High-pressure phase transition in CsBr

Static-compression data have been collected on cesium bromide up to a pressure of 70 GPa (V/$V_0$=0.500) with use of x-ray diffraction through the diamond-anvil cell at room temperature. CsBr, which is in the CsCl (B2) structure at zero pressure, undergoes a second-order phase transition to the tetragonal CuAu I structure at 53 (±2) GPa. Only one other alkali halide, CsI, has been shown to undergo a similar distortional transition at high pressures. With the extrapolation of the available data, both halides are expected to achieve the fcc lattice by about 130 GPa. Our new CsBr data are in good agreement with an Eulerian finite-strain equation of state derived from the ultrasonically measured elastic constants.