Structural, electronic and optical properties of ilmenite and perovskiteCdSnO3 from DFT calculations

Abstract

CdSnO3 ilmenite and perovskite crystals were investigated using both the local density and generalizedgradient approximations, LDA and GGA, respectively, of the density functional theory(DFT). The electronic band structures, densities of states, dielectric functions, opticalabsorption and reflectivity spectra related to electronic transitions were obtained, as well asthe infrared absorption spectra after computing the vibrational modes of the crystals atq = 0. Dielectric optical permittivities and polarizabilities atω = 0 and were also calculated. The results show that GGA-optimized geometries are moreaccurate than LDA ones, and the Kohn–Sham band structures obtained for theCdSnO3 polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a directband gap, both being semiconductors. Effective masses for both crystals are obtained forthe first time, being highly isotropic for electrons and anisotropic for holes. Theoptical properties reveal a very small degree of anisotropy of both crystals withrespect to different polarization planes of incident light. The phonon calculation atq = 0 forperovskite CdSnO3 does not show any imaginary frequencies, in contrast to a previousreport suggesting the existence of a more stable crystal of perovskiteCdSnO3 with ferroelectric properties.