Experimental evidence for pressure-driven isostructural and symmetry-breaking phase transitions on Bi14CrO24

We performed in situ X-ray diffraction experiments on Bi14CrO24 under pressure up to 17.4 GPa. We discovered two reversible phase transitions that take place at 7.3 and 12.1 GPa. The first transition is isostructural and the second-transition involves a tetragonal-monoclinic symmetry reduction. Both transitions involve a small volume collapse indicating that they have a first-order character. For the three observed phases we determined a P–V equation of state. All of them are highly compressible having bulk moduli that range from 64 to 70 GPa. We also determined the axial compressibilities for difference phases, being the response of the structures to pressure anisotropic. This behavior is more notorious in the high-pressure monoclinic phase. Finally, the observed structures are related and compared with the two previously known polymorphs of Bi14CrO24.