition (MPCVD) reactor was designed and built in-house by collaborating with Guangdong TrueOne Semiconductor Technology Co., Ltd. A cylindrical cavity was designed as the deposition chamber and a circumferential coaxial-mode transformer located at the top of the cavity was adopted as the antenna. Two quartz-ring windows that were placed far away from the plasma and cooled by water-cooling cavity walls were used to affix the antenna to the cavity and act as a vacuum seal for the reactor, respectively. This design improved the sealing and protected the quartz windows. In addition, a numerical simulation was proposed to predict the electric-field and plasma-density distributions in the cavity. Based on the simulation results, a microwave-plasma reactor with TM₀₂₁ mode was built. The leak rate of this new reactor was tested to be as low as 1 × 10⁻⁸ Pa·m³·s⁻¹, and the maximal microwave power was as high as 10 kW. Then, single-crystal diamond films were grown with the morphology and crystalline quality characterized by an optical microscope, atomic force microscope (AFM), Raman spectrometer, photoluminescence (PL) spectrometer, and high-resolution X-ray diffractometer. It was shown that the newly developed MPCVD reactor can produce diamond films with high quality and purity. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Diamond Crystals)

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10 pages, 1230 KiB

Open AccessArticle

Extended Assemblies of Ru(bpy)(CO)₂X₂ (X = Cl, Br, I) Molecules Linked by 1,4-Diiodotetrafluoro-Benzene (DITFB) Halogen Bond Donors

by Xin Ding, Matti Tuikka, Kari Rissanen and Matti Haukka

Crystals 2019, 9(6), 319; https://doi.org/10.3390/cryst9060319 - 24 Jun 2019

Cited by 9 | Viewed by 4013

Abstract

The ruthenium carbonyl compounds, Ru(bpy)(CO)₂X₂ (X = Cl, Br or I) act as neutral halogen bond (XB) acceptors when co-crystallized with 1,4-diiodotetrafluoro-benzene (DITFB). The halogen bonding strength of the Ru-X⋅⋅⋅I halogen bonds follow the nucleophilic character of the halido ligand. [...] Read more.

The ruthenium carbonyl compounds, Ru(bpy)(CO)₂X₂ (X = Cl, Br or I) act as neutral halogen bond (XB) acceptors when co-crystallized with 1,4-diiodotetrafluoro-benzene (DITFB). The halogen bonding strength of the Ru-X⋅⋅⋅I halogen bonds follow the nucleophilic character of the halido ligand. The strongest halogen bond occurs between the chlorido ligand and the iodide atoms of the DITFB. All three halogen bonded complexes form polymeric assemblies in the solid state. In Ru(bpy)(CO)₂Cl₂⋅DITFB (1) and in Ru(bpy)(CO)₂Br₂⋅DITFB (2) both halido ligands are halogen bonded to only one DITFB donor. In Ru(bpy)(CO)₂I₂⋅DITFB (3) only one of the halido ligands is involved in halogen bonding acting as ditopic center for two DITFB donors. The polymeric structures of 1 and 2 are isomorphic wave-like single chain systems, while the iodine complexes form pairs of linear chains attached together with weak F⋅⋅⋅O≡C interactions between the closest neighbors. The stronger polarization of the iodide ligand compared to the Cl or Br ligands favors nearly linear C-I⋅⋅⋅I angles between the XB donor and the metal complex supporting the linear arrangement of the halogen bonded chain. Full article

(This article belongs to the Special Issue Halogen-Bonded Cocrystals)

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8 pages, 3050 KiB

Open AccessArticle

Effects of Sm₂O₃ and V₂O₅ Film Stacking on Switching Behaviors of Resistive Random Access Memories

by Jian-Yang Lin, Kuang-Yao Wu and Kai-Huang Chen

Crystals 2019, 9(6), 318; https://doi.org/10.3390/cryst9060318 - 19 Jun 2019

Cited by 1 | Viewed by 3589

Abstract

In this work, the resistive switching characteristics of resistive random access memories (RRAMs) containing Sm₂O₃ and V₂O₅ films were investigated. All the RRAM structures made in this work showed stable resistive switching behavior. The High-Resistance State and [...] Read more.

In this work, the resistive switching characteristics of resistive random access memories (RRAMs) containing Sm₂O₃ and V₂O₅ films were investigated. All the RRAM structures made in this work showed stable resistive switching behavior. The High-Resistance State and Low-Resistance State of Resistive memory (R_HRS/R_LRS) ratio of the RRAM device containing a V₂O₅/Sm₂O₃ bilayer is one order of magnitude higher than that of the devices containing a single layer of V₂O₅ or Sm₂O₃. We also found that the stacking sequence of the Sm₂O₃ and V₂O₅ films in the bilayer structure can affect the switching features of the RRAM, causing them to exhibit both bipolar resistive switching (BRS) behavior and self-compliance behavior. The current conduction mechanisms of RRAM devices with different film structures were also discussed. Full article

(This article belongs to the Special Issue Selected Papers from Taiwan Association for Academic Innovation, TAAI 2019)

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10 pages, 1705 KiB

Open AccessArticle

High-Density Well-Aligned Dislocations Introduced by Plastic Deformation in Bi_1−xSb_x Topological Insulator Single Crystals

by Yuki Tokumoto, Riku Fujiwara and Keiichi Edagawa

Crystals 2019, 9(6), 317; https://doi.org/10.3390/cryst9060317 - 19 Jun 2019

Cited by 3 | Viewed by 2754

Abstract

Topological insulators (TIs) have a bulk bandgap and gapless edge or surface states that host helically spin-polarized Dirac fermions. Theoretically, it has been predicted that gapless states could also be formed along dislocations in TIs. Recently, conductivity measurements on plastically deformed bismuth antimony [...] Read more.

