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Abstract ZrO2 ceramics have wide applications as structural materials in industrial, scientific, and technological fields. Despite the large number of works devoted to the influence of synthesis parameters on the formation of different phases of ZrO2 and the properties of the obtained ceramics, the effect of sintering temperature on the characteristics of the porous ZrO2 ceramics has not been addressed sufficiently. This study focuses on examining how sintering temperature affects the phase composition, microstructure, dielectric properties, and mechanical properties of porous stabilized zirconium dioxide ceramics. Phase transformations during sintering at various temperatures were identified using powder X-ray diffraction and Raman spectroscopy. The results indicate that fully stabilized cubic ZrO2 with satisfactory mechanical properties (HV0.5 = 580) and a porosity of 21.5% was achieved at temperatures of 1400 and 1500 ℃. At lower sintering temperatures, the obtained samples exhibited multiphase composition and high porosity. The reasons for the formation of the CaZrO3 phase at sintering temperatures of 1000–1200 ℃ were established using scanning electron microscopy, energy dispersive analysis, and thermodynamic considerations of the solid-phase reactions. AC dielectric measurements showed that the synthesized samples have high-Q characteristics; and that the dielectric constant can be controlled by changing the sintering temperature.

Ceramics based on zirconium dioxide are very important compounds for dental, implant, and structural material applications. Despite the fact that tetragonally stabilized YSZ has been well studied, the search for new compositions of zirconia-based ceramics is still in progress. The ZrO2-CeO2 system is one of the alternatives for YSZ materials, but there is conflicting experimental data on its phase composition and mechanical properties depending on the ratio of components. In this study, we investigated the phase composition, and microstructural, mechanical, and physical properties of (1 − x)∙ZrO2-x∙CeO2 (step of x = 0.05) ceramics obtained by the solid-state sintering process from micron-sized powders. For the characterization of samples, XRD, Raman spectroscopy, SEM, the Vickers Microhardness Test, and dielectric spectroscopy were implemented. The results showed that by varying the CeO2 concentration, it is possible to synthesize stable tetragonal ZrO2 at room temperature with a high microhardness HV0.05 value of ~1500, low porosity (~2.5%), and a high dielectric constant of 36. The pronounced combined effect of tetragonal phase formation, densification, and grain size reduction on the mechanical and dielectric properties of the experimental samples was investigated. Refined experimental data make it possible to synthesize high-quality zirconia–ceria ceramics for use as refractories, dispersed nuclear fuel, or solid oxide fuel cells.

In this work, ceramic samples of cerium oxide doped with yttrium were investigated. The concentration of a dopant Y(NO3)3 varied from 5 to 25 wt% in the initial charge. In the course of the experiment, a simple method was developed to obtain ceramics with a porosity of ~20% via one-step annealing in air in a muffle furnace. For comparison, samples with two annealings were also synthesized to determine the effects of pores on electrical, structural, and mechanical characteristics. The obtained samples were examined via X-ray powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, Raman spectroscopy, dielectric spectroscopy, and Vickers microhardness measurements. The substitution of Ce4+ ions with Y3+ ions led to a significant decrease in the lattice parameter, average crystallite size, and average grain size, with a simultaneous increase in the lattice defectivity, dielectric constant, electrical conductivity, and microhardness values. It is shown that samples with a dopant weight fraction of 0.05–0.15 and one-step annealing have favorable electrical and mechanical characteristics for energy applications as porous materials with ionic conductivity.

Ti-Al-Ta-N coatings are characterized by attractive mechanical properties, thermal stability and oxidation resistance, which are superior to ternary compositions, such as Ti-Al-N. However, because of their open columnar microstructure, the Ti-Al-Ta-N coatings deposited by conventional direct current magnetron sputtering (DCMS) exhibit insufficient wear resistance. This work is focused on obtaining the Ti-Al-Ta-N coatings with improved microstructure and mechanical and tribological properties by middle-frequency magnetron sputtering (MFMS). The coatings are deposited by the co-sputtering of two separate targets (Ti-Al and Ta) using pure DCMS and MFMS modes as well as hybrid modes. It is found that the MFMS coating has a denser microstructure consisting of fragmented columnar grains interspersed with equiaxed grains and a smaller grain size than the DCMS coating, which is characterized by a fully columnar microstructure. The modification of the microstructure of the MFMS coating results in the simultaneous enhancement of its hardness, toughness and adhesion. As a result, the wear rate of the MFMS coating is less than half of that of the DCMS coating.

The effect of the Ta content on the structure, mechanical properties and adhesion of magnetron-sputtered Ti1-x-y-zAlxTaySizN coatings was studied. According to the energy-dispersive X-ray spectroscopy analysis, the coatings studied had the following chemical compositions: Ti0.41Al0.49Si0.10N, Ti0.38Al0.47Ta0.05Si0.10N, Ti0.36Al0.44Ta0.10Si0.10N and Ti0.35Al0.40Ta0.15Si0.10N. The X-ray diffraction experiments revealed the B1-type fcc crystal structure of the coatings. The increasing Ta content was found to induce the texture evolution from (200) to (111), which was attributed to a significant increase in the residual compressive stress in the coatings. The hardness monotonically increased from 32.7 to 42.2 GPa with increasing the Ta content, while the reduced Young’s modulus decreased from 369 to 353 GPa. The adhesion of the coatings to the Ti substrate was evaluated by scratch testing. It was found that the Ti0.36Al0.44Ta0.10Si0.10N coating was characterized by maximum adhesion strength, while incorporation of a larger amount of Ta resulted in earlier coating spallation due to the high residual compressive stress.

In modern materials science, a considerable amount of research is focused on obtaining new ceramic materials to create efficient functional elements. Acquiring highly efficient and stable ceramic catalysts for alternative energy is an important task that demands an urgent solution. Solving this problem as fast as possible is essential, as it will facilitate the development of new technologies that can prevent future energy crises. Nickel oxide (NiO) and spinel with the composition NiAl _2 O _4 are excellent candidates as high temperature catalysts used in alternative energy applications. This paper studies the synthesis of NiO/NiAl _2 O _4 composite ceramics and the effect of high-temperature aging on their phase composition, crystalline properties, and dielectric characteristics. The study found that the phase composition and microstructure of the ceramics remain unchanged after several thermal aging cycles at 700 °C. However, the crystalline parameters and low-frequency dielectric characteristics may fluctuate significantly depending on the duration of aging. The observed variations were predominantly influenced by the microstructural features of the composite ceramics. As the average grain size increased and the phase transformations were completed, the crystalline parameters and low-frequency dielectric characteristics reached a stable state without further alteration. For NiO/NiAl _2 O _4 ceramics with a sintering temperature of 1500 °C, the highest shrinkage, low dielectric loss values and acceptable hardness were observed, indicating that the fabricated ceramics are suitable for mechanical processing. In general, the obtained composite ceramics show high temperature stability and are well-suited for use as functional elements in hydrogen energy applications.