Solids, Volume 5, Issue 4 (December 2024) – 14 articles

Triply periodic minimal surface (TPMS) structures raised significant interest in several areas of research due to their unique properties and broad range of applications. The aim of the paper is to verify if such complex metamaterials can be fabricated effectively without defects that could compromise their mechanical response. An implicit modeling approach was used to generate eight novel TPMS structures and one stochastic topology. Multiple specimens were fabricated from a photopolymeric resin using a stereolithography (SLA) technique, and an analysis of the manufactured samples was carried out in terms of surface quality, dimensional and mass deviations, and internal porosity of the material. Laser scanning showed no significant deviations from the designed geometry but highlighted errors during the post-processing stages of manufacturing. Surface analysis resulted in an average roughness of 2.47 µm, a value specific to well-controlled additive manufacturing (AM) techniques. A microscopic examination portrays common types of defects, while an ultrasonic non-destructive inspection method showed no indication of defects in the depth of the samples. Sectioning the samples through water jet cutting exposed interior surfaces with better homogeneity than the exterior ones and the absence of a layer-by-layer aspect. Overall, the samples displayed no major defects and good accuracy, with minor inconsistencies and methods of mitigating them having been presented. Full article

Doping engineering has been applied in niobium-doped NiO (NiO:Nb) by adding nitrogen (N) in its structure. The rf-sputtered films were made from a Ni-Nb composite target on unheated substrates at 300 W rf power and 5 mTorr total pressure. The plasma contained 50% Ar and 50% O₂ for the fabrication of the single-doped NiO:Nb film (AΝ film), and N₂ gas for the incorporation of N in the Ni-O-Nb structure. The N₂ in plasma was introduced by keeping constant the flow rates of O₂ and N₂ gasses (O₂/N₂ = 1) and reducing the amount of Ar gas, namely 94% Ar, 3% O₂, and 3% N₂ (film AN1); 50% Ar, 25% O₂, and 25% N₂ (film AN2); and 6% Ar, 47% O₂, and 47% N₂ (film AN3). All films had the single phase of cubic NiO and both Nb and N in the Ni-O structure were revealed by XPS experiments. The roughness of the films was increased with the increase in N in plasma. Post-deposition thermal treatment improved the crystallinity and reduced the structural disorder of the films. The AN2 film was found to be the most transparent of all films, exhibiting the widest band gap, 3.72 eV, and the narrowest Urbach tail states’ width, 313 meV. The AN and the AN2 films were employed to form NiO/TiO₂ heterostructures. The NiO:Nb/TiO₂ and NiO:(Nb,N)/TiO₂ heterostructures exhibited a visible transmittance of around 42% and 75%, respectively, and both showed rectification properties. Upon illumination with UV light, the NiO:(Nb,N)/TiO₂ diode exhibited enhanced photovoltaic performance when compared to the NiO:Nb/TiO₂ solar cell: the short-circuit current densities were 0.2 mA/cm² versus 1.4 μA/cm² and the open-circuit voltages were 0.5 V versus 0.2 V. The output characteristics of the p-NiO:(Nb,N)/n-TiO₂ UV photovoltaics can be further improved by proper engineering of the individual layers and device processing procedures. Full article

Applying an extended Peierls–Hubbard model to $\pi$ electrons in a coronene isomer, we investigate their ground-state properties and photoinduced dynamics with particular interest in possible loop current states. Once we switch on a static magnetic field perpendicular to the coronene disk, diamagnetic (diatropic) and paramagnetic (paratropic) loop currents appear on the rim circuit and inner hub, respectively. Besides this well-known homocentric two-loop current state, heterocentric multiloop current states can be stabilized by virtue of possible electron–lattice coupling. These multiloop current states generally have a larger diamagnetic moment than the conventional two-loop one, and hence it follows that coronene, or possibly polycyclic conjugated hydrocarbons in general, may become more aromatic than otherwise with their $\pi$ electrons being coupled to phonons. When we photoirradiate a ground-state coronene isomer without applying a static magnetic field, loop currents are induced in keeping with the incident light polarization. Linearly and circularly polarized lights induce heterocentric two-loop and multiloop currents, respectively, without and together with two homocentric loop currents of the conventional type, respectively. The heterocentric two-loop currents occur in a mirror-symmetric manner, which reads as the emergence of a pair of antiparallel magnetic moments, whereas the heterocentric multiloop ones appear at random in both space and time, which reads as the emergence of disordered local magnetic moments. Full article

The literature on aluminum coordination networks so far contains data on COO-bridged derivatives exclusively. This paper addresses the question whether or not aluminum complexes, especially carbamate-bridged {Al₃($\mu$₃−O)}⁷⁺ units, can also form networks via the neutral ligand positions. Our findings show that a highly unexpected polymerization of the aluminum carbamates can occur during the isolation of the initially targeted compound. Although bidentate ligands bind to the neutral ligand coordination sites as expected, they do not act as linker molecules but cause an uncontrolled networking via the carbamate ligands. One- and two-dimensional solution and solid-state NMR experiments were primarily used to investigate the coordination behavior of the ligands and to elucidate the actual obtained product. Full article

