SOME FEATURES OF 3-PHASE STATES IN PBZR1-XTIXO3 CRYSTALS

Three-phase states (the paraelectric phase Pm3m and the ferroelectric phases R3m and P4mm), which can arise in the vicinity of the triple po int in PbZr1 - xTixO3 crystals, are described in terms of thermodynami cs, It is shown that internal mechanical stresses of electrostriction nature and their relaxation in the region of coexistence of three phas es play an important role for phase transitions occurring in various d irections in the T,x-diagram. The thermodynamic and concentration crit eria of nucleation of a new phase are Formulated with clue regard for the contributions made by elastic and electrostriction energy to the f ree energy of the heterophase system. The thermodynamic parameters cha racterizing the three-phase states in the PbZr1 - xTixO3 crystals are estimated numerically.