Optical properties of pyrochlore lead scandium tantalate crystals

Optically homogeneous Pb2Sc0.5Ta1.5O6.5 crystals with pyrochlore structure are prepared by the method of high-temperature solution growth (HTSG). The refractive index in the visible region of the spectrum is measured. From the transmission spectra in the visible and infrared region the optical transmission window is estimated. From the fundamental absorption edge in the visible region of the spectrum the optical bandgap is determined corresponding to the intrinsic absorption. From the behaviour of the absorption coefficient alpha(hv) and alpha(1/2)(hv) and the Raman spectrum permit to suggest that the absorption edge below 2.75 eV is due to indirect transitions.