Phonons and Jahn-Teller distortion in manganites

Abstract

In this work, we present the calculated results phonon properties of rhombohedral (R over(3, -) c) La0.7 A0.3′ MnO3 (A′: Sr, Ba and Pb) manganites by using a lattice dynamical model theory. The effect of internal pressure determined by the average A-site atomic radius 〈rA〉 is discussed. The computed zone centre phonon frequencies at ambient condition agree fairly well with the experimental results. The Raman active A1g mode is most sensitive to the change of A-site atomic radius. The internal pressure hardens the A1g phonon mode and reduces the electron-phonon interactions and hence the Jahn-Teller distortion. Change in the frequency of the Raman active Eg modes with 〈rA〉 is also observed. Different effect is observed for the low and high average A-site atomic radius. Effect of internal pressure modifies the phonon modes, which is observed to be reflected in calculated phonon density of states. © 2007 Elsevier B.V. All rights reserved.