Crystals

Editorial

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2 pages, 149 KiB

Open AccessEditorial

Ceramic Conductors

by Maria Gazda and Aleksandra Mielewczyk-Gryń

Crystals 2019, 9(3), 173; https://doi.org/10.3390/cryst9030173 - 25 Mar 2019

Cited by 2 | Viewed by 2240

Abstract

For more than 4000 years, mankind has used and developed ceramics [...] Full article

(This article belongs to the Special Issue Ceramic Conductors)

Research

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14 pages, 4482 KiB

Open AccessArticle

Terbium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties

by Kacper Dzierzgowski, Sebastian Wachowski, Maria Gazda and Aleksandra Mielewczyk-Gryń

Crystals 2019, 9(2), 91; https://doi.org/10.3390/cryst9020091 - 11 Feb 2019

Cited by 13 | Viewed by 3642

Abstract

The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La_1−xTb_xNbO_4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 [...] Read more.

The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La_1−xTb_xNbO_4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 °C, and 530 °C for La_0.9Tb_0.1NbO_4+δ, La_0.8Tb_0.2NbO_4+δ, and La_0.7Tb_0.3NbO_4+δ, respectively. The impedance spectroscopy results suggest mixed conductivity of oxygen ions and electron holes in dry conditions and protons in wet. The water uptake has been analyzed by the means of thermogravimetry revealing a small mass increase in the order of 0.002% upon hydration, which is similar to the one achieved for undoped lanthanum orthoniobate. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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12 pages, 3537 KiB

Open AccessFeature PaperArticle

Influence of the Initial Powder’s Specific Surface Area on the Properties of Sm-Doped Ceria Thin Films

by Mantas Sriubas, Kristina Bockute, Nursultan Kainbayev and Giedrius Laukaitis

Crystals 2018, 8(12), 443; https://doi.org/10.3390/cryst8120443 - 27 Nov 2018

Cited by 2 | Viewed by 3101

Abstract

The influence of a specific surface area of evaporating powder on the properties of thin Sm-doped cerium (SDC) oxide films has not yet been sufficiently investigated. Therefore, SDC films were deposited by e-beam evaporation using Sm_0.2Ce_0.8O_2-δ powders of [...] Read more.

The influence of a specific surface area of evaporating powder on the properties of thin Sm-doped cerium (SDC) oxide films has not yet been sufficiently investigated. Therefore, SDC films were deposited by e-beam evaporation using Sm_0.2Ce_0.8O_2-δ powders of 6.2 m²/g, 11.3 m²/g, and 201.3 m²/g specific surface area on SiO₂, and Al₂O₃ substrates. X-Ray Diffraction (XRD) analysis showed that SDC thin films deposited on 600 °C SiO₂ substrates changed their preferred orientation from (111) to (311), (200), and (220) when evaporating 6.2 m²/g and 11.3 m²/g powders and using 0.2 nm/s, 1.2 nm/s, and 1.6 nm/s deposition rates. However, thin films deposited by evaporating powder of 201.3 m²/g specific surface area do not change their preferred orientation. The crystallite size of the SDC thin films depends on the substrate temperature and specific surface area of the evaporating powder. It increases from 6.40 nm to 89.1 nm with increasing substrate temperature (50–600 °C). Moreover, crystallites formed by evaporating a powder of 201.3 m²/g specific surface area are 1.4 times larger than crystallites formed by evaporating a powder of 6.2 m²/g specific surface area. An impedance analysis revealed that the normalized resistance of “grains” is higher than the normalized resistance of grain boundaries. Moreover, a total conductivity depends on crystallite size. It changes from 4.4 × 10⁻⁷ S/cm to 1.1 × 10⁻² S/cm (600 °C) when the crystallite sizes vary from 6.40 nm to 89.10 nm. In addition, the optical band gap becomes wider with increasing crystallite size proving that the Ce³⁺ concentration decreases with an increasing crystallite size. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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9 pages, 2946 KiB

