First-principles lattice dynamics calculations are systematically made on four polymorphs of SrHfO3. The hierarchy of the total energy at the ground state is Pm3m > I4/mcm > Cmcm > Pnma, which agrees with the sequence of iterative transitions with temperature as reported by experiments. Three structures, Pm3m, I4/mcm and Cmcm, are found to be dynamically unstable at the ground state. A soft mode of phonons appears in I4/mcm and Cmcm at the Γ-point. The atomic displacements for the soft mode are analogous to those of the R25 mode of Pm3m, which is related to the rotation of the HfO6 octahedron. Pnma phase shows lowest energy and it is the only dynamically stable structure among the four phases. The volume expansion coefficient, bulk modulus and heat capacity are computed within quasi-harmonic approximations using the vibrational density of states. They are compared to experimental data.
ASJC Scopus subject areas