Crystal structure of lead tungstate at 1.4 and 300 K

The crystal structure of lead tungstate, PbWO4, is tetragonal, scheelite type, space group I4(1)/a. This compound is frequently subjected to lead deficiency, due to the difference in the vapour pressure of the two oxides, WO3 and PbO, used in the crystal growth. One group has reported that lead vacancies can order in a crystal structure derived from the scheelite type, but of lower symmetry and described by the space group P4/nnc or P4. We report here on neutron diffraction measurements performed on three different powdered samples. Our measurements do not show any indication of structural transition between 1.4 and 300 K. The structure is undoubtedly the tetragonal one. The existence of a lead deficient structure remains unconfirmed. (C) 2001 Elsevier Science B.V. All rights reserved.