Elastic anomalies of barium titanate

The derivation of the elastic constants of anomalies of the second-, third- and fourth-order for basium titanate and related compounds yields the temperature variation of the third-order elastic and fourth-order elastic constants for the phase transition from the tetragonal to orthorhombic phases. From the stability conditions, the equilibrium values of the three components of the order parameter and the strain variables have been ascertained. The Landau-Khalatnikov equations are used for determining the order parameter in the two phases.