Applications of the thermal analysis in preparation and investigation of the ceramic ferroics and multiferroics

Abstract

Results of investigations on selected ceramic ferroics and multiferroics by TA method were presented. The authors of the work used the thermal analysis both to optimize a process of producing the ceramic ferroics and multiferroics and to examine phase transitions in that type of materials. In the case of synthesis of the ferroics and multiferroics as a result of sintering of a mixture of simple oxides, the TA method enables to determine the optimum synthesis temperature and temperatures of re-crystallization and disintegration of compounds and solid solutions. In the case of the sol–gel method, temperatures of dehydratization, burning of an organic phase, and crystallization of an amorphous powder formed from the residual gel were determined by the TA method. The TA method was also used to control a process of compacting and sintering the powders at high temperatures (T _s > 1,200 K), thus in a process of ceramic specimen formation. During rapid phase transitions, the ferroelectric specimens of a first type emit (in the cooling process) or absorb (in the heating process) so called latent heat of the phase transitions. On the DTA courses, it may be manifested in a form of exo- or endothermic peaks in the Curie temperature area (T _C). The test materials included the ferroelectric ceramics of composition x/65/35 PLZT (ferroic for x < 9 at%) and mixed bismuth oxide layered perovskites (M-BOLP) of composition Bi₅TiNbWO₁₅ with <m> = 1.5 and the mutliferroic Pb(Fe_1−x Nb _x )O₃ ceramics (PFN) and Bi₅TiFeO₁₅ (BTF).