Phonon properties of the spinel oxideMgTi2O4with theS=1/2pyrochlore lattice

Abstract

We study the phonon dynamics of ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ spinel by measuring the Raman and infrared reflectivity spectra in a wide frequency $(100--3000{\mathrm{cm}}^{\ensuremath{-}1})$ and temperature (10 K--300 K) range. The reflectivity spectra are analyzed by a fitting procedure based on a model which includes both Drude and phonon oscillator contributions to the dielectric constant. The phonon assignment is done from comparison between experimental data and shell model lattice dynamical calculations. We find two infrared-active ${F}_{1u}$ symmetry modes superimposed on the free carrier continuum, and four Raman-active modes of ${1A}_{1g},$ ${1E}_{g},$ and ${2F}_{2g}$ symmetry. At the phase transition temperature of about 250 K we observe an abrupt change of optical parameters, accompanied with the appearance of new phonon modes.