Abstract
Perovskite materials whose general chemical formula is ABO3 are one of the most study ferroelectrics due to the interesting properties that they have for technological applications. However, their properties are directly related to structural phase transitions that could depend of temperature, composition and pressure. In the studies presented here, we first examined the high-pressure behavior of two perovskite materials SrTi1-xZrxO3 (STZ) and KNb1-XTaXO3 (KNT), and we later continued to investigate different sintering techniques in order to improve the densification, dielectric and ferroelectric properties of K(Nb0.40Ta0.60)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics.High-pressure Raman scattering and X-ray diffraction investigations of SrTi1-xZrxO3 (x= 0.3, 0.4, 0.5, 0.6, 0.7) and KNb1-XTaXO3 (x=0.4, 0.5, 0.6, 0.9) powders were conducted in diamond anvil cells. Raman scattering experiments showed and increased of Raman modes with pressure for the STZ samples, which indicates that pressure induced phase transitions towards lower symmetry for these compounds.Moreover, high pressure Raman spectroscopy experiments showed a decrease of the Raman modes as the pressure was increased for the KNT samples, showing that pressure induced phase transitions towards higher symmetries. The evolution of the main Raman modes for the orthorhombic and tetragonal phases were followed until the cubic phase was reach, and allowed us to propose a pressure-composition phase diagram for the KNT compounds.Three different sintering techniques, sintered aids, two step sintering and spark plasma sintering, were used on K(Nb0.4Ta0.6)O3 and (KxNa1-x)Nb0.6Ta0.4O3 ceramics. The use of KF as sintered aid and the two step sintering method showed an improvement of the dielectric constant and dielectric losses of these samples. SPS samples presented a fine microstructure with the highest density and the best ferroelectric behavior. We did not detect any changes on the Curie temperature due the amount of Na but and increase of the dielectric constant and the ferroelectric properties was observed due to the amount of Na.