HYDROTHERMAL SYNTHESIS AND STRUCTURE DETERMINATION OF CS2ZRSI6O15

A new cesium zirconosilicate, Cs2ZrSi6O15, is obtained by hydrothermal synthesis at T=1083K, P=218MPa. Despite a systematic crystal twinning , the structure was determinated from X-ray diffraction crystal data. Cs2ZrSi6O15 is monoclinic, C2/m, a=26.61(1)Angstrom, b=7.506(2)Angstro m, c=11.602(4)Angstrom, beta=107.43(2)degrees, Z=6. The structure can be described from the stacking of silicate Si6O156- slabs linked by Zr O6 octahedra, or by a slightly distorted ABCA... compact type packing of ZrSi6O22 Secondary Building Units. Cesium atoms are located in larg e cavities with X, XII and XIII coordination; Cs-O distances vary from 2.98 Angstrom to 3.75 Angstrom. The connection of cesium polyhedra in volves vertex or edge sharing along all the possible directions. This feature explains the low cesium release of Cs2ZrSi6O15 at high tempera ture.