Crystal structure and cation transport properties of the layered monodiphosphates Rb6Bi4(PO4)2(P2O7)3

Single crystals of the new Bi(III) phosphates, Rb6Bi4(PO4)(2)(P2O7)(3), have been isolated and their structure has been determined by X-ray diffraction techniques. This compound crystallizes in the monoclinic space group P2(1)/c with a = 9.077(1) Angstrom, b = 9.268(2) Angstrom, c = 36.418(6) Angstrom, beta = 95.75(1)degrees and Z = 8. The crystal structure is made up of BiO5 and BiO6 polyhedra sharing the corners with PO4 tetrahedra and P2O7 diphosphate groups. The structure can be described as infinite anionic layers with composition [Bi-4(PO4)(2)(P2O7)(3)](infinity)(6-) parallel to the [301] plane, connected via P-O-Bi bridges to form a three-dimensional open framework. This framework delimits tunnels running along [100] and [010] directions, where the rubidium ions reside. This compound exhibits a rubidium ion conduction but with rather low conductivity value sigma = 2.45 x 10(-7) Omega(-1) cm(-1) at 640 K. (C) 2003 Elsevier Science (USA). All rights reserved.