Topological insulators (TIs) have a bulk bandgap and gapless edge or surface states that host helically spin-polarized Dirac fermions. Theoretically, it has been predicted that gapless states could also be formed along dislocations in TIs. Recently, conductivity measurements on plastically deformed bismuth antimony (Bi_1−xSb_x) TIs have revealed excess conductivity owing to dislocation conduction. For further application of them, fundamental study on dislocations in TIs is indispensable. Dislocations controlled based on fundamental studies could potentially be useful not only for experimental investigations of the dislocation properties but also for diverse device applications. In the present study, Bi_1−xSb_x TI single crystals were fabricated by a zone-melting method. The crystals were plastically deformed at room temperature. The resultant dislocations were observed by transmission electron microscopy (TEM). It was found that high-density dislocations with the Burgers vector satisfying the condition for the formation of gapless states were successfully introduced. The dislocations were mostly of edge type with lengths on the order of more than a few micrometers. Full article

(This article belongs to the Section Crystal Engineering)

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8 pages, 1385 KiB

Open AccessArticle

Structural Insights into the Two-Step Spin-Crossover Compound Fe(3,4-dimethyl-pyridine)₂[Ag(CN)₂]₂

by José Alberto Rodríguez-Velamazán, Kosuke Kitase, Elías Palacios, Miguel Castro, Ángel Fernández-Blanco, Ramón Burriel and Takafumi Kitazawa

Crystals 2019, 9(6), 316; https://doi.org/10.3390/cryst9060316 - 19 Jun 2019

Cited by 4 | Viewed by 3787

Abstract

The crystal structure of the polymeric spin crossover compound Fe(3,4-dimethyl-pyridine)₂[Ag(CN)₂]₂ has been solved and its temperature dependence followed by means of single-crystal and powder X-ray diffraction. This compound presents a two-step spin transition with relatively abrupt steps centred [...] Read more.

The crystal structure of the polymeric spin crossover compound Fe(3,4-dimethyl-pyridine)₂[Ag(CN)₂]₂ has been solved and its temperature dependence followed by means of single-crystal and powder X-ray diffraction. This compound presents a two-step spin transition with relatively abrupt steps centred at ca. 170 K and 145 K and a plateau at around 155 K. The origin of the two-step transition is discussed in light of these structural studies. The observations are compatible with a mostly disordered state between the two steps, consisting of mixing of high-spin and low-spin species, while weak substructure reflections in the mixed phase could indicate some degree of long-range order of the high-spin and low-spin sites. Full article

(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)

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11 pages, 1486 KiB

Open AccessArticle

High-Responsivity Photovoltaic Photodetectors Based on MoTe₂/MoSe₂ van der Waals Heterojunctions

by Hao Luo, Bolun Wang, Enze Wang, Xuewen Wang, Yufei Sun and Kai Liu

Crystals 2019, 9(6), 315; https://doi.org/10.3390/cryst9060315 - 19 Jun 2019

Cited by 27 | Viewed by 6036

Abstract

Van der Waals heterojunctions based on transition metal dichalcogenides (TMDs) show promising potential in optoelectronic devices, due to the ultrafast separation of photoexcited carriers and efficient generation of the photocurrent. Herein, this study demonstrated a high-responsivity photovoltaic photodetector based on a MoTe₂ [...] Read more.

Van der Waals heterojunctions based on transition metal dichalcogenides (TMDs) show promising potential in optoelectronic devices, due to the ultrafast separation of photoexcited carriers and efficient generation of the photocurrent. Herein, this study demonstrated a high-responsivity photovoltaic photodetector based on a MoTe₂/MoSe₂ type-II heterojunction. Due to the interlayer built-in potential, the MoTe₂/MoSe₂ heterojunction shows obvious photovoltaic behavior and its photoresponse can be tuned by the gate voltage due to the ultrathin thickness of the heterojunction. This self-powered photovoltaic photodetector exhibits an excellent responsivity of 1.5 A W⁻¹, larger than previously reported TMDs-based photovoltaic photodetectors. Due to the high-efficiency separation of electron-hole pairs and ultrafast charge transfer, the light-induced on/off ratio of current switching is larger than 10⁴ at zero bias, and the dark current is extremely low (~10⁻¹³ A). These MoTe₂/MoSe₂ type-II heterojunctions are expected to provide more opportunities for future nanoscale optoelectronic devices. Full article

(This article belongs to the Special Issue Inorganic Layered Crystals: From Fundamentals to Materials Performance)

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8 pages, 1508 KiB

Open AccessArticle

Electro-Optical Switching of Dual-Frequency Nematic Liquid Crystals: Regimes of Thin and Thick Cells

by Olha Melnyk, Yuriy Garbovskiy, Dario Bueno-Baques and Anatoliy Glushchenko

Crystals 2019, 9(6), 314; https://doi.org/10.3390/cryst9060314 - 18 Jun 2019

Cited by 22 | Viewed by 4913

Abstract

Conventional display applications of liquid crystals utilize thin layers of mesogenic materials, typically less than 10 µm. However, emerging non-display applications will require thicker, i.e., greater than 100 µm, layers of liquid crystals. Although electro-optical performance of relatively thin liquid crystal cells is [...] Read more.

Conventional display applications of liquid crystals utilize thin layers of mesogenic materials, typically less than 10 µm. However, emerging non-display applications will require thicker, i.e., greater than 100 µm, layers of liquid crystals. Although electro-optical performance of relatively thin liquid crystal cells is well-documented, little is known about the properties of thicker liquid crystal layers. In this paper, the electro-optical response of dual-frequency nematic liquid crystals is studied using a broad range (2–200 µm) of the cell thickness. Two regimes of electro-optical switching of dual-frequency nematics are observed and analyzed. Full article

(This article belongs to the Special Issue Advances in Nematic Liquid Crystals)

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10 pages, 2809 KiB

Open AccessArticle

Topological Phase Transition in a One-Dimensional Elastic String System

by Ya-Wen Tsai, Yao-Ting Wang, Pi-Gang Luan and Ta-Jen Yen

Crystals 2019, 9(6), 313; https://doi.org/10.3390/cryst9060313 - 18 Jun 2019

Cited by 7 | Viewed by 4106

Abstract

We show that topological interface mode can emerge in a one-dimensional elastic string system which consists of two periodic strings with different band topologies. To verify their topological features, Zak-phase of each band is calculated and reveals the condition of topological phase transition [...] Read more.

