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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(Fe1−xNbx)O3 ceramics (PFN) and Bi5TiFeO15 (BTF).

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The influence of the temperature program parameters of an ODSC experiment on the calculated “reversing” and “kinetic” signals has been studied. Mixed orthophosphate salts of KMPO4 (where M=Ni2+, Co2+ and Fe2+) which present at least one structural phase transition have been used for this purpose. On these crystalline compounds we have shown that the non reversing heat flow is partly associated with the formation and disappearance of ferroelastic and ferroelectric domain walls. However a proper choice of the temperature program parameters is important so that the calculated “reversing” and “kinetic” curves have the supposed physical meaning according to the assumptions made for the calculations.

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Introduction Multi-ferroics are materials that are magnetically ordered, being at the same time in a ferroelectric state. The coupling between the electric and magnetic polarizations, i.e., the magnetoelectric effect, imparts

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