Crystal structures of double vanadates, Ca₉ R(VO₄)₇ ⋅ III. R = Nd, Sm, Gd, or Ce

Authors: Belik, A.; Morozov, V.; Grechkin, S.; Khasanov, S.; Lazoryak, B.

Source: Crystallography Reports, Volume 45, Number 5, September 2000 , pp. 728-733(6)

Publisher: MAIK Nauka/Interperiodica

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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 Ca_9.81Ce_0.42(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.

Document Type: Research article

DOI: http://dx.doi.org/10.1134/1.1312910

Affiliations: 1: Email: belik@tech.chem.msu.ru

Publication date: 2000-09-01