KTaO3 Ceramics Prepared by the Mechanochemically Activated Solid-State Synthesis

Abstract

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 K6Ta10.8O30 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.

Nonstoichiometry Role on the Properties of Quantum-Paraelectric Ceramics

“…On the other hand, the dielectric permittivity of similarly dense KT ceramics with initial K/Ta ratio of 1.02 and 1.05 reach a value of about 4000, which is much higher than the values, reported for K/Ta = 1 by Chen et al [24], higher than the value of 3100, reported for K/Ta = 1.05 by Axelsson et al [25], and is not much below 5000, which was reported for KT single crystals [7]. In parallel to our work, Glinšek et al, obtained monophasic KT ceramics with relative density ≥95% using hot-pressing of mechanically activated powders at 1250°C and 25 MPa for 2 h [30]. However, the maximum permittivity of the ceramics prepared from single calcined powder was still about 2500.…”

“…In the case of KT, in which the dielectric losses can be even lower than those of ST, thus exhibiting a dissipation factor tanδ of ~10 −4 in the GHz range [6,7], stoichiometry effect is even more important and, additionally, more difficult to control due to the high volatility of the alkali element as potassium [24,25]. As a result, the dielectric properties have been mainly reported for KT single crystals [6,7,10,24,[26][27][28][29], whereas the studies on polycrystalline bulk are seldom reported [24,25,30], even though ceramics are simpler and less expensive to produce than single crystals. This scarcity is enhanced by the fact that although KT melts easily above 1350°C, it is hard to obtain a highly dense monophasic stoichiometric polycrystalline KT below this temperature [25].…”

Hallmarks of mechanochemistry: from nanoparticles to technology

“…[301][302][303]305 In addition, direct observations of the bonding between Na + or K + and Nb 5+ via the CO 3 2À group were obtained by means of Raman spectroscopy and nuclear magnetic resonance (NMR). 224,302 Finally, HRTEM analysis of the activated powder (Fig.…”

Combined Analytical Transmission Electron Microscopy Approach to Reliable Composition Evaluation of KTaO3

“…Mechanochemically activated powder was prepared by high‐energy milling of the starting compounds in a 250 mL tungsten carbide vial, which was filled with 16 tungsten‐carbide‐milling balls with diameter of 15 mm. The disk and the vial rotational frequencies were set to 350 and 700 min −1 , respectively, and the high‐energy milling was performed for 10 h. Detailed description of the processing is published elsewhere 14 …”

“…However, TEM spectroscopic analysis revealed substantial compositional deviations associated with the powder pretreatment in the form of mechanochemical activation and pressure‐assisted sintering. The details of processing of KTaO 3 are described in a separate article 14 …”