The nature of the high pressure phase transitions in InAs, BaTe and CsI are discussed. X-ray diffraction studies in the Cornell High Energy Synchrotron Source to 101 GPa show that CsI becomes tetragonal at about 38 GPa and orthorhombic at about 56 GPa. The separation of the nearest like neighbors is reduced dramatically when the orthorhombic phase forms; at 56 GPa this separation is 28% less than the zero pressure value. At 56 GPa the coordination is essentially ten-fold with eight unlike neighbors and two like neighbors.
