Aging characteristics of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ single crystals with different crystal orientations

In this work, the time and temperature dependence of the piezoelectric and ferroelectric properties of the 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (0.7PMN-0.3PT) single crystals were investigated in order to search for an effective method to improve their properties further. The piezoelectric properties of the [001]-, [110]- and [111]-oriented 0.7PMN-0.3PT single crystals exhibit excellent time stability during the 2-month room-temperature aging process. The re-poling process leads to the improvement of piezoelectric constant d₃₃ for the [001]-, [110]- and [111]-oriented 0.7PMN-0.3PT single crystals, while the values of electromechanical coupling coefficient k_t change little. During the thermal aging, the values of the measured d₃₃, calculated converse piezoelectric constant d₃₃^*, maximum strain S_max% and longitudinal electrostrictive coefficient Q of the [001]-, [110]- and [111]-oriented crystal plates increase gradually before the ferroelectric phase transition temperatures (T_FPT, T_R-M, T_R-O and T_R-T) and then decline continuously. The increase in these values before the T_FPT is a result of the phase instability. In general, the [001]- and [110]-oriented 0.7PMN-0.3PT single crystals exhibit large piezoelectricity, excellent time stability and relatively high thermal stability between 20 and 80 C, which is favorable to the piezoelectric applications. (orig.)