Ambient-temperature high-pressure-induced ferroelectric phase transition in CaMnTi2O6

The ferroelectric to paraelectric phase transition of multiferroic CaMnTi2O6 has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that CaMnTi2O6 undergoes a pressure-induced structural phase transition (P42mc→P42/nmc) at ∼7GPa to the same paraelectric structure found at ambient pressure and Tc=630K. The continuous linear decrease of the SHG intensity that disappears at 7 GPa and the existence of a Raman active mode at 244 cm−1 that first softens up to 7 GPa and then hardens with pressure are used to discuss the nature of the phase transition of CaMnTi2O6, for which a dTc/dP=−48 K/GPa has been found. Neither a volume contraction nor a change in the normalized pressure on the Eulerian strain is observed across the phase transition with all the unit-cell volume data following a second-order Birch-Murnaghan equation of state with a bulk modulus of B0=182.95(2)GPa.