For the first time, inductively coupled plasma mass spectrometry (ICP-MS) was developed for determining the target elemental composition of gadolinium–aluminum garnets with the varying composition Gd_3–xCe_xSc_yAl_5–yO₁₂, where x = 0.01–0.16 and y = 0.25–1.75. This fact has a fundamental importance for obtaining optical ceramics with predictable properties. Using the proposed acid mixture and temperature-time program, microwave digestion of these materials and complete transfer of the sample’s components into solution were possible. Moreover, we estimated the influence of the matrix composition, sample introduction system and collision cell on the limits of determination (LOD) of impurity elements by ICP-MS (Mg, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, La, Pr, Nd, Sm, Eu, Tb, Er, Ho, Tm, Yb, and Lu). It has been shown that the conditions of mass spectral analysis proposed in this work provide LOD of target analytes in the range of 1∙10⁻⁶–4.15∙10⁻³ wt.%. The accuracy of the obtained results has been confirmed by the added-found method and by analyzing samples with known chemical composition. The standard deviation of repeatability (S_r) of the developed technique lies in the range from 1 to 6%. The developed analysis method is characterized by sensitivity, robustness and multi-elementality. It has application potential for other optical and ceramic materials of similar composition. Full article

Ferroelectric and antiferroelectric materials are technologically important by the richness of applications such as piezoelectric, pyroelectric, electro-optic, elasto-optic, and nonlinear optic effects. Especially, oxides with a perovskite structure are very important. Its chemical formula is ABO₃, where A is a cation with a larger ionic radius, and B is a cation with a smaller ionic radius. Various elements are available in A- and B-sites. For example, the large piezoelectricity of well-known Pb(Zr_xTi_1−x)O₃ (PZT) solid solutions was found in a morphotropic phase boundary (MPB). The very high dielectric constant, colossal piezoelectric effect, and large electro-optic effect are induced by ferroelectric phase transitions. Such excellent functionalities are closely related to lattice dynamical instability. The vibrational spectroscopy, i.e., Raman scattering, Brillouin scattering, far-infrared, and terahertz time-domain spectroscopy, is a powerful tool for lattice dynamical anomalies. This paper intended a brief review of vibrational spectroscopy on ferroelectric phase transitions of advanced perovskite oxides. Full article

Hardness decreases as indentation depth increases at both the nano- and micro-meter scales. By incorporating interfacial contributions, the indentation size effect can provide valuable information on the deformation behaviors of Ni-based single-crystal superalloys. In this paper, through experimental studies and atomistic simulations, we examine the indentation size effect and mechanical behaviors of Ni-based single-crystal superalloys. The results demonstrate that the indentation size effect, in conjunction with the Ni₃Al/Ni interfacial network, is effectively captured by a modified Nix–Gao model. Molecular dynamics simulations further reveal the underlying atomistic mechanisms and microstructural evolution during nanoindentation. These findings provide new insights into the deformation behavior of Ni-based single-crystal superalloys and support their wide applications in the aerospace industry. Full article

Slags generated from pyrometallurgical processing of spent Li-ion batteries are reservoirs of Li compounds that, on recycling, can reintegrate Li into the material stream. In this context, γ-LiAlO₂ is a promising candidate that potentially increases recycling efficiency due to its high Li content and favorable morphology for separation. However, its solidification kinetics depends on melt compositions and cooling strategies. The Engineered Artificial Minerals approach aims to optimize process conditions that maximize the desired solid phases. To realize this goal, understanding the coupled influence of external cooling kinetics and internal kinetics of solid/liquid interface migration and mass and thermal diffusion on solidification is critical. In this work, the solidification of γ-LiAlO₂ from a Li₂O-Al₂O₃ melt is computationally investigated by applying a non-equilibrium thermodynamic model to understand the influence of varying processing conditions on crystallization kinetics. A strategy is illustrated that allows the effective utilization of thermodynamic information obtained by the CALPHAD approach and molecular dynamics-generated diffusion coefficients to simulate kinetic-dependent solidification. Model calculations revealed that melts with compositions close to γ-LiAlO₂ remain comparatively unaffected by the external heat extraction strategies due to rapid internal kinetic processes. Kinetic limitations, especially diffusion, become significant for high cooling rates as the melt composition deviates from the stoichiometric compound. Full article