Open AccessArticle

Structural and Magnetic Studies of Cr³⁺ Substituted Nickel Ferrite Nanomaterials Prepared by Sol-Gel Auto-Combustion

by Jinpei Lin, Yun He, Xianglin Du, Qing Lin, Hu Yang and Hongtao Shen

Crystals 2018, 8(10), 384; https://doi.org/10.3390/cryst8100384 - 9 Oct 2018

Cited by 23 | Viewed by 4612

Abstract

The present study envisages the preparation of chromium substituted Nickel ferrite NiCr_xFe_2−xO₄ (x = 0~1.0) powders by a sol-gel auto-combustion method. X-ray diffraction analysis (XRD) showed that the specimens with x > 0.2 exhibited a single-phase spinel [...] Read more.

The present study envisages the preparation of chromium substituted Nickel ferrite NiCr_xFe_2−xO₄ (x = 0~1.0) powders by a sol-gel auto-combustion method. X-ray diffraction analysis (XRD) showed that the specimens with x > 0.2 exhibited a single-phase spinel structure, and that more content of Cr within a specimen is favorable for the synthesis of pure Ni-Cr ferrites. The lattice parameter decreased with an increase in the Cr concentration. The sample without calcining exhibited a good crystallinity. Scanning Electron Microscopy (SEM) showed the formation of ferrite powders nano-particles, and that the substitution of Cr weakened the agglomeration between the particles. Mössbauer spectra of NiCr_xFe_2−xO₄ showed two normal Zeeman-split sextets that displayed a ferrimagnetic behavior. Furthermore, the spectra indicated that iron was in the Fe³⁺ state, and the magnetic hyperfine field at the tetrahedral tended to decrease with an increase in the Cr substitution. The saturation magnetization decreased by the Cr³⁺ ions, and reached a minimum value (Ms = 4.46 emu/g). With an increase in the annealing temperature, the coercivity increased initially, which later decreased. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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13 pages, 22309 KiB

Open AccessArticle

Quasi-Equilibrium, Multifoil Platelets of Copper- and Titanium-Substituted Bismuth Vanadate, Bi₂V_0.9(Cu_0.1−xTi_x)O_5.5−δ, by Molten Salt Synthesis

by Kevin Ring and Paul Fuierer

Crystals 2018, 8(4), 170; https://doi.org/10.3390/cryst8040170 - 17 Apr 2018

Cited by 2 | Viewed by 4755

Abstract

10% copper-substituted (BiCUVOX/Bi₂V_0.9Cu_0.1O_5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi₂V_0.9(Cu_0.05Ti_0.05)O_5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The [...] Read more.

10% copper-substituted (BiCUVOX/Bi₂V_0.9Cu_0.1O_5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi₂V_0.9(Cu_0.05Ti_0.05)O_5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The product was phase-pure within the limits of X-ray diffraction. The size and form of the platelets could be controlled by changing the heating temperature and time. The crystallite growth rate at a synthesis temperature of 650 °C and the activation energy for grain growth were determined for BICUTIVOX, which experienced inhibited growth compared to BICUVOX. Quasi-equilibrium, multifoil shapes consisting of lobes around the perimeter of the platelets were observed and explained in the context of relative two-dimensional nucleation and edge growth rates. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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15 pages, 7313 KiB

Open AccessArticle

Crystal Structure, Hydration, and Two-Fold/Single-Fold Diffusion Kinetics in Proton-Conducting Ba_0.9La_0.1Zr_0.25Sn_0.25In_0.5O_3−a Oxide

by Wojciech Skubida, Anna Niemczyk, Kun Zheng, Xin Liu and Konrad Świeczek

Crystals 2018, 8(3), 136; https://doi.org/10.3390/cryst8030136 - 16 Mar 2018

Cited by 7 | Viewed by 4533

Abstract

In this work, hydration kinetics related to the incorporation of water into proton-conducting Ba_0.9La_0.1Zr_0.25Sn_0.25In_0.5O_3−a perovskite-type oxide are presented, with a recorded transition on temperature from a single-fold to a two-fold behavior. This [...] Read more.

