UV-Vis-NIR optical properties of Pb(Mg_1/3Nb_2/3) O₃-0. 3PbTiO₃ single crystal

The optical properties of Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ single crystal near morphotropic phase boundary were investigated by temperature dependent transmittance and reflectance spectra. The temperature dependent absorption edges show blueshifts below 300 K while they show redshifts above 300 K. At 303 K, optical band gap E_g is 3.25 eV, critical point energies E_a and E_b are 3.93 and 4.65 eV, respectively. With increasing temperature, E_g, E_a and E_b decrease and they are 3.05, 3.57, 4.56 eV at 453 K, respectively. Three critical point energies E_g, E_a and E_b are corresponding to O 2p to Ti d, and Pb 6p, respectively. Such narrowing trends with increasing temperature can be explained by thermal expansion of the lattice and electron-phonon interaction. Based on Tauc-Lorentz dispersion models, the dielectric functions from 3.1 to 6.5 eV have been extracted from 303 to 453 K. It was found that the refractive index n increases with increasing temperature.