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Devonshire-Landau free energy of BaTiO3 from first principles

Jorge Iniguez·S. Ivantchev·J. M. Perez-Mato·Alberto Garcia
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Abstract

We have studied the Devonshire-Landau potential underlying the phase transition sequence of BaTiO3 using the first-principles effective Hamiltonian of Zhong, Vanderbilt, and Rabe [Phys. Rev. Lett. 73, 1861 (1994)], which has been very successful in reproducing the phase transitions and the dielectric and piezoelectric properties of this compound. The configuration space (determined by the polarization P as order parameter) was explored with the help of auxiliary electric fields. We show that the typically assumed form of the potential, a sixth-order expansion in P around the paraelectric cubic phase, properly accounts for the behavior of the system, but we find a non-trivial temperature dependence for all the coefficients in the expansion, including the quadratic one, which is shown to behave non-linearly. Our results also prove that the sixth-order terms in the free-energy expansion (needed to account for the first-order character of the transitions and the occurrence of an orthorhombic phase) emerge from an interaction model that only includes terms up to fourth order.

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Jorge Iniguez, S. Ivantchev, J. M. Perez-Mato, Alberto Garcia. 2000-09-27. Devonshire-Landau free energy of BaTiO3 from first principles. https://doi.org/10.1103/physrevb.63.144103

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