We show that topological interface mode can emerge in a one-dimensional elastic string system which consists of two periodic strings with different band topologies. To verify their topological features, Zak-phase of each band is calculated and reveals the condition of topological phase transition accordingly. Apart from that, the transmittance spectrum illustrates that topological interface mode arises when two topologically distinct structures are connected. The vibration profile further exhibits the non-trivial interface mode in the domain wall between two periodic string composites. Full article

(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)

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12 pages, 4235 KiB

Open AccessArticle

Effect of Local Recrystallized Grains on the Low Cycle Fatigue Behavior of a Nickel-Based Single Crystal Superalloy

by Xianfeng Ma, Jishen Jiang, Wenjie Zhang, Hui-ji Shi and Jialin Gu

Crystals 2019, 9(6), 312; https://doi.org/10.3390/cryst9060312 - 18 Jun 2019

Cited by 18 | Viewed by 4894

Abstract

This paper aims to understand the effect of local recrystallization (RX) on the low cycle fatigue fracture of a turbine-blade single crystal nickel-based superalloy. The fatigue life of the single crystal superalloy was evidently decreased by local recrystallization. In single crystal specimens, casting [...] Read more.

This paper aims to understand the effect of local recrystallization (RX) on the low cycle fatigue fracture of a turbine-blade single crystal nickel-based superalloy. The fatigue life of the single crystal superalloy was evidently decreased by local recrystallization. In single crystal specimens, casting porosity is the preferential fatigue crack initiation site, which is followed by crystallographic crack propagation along one or several octahedral slip planes. For all RX specimens, fatigue cracks preferred to initiate from local recrystallized grains and propagated through the recrystallized grains in a transgranular manner, followed by crystallographic crack propagation in the substrate single crystal superalloy. Moreover, fatigue tests indicated that locally recrystallized specimens exhibited temperature dependent fracture modes, i.e., transgranular cracking dominated at 550 °C, whereas intergranular cracking was preferred at 850 °C. Evident oxidation of fracture surfaces and strength degradation of grain boundaries at 850 °C was evidenced by scanning electronic microscopic observations. The present study emphasized the need to evaluate the effect of recrystallization according to the working conditions of turbine components, i.e., the local temperature. Full article

(This article belongs to the Special Issue Fundamentals of Superalloys)

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9 pages, 3049 KiB

Open AccessArticle

Liquid Crystal Based Head-Up Display with Electrically Controlled Contrast Ratio

by Yueda Liu, Yan Li, Quanming Chen, Sida Li and Yikai Su

Crystals 2019, 9(6), 311; https://doi.org/10.3390/cryst9060311 - 18 Jun 2019

Cited by 1 | Viewed by 4184

Abstract

With the growing demand for driving safety and convenience, Head-Up Displays (HUDs) have gained more and more interest in recent years. In this paper, we propose a HUD system with the ability to adjust the relative brightness of ambient light and virtual information [...] Read more.

With the growing demand for driving safety and convenience, Head-Up Displays (HUDs) have gained more and more interest in recent years. In this paper, we propose a HUD system with the ability to adjust the relative brightness of ambient light and virtual information light. The key components of the system include a cholesteric liquid crystal (CLC) film, a geometric phase (GP) liquid crystal lens, and a circular polarizer. By controlling the voltage applied to the GP lens, the contrast ratio of the virtual information light to ambient light could be continuously tuned, so that good visibility could always be obtained under different driving conditions. Full article

(This article belongs to the Special Issue Advances in Cholesteric Liquid Crystals)

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7 pages, 1706 KiB

Open AccessArticle

Effect of Nitrogen Flow in Hydrogen/Nitrogen Plasma Annealing on Aluminum-Doped Zinc Oxide/Tin-Doped Indium Oxide Bilayer Films Applied in Low Emissivity Glass

by Shang-Chou Chang and Huang-Tian Chan

Crystals 2019, 9(6), 310; https://doi.org/10.3390/cryst9060310 - 17 Jun 2019

Cited by 7 | Viewed by 3693

Abstract

Low emissivity glass (low-e glass), which is often used in energy-saving buildings, has high thermal resistance and visible light transmission. Heavily doped wide band gap semiconductors like aluminum-doped zinc oxide (AZO) and tin-doped indium oxide (ITO) have these properties, especially after certain treatment. [...] Read more.

Low emissivity glass (low-e glass), which is often used in energy-saving buildings, has high thermal resistance and visible light transmission. Heavily doped wide band gap semiconductors like aluminum-doped zinc oxide (AZO) and tin-doped indium oxide (ITO) have these properties, especially after certain treatment. In our experiments, in-line sputtered AZO and ITO bilayer (AZO/ITO) films on glass substrates were prepared first. The deposition of AZO/ITO films was following by annealing in hydrogen/nitrogen (H₂/N₂) plasma with different N₂ flows. The structure and optical and electrical properties of AZO/ITO films were surveyed. Experiment results indicated that N₂ flow in H₂/N₂ plasma annealing of AZO/ITO films slightly modified the structure and electrical properties of AZO/ITO films. The X-ray diffraction peak corresponding to zinc oxide (002) crystal plane slightly shifted to a higher angle and its full width at half maximum decreased as the N₂ flow increased. The electrical resistivity and the emissivity reduced for the plasma annealed AZO/ITO films when the N₂ flow was raised. The optimum H₂/N₂ gas flow was 100/100 for plasma annealed AZO/ITO films in this work for low emissivity application. The emissivity and average visible transmittance for H₂/N₂ = 100/100 plasma annealed AZO/ITO were 0.07 and 80%, respectively, lying in the range of commercially used low emissivity glass. Full article

(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)

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9 pages, 2799 KiB

Open AccessCommunication

Design of Ionic Liquid Crystals Forming Normal-Type Bicontinuous Cubic Phases with a 3D Continuous Ion Conductive Pathway

by Takahiro Ichikawa, Yui Sasaki, Tsubasa Kobayashi, Hikaru Oshiro, Ayaka Ono and Hiroyuki Ohno

Crystals 2019, 9(6), 309; https://doi.org/10.3390/cryst9060309 - 14 Jun 2019

Cited by 5 | Viewed by 4846

Abstract

We have prepared a series of pyridinium-based gemini amphiphiles. They exhibit thermotropic liquid–crystalline behavior depending on their alkyl chain lengths and anion species. By adjusting the alkyl chain lengths and selecting suitable anions, we have obtained an ionic amphiphile that exhibits a normal-type [...] Read more.

