Whitlockite-Related Phosphates Sr9A(PO4)7 (A=Sc, Cr, Fe, Ga, and In): Structure Refinement of Sr9In(PO4)7 with Synchrotron X-Ray Powder Diffraction Data

✍ Scribed by A.A. Belik; F. Izumi; T. Ikeda; M. Okui; A.P. Malakho; V.A. Morozov; B.I. Lazoryak

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 437 KB
• Volume: 168
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.2002.9716

✦ Synopsis

Five phosphates, Sr 9 A(PO 4 ) 7 (A=Sc, Cr, Fe, Ga, and In), were synthesized by the solid state method at (1270 to 1420) K and characterized by X-ray powder diffraction, infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and second-harmonic generation (SHG). SHG showed Sr 9 A(PO 4 ) 7 to be centrosymmetric. Sr 9 In(PO 4 ) 7 is structurally related to b-Ca 3 (PO 4 ) 2 (space group R3c; a ¼ 10:439 ( A and c ¼ 37:375 ( A; Z ¼ 21) and Sr 9+x A 0 1.5Àx (PO 4 ) 7 (A 0 =Mn, Fe, Co, Ni, Cu, and Cd; space group R % 3m; aE10:6 ( A and cE19:7 ( A; Z ¼ 3), having a new type of a monoclinic superstructure. Structure parameters of Sr 9 In(PO 4 ) 7 were refined by the Rietveld method from synchrotron X-ray diffraction data on the basis of space group I2=a to afford lattice parameters of a ¼ 18:0425ð2Þ ( A, b ¼ 10:66307ð4Þ ( A, c ¼ 18:3714ð2Þ ( A, and b ¼ 132:9263ð5Þ1 (Z=4). The asymmetric unit of Sr 9 In(PO 4 ) 7 contains five Sr, one In, four P, and 14 O sites. Sr 2+ ions are coordinated to either eight or nine oxide ions. Sr 2+ ions at an Sr4 site are disordered over two positions near a center of symmetry. In 3+ ions occupy an octahedral site. O12 atoms belonging to P1O 4 tetrahedra are highly disordered because they are bonded to the Sr4 atoms.