G. W. Beall

Structural investigations of YPO4, ScPO4, and LuPO4

Abstract YPO4, ScPO4, and LuPO4 crystallize in the tetragonal system conforming to space group model I41/ amd (D194h, No. 141), Z = 4. The refined crystal structures have been determined from three-dimensional single-crystal X-ray diffraction data. Final least-squares full-matrix refinement yielded respective R-values of 0.024, 0.028, and 0.038. The metal atom in each compound is 8-coordinated to oxygen atoms. The resultant polyhedron is viewed as two interpenetrating tetrahedra forming a bis-bisphenoid (D2d). The phosphate group in each compound is a distorted tetrahedron. Important bond and contact distances and bond angles as well as Ortep-II drawings are presented to foster a wider base for future investigations related to potential employment of lanthanide orthophosphates as hosts for radioactive nuclear waste.

Ninefold coordination LaPO4: Pentagonal interpenetrating tetrahedral polyhedron

Abstract The crystal structure of LaPO4 has been determined from three-dimensional single-crystal X-ray diffraction data. The respective residual indices R1 and R2 have been refined to 0.020 and 0.021, based on 625 unique reflections. Crystallization occurs in the monoclinic space group P21/n (No. 14) with a = 6.825(4), b = 7.057(2), c = 6.482(2) A, and β = 103.21(4)°. Z = 4. The lanthanum metal atom is nine-coordinated to oxygen atoms forming a polyhedron best described as a pentagonal interpenetrating tetrahedron. The nine-coordinated La atoms are linked together by distorted tetrahedral phosphate groups. Important interatomic distances and angles are presented.

The structure of cerium orthophosphate, a synthetic analogue of monazite

The crystal structure of CePO4 has been determined by modern X-ray crystallographic techniques. The unit cell is monoclinic (space group P21n) with a = 6.7777(3), b = 6.993(3), c = 6.445(3) A, and β = 103.54(4)°. The final least-squares refinement yielded R = 0.0276, and Rw = 0.0280. The structure is made up of irregular 9-coordinated cerium atoms linked together by distorted tetrahedral phosphate groups. Comparisons with previous structural determinations of naturl monazites are made. A potential application of the lanthanide orthophosphates as a nuclear waste matrix material is briefly discussed.

THE STRUCTURES OF THREE LANTHANIDE ORTHOPHOSPHATES

Abstract TbPO 4 , DyPO 4 , and HoPO 4 crystallize in space group [4 1 /amd (No. 141), zircon structure, Z=4. The crystal structures have been determined from automated three-dimensional single crystal X-ray diffraction analyses. Least-squares full matrix refinements yielded final weighted R-values equal to 00.035, 0.037, and 0.036, respectively. The lanthanide metal atom in each compound is eight-coordinated to oxygen atoms forming two orthogonal interpenetrating tetrahedra. Each tetrahedron has distinct bond distances. The resultant polyhedron is best described as distorted dodecahedron (D 2d ). Important crystal data, parameters, bond lengths, and angles are tabularized.