We have prepared a series of pyridinium-based gemini amphiphiles. They exhibit thermotropic liquid–crystalline behavior depending on their alkyl chain lengths and anion species. By adjusting the alkyl chain lengths and selecting suitable anions, we have obtained an ionic amphiphile that exhibits a normal-type bicontinuous cubic phase from 38 °C to 12 °C on cooling from an isotropic phase. In the bicontinuous cubic liquid–crystalline assembly, the pyridinium-based ionic parts align along a gyroid minimal surface forming a 3D continuous ionic domain while their ionophobic alkyl chains form 3D branched nanochannel networks. This ionic compound can form homogeneous mixtures with a lithium salt and the resultant mixtures keep the ability to form normal-type bicontinuous cubic phases. Ion conduction measurements have been performed for the mixtures on cooling. It has been revealed that the formation of the 3D branched ionophobic nanochannels does not disturb the ion conduction behavior in the ionic domain while it results in the conversion of the state of the mixtures from fluidic liquids to quasi-solids, namely highly viscous liquid crystals. Although the ionic conductivity of the mixtures is in the order of 10^–7 S cm^–1 at 40 °C, which is far lower than the values for practical use, the present material design has a potential to pave the way for developing advanced solid electrolytes consisting of two task-specific nanosegregated domains: One is an ionic liquid nano-domain with a 3D continuity for high ionic conductivity and the other is ionophobic nanochannel network domains for high mechanical strength. Full article

(This article belongs to the Special Issue Liquid-Crystalline Ion Conductors)

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10 pages, 2380 KiB

Open AccessArticle

Indium-Incorporation with In_xGa_1-xN Layers on GaN-Microdisks by Plasma-Assisted Molecular Beam Epitaxy

by ChengDa Tsai, Ikai Lo, YingChieh Wang, ChenChi Yang, HongYi Yang, HueiJyun Shih, HuiChun Huang, Mitch M. C. Chou, Louie Huang and Binson Tseng

Crystals 2019, 9(6), 308; https://doi.org/10.3390/cryst9060308 - 14 Jun 2019

Cited by 4 | Viewed by 3373

Abstract

Indium-incorporation with In_xGa_1-xN layers on GaN-microdisks has been systematically studied against growth parameters by plasma-assisted molecular beam epitaxy. The indium content (x) of In_xGa_1-xN layer increased to 44.2% with an In/(In + Ga) flux ratio [...] Read more.

Indium-incorporation with In_xGa_1-xN layers on GaN-microdisks has been systematically studied against growth parameters by plasma-assisted molecular beam epitaxy. The indium content (x) of In_xGa_1-xN layer increased to 44.2% with an In/(In + Ga) flux ratio of up to 0.6 for a growth temperature of 620 °C, and quickly dropped with a flux ratio of 0.8. At a fixed In/(In + Ga) flux ratio of 0.6, we found that the indium content decreased as the growth temperature increased from 600 °C to 720 °C and dropped to zero at 780 °C. By adjusting the growth parameters, we demonstrated an appropriate In_xGa_1-xN layer as a buffer to grow high-indium-content In_xGa_1-xN/GaN microdisk quantum wells for micro-LED applications. Full article

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10 pages, 2954 KiB

Open AccessArticle

Morphology Investigation on Cyclopentane Hydrate Formation/Dissociation in a Sub-Millimeter-Sized Capillary

by Qiang Sun, Mei Du, Xingxun Li, Xuqiang Guo and Lanying Yang

Crystals 2019, 9(6), 307; https://doi.org/10.3390/cryst9060307 - 14 Jun 2019

Cited by 4 | Viewed by 3522

Abstract

The formation, dissociation, and reformation of cyclopentane (CP) hydrate in a sub-millimeter-sized capillary were conducted in this work, and the morphology of CP hydrate was obtained during above processes, respectively. The influences of the supercooling degree, i.e., the hydrate formation driving force, on [...] Read more.

The formation, dissociation, and reformation of cyclopentane (CP) hydrate in a sub-millimeter-sized capillary were conducted in this work, and the morphology of CP hydrate was obtained during above processes, respectively. The influences of the supercooling degree, i.e., the hydrate formation driving force, on CP hydrate crystals’ aspect and growth rate were also investigated. The results demonstrate that CP forms hydrate with the water melting from ice at the interface between the CP and melting water at a temperature slightly above 273.15 K. With the action of hydrate memory effect, the CP hydrate in the capillary starts forming at the CP-water interface or CP–water–capillary three-phase junction and grows around the CP–water interface. The appearance and growth rate of CP hydrate are greatly influenced by the supercooling degree. It indicates that CP hydrate has a high aggregation degree and good regularity at a high supercooling degree (or a low formation temperature). The growth rate of CP hydrate crystals greatly increases with the supercooling degree. Consequently, the temperature has a significant influence on the formation of CP hydrate in the capillary. That means the features of CP hydrate crystals in a quiescent system could be determined and controlled by the temperature setting. Full article

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14 pages, 8166 KiB

Open AccessArticle

Research on Optical Properties of Tapered Optical Fibers with Liquid Crystal Cladding Doped with Gold Nanoparticles

by Joanna E. Moś, Joanna Korec, Karol A. Stasiewicz, Bartłomiej Jankiewicz, Bartosz Bartosewicz and Leszek R. Jaroszewicz

Crystals 2019, 9(6), 306; https://doi.org/10.3390/cryst9060306 - 14 Jun 2019

Cited by 7 | Viewed by 5206

Abstract

This paper presents results obtained for biconical tapered fibers surrounded/immersed in liquid crystal mixtures. The phenomenon of light propagating in the whole structure of a tapered fiber allows the creation of a sensor where the tapered region represents a core whereas the surrounding [...] Read more.

