PHASE-TRANSITION SEQUENCE INDUCED BY HIGH-PRESSURE IN CACL2

The high-pressure behaviour of CaCl2 has been investigated by angle di spersive x-ray powder diffraction in a diamond anvil cell at room temp erature up to 25 GPa. Five phases with different structures are observ ed under increasing pressure: CaCl2, alpha-PbO2, EuI2, SrI2 and PbCl2. The phase transition sequence induced by high-pressure in CaCl2 betwe en the CaCl2 and cotunnite structures confirms that the presence of an empty d shell in the cation is crucial for obtaining a transition seq uence via the EuI2 structure rather than via the Pa (3) over bar struc ture. (C) 1998 Elsevier Science Ltd. All rights reserved.