Abstract:
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The crystal structure of lead tungstate, PbWO4, is tetragonal, scheelite type,
space group I41/a. This compound, due to the difference in the vapour pressure
of the two raw oxides, WO3 and PbO, used in the crystal growth, is frequently
subjected to lead deficiency. It has been reported by one group 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 P-4. We report
here on neutron diffraction measurements performed on three different single
crystals, two of them being presented to us as possibly presenting the lead
deficient phase. Our measurements do not show any indication of structural
distortion, even at 70 K for one of the samples. The existence of a lead
deficient structure remains unconfirmed.
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