Brillouin zone center phonon modes in ZnGa_2O_4

摘要

Infrared-active lattice mode properties of melt-grown high-quality single bulk crystals of ZnGa_2O_4 are investigated by combined spectro-scopic ellipsometry and density functional theory computation analysis. The normal spinel structure crystals are measured by spectroscopic ellipsometry at room temperature in the range of 100cm~(-1)-1200cm~(-1). The complex-valued dielectric function is determined from a wavenumber-by-wavenumber approach, which is then analyzed by the four-parameter semi-quantum model dielectric function approach augmented by impurity mode contributions. We determine four infrared-active transverse and longitudinal optical mode pairs, five localized impurity mode pairs, and the high frequency dielectric constant. All four infrared-active transverse and longitudinal optical mode pairs are in excellent agreement with results from our density functional theory computations. With the Lyddane-Sachs-Teller relationship, we determine the static dielectric constant, which agrees well with electrical capacitance measurements performed on similarly grown, samples. We also provide calculated parameters for all Raman-active and for all silent modes and, thereby, provide a complete set of all symmetry predicted Brillouin zone center modes.