Ag2Te2O7, a novel silver tellurate of weberite structure type

Ag2Te2O7 has been synthesized by solid state reaction of Ag2O and TeO2 under elevated oxygen pressure. The compound is diamagnetic and insulating, and decomposes at 560 degrees C in an Ar atmosphere into oxygen, Ag2TeO3 and TeO2. Ag2Te2O7 crystallizes orthorhombic in space group Imma with a = 7.266(2), b = 10.1430(9), c = 7.6021(17) angstrom, V = 560.3(2) angstrom(3), Z = 4,410 independent reflections, R-1 = 4.65 %, wR(2) = 11.13 %. The crystal structure consists of a three-dimensional framework of TeO6 octahedra which are linked by common vertices. Voids of the framework accommodate silver atoms which are coordinated by eight oxygen atoms. The structure derives from that one of naturally occurring Weberite, Na(2)MgA1F(7). The relationship to the pyrochlore structure type is discussed.