This paper presents results obtained for biconical tapered fibers surrounded/immersed in liquid crystal mixtures. The phenomenon of light propagating in the whole structure of a tapered fiber allows the creation of a sensor where the tapered region represents a core whereas the surrounding medium becomes a cladding. Created devices are very sensitive to changing refractive index value in a surrounding medium caused by modifying external environmental parameters like temperature, electric or magnetic field. For this reason, the properties of materials used as cladding should be easily modified. In this investigation, cells have been filled with two different nematic liquid crystals given as 1550* and 6CHBT (4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate), as well as with the same mixtures doped with 0.1 wt% gold nanoparticles (AuNPs). Optical spectrum analysis for the wavelength range of 550–1150 nm and time-courses performed for a wavelength of 846 nm at the temperature range of T = 25–40 °C were provided. For all investigations, a steering voltage in the range of 0–200 V which allows establishing the dopes’ influence on transmitted power and time response at different temperatures was applied. Full article

(This article belongs to the Special Issue Liquid Crystal Optical Device)

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11 pages, 3370 KiB

Open AccessArticle

Advanced AlGaAs/GaAs Heterostructures Grown by MOVPE

by Maxim A. Ladugin, Irina V. Yarotskaya, Timur A. Bagaev, Konstantin Yu. Telegin, Andrey Yu. Andreev, Ivan I. Zasavitskii, Anatoliy A. Padalitsa and Alexander A. Marmalyuk

Crystals 2019, 9(6), 305; https://doi.org/10.3390/cryst9060305 - 14 Jun 2019

Cited by 16 | Viewed by 5552

Abstract

AlGaAs/GaAs heterostructures are the base of many semiconductor devices. The fabrication of new types of devices demands heterostructures with special features, such as large total thickness (~20 μm), ultrathin layers (~1 nm), high repeatability (up to 1000 periods) and uniformity, for which a [...] Read more.

AlGaAs/GaAs heterostructures are the base of many semiconductor devices. The fabrication of new types of devices demands heterostructures with special features, such as large total thickness (~20 μm), ultrathin layers (~1 nm), high repeatability (up to 1000 periods) and uniformity, for which a conventional approach of growing such heterostructures is insufficient and the development of new growth procedures is needed. This article summarizes our work on the metalorganic vapour-phase epitaxy (MOVPE) growth of AlGaAs/GaAs heterostructures for modern infrared devices. The growth approaches presented allow for the improved output characteristics of different emitting devices such as multi active region lasers, epitaxially integrated via highly doped tunnel junctions (emission wavelength λ ~ 1 μm), quantum cascade lasers (λ ~10 μm) and THz laser (λ ~100 μm), based on short-period superlattice with 500–2000 layers. Full article

(This article belongs to the Special Issue MOVPE Growth of Crystalline Film)

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13 pages, 1340 KiB

Open AccessArticle

Effects of Anion Impurities on the Solubility and Nucleation of Borax Decahydrate Crystals in Carbonate-Type Brine

by Jing Chen, Jiaoyu Peng, Xingpeng Wang, Yaping Dong and Wu Li

Crystals 2019, 9(6), 304; https://doi.org/10.3390/cryst9060304 - 13 Jun 2019

Cited by 8 | Viewed by 4219

Abstract

Measurements of the solubility and metastable zone width (MSZW) of borax decahydrate (disodium tetraborate decahydrate) within chloride, sulfate and carbonate solutions were carried out. The MSZW was measured by the conventional polythermal method with turbidity technology. The results showed that the addition of [...] Read more.

Measurements of the solubility and metastable zone width (MSZW) of borax decahydrate (disodium tetraborate decahydrate) within chloride, sulfate and carbonate solutions were carried out. The MSZW was measured by the conventional polythermal method with turbidity technology. The results showed that the addition of impurities decreased solubility. The main factor reducing solubility is the common ion effect, but the salt effect is also significant in the complex system. The addition of impurities broadened the MSZW. The MSZW was wider at first, then decreased with the addition of NaCl, yet the MSZW widened with the addition of Na₂SO₄ within the concentration range studied. This can be explained by adsorption and diffusion. The data of solubility and MSZW were analyzed by applying the Van’t Hoff equation and the classical 3D nucleation theory approach, respectively. By calculating the corresponding parameters, the experimental phenomena are further explained from the perspective of thermodynamics and dynamics. Full article

(This article belongs to the Section Crystal Engineering)

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11 pages, 3383 KiB

Open AccessArticle

Novel Cerium Bisphosphinate Coordination Polymer and Unconventional Metal–Organic Framework

by Jan Rohlíček, Daniel Bůžek, Petr Brázda, Libor Kobera, Jan Hynek, Jiří Brus, Kamil Lang and Jan Demel

Crystals 2019, 9(6), 303; https://doi.org/10.3390/cryst9060303 - 12 Jun 2019

Cited by 8 | Viewed by 4805

Abstract

The first Ce(III)-based coordination polymer ICR-9 (ICR stands for Inorganic Chemistry Řež), with the formula Ce₂(C₈H₁₀P₂O₄)₃, containing ditopic phenylene-1,4-bis(methylphosphinic acid) linker, was synthetized under solvothermal conditions. The crystal structure, solved using [...] Read more.

The first Ce(III)-based coordination polymer ICR-9 (ICR stands for Inorganic Chemistry Řež), with the formula Ce₂(C₈H₁₀P₂O₄)₃, containing ditopic phenylene-1,4-bis(methylphosphinic acid) linker, was synthetized under solvothermal conditions. The crystal structure, solved using electron diffraction tomography (EDT), revealed 2D layers of octahedrally coordinated cerium atoms attached together through O-P-O bridges. The structure is nonporous, however, the modification of synthetic conditions led to unconventional metal–organic framework (or defective amorphous phase) with a specific surface area up to approximately 400 m² g^-1. Full article

(This article belongs to the Special Issue Metal Phosphonates and Phosphinates)

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10 pages, 1870 KiB

Open AccessArticle

A High-Resolution Terahertz Electric Field Sensor Using a Corrugated Liquid Crystal Waveguide

by Lan-Lan Xu, Yi Gong, Ya-Xian Fan and Zhi-Yong Tao

Crystals 2019, 9(6), 302; https://doi.org/10.3390/cryst9060302 - 12 Jun 2019

Cited by 3 | Viewed by 3289

Abstract

Liquid crystals (LCs) can always reflect variable optical properties in a broad terahertz (THz) band under external electric or magnetic fields. Based on the measurements of these varying properties, we can realize electric and magnetic field sensing with very high sensitivity. Here, we [...] Read more.

