Magnetic and vibrational properties and crystal structure of Sr9.2Co1.3(PO4)(7) with disordered arrangements of some strontium, cobalt, and phosphate ions

摘要

Solid solutions of, Sr9+ Co1.5-x(PO4)(7) were found in the compositional range of 0.05 <= x <= 0.30. The structure of Sr9.2Co1.3(PO4)(7) (x = 0.2) was determined from single crystal X-ray diffraction (space group R (3) over barm (No. 166); Z = 31 a = 10.6100(5) angstrom and c = 19.6960(5) angstrom; V = 1920.17(14) angstrom(3); rho(cal) = 4.014 g cm(-3); mu = 20.377 mm(-1)) and refined to R-1 = 0.0343 and wR(2) = 0.0633 for 586 reflections with I > 2 sigma(I). Sr9.2Co1.3(PO4)(7) is structurally related to beta-Ca-3(PO4)(2) and Sr-3(PO4)(2) and has disordered arrangements of some Sr2+, Co2+, and PO43- ions. Sr2+ ions at a 9e site are statistically disordered among four positions near the center of symmetry. Co2+ and Sr2+ ions are split along the c-axis to occupy a 6c site that is 75% vacant. The PlO(4) tetrahedra are orientationally disordered. Sr2+ ions at an 8-fold coordinated 18h site, Co2+ ions at an octahedral 3a site, and the PlO(4) tetrahedra are ordered in the structure of Sr9.2Co1.3(PO4)(7). Features of Raman spectra are discussed in relation to the crystallographic structure of Sr9.2Co1.3(PO4)(7))7 and in comparison with Raman spectra of beta-Ca-3 (PO4)(2)- type and Sr-3(PO4)(2)-type Compounds. Sr9.2Co1.3(PO4)(7))7 is paramagnetic between 2 and 300 K with an effective magnetic moment of 4.98/mu(B) per Co2+ ion. (c) 2005 Elsevier Inc. All rights reserved.