Acoustic emission and thermal expansion of Pb(Mg1/3Nb2/3)O-3 and Pb(Mg1/3Nb2/3)O-3-PbTiO3 crystals

The temperature dependence of the elongation per unit length for Pb(Mg1/3Nb2/3)O-3 crystals unannealed after growth and mechanical treatment is investigated in the course of thermocycling. It is revealed that this dependence deviates from linear behavior at temperatures below 350degreesC. The observed deviation is characteristic of relaxors, is very small in the first cycle, increases with increasing number n of thermocycles, and reaches saturation at n greater than or equal to 3. In the first cycle, a narrow maximum of the acoustic emission activity is observed in the vicinity of 350degreesC. In the course of thermocycling, the intensity of this maximum decreases and becomes zero at n > 3. For (1 - x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) crystals, the dependence of the temperature of this acoustic emission maximum on x exhibits a minimum. It is assumed that the phenomena observed are associated with the phase strain hardening due to local phase transitions occurring in compositionally ordered and polar nanoregions. (C) 2003 MAIK Nauka/Interperiodica.