ANHARMONIC EFFECTS IN THE BASAL EXPANSION OF LAYERED SOLIDS - THE LAYERED PEROVSKITES

The composition-dependent basal-spacing of the mixed-alkali layered pe rovskites CsxRb1-xCa2Nb3O10, has been measured over the range, 0 less than or equal to x less than or equal to 1 using high resolution X-ray diffraction and is compared with previous results on other layered so lids. The perovskite results are incompatible with both the flexible l ayer model, which has been successfully applied to graphite, dichalcog enides and clays and also with the harmonic rigid layer model but are in excellent agreement with the anharmonic Leonard-Jones model. The cr ucial role of anharmonicity is experimentally confirmed for the first time. Copyright (C) 1996 Published by Elsevier Science Ltd