Ferroelectricity and pressure-induced phase transitions in HgTiO3
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Using ab initio density functional theory, the ground state of mercury titanate is determined and phase transitions occurring in it at pressures P ≤ 210 kbar are analyzed. It is shown that the R3c structure experimentally observed in HgTiO3 is metastable at P = 0. The ground state structure at T = 0 varies according to the scheme \(R3c \to R\bar 3c \to Pbnm\) with increasing pressure in agreement with available experimental data. It is shown that the appearance of ferroelectricity in HgTiO3 at P = 0 is associated with an unstable soft mode. Some properties of crystals in the \(R\bar 3c\) phase are calculated, in particular, the band gap in the GW approximation (E g = 2.43 eV), which is in better agreement with experimental data than the value obtained in the LDA approximation (1.49 eV). An analysis of the thermodynamic stability explains why the synthesis of mercury titanate is possible only at high pressures.
KeywordsPhonon Spectrum Ground State Structure Ferroelectric Phase Transition Interplane Distance Brillouin Zone Boundary
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- 7.Springer Materials: The Landolt-Börnstein Database; URL http://www.springermaterials.com/navigator/.