First-principles theory of structural phase transitions for perovskites: Competing instabilities

Abstract

We extend our previous first-principles theory for perovskite ferroelectric phase transitions to treat also antiferrodistortive phase transitions. Our approach involves construction of a model Hamiltonian from a Taylor expansion, first-principles calculations to determine expansion parameters, and Monte-Carlo simulations to study the resulting system. We apply this approach to three cubic perovskite compounds, SrTiO₃, CaTiO₃ and NaNbO₃, that are known to undergo antiferrodistortive phase transitions. We calculate their transition sequences and transition temperatures at the experimental lattice constants. For SrTiO₃, we find our results agree well with experiment. For more complicated compounds like CaTiO₃ and NaNbO₃. which can have many different structures with very similar energy, the agreement is somewhat less satisfactory.

Key Words:

• Structural phase transitions: ferroelectrics
• SrTiO₃
• CaTiO₃
• NaNbO₃