Liquid crystals (LCs) can always reflect variable optical properties in a broad terahertz (THz) band under external electric or magnetic fields. Based on the measurements of these varying properties, we can realize electric and magnetic field sensing with very high sensitivity. Here, we theoretically and numerically demonstrate a type of electric field sensor in the THz frequency range based on the defect mode arising in a periodically corrugated waveguide with liquid crystals. The Bragg defect structure consisting of periodically corrugated metallic walls and a defect in the middle can provide a narrow transmitted peak with controllable bandwidth, which can be used for external field sensing when it is filled with LCs. The molecular orientation of nematic LCs (E7) is not only very sensitive to the applied DC electric field but also very crucial to the effective refractive index of E7. Changing the effective index can efficiently shift the frequency of the transmitted peak in the THz spectrum. The simulated results show that the sensitivity can reach as high as 9.164 MHz/(V/m) and the smallest resolution is 0.1115 V/m. The proposed sensor and its significant performance could benefit electric field sensing and extend the applications of THz technology. Full article

(This article belongs to the Special Issue Liquid Crystal Optics and Physics: Recent Advances and Prospects)

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18 pages, 3422 KiB

Open AccessArticle

Platonic Relationships in Metal Phosphonate Chemistry: Ionic Metal Phosphonates

by Konstantinos Xanthopoulos, Zafeiria Anagnostou, Sophocles Chalkiadakis, Duane Choquesillo-Lazarte, Gellert Mezei, Jan K. Zaręba, Jerzy Zoń and Konstantinos D. Demadis

Crystals 2019, 9(6), 301; https://doi.org/10.3390/cryst9060301 - 11 Jun 2019

Cited by 11 | Viewed by 5253

Abstract

Phosphonate ligands demonstrate strong affinity for metal ions. However, there are several cases where the phosphonate is found non-coordinated to the metal ion. Such compounds could be characterized as salts, since the interactions involved are ionic and hydrogen bonding. In this paper we [...] Read more.

Phosphonate ligands demonstrate strong affinity for metal ions. However, there are several cases where the phosphonate is found non-coordinated to the metal ion. Such compounds could be characterized as salts, since the interactions involved are ionic and hydrogen bonding. In this paper we explore a number of such examples, using divalent metal ions (Mg²⁺, Ca²⁺, Sr²⁺ and Ni²⁺) and the phosphonic acids: p-aminobenzylphosphonic acid (H₂PABPA), tetramethylenediamine-tetrakis(methylenephosphonic acid) (H₈TDTMP), and 1,2-ethylenediphosphonic acid (H₄EDPA). The compounds isolated and structurally characterized are [Mg(H₂O)₆]·[HPABPA]₂·6H₂O, [Ca(H₂O)₈]·[HPABPA]₂, [Sr(H₂O)₈]·[HPABPA]₂, [Mg(H₂O)₆]·[H₆TDTMP], and [Ni(H₂O)₆]·[H₂EDPA]·H₂O. Also, the coordination polymer {[Ni(4,4’-bpy)(H₂O)₄]·[H₂EDPA]·H₂O}_n was synthesized and characterized, which contains a bridging 4,4’-bipyridine (4,4’-bpy) ligand forming an infinite chain with the Ni²⁺ cations. All these compounds contain the phosphonate anion as the counterion to charge balance the cationic charge originating from the metal cation. Full article

(This article belongs to the Special Issue Metal Phosphonates and Phosphinates)

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13 pages, 2248 KiB

Open AccessArticle

Effect of Rare-Earth Element Oxides on Diamond Crystallization in Mg-Based Systems

by Yuri N. Palyanov, Yuri M. Borzdov, Alexander F. Khokhryakov and Igor N. Kupriyanov

Crystals 2019, 9(6), 300; https://doi.org/10.3390/cryst9060300 - 11 Jun 2019

Cited by 10 | Viewed by 3992

Abstract

Diamond crystallization in Mg-R₂O₃-C systems (R = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) was studied at 7.8 GPa and 1800 °C. It was found that rare-earth oxide additives in an amount of 10 wt % [...] Read more.

Diamond crystallization in Mg-R₂O₃-C systems (R = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) was studied at 7.8 GPa and 1800 °C. It was found that rare-earth oxide additives in an amount of 10 wt % did not significantly affect both the degree of graphite-to-diamond conversion and crystal morphology relative to the Mg-C system. The effect of higher amounts of rare-earth oxide additives on diamond crystallization was studied for a Mg-Sm₂O₃-C system with a Sm₂O₃ content varied from 0 to 50 wt %. It was established that with an increase in the Sm₂O₃ content in the growth system, the degree of graphite-to-diamond conversion decreased from 80% at 10% Sm₂O₃ to 0% at 40% Sm₂O₃. At high Sm₂O₃ contents (40 and 50 wt %), instead of diamond, mass crystallization of metastable graphite was established. The observed changes in the degree of the graphite-to-diamond conversion, the changeover of diamond crystallization to the crystallization of metastable graphite, and the changes in diamond crystal morphology with increasing the Sm₂O₃ content attested the inhibiting effect of rare-earth oxides on diamond crystallization processes in the Mg-Sm-O-C system. The crystallized diamonds were studied by a suite of optical spectroscopy techniques, and the major characteristics of their defect and impurity structures were revealed. For diamond crystals produced with 10 wt % and 20 wt % Sm₂O₃ additives, a specific photoluminescence signal comprising four groups of lines centered at approximately 580, 620, 670, and 725 nm was detected, which was tentatively assigned to emission characteristic of Sm³⁺ ions. Full article

(This article belongs to the Special Issue Diamond Crystals Volume II)

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16 pages, 4061 KiB

Open AccessArticle

Elasticity of Phases in Fe-Al-Ti Superalloys: Impact of Atomic Order and Anti-Phase Boundaries

by Martin Friák, Vilma Buršíková, Naděžda Pizúrová, Jana Pavlů, Yvonna Jirásková, Vojtěch Homola, Ivana Miháliková, Anton Slávik, David Holec, Monika Všianská, Nikola Koutná, Jan Fikar, Dušan Janičkovič, Mojmír Šob and Jörg Neugebauer

Crystals 2019, 9(6), 299; https://doi.org/10.3390/cryst9060299 - 8 Jun 2019

Cited by 10 | Viewed by 4796

Abstract

We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys. Focusing on samples with chemical composition Fe₇₁Al₂₂Ti₇, we use transmission electron microscopy (TEM) to detect their two-phase superalloy nano-structure (consisting of cuboids embedded into [...] Read more.

