Phase transition of Bi₅Ti₃FeO₁₅ceramics discovered by Raman spectroscopy and in situ synchrotron XRD under stress field

Bi5Ti3FeO15 (BTFO) ceramics have been widely studied as a multiferroic material with some potential applications. However, the effect of the stress field on BTFO ceramics with complex lattice structures is unknown. Here, we use pressure-dependent Raman scattering spectroscopy to study the structure/phase transition of BTFO samples. Because the phonon mode changes significantly, there could be a phase transition in the range of 4.5-14.8 GPa. In order to further prove the occurrence of phase transition, we carried out in situ high-pressure angular dispersion x-ray diffraction (XRD), which clearly proved the structural evolution of BTFO: orthorhombic crystal A21am transformed into tetragonal I4/mmm. Note that the results from the XRD experiment are self-consistent with the data derived from Raman spectroscopy. It provides an effective method to explore the phase transition of complex oxide structures under high pressure.