The KTaO3 powder was prepared by heating the mechanochemically activated K2CO3-Ta2O5 powder mixture at 800 °C. Phase-pure KTaO3 ceramics, as determined by the X-ray diffraction, were obtained by hot-pressing the calcined powder compacts at 1250°C and reached relative densities exceeding 95 %. A combination of two analytical spectroscopic methods of transmission electron microscopy was employed for the nanoscale compositional analysis: energy-dispersive X-ray (EDXS) and electron energy-loss spectroscopy (EELS). Compositional inhomogeneities, which were identified in the as-calcined powder sample, were found to affect the subsequently produced ceramic, which showed compositional deviations of up to 5%. These findings lead to the improvement of the KTaO3 processing procedure, namely, another heating of the powder at 800 °C was performed. The double-calcination of the powder resulted in high-quality ceramics with almost doubled value of dielectric permittivity, i. e. 4080 (1 kHz, 5 K), as compared to the ceramics from the powders, prepared by one calcination step. The value is comparable to the literature reports on single-crystals
COBISS.SI-ID: 24386343
We have demonstrated a new approach to solid-state synthesis of Pb(Mg1/3Nb2/3)O3 (PMN) based materials. It is not easy to prepare pyrochlore-free PMN by the one-step solid-state synthesis. With the appropriate manipulation of charges on the reagent particles, we were able to prepare water-based suspension mixtures with the distribution of particles favorable for the perovskite phase formation. The surface charge was tuned by the pH of the suspension. We have modeled the formation of the contacts between the particles in the suspension with the use of Monte Carlo simulations. At pH values higher than 11.8 the contacts between the particles are formed, which slow down the formation of secondary phases. After drying, the mixture was heated and single-phase PMN was synthesized. The ceramics, sintered at only 950 °C, exhibited properties comparable to those of the ceramics sintered at 200 °C higher temperatures.
COBISS.SI-ID: 24810535
Measurements of electromechanical response of BiFeO3, which is receiving an increasing interest as a material for high-temperature piezoelectric applications, revealed a large electric-field induced strain (0.36%), comparable to that achieved in lead-based perovskites. We attribute this strain to the non-180° domain-wall switching and rearrangement of defects under electric field, which further increases the mobility of such domain walls.
COBISS.SI-ID: 25376295