The structure of ce-doped Bi2(MoO4)3 as determined by neutron profile refinement

The structure of Bi_1.8Ce_0.2(MoO₄)₃ has been refined with powder neutron diffraction data by the Rietveld method. The structure can be derived by severely distorting the scheelite structure (AMO₄) and is perhaps better written $\text{A}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{Ø}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{M}\text{O}{}_4$, where Ø = cation vacancy. Of the two bismuth atom sites, cerium preferentially occupies the more symmetric of the two (Bi(2) in the structure) with some cerium found in the scheelite subcell vacancies also. This site preference is understood by examining the symmetries of the two Bi sites. Crystal data: monoclinic, space group $\text{P2}{}_1\text{c}\text{, Z = 4, a = 7.697(2), b = 11.535(3), c = 11.944(3)}$, β = 115.19.