KTaO₃ Ceramics Prepared by the Mechanochemically Activated Solid-State Synthesis

Processing of dense potassium tantalate ceramics is a challenging task. In our study, KTaO₃ powder was prepared by heating the mechanochemically activated K₂CO₃–Ta₂O₅ powder mixture at 800°C for 4 h. Another heating at 800°C was needed to improve the structural homogeneity of the powder. Sintering in air and oxygen atmospheres at 1325°C for 1 h resulted in the ceramics with relative densities around 85% and inclusions of the K₆Ta_10.8O₃₀ secondary phase. Phase-pure KTaO₃ ceramics with relative densities of 98% and 95% were obtained by hot-pressing the single- and the double-calcined powder compacts, respectively, at 1250°C for 2 h. The dielectric permittivity of the hot-pressed ceramic, prepared from the double-calcined powder, measured at 5 K and 1 kHz is 4080, which is almost twice the value obtained for the ceramic, prepared from the single-calcined powder, i.e. 2450, and is comparable with the value reported for the single crystals.