In this work, hydration kinetics related to the incorporation of water into proton-conducting Ba_0.9La_0.1Zr_0.25Sn_0.25In_0.5O_3−a perovskite-type oxide are presented, with a recorded transition on temperature from a single-fold to a two-fold behavior. This can be correlated with an appearance of the electronic hole component of the conductivity at high temperatures. The collected electrical conductivity relaxation data allowed to calculate chemical diffusion coefficient D and surface exchange reaction coefficient k, as well as respective activation energies of their changes on temperature. Presented results are supplemented with a systematic characterization of the structural properties of materials synthesized at different temperatures, amount of incorporated water after hydration in different conditions, influence of water content on the crystal structure, as well as electrical conductivity in dry, H₂O- and D₂O-containing air, which enabled to evaluate proton (deuterium) conductivity. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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15 pages, 3597 KiB

Open AccessArticle

Application of La-Doped SrTiO₃ in Advanced Metal-Supported Solid Oxide Fuel Cells

by Sabrina Presto, Antonio Barbucci, Maria Paola Carpanese, Feng Han, Rémi Costa and Massimo Viviani

Crystals 2018, 8(3), 134; https://doi.org/10.3390/cryst8030134 - 13 Mar 2018

Cited by 17 | Viewed by 5169

Abstract

Composite materials frequently allow the drawbacks of single components to be overcome thanks to a synergistic combination of material- and structure-specific features, leading to enhanced and also new properties. This is the case of a metallic-ceramic composite, a nickel-chromium-aluminum (NiCrAl) foam impregnated with [...] Read more.

Composite materials frequently allow the drawbacks of single components to be overcome thanks to a synergistic combination of material- and structure-specific features, leading to enhanced and also new properties. This is the case of a metallic-ceramic composite, a nickel-chromium-aluminum (NiCrAl) foam impregnated with La-doped Strontium Titanate (LST). This particular cermet has very interesting properties that can be used in different fields of application, namely: mechanical robustness provided by the metal foam; and chemical stability in harsh conditions of temperature and atmosphere by promotion of a thin protective layer of alumina (Al₂O₃); high electronic conductivity given by a percolating ceramic conducting phase, i.e., La-doped Strontium Titanate. In this paper, its application as a current collector in a metal-supported Solid Oxide Fuel Cells (SOFC) was studied. Firstly, the electronic properties of different compositions, stoichiometric and under stoichiometric, of LST were analyzed to choose the best one in terms of conductivity and phase purity. Then, LST chemical stability was studied in the presence of Al₂O₃ at different temperatures, gas compositions and aging times. Finally, stability and conductivity of LST-impregnated NiCrAl foam composite materials were measured, and LST was found to be fully compatible with the NiCrAl foam, as no reactions were detected in oxidizing and reducing atmosphere after up to 300 h operation at 750 °C and 900 °C between the Al₂O₃ layer and LST. Results showed that the composite is suitable as a current collector in innovative designs of metal-supported SOFC, like the Evolve cell, in which the metallic part is supposed not only to provide the structural stability to the cell, but also to play the role of current collector due to the impregnation of ceramic material. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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10 pages, 817 KiB

Open AccessArticle

Fluorine Translational Anion Dynamics in Nanocrystalline Ceramics: SrF₂-YF₃ Solid Solutions

by Stefan Breuer, Bernhard Stanje, Veronika Pregartner, Sarah Lunghammer, Ilie Hanzu and Martin Wilkening

Crystals 2018, 8(3), 122; https://doi.org/10.3390/cryst8030122 - 5 Mar 2018

Cited by 11 | Viewed by 4756

Abstract

Nanostructured materials have already become an integral part of our daily life. In many applications, ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and [...] Read more.

