The temperature dependence of the elongation per unit length for Pb(Mg1/3Nb2/3)O3 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 350°C. 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 ≥ 3. In the first cycle, a narrow maximum of the acoustic emission activity is observed in the vicinity of 350°C. In the course of thermocycling, the intensity of this maximum decreases and becomes zero at n > 3. For (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 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.
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ACKNOWLEDGMENTS This work was supported in part by the Russian Foundation for Basic Research (project no. 01-03-33119) and the Ministry of Education of the Russian Federation (project no. E00-3.4-287)