Low-temperature structure and the ferroelectric phase transitions in the CdTiO3 perovskite

The paraelectric-ferroelectric transition in $\mathrm{CdTi}{\mathrm{O}}₃$ has been monitored using high-resolution neutron diffraction data. This necessitated preparing a sample enriched in $¹¹⁴\mathrm{Cd}$. A subtle, but significant, anisotropy in the thermal expansion of the lattice parameters for $\mathrm{CdTi}{\mathrm{O}}₃$ associated with the transition to the polar structure was observed. First-principles calculations are presented to understand energies, phonon dispersion, and structures of possible phases with different symmetries.