Fizika Tverdogo Tela, 2025 Volume 67, Issue 3,Pages 520–527(Mi ftt11364)
Ferroelectricity
Construction of the interatomic potential of the ferroelectric barium titanate based on the temperature dependence of the heat capacity near the phase transition
Abstract:
The article presents the results of studying the temperature dependence of the heat capacity of the ferroelectric BaTiO$_3$ in the vicinity of the phase transition in order to construct the interatomic potential. An effective interatomic potential is introduced to take into account the type of chemical bond (covalent for Ti–O or ionic for Ba–O bond). To assess the correctness of the choice of the effective potential, it is proposed to calculate the enthalpy of the phase transition taking into account the presence of several activation processes in the vicinity of the phase transition. The presence of two activation processes when approaching the Curie temperature in the ferroelectric phase with activation energies $U$ is established. The first is due to the motion of oxygen vacancies ($U_1$ = 0.99 eV). The second begins at the critical temperature $T_{\text{crit}}$. (5 K below the Curie temperature $T_C$) and is associated with the electron-phonon interaction in the presence of electron orbital degeneracy and mixing of the electron bands of the 2$p$-states of O with the $d$-states of Ti ($U_2$ = 2.46 eV). The activation process in the paraelectric phase ($U_3$ = 2.87 eV) is associated with the relaxation of the structure after a change in the symmetry of the crystal lattice. The results obtained are discussed within the framework of the vibronic theory of ferroelectricity, taking into account the
Jahn–Teller effect (or pseudo-effect).
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