Optical properties of (1-x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 single crystals studied by spectroscopic ellipsometry

( 1 - x ) Pb ( Mg 1 ∕ 3 Nb 2 ∕ 3 ) O 3 - x PbTiO 3 (PMN-xPT) single crystals with x=0.24, 0.30, 0.31, and 0.33 have been investigated by spectroscopic ellipsometry. The refractive indices and extinction coefficients were obtained. The modified Sellmeier equations for the refractive indices were obtained by least-squares fit. The equations can be used to calculate the refractive index with high accuracy in the low absorption wavelength range, namely, from 400 to 5800nm. The Sellmeier optical coefficients E0, λ0, S0, and Ed were calculated by fitting the single-term oscillator equation. They are related directly to the electronic energy band structure and have the physical significance. The optical band gap energies were also obtained from absorption coefficient spectra. Our results show that as the PT content increases, the refractive index of PMN-xPT single crystals increases, while the optical band gap energy decreases. Some discussions about the BO6 octahedron building block that determines the basic energy level of PMN-xPT single crystals are also presented in this article.