High Pressure Structural Stability of Multiferroic Hexagonal REMnO3

TL;DR

This study investigates the structural stability of hexagonal REMnO3 (RE=Y, Ho, Lu) under high pressure, revealing phase transitions and stability ranges using advanced x-ray and spectroscopic methods.

Contribution

It provides new insights into the pressure-induced phase transition from hexagonal to orthorhombic in REMnO3 and details the stability of the hexagonal phase up to 20 GPa.

Findings

Hexagonal structure stable below ~20 GPa.

Phase transition to orthorhombic occurs starting at ~22 GPa.

Orthorhombic phase persists after pressure release.

Abstract

Structural changes in REMnO3 (RE= Y, Ho, Lu) under high pressure were examined by synchrotron x-ray diffraction methods at room temperature. Compression occurs more readily in the ab plane than along the c-axis. Under hydrostatic pressure (~11 GPa), the atoms hold their approximate ambient fractional positions in the unit cell and the spontaneous polarization shows no significant change. With increased pressure, a pressure-induced hexagonal to orthorhombic phase transition was observed starting at ~ 22GPa for Lu(Y)MnO3. A small volume fraction of Lu(Y)MnO3 is converted to the orthorhombic phase when the pressure is increased to 35 GPa and the orthorhombic phase is maintained on pressure release. High pressure IR absorption spectroscopy and Mn K-edge near edge x-ray absorption spectroscopy confirm that the hexagonal P63cm structure is stable below ~20 GPa and the environment around Mn ion is not changed. Shifts in the unoccupied p-band density of states with pressure are observed in the Mn K-Edge spectra. A schematic pressure-temperature phase diagram is given for the small ion REMnO3 system.