Structural characterization of PbWO4 and related new phase Pb7W8O(32-x)

Single crystals of PbWO4 have been obtained by the Czochralski method. Atomic structure has been determined by X-ray diffraction (scheelite type, tetragonal, space group I4(1)/a, a = 5.456(2), c = 12.020(2) Angstrom). With PbO deficiency in the melt, crystallization occurred with a new atomic arrangement determined by X-ray diffraction (tetragonal, space group P4/nnc, a = 7.719(2), c = 12.018(2) Angstrom). Unit cell parameter a related to the scheelite type by a factor of root 2. Oxygen and lead sites not fully occupied gave a formula Pb7W8O(32-x) with x = 3.2(8).