Study of the Aid Effect of CuO-TiO2-Nb2O5 on the Dielectric and Structural Properties of Alumina Ceramics

Abstract

The aim of this work is to study the structural, dielectric, and mechanical properties of aluminum oxide ceramics with the triple sintering additive 4CuO-TiO2-2Nb2O5. With an increase in sintering temperature from 1050 to 1500 °C, the average grain size and the microhardness value at a load of 100 N (HV0.1) increased with increasing density. It has been shown that at a sintering temperature of 1300 °C, the addition of a 4CuO-TiO2-2Nb2O5 additive increases the low-frequency permittivity (2–500 Hz) in alumina ceramic by more than an order of magnitude due to the presence of a quadruple perovskite phase. At the same time, the density of such ceramics reached 89% of the theoretical density of α-Al2O3, and the microhardness value HV0.1 was 1344. It was observed that the introduction of 5 wt.% 4CuO-TiO2-2Nb2O5 in the raw mixture remarkably increases values of shrinkage and density of sintered ceramics. Overall, the results of this work confirmed that introducing the 4CuO-TiO2-2Nb2O5 sintering additive in the standard solid-phase ceramics route can significantly reduce the processing temperature of alumina ceramics, even when micron-sized powders are used as a starting material. The obtained samples demonstrated the potential of α-Al2O3 with the triple additive in such applications as electronics, microwave technology, and nuclear power engineering.

Investigation of the Phase Composition, Structural, Mechanical, and Dielectric Properties of (1 − x)∙ZrO2-x∙CeO2 Ceramics Synthesized by the Solid-State Method

“…The analysis of the phase composition of the sintered samples using the XRD and Raman spectroscopy methods made it possible to clarify the known phase diagrams of the ZrO 2 -CeO 2 system, namely, to determine the areas of formation of the pure tetragonal ZrO 2 -t phase and the ZrO 2 -t+ ZrO 2 -c mixture (predominance of the t-phase), as well as the region of formation of substitutional solid solutions with a fluorite crystal structure. Density measurements and porosity evaluations of the resulting ceramics showed that porosity decreased with decreasing x values above x = 0.25, while density varied non-monotonically within the range of 5.6-6.2 g/cm 3 . Below this concentration, a significant decrease in density, shrinkage, and an increase in porosity was observed due to the formation of cracks due to the martensitic transition t→m upon cooling.…”

“…The tangent loss frequency dependencies also showed pronounced dispersion throughout the whole measured range. This feature can be explained by the relatively high conductivity of ceramics [3]. If a metal oxide consists of multivalence cations, its conductivity becomes higher due to the hopping electron mechanism [31].…”

“…This is due to the necessity of finding new approaches for enhancing the performance characteristics and physical properties of technical ceramics. For example, cation substitution (doping) or the use of different sintering aids are effective ways to adjust the structure and phase composition of ceramics [3,4]. Changes in microstructure (grain size, morphology of grains) and phase composition can improve mechanical properties, have an effect on temperature resistance, and significantly vary the electrical properties of technical ceramics [5].…”

Study of the Structural, Electrical, and Mechanical Properties and Morphological Features of Y-Doped CeO2 Ceramics with Porous Structure

“…For all the samples, the apparent density and porosity were calculated using the X-ray density values (Table 1). The highest HV0.2 value was obtained for the least porous sample, which demonstrates a pronounced dependence of microhardness on the presence of pores in the sample [48,49]. On the other hand, despite the decrease in apparent density (increase in porosity), in some cases, it was observed that microhardness does not follow the change in apparent density (e.g., sample with two annealings and concentration x = 0.2).…”