Nanostructured materials have already become an integral part of our daily life. In many applications, ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and disordered interfacial regions. In particular, anion conductivity in nonstructural binary fluorides easily exceeds that of their coarse-grained counterparts. To further increase ion dynamics, aliovalent substitution is a practical method to influence the number of (i) defect sites and (ii) the charge carrier density. Here, we used high energy-ball milling to incorporate Y

^{3 +}

ions into the cubic structure of SrF

_{2}

. As compared to pure nanocrystalline SrF

_{2}

the ionic conductivity of Sr

_{1 - x}

Y

_{x}

F

_{2 + x}

with

x = 0.3

increased by 4 orders of magnitude reaching

0.8 \times 10^{- 5} S {cm}^{- 1}

at 450 K. We discuss the effect of YF

_{3}

incorporation on conductivities isotherms determined by both activation energies and Arrhenius pre-factors. The enhancement seen is explained by size mismatch of the cations involved, which are forced to form a cubic crystal structure with extra F anions if x is kept smaller than 0.5. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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14 pages, 5011 KiB

Open AccessArticle

Effect of MnO₂ Concentration on the Conductivity of Ce_0.9Gd_0.1Mn_xO_2−δ

by Kerstin Neuhaus, Stefan Baumann, Raimund Dolle and Hans-Dieter Wiemhöfer

Crystals 2018, 8(1), 40; https://doi.org/10.3390/cryst8010040 - 17 Jan 2018

Cited by 11 | Viewed by 4537

Abstract

Samples with the composition Ce_0.9Gd_0.1Mn_xO_2−δ with x = 0.01, 0.02, and 0.05 Mn-addition were prepared by mixed oxide route from Ce_0.9Gd_0.1O_2−δ and MnO₂ and sintered at 1300 °C. The electronic [...] Read more.

Samples with the composition Ce_0.9Gd_0.1Mn_xO_2−δ with x = 0.01, 0.02, and 0.05 Mn-addition were prepared by mixed oxide route from Ce_0.9Gd_0.1O_2−δ and MnO₂ and sintered at 1300 °C. The electronic conductivity was measured using a modified Hebb-Wagner technique, the electrical conductivity was investigated by impedance spectroscopy, and oxygen permeation was measured for the sample with x = 0.05. An increase of the electronic partial conductivity with increasing Mn addition was observed, which can be attributed to an additional Mn 3d-related state between the top of the valence band and the bottom of the Ce 4f band. The grain boundary conductivity was found to be suppressed for low Mn contents, but enhanced for the sample with x = 0.05. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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Review

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68 pages, 5563 KiB

Open AccessReview

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

by Andreas Løken, Sandrine Ricote and Sebastian Wachowski

Crystals 2018, 8(9), 365; https://doi.org/10.3390/cryst8090365 - 14 Sep 2018

Cited by 126 | Viewed by 11505

Abstract

This review paper focuses on the phenomenon of thermochemical expansion of two specific categories of conducting ceramics: Proton Conducting Ceramics (PCC) and Mixed Ionic-Electronic Conductors (MIEC). The theory of thermal expansion of ceramics is underlined from microscopic to macroscopic points of view while [...] Read more.

This review paper focuses on the phenomenon of thermochemical expansion of two specific categories of conducting ceramics: Proton Conducting Ceramics (PCC) and Mixed Ionic-Electronic Conductors (MIEC). The theory of thermal expansion of ceramics is underlined from microscopic to macroscopic points of view while the chemical expansion is explained based on crystallography and defect chemistry. Modelling methods are used to predict the thermochemical expansion of PCCs and MIECs with two examples: hydration of barium zirconate (BaZr_1−xY_xO_3−δ) and oxidation/reduction of La_1−xSr_xCo_0.2Fe_0.8O_3−δ. While it is unusual for a review paper, we conducted experiments to evaluate the influence of the heating rate in determining expansion coefficients experimentally. This was motivated by the discrepancy of some values in literature. The conclusions are that the heating rate has little to no effect on the obtained values. Models for the expansion coefficients of a composite material are presented and include the effect of porosity. A set of data comprising thermal and chemical expansion coefficients has been gathered from the literature and presented here divided into two groups: protonic electrolytes and mixed ionic-electronic conductors. Finally, the methods of mitigation of the thermal mismatch problem are discussed. Full article

(This article belongs to the Special Issue Ceramic Conductors)

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