Pressure-dependent phonon properties ofLa0.7Sr0.3MnO3

Abstract

In this work, we present the calculated results on the pressure dependent phonon properties of rhombohedral $(R\overline{3}c)$ ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ manganite by using a lattice dynamical model theory. The effect of internal pressure determined by the average $A$-site atomic radius is also investigated and compared with the effect of applied pressure. The computed zone center phonon frequencies at ambient pressure agree fairly well with the experimental results and the modes related to the octahedral distortion exhibit hardening with the increase in pressure. The Raman active ${A}_{1g}$ mode is most sensitive to pressure with a slope of $1.0\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}∕\mathrm{GPa}$ and shows unusual couple of slope change. Both internal and external pressures harden the ${A}_{1g}$ phonon mode and reduce the electron-phonon interactions. Change in the frequency of the Raman active ${E}_{g}$ modes with frequency is also observed. Different effect is observed for the low and high average $A$-site atomic radius. The phonon dispersion curves in high symmetry directions of the Brillouin zone and phonon density of states are also calculated. The pronounced shift of the peak positions in phonon DOS is observed with the increase in pressure. The analysis of the reduction of the high frequency phonon peak width and effective mode-Gr\"uneisen parameter allows us to draw a conclusion for the decrease in lattice distortion and to some extent Jahn-Teller (JT) distortion, a signature of rhombohedral structure for the manganites. The role of pressure on the lattice specific heat is also discussed.