Abnormal temperature dependence of interband electronic transitions in relaxor-based ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (x=0.24 and 0.31) single crystals

The transmittance spectra of (1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (x=0.24 and 0.31) single crystals have been studied in the temperature range of 5.3-300 K. It was found that the direct band gap E-gd is 3.150 +/- 0.016 eV, indirect band gap E-gi is 2.939 +/- 0.014 eV, and the phonon energy E-p is 0.098 +/- 0.014 eV for the PMN-0.24PT crystal at 300 K. With increasing the temperature, the E-gd of the PMN-0.24PT crystal decreases from 3.263 +/- 0.017 to 3.150 +/- 0.016 eV while the E-gd of the PMN-0.31PT crystal increases from 3.050 +/- 0.015 to 3.101 +/- 0.016 eV. The peculiar characteristic can be ascribed to the monoclinic and rhombohedral multiphase coexistence in the PMN-0.31PT crystal. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3560342]