1. Centre for Science at Extreme Conditions (CSEC) and School of Chemistry University of Edinburgh Mayfield Road Edinburgh EH9 3JZ UK
2. Univ. Lille CNRS Centrale Lille Univ. Artois UMR 8181 UCCS Unitéde Catalyse et Chimie du Solide F-59000 Lille France
3. Institut Laue-Langevin 38042 Grenoble Cedex France