The excellent mechanical properties of alkaline-activated tailings are essential for their increased use in building materials. While numerous studies have been conducted on activated tailings, the strength of alkaline-activated tungsten slag has not been extensively explored due to the low reactivity of silicon and aluminum in these tailings. This research delves into the early unconfined compressive strength of tungsten tailings activated by two alkali solutions (NaOH and KOH) at three different alkali concentrations (mass ratio of alkali to tungsten tailings), cured at 80 °C over periods of one day, three days, and seven days. The study finds significant improvements in the stability of tungsten tailings when forming (C, N)-A-S-H or (C, K)-A-S-H gels with both alkalis. Scanning Electron Microscope (SEM) results show that the morphology of the (C, N)-A-S-H gels transitions from membranous to flocculated and then to a three-dimensional network as the NaOH content and curing time increase. Conversely, the (C, K)-A-S-H gels primarily exhibit thin-film morphology with some three-dimensional network structures. The presence of flocculation and three-dimensional mesh in the gels fosters the formation of a robust skeletal structure, enhancing the strength of the samples. Furthermore, specimens treated with NaOH solution exhibit a higher gel content compared to those treated with KOH solution. These factors contribute to the superior efficacy of sodium hydroxide in enhancing the strength of tungsten tailings compared to potassium hydroxide. X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) results identify the formation of new phases such as pirssonite, buetschliite, potassium bicarbonate, and potassium carbonate. The first new phase results from the carbonization of excess NaOH solution, while the latter phases arise from the carbonization of excess KOH solution. These carbonization processes negatively impact the strength of the materials. Full article

Heusler compounds and alloys represent a rapidly expanding family of materials that exhibit novel properties of significant interest for advanced technological applications. Electronic band structure calculations play a pivotal role in advancing research in this area. In an earlier study, we explored the properties of a new class of Heusler compounds based on Li, referred to as “$p^0$-d semi-Heusler Compounds”. In this study, we take the research a step further by focusing on “$d^0$-d semi-Heusler Compounds”, with the chemical formula KZ(Ga, Ge, As, or Se), where Z represents a transition metal. Our investigation centers on the structural, electronic, and magnetic properties of these compounds, particularly in relation to the three possible $C{1}_{\mathrm{b}}$ structures. Most of these compounds are found to be magnetic and, notably, several among them exhibit half-metallicity making them appealing for applications in spintronics. Our findings provide a foundation for future experimental research on these materials. Full article

Organic solid-state lasers are highly promising devices known for their low-cost fabrication processes and compact sizes and the tunability of their emission spectrum. These lasers are in high demand across various industries including biomedicine, sensors, communications, spectroscopy, and military applications. A key requirement for light-emitting materials used in a light-amplifying medium is a low threshold value of the excitation energy of the amplified spontaneous emission (ASE). A newly synthesized non-symmetric red-light-emitting laser dye, Ethyl 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-tert butyl-4H-pyran-4-ylidene)-2-cyanoacetate (KTB), has shown great promise in meeting this requirement. KTB, with its attached bulky trityloxyethyl groups, has the ability to form amorphous thin films from a solution using a wet-casting method. Recent experiments have demonstrated that KTB exhibits a low ASE threshold value. This study focused on investigating the optical and amplified spontaneous emission properties of KTB in poly(N-vinylcarbazole) (PVK), polysulfone (PSU), and polystyrene (PS) matrices at various concentrations. The results showed that as the concentration of the dye increased, a redshift of the photoluminescence and ASE spectra occurred due to the solid-state solvation effect. The lowest ASE threshold value of 9 µJ/cm² was achieved with a 20 wt% concentration of KTB in a PVK matrix, making it one of the lowest excitation threshold energies reported to date. Full article

Due to its unique electronic and optical properties, tungsten disulfide (WS₂) is a promising material for various device applications. However, achieving an efficient and cost-effective method for synthesizing large-area uniform WS₂ is still challenging. In this work, we demonstrate the synthesis of few-layer WS₂ crystallites by NaCl-assisted low-pressure chemical vapor deposition and study the effect of temperature and the carrier gas flow rate on the morphology, structure, and optical properties of the as-grown WS₂ films. We observe transitions between regular triangular to strongly disordered structures with sizes up to 50 µm through temperature and carrier gas flow rate tuning. As-grown samples were characterized by Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The result of this work provides a path toward the optimization of growth conditions for obtaining WS₂ with desired morphologies for various applications. Full article

The rotational correlation times of a small compact spin probe (2,2,6,6-tetramethylpiperidin-1-yl)oxyl in isotactic polypropylene were obtained over a wide temperature range by EPR spectra simulation taking into account rotational anisotropy as well as distribution of the probe molecules by rotational mobility. The averaged values of the rotational correlation times were compared with the corresponding values calculated using well-known approximated formulas based on the intensities and widths of the spectral lines. It was shown that the calculated values can be used as effective parameters to characterize the rotational mobility of the spin probe in the polymer matrix in a wide range of rotational correlation times. Full article

The glass-ceramic materials studied in this work are designed using combinations of lithium vanadate borate glass matrices and lanthanum/rare earth (RE) vanadate nanoparticles. Three different techniques of sintering of the glass matrix and vanadate nanoparticles are investigated. The morphological characteristics and spectral properties of the glass-ceramic samples obtained by different techniques are investigated and analyzed in comparison with the properties of the original glass matrices and nanoparticles. The luminescence spectra of all glass-ceramic samples consist of a wideband glass matrix emission and the characteristic line emission of the RE ions that are incorporated into the glass matrices as nanoparticles. The RE luminescence of these glass-ceramics is promising for various optoelectronic applications. Full article