An investigation on phase transition behaviors in MgO-doped Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ ferroelectric ceramics by Raman and dielectric measurements

The phase transition behaviors of Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ ferroelectric ceramics doped with different MgO concentrations (0-0.2 wt%) were systematically investigated by Raman and dielectric measurements. Raman results showed that the phase transitions were strongly dependent on MgO concentration. It was found that the low temperature rhombohedral (F_R(LT))-high temperature rhombohedral (F_R(HT)) ferroelectric phase transition shifted toward a lower temperature with increasing MgO concentration up to 0.1 wt%, while the F_R(HT)-cubic paraelectric (P_C) phase transition changed to a higher temperature. The Raman results were in good agreement with phase transition determined by dielectric measurements. Moreover, it was indicated that the changes of Raman active modes were related to distortion of BO₆ octahedra during the phase transitions. Then, the distortion of BO₆ octahedron caused by B-site replacement of Mg²⁺ ions was proposed to explain the observed behaviors. In addition, the effects of MgO doping on the dielectric, ferroelectric and pyroelectric properties were also discussed.