The crystal structure of eulytite Na3Bi5(PO4)6

The crystal structure of Na3Bi5(PO4)(6) was solved using the single-crystal X-ray diffraction technique. The structural refinement has led to a reliability factor of R-1 = 0.0257 (wR(2) = 0.0533) for 428 independent reflections. This compound was found to crystallize in the cubic system (space group I (4) over bar 3d) with eulytite structure and the lattice parameters: a = 10.097 (4) Angstrom, V = 1029.38 Angstrom(3), Z = 2, D-calc. = 5.43 g cm(-3) (D-exp. = 5.32(5) g cm(-3)). The structure is characterized by the existence of one single general position (48a) for oxygen anions and two distinguished positions (16c)occupied by Na+ and Bi3+ cations, respectively. The site occupation factors are equal to 3/8 and 5/8 for sodium and bismuth, respectively. Although all P-O distances are identical (1.529(4) Angstrom), the O-P-O angles ranging from 108.06 (15) to 112.32 (31)degrees, show that [PO4](3-) are rather distorted. Both sodium and bismuth cations are located in octahedral sites with corresponding mean distances of Na-O and Bi-O equal to 2.428 and 2.386 Angstrom, respectively. As expected from the close values of the ionic radii of Na+ and Bi3+, these distances lie in the same range. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.