EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE STUDY OF THE JAHN-TELLER PHASE-TRANSITIONS IN CSCRCL3 AND RBCRCL3 HEXAGONAL PEROVSKITES

The local structure of the (CrCl6) complex, in the different phases of CsCrCl3 and RbCrCl3 compounds, is determined by means of the extended x-ray-absorption fine-structures technique. It is proved that the complexes are distorted (elongated) in the high-temperature symmetrical (P63/mmc) alpha-phase and in the intermediate (C2/m) beta-phase present in RbCrCl3. The disortion amounts to rho-0 = 0. 39 angstrom at all temperatures. These results clarify the validity of the different conjectures on the possibility of distortion in the alpha-phase derived from different experimental techniques.