CRYSTAL-STRUCTURES OF 2 SODIUM YTTRIUM MOLYBDATES - NAY(MOO4)2 AND NA5Y(MOO4)4

The crystal structure of NaY(MoO4)2 has been determined from powder X-ray diffraction data [space group I4(1)/a, Z= 2, a = 5.19890(5) angstrom, c = 11.3299(1) angstrom]. The Na and Y atoms are disordered over the eight-coordinate sites of a scheelite structure. The crystal structure of Na5Y(MoO4)4 has been determined from single-crystal X-ray diffraction data [space group I4(1)/a, Z = 4, a = 11.374(3) angstrom, c = 11.440(5) angstrom] and found to be scheelite related, with the tetrahedral sites occupied by an ordered arrangement of Mo and Na in a 4:1 ratio. Comparisons are drawn between the structures of these two closely related phosphor materials.