Ferroelectric phase transition in orthorhombic CdTiO3: First-principles studies
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Parameters of the crystal structure and phonon spectra for orthorhombic cadmium titanate with space group Pbnm and its two possible ferroelectrically distorted phases (with space groups Pbn21 and Pb21 m) were calculated from first principles within the density functional theory. The obtained structural parameters and frequencies of Raman- and infrared-active modes are in good agreement with available experimental data for the Pbnm phase. Expansion of the total energy in a Taylor series of two order parameters showed that the ground state of the system corresponds to the Pbn21 structure into which the Pbnm phase transforms through a second-order phase transition without intermediate phases. A substantial discrepancy between calculated and experimentally observed lattice distortions and spontaneous polarization in the polar phase was explained by quantum fluctuations, as well as by existence of twins and competing long-period structures.
PACS numbers61.50.Ah 63.20.D- 77.84.Dy
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