0000000000594212
AUTHOR
M. Isobe
Phonon properties of the spinel oxideMgTi2O4with theS=1/2pyrochlore lattice
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 ${2F}_{2g}$ symme…
Optical phonons in theNaTiSi2O6oxide withS=12spin chains
. The infrared-active phonon frequencies are obtained by Kramers-Kronig analy-sis of the reflectivity data. The assignment of the observed modes is done using lattice dynamical calculationsbased on the valence shell model. A phase transition at about 210 K is manifested through a dramatic changeof the mode frequency and broadening, and the appearance of new phonon modes. Analyzing the phononfrequency and damping vs temperature we have found that the phase transition leaves a fingerprint in thephonon dynamics of NaTiSi