Optical interband transitions in [111] poled relaxor-based ferroelectric 0.24Pb(In1/2Nb1/2)O3–(0.76 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystal

Optical transmission spectra of single crystal 0.24Pb(In_1/2Nb_1/2)O₃-(0.76 - x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (x = 0.27, 0.33) were measured in the pseudo-cubic crystallographic directions [111] and [112̄]. Ferroelectric domain structures were observed in order to explain the difference of transmittance for the two composition crystals. Wavelength dependence of the absorption coefficients was measured and the optical energy band gaps were calculated for both direct and indirect transitions, which are E_gd = 3.09-3.18 eV and E_gi = 2.89-2.96 eV, respectively, and the phonon energy is E_p = 0.07-0.08 eV. The transmission spectra were explained by the refractive indices and extinction coefficients measured by spectroscopic ellipsometry.