The Influence of Microstructure and Lattice Strain on Tetragonality Factor and Dielectric Properties of Ferroelectric Ceramics BaTiO_3

Abstract

This work is devoted to direct process of molten salt synthesis and studies on barium titanate (BaTiO3, BT), belonging to ferroelectric crystal group type perovskite BO3. This material thanks to its noncentrosymmetric, fully tetragonal structure possesses at room temperature (up to Tc = 135 ◦C) the spontaneous polarization. Due to this fact BT can be applied as piezoelectric material in electromechanical transducers, so as an excellent dielectric in multilayer capacitors and many other devices. With grain size reduction of BT ceramics to nanometric level it leads to permanent transformation into paraelectric state with minimized energy and to lose its speci c features as a consequence, even at room temperature. In case of structural agent, means as tetragonality factor, it has a crucial in uence on investigated material properties and it is referred in current paper. It is a row of complementary researching methods allows to con rm the presence of desired tetragonal BT phase in nano or micropowders obtained by means of molten salt synthesis route. For di erent temperature variants of synthesis X-ray di raction analysis were undertaken and precise unit cells parameters both with tetragonality factor were determined using the Cohen method. Based on structural studies the lattice strains and crystallite sizes were estimated through the Williamson Hall method. Using scanning electron microscopy the powders morphology and grain size distribution were done. Dielectric measurements of sintered BT ceramics were carried out to determine the Curie temperatures, dielectric permittivities and loss factors in prepared capacitors.