Structural polymorphism in multiferroic BiMnO3 at high pressures and temperatures

•The detailed P–T phase diagram of BiMnO3 was established.•We found three monoclinic modifications of BiMnO3 at pressure and temperature.•A suppression of monoclinic C2/c phase have been observed under pressure.•We found a new orthorhombic Imma phase of BiMnO3 at P>20GPa. Structural phase transitions in BiMnO3 were studied by means of energy-dispersive X-ray diffraction in the pressure 0–4GPa and temperature 300–900K ranges, and also by means of angle-dispersive X-ray diffraction and Raman spectroscopy at high pressures up to 50GPa and ambient temperature. The P–T phase diagram of BiMnO3 was constructed. A suppression of the transition temperatures between monoclinic C2/c and orthorhombic Pnma phases was observed under pressure. The temperature and pressure dependencies of lattice parameters were obtained. A new orthorhombic Imma phase was observed at P>20GPa. The lattice dynamics calculations were performed for the analysis of the Raman spectra of BiMnO3.