We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys. Focusing on samples with chemical composition Fe₇₁Al₂₂Ti₇, we use transmission electron microscopy (TEM) to detect their two-phase superalloy nano-structure (consisting of cuboids embedded into a matrix). The chemical composition of both phases, Fe_66.2Al_23.3Ti_10.5 for cuboids and Fe₈₁Al₁₉ (with about 1% or less of Ti) for the matrix, was determined from an Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The phase of cuboids is found to be a rather strongly off-stoichiometric (Fe-rich and Ti-poor) variant of Heusler Fe₂TiAl intermetallic compound with the L2₁ structure. The phase of the matrix is a solid solution of Al atoms in a ferromagnetic body-centered cubic (bcc) Fe. Quantum-mechanical calculations were employed to obtain an insight into elastic properties of the two phases. Three distributions of chemical species were simulated for the phase of cuboids (A2, B2 and L2₁) in order to determine a sublattice preference of the excess Fe atoms. The lowest formation energy was obtained when the excess Fe atoms form a solid solution with the Ti atoms at the Ti-sublattice within the Heusler L2₁ phase (L2₁ variant). Similarly, three configurations of Al atoms in the phase of the matrix with different level of order (A2, B2 and D0₃) were simulated. The computed formation energy is the lowest when all the 1st and 2nd nearest-neighbor Al-Al pairs are eliminated (the D0₃ variant). Next, the elastic tensors of all phases were calculated. The maximum Young’s modulus is found to increase with increasing chemical order. Further we simulated an anti-phase boundary (APB) in the L2₁ phase of cuboids and observed an elastic softening (as another effect of the APB, we also predict a significant increase of the total magnetic moment by 140% when compared with the APB-free material). Finally, to validate these predicted trends, a nano-scale dynamical mechanical analysis (nanoDMA) was used to probe elasticity of phases. Consistent with the prediction, the cuboids were found stiffer. Full article

(This article belongs to the Special Issue Fundamentals of Superalloys)

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14 pages, 766 KiB

Open AccessArticle

Stress Heterogeneity Leading to Void Nucleation within Spherulites for Semi-Crystalline Polymers

by Lucien Laiarinandrasana

Crystals 2019, 9(6), 298; https://doi.org/10.3390/cryst9060298 - 8 Jun 2019

Cited by 5 | Viewed by 3295

Abstract

Linking the microstructure to the mechanical properties is a key feature in the design and assessment of the durability of semi-crystalline polymers. This paper addresses the importance of a particular architecture inside spherulites. The use of the theoretical tools of continuum mechanics has [...] Read more.

Linking the microstructure to the mechanical properties is a key feature in the design and assessment of the durability of semi-crystalline polymers. This paper addresses the importance of a particular architecture inside spherulites. The use of the theoretical tools of continuum mechanics has been combined with experimental observations of the deformation of the microstructure. Microstructural heterogeneities at various scales induced critical regions in the spherulite where voiding has been reported. The local stress state has been investigated using a Finite Element code. A simple Hooke’s law was used for meshes accounting for the alternating crystalline and amorphous lamellae. This allowed a better understanding of the loci of void nucleation in the equatorial region, as well as in the “polar fans”, and were explained by using a criterion based on stress equi-triaxiality. Full article

(This article belongs to the Special Issue Microstructure Evolutions and Mechanical Behavior of Semicrystalline Polymers)

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14 pages, 2771 KiB

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X-ray Structure Refinement and Vibrational Spectroscopy of Metavauxite FeAl₂(PO₄)₂(OH)₂·8H₂O

by Giancarlo Della Ventura, Francesco Capitelli, Giancarlo Capitani, Gennaro Ventruti and Alessandro Monno

Crystals 2019, 9(6), 297; https://doi.org/10.3390/cryst9060297 - 6 Jun 2019

Cited by 2 | Viewed by 3769

Abstract

In this paper, we provide a crystal-chemical investigation of metavauxite, ideally FeAl₂(PO₄)₂(OH)₂·8H₂O, from Llallagua (Bolivia) by using a multi-methodological approach based on EDS microchemical analysis, single crystal X-ray diffraction, and Raman and Fourier [...] Read more.

In this paper, we provide a crystal-chemical investigation of metavauxite, ideally FeAl₂(PO₄)₂(OH)₂·8H₂O, from Llallagua (Bolivia) by using a multi-methodological approach based on EDS microchemical analysis, single crystal X-ray diffraction, and Raman and Fourier transform infrared (FTIR) spectroscopy. Our new diffraction results allowed us to locate all hydrogen atoms from the structure refinements in the monoclinic P2₁/c space group. Metavauxite structure displays a complex framework consisting of a stacking of [Al(PO₄)₃(OH)(H₂O)₂]⁷⁻ layers linked to isolated [Fe(H₂O)₆]²⁺ cationic octahedral complex solely by hydrogen bonding. The hydrogen-bonding scheme was inferred from bond-valence calculations and donor-acceptor distances. Accordingly, strong hydrogen bonds, due to four coordinated H₂O molecules, bridge the [Fe(H₂O)₆]²⁺ units to the Al/P octahedral/tetrahedral layer. The hydroxyl group, coordinated by two Al atoms, contributes to the intra-layer linkage. FTIR and Raman spectra in the high-frequency region (3700–3200 cm⁻¹) are very similar, and show a complex broad band consisting of several overlapping components due to the H₂O molecules connecting the isolated Fe(H₂O)₆ and the adjacent Al/P octahedral/tetrahedral layers. A sharp peak at 3540 cm⁻¹ is assigned to the stretching mode of the OH group. The patterns collected in the low-frequency region are dominated by the stretching and bending modes of the PO₄³⁻ group and the metal-oxygen polyhedra. Full article

