Pressure induced phase transitions in Sm-doped BiFeO3 in the morphotropic phase boundary.

Sm-doped BiFeO3 compacted powders with composition across the morphotropic phase boundary region were prepared by sol-gel method. Crystal structure, morphology and magnetic state of the compounds were analyzed as a function of dopant concentration, temperature and external pressure using synchrotron and laboratory X-ray diffraction, electron microscopy, Raman and Mossbauer spectroscopy. Application of external pressure shifts the phase transition from the rhombohedral structure to the nonpolar orthorhombic structure towards lower concentration of the dopant content, wherein the amount of the anti-polar orthorhombic phase notably decreases. Raman and Mossbauer spectroscopy data provides additional information about the structural distortion on local scale level which testifies faster formation of nonpolar orthorhombic phase and associated modification in the magnetic state in the compounds subjected to high pressure. Temperature increase leads to the structural transition to the nonpolar orthorhombic phase regardless the structural state at room temperature; furthermore, application of external pressure decreases the phase transition temperature.