Evidence of an intermediate high-pressure phase in BaFBr and BaFI

Abstract

Structural behaviour of BaFX (X=Br or I) has been studied under pressure using powder X-ray diffraction method. Both systems show a gradual pressure-induced distortion to a final monoclinic phase via an intermediate orthorhombic phase. This interesting behaviour is found to be consistent with a picture, wherein, upon increasing compression, there is a gradual anisotropic distortion of the electronic charge cloud in the weakly bound X − bi-layer perpendicular to the stacking direction ( c-axis), which renders the unit cell unstable against symmetry lowering deformations.