ISSN:
1063-7745
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract The crystal structures of Ca9 R(VO4)7 (R = Nd (I), Sm (II), or Gd (III)) were studied by the Rietveld method. The compounds are isostructural to Ca3(VO4)2 and are crystallized in the trigonal system (sp. gr. R3c, Z = 6). The unit-cell parameters are as follows: for I, a = 10.8720(5) Å, c = 38.121(1) Å; for II, a = 10.8652(5) Å, c = 38.098(1) Å; and for III, a = 10.8631(5) Å, c = 38.072(1) Å. In the structures of I and II, the M(1), M(2), and M(3) positions are statistically occupied by the rare-earth cations and calcium anions. In the structure of III, the Gd3+ cations occupy the M(1) and M(2) positions. The distributions of the R 3+ cations over the positions are characteristic of each structure. The composition of the cerium-ontaining compound Ca9.81Ce0.42(VO4)7 (a = 10.8552(5) Å, c = 38.037(1) Å) was refined and its crystal structure was solved from the X-ray powder data. In this compound, cerium atoms are in the oxidation states +3 and +4.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1134/1.1312910
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