Random fields and their influence on the phase transitions in disordered ferroelectrics

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Abstract
Calculations of the phase transition temperature and the critical concentration of electric dipoles which induce in the host crystal lattice the phase transition with the appearance of long-range order are carried out. These calculations are made by considering the additional static random electric fields owing to defects of other types: elastic dipoles and point electric charges. The distribution function of the joint action of the aforementioned random fields is also calculated. It is shown that the presence of the defects of other types inhibits phase transition so that, for the occurrence of long-range order, in this case larger concentrations of electric dipoles are necessary. The theoretical results obtained are found to be important for a description of the experimental situation in K1-xLixTaO3, PbMg13/Nb23/O3 and other disordered ferroelectrics.