Phonons and Jahn–Teller distortion in manganites

Abstract

In this work, we present the calculated results phonon properties of rhombohedral ( R 3 ¯ c ) La 0.7 A 0.3 ′ MnO 3 (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 〈 r A〉 is discussed. The computed zone centre phonon frequencies at ambient condition agree fairly well with the experimental results. The Raman active A 1g mode is most sensitive to the change of A-site atomic radius. The internal pressure hardens the A 1g phonon mode and reduces the electron–phonon interactions and hence the Jahn–Teller distortion. Change in the frequency of the Raman active E g modes with 〈 r A〉 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.