Revision of the structure of Cs2CuSi5O12 leucite as orthorhombic Pbca.

The crystal structure of a hydrothermally synthesized leucite analogue Cs(2)CuSi(5)O(12) has been determined and refined using the Rietveld method from high-resolution synchrotron X-ray and neutron powder diffraction data. This structure is based on the topology and cation-ordering scheme of the Pbca leucite structure of Cs(2)CdSi(5)O(12), and exhibits five ordered Si sites and one ordered Cu tetrahedrally coordinated (T) site. This structure for Cs(2)CuSi(5)O(12) is topologically identical to other known leucite structures and is different from that originally proposed by Heinrich & Baerlocher [(1991), Acta Cryst. C47, 237-241] in the tetragonal space group P4(1)2(1)2. The crystal structure of a dry-synthesized leucite analogue Cs(2)CuSi(5)O(12) has also been refined; this has the Ia3d cubic pollucite structure with disordered T sites.