Improved structural parameters for the lanthanide orthovanadates (including also (\mathrm{YVO}{4}) and (\mathrm{ScVO}{4}) and new results for (\mathrm{PrVO}{4}), (\mathrm{TmVO}{4}), and the (\mathrm{LuVO}{4}) end members) have been determined by employing a full-profile Rietveld structure analysis of neutron powder-diffraction data. High-quality powders of the zircon-type (M \mathrm{VO}{4}) vanadates were prepared by a homogeneous coprecipitation in molten urea. The zircon structure has space group symmetry (I 4_{1} / a m d, Z=4), with 3 atoms occupying the asymmetric unit. In all, 22 parameters were refined with final agreement values of (R_{\mathrm{p}}=) (0.0313-0.0421, R_{w \mathrm{p}}=0.0361-0.0511), and G-of- (\mathrm{F}=1.210-1.962). The average V-O bond length for all of the (\mathrm{MVO}{4}) samples is 1.709(2) (\AA), and the V-O distance exhibits a small systematic shortening with decreasing (M) atom size. The oxygen positional parameters, the cell dimensions, and the (M-O) distances vary systematically with the metal-ion atomic number. The anisotropic thermal motion of the oxygen atom has the largest amplitude normal to the shared polyhedral edge between the (\mathrm{VO}{4}) tetrahedron and (\mathrm{MO}_{8}) bisdisphenoid. Empirical relations are given for the cell dimensions and oxygen atom position as a function of the size of the lanthanide ion which can be used to estimate structural parameters for other zircon-type lanthanide vanadate end-members and vanadate solid solutions. O 1994 Academic Press, Inc.