First principles study of zone centre phonons in rare-earth pyrochlore titanates, RE2Ti2O7 (RE = Gd, Dy, Ho, Er, Lu; Y)

We present first principles study of zone centre phonons in rare-earth pyrochlore titanates, RE2Ti2O7 (RE = Gd, Dy, Ho, Er, Lu; Y). The study has been made within the density functional theory and linear response formalism to calculate, understand, and assign the various Raman and infra-red mode frequencies. Our DFT calculated Raman mode frequencies are in excellent agreement with experimental results except one F-2g mode frequency around 800 cm(-1), which is not observed in experimental measurements, in the same manner as that of ab initio calculations of Fischer et al. [Phys. Rev. B 78 (2008)014108] [19]. Increase in frequency of this F-2g mode indicates that TiO6 octahedra becomes more tightly packed as we go from Gd -> Dy -> Ho -> Y -> Er -> Lu. Experimentally observed frequency around 450 cm(-1) is confirmed in our calculations, and has been assigned to F-2g mode, which was assigned to TiO2 as an impurity phase in Gd2Ti2O7, Er2Ti2O7, and Y2Ti2O7 Pyrochlore oxides. (C) 2012 Elsevier B.V. All rights reserved.