The crystal structure of lead tungstate, PbWO4,
is tetragonal, scheelite type, space group I41/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 P-4.
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.
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