First principles study of dielectric and vibrational properties of pyrochlore hafnates

We present the first principles study of dielectric, and vibrational properties of pyrochlore hafnates, RE2Hf2O7 (RE = La, Nd, Sm, Eu, Gd, Tb) in their cubic structure using density functional theory and density functional perturbation theory, incorporating ultrasoft pseudopotentials and plane waves. The full set of zone centre Raman and infra red frequencies, along with the contribution of all infra red active modes towards dielectric constant and mode effective charges is calculated and discussed. In all the studied hafnates dominant contribution to static dielectric constant is found to come from three infrared active phonons around 125 cm−1, 170 cm−1 and 305 cm−1. In addition, calculated structural properties are in very good agreement with experimental results. Mixed ionic-covalent bonding is found from the analysis of dynamical charges, static charges and density of states.

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