(This article belongs to the Special Issue Structural Characterization of Calcium Phosphates by Means of X-ray Diffraction)

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10 pages, 4724 KiB

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Luminescent and Scintillation Properties of CeAlO₃ Crystals and Phase-Separated CeAlO₃/CeAl₁₁O₁₈ Metamaterials

by Oleg Sidletskiy, Pavlo Arhipov, Serhii Tkachenko, Iaroslav Gerasymov, Georgy Trushkovsky, Tetyana Zorenko, Yuriy Zorenko, Pavel Mateychenko, Anna Puzan, Wojciech Gieszczyk and Pawel Bilski

Crystals 2019, 9(6), 296; https://doi.org/10.3390/cryst9060296 - 6 Jun 2019

Cited by 8 | Viewed by 3783

Abstract

This work is dedicated to the growth process and investigation of luminescent and scintillation properties of CeAlO₃ single crystals and CeAlO₃/CeAl₁₁O₁₈ metamaterials under e-beam and α-particles excitation. It has been shown that cathodoluminescence and radioluminescence spectra of [...] Read more.

This work is dedicated to the growth process and investigation of luminescent and scintillation properties of CeAlO₃ single crystals and CeAlO₃/CeAl₁₁O₁₈ metamaterials under e-beam and α-particles excitation. It has been shown that cathodoluminescence and radioluminescence spectra of CeAlO₃ crystals contain two bands, peaking at 440 and 500 nm, and caused by the Ce³⁺ 5d–4f transitions into CeAl₁₁O₁₈ phase, which is present in these crystals as an admixture. Under 270 nm ultraviolet (UV) light excitation, a CeAlO₃ crystal possesses complicated non-exponential luminescence decay, with the average decay time of 16 ns. The light yield of CeAlO₃ crystals under α-particle excitation is about 16% and 12%, in respect to the standard Bi₄Ge₃O₁₂ (BGO) crystal and Y₃Al₅O₁₂:Ce (YAG:Ce) single crystalline film samples, respectively. The CeAlO₃ scintillation decay is quite fast, with the decay time value t_1/e in the 54–56 ns range. Full article

(This article belongs to the Special Issue Crystals, Films and Nanocomposite Scintillators)

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15 pages, 4449 KiB

Open AccessArticle

Comparative Study of Different Crystallization Methods in the Case of Cilostazol Crystal Habit Optimization

by Tímea Tari, Piroska Szabó-Révész and Zoltán Aigner

Crystals 2019, 9(6), 295; https://doi.org/10.3390/cryst9060295 - 5 Jun 2019

Cited by 14 | Viewed by 6128

Abstract

The therapeutic usage of cilostazol is limited owing to its poor aqueous solubility and oral bioavailability. Our aim was to produce cilostazol crystals with small average particle size; besides suitable roundness, narrow particle size distribution and stable polymorphic form to increase its dissolution [...] Read more.

The therapeutic usage of cilostazol is limited owing to its poor aqueous solubility and oral bioavailability. Our aim was to produce cilostazol crystals with small average particle size; besides suitable roundness, narrow particle size distribution and stable polymorphic form to increase its dissolution rate and improve processability. Different conventional crystallization methods with or without sonication were compared with impinging jet crystallization combined with cooling, and the optimization of the various parameters was also implemented. The effects of post-mixing time and temperature difference were studied by means of a full factorial design. The physical properties of powder particles were characterized by, i.a., XRPD, DSC and SEM. The dissolution rate and the contact angle of solid surfaces were also determined to elucidate the relationship between wettability and dissolution. It was observed that impinging jet crystallization combined with cooling is a very effective and reproducible method for reducing the particle size of cilostazol. This method resulted in significantly smaller particle size (d(0.5) = 3–5 μm) and more uniform crystals compared to the original ground material (d(0.5) = 24 μm) or the conventional methods (d(0.5) = 8–14 μm), and it also resulted in a stable polymorphic form and enhanced the dissolution rate. Full article

(This article belongs to the Special Issue Anti-Solvent Crystallization)

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9 pages, 1766 KiB

Open AccessArticle

The Orientation of Strain-Induced Crystallites in Uniaxially-Strained, Thin and Wide Bands Made from Natural Rubber

by Konrad Schneider and Matthias Schwartzkopf

Crystals 2019, 9(6), 294; https://doi.org/10.3390/cryst9060294 - 5 Jun 2019

Cited by 10 | Viewed by 3167

Abstract

Vulcanized natural rubber (unfilled and filled with 20 phr carbon black) is strained. We suppress the macroscopic formation of fiber symmetry by choosing strip-shaped samples ("pure-shear geometry") and investigate the orientation of the resulting crystallites by two-dimensional wide-angle X-ray diffraction (WAXD), additionally rotating [...] Read more.

Vulcanized natural rubber (unfilled and filled with 20 phr carbon black) is strained. We suppress the macroscopic formation of fiber symmetry by choosing strip-shaped samples ("pure-shear geometry") and investigate the orientation of the resulting crystallites by two-dimensional wide-angle X-ray diffraction (WAXD), additionally rotating the sample tape about the straining direction. Indications of a directed reinforcing effect of the strain-induced crystallization (SIC) in the thin strip are found. In the filled material fewer crystallites are oriented and the orientation distribution of the oriented crystallites is less perfect. The results confirm, that it is important for the evaluation of crystallinity under deformation to check, whether fiber symmetry can be assumed. This has consequences in particular on the quantitative interpretation of space-resolved scanning experiments in the vicinity of crack tips. Furthermore it raises the question, whether there is an asymmetric reinforcing effect of the SIC in the vicinity of crack tips inside natural rubber. Full article

(This article belongs to the Special Issue Microstructure Evolutions and Mechanical Behavior of Semicrystalline Polymers)

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