Structural investigation of Pb(Mo@@ xW1-@@ x)O4 solid solutions via X-ray and neutron diffraction

Abstract

PbMo@@ xW1-@@ xO4 single-crystal solid solutions with @@ x=0.2, 0.5, 0.8 have been grown by the Czochralski method in air atmosphere from the initial charge with over-stoichiometric amount of YNbO4 (15wt%). X-ray and neutron single-crystal and X-ray powder (Rietveld method) diffraction investigations of PbMo@@ xW1-@@ xO4 crystals indicate bulk inhomogeneity of their compositions, absence of color centers, and deviation of refined compositions from initial ones: the Nb5+ and Y3+ contents as well as oxygen vacancies content increase with increasing @@ x in PbMo@@ xW1-@@ xO4. It was found that PbMo@@ xW1-@@ xO4 with @@ x=0.2, 0.5, 0.8, 1.0 crystallizes in the scheelite-type structure with space group @@ I41@@ /a, unlike crystal with @@ x=0, which is characterized by the symmetry reduction to space group I4_ caused by ordering of oxygen vacancies. The correlation between the @@ a and @@ c unit cell parameters and composition of cation sites, dodecahedral and tetrahedral, and deficiency of oxygen site was revealed.