Bismutocolumbite, Bi(Nb0.79Ta0.21)O4, stibiocolumbite, Sb(Nb0.67Ta0.33)O4, and their structural relation to the other ABO4 minerals with stibiotantalite (SbTaO4) structure

Author(s): Natalia V Zubkova, Dmitry Y. Pushcharovsky, Gerald Giester, A S Smolin, Ekkehart Tillmanns, Franz Brandstätter, Vera Hammer, I S Peretyazhko, A N Sapozhnikov, A A Kashaev
Abstract: The crystal structures of bismutocolumbite, (Bi0.99Sb0.01)(Nb0.79Ta0.21 O4 (I) and stibiocolumbite, Sb(Nb0.67Ta0.33)O4 (II) were established from X-ray single crystal diffraction: I, orthorhombic, space group Pnna, a = 5.668(1) A°, b = 11.725(2) A°, c = 4.971(1)A°, V = 330.4 A°3, Z = 4, dcalc. = 7.726,dobs. = 7.17-7.56 g/cm3, F(000) = 614, R = 0.025 for 820 unique reflections with 1>2s(1); II orthorhombic, space group Pna2I a = 5.557(1) A°, b = 4.932(1) A°, c = 11.808(2)A°, V = 323.6 A°3, Z= 4, dcalc. = 6.316, F(000) = 538, R = 0.023 for 1437 reflections with 1>2s(1). In both structures (Nb, Ta) atoms have octahedral coordination. In I Bi-O distances within distorted octahedron range from 2.126 to 2.738 A°; (Nb, Ta)-O distances are between 1,852-2.148A°, in II Sb-O distances range from 2.008 to 2.619 A° within distorted pseudotrigonal bypiramid; (Nb, Ta)-O distances are between 1.848 - 2.085 A°. Both structures contain sheets of corner-linked (Nb, Ta)O6-octahedra separated by significantly distorted BiO6(SbO5)-polyhedra with four shorter distances opposite to the lone-pair electrons of Bi3+ (Sb3+). The repulsive forces between lone-pair electrons and the O atoms lead to the distortion of (Nb, Ta)O6 octahedra in the stibiotantalite structure type. Two shortest bonds (Nb, Ta)-O(1) = 1.852 A° in I as well as (Nb, Ta)-O(4) and -O(3) = 1.848 and 1.891 A°, respectively, in II occur with ligands which are oriented in the direction of the lone-pair electrons of Bi3+(Sb3+) and which form the elongated bonds Bi-O(1) = 2.738 A° in I and Sb-O(3) = 2.619 A° and Sb-O(4) = 3.012 A° in II. The structures of I and II with a close packing indices (CPI) of 54 and 55, respectively, can not be considered as atomic ones in contrast to some other ABO4 oxides with 6-fold coordination of cations, namely wolframite (Fe,Mn )[6]W[6]O4 (CPI = 68) and rutile-like CrVO4 (CPI = 74). The structural transitions (Pna21 to Pnna) in (Bi, Sb)(Nb, Ta)O4 series should be considered as a function of chemical composition, temperature and pressure. Œ 2002 E. Schweizerbart'sche Verlagsbuchhandlung.
Organisation(s): Department of Mineralogy and Crystallography
External organisation(s): Anuchin Research Institute and Museum of Anthropology
Journal: Neues Jahrbuch für Mineralogie. Monatshefte
Pages: 145-159
No. of pages: 15
ISSN: 0028-3649
DOI: https://doi.org/10.1127/0028-3649/2002/2002-0145
Publication date: 2002
Peer reviewed: Yes
Austrian Fields of Science 2012: 1051 Geology, Mineralogy
Portal url: https://ucrisportal.univie.ac.at/en/publications/bismutocolumbite-binb079ta021o4-stibiocolumbite-sbnb067ta033o4-and-their-structural-relation-to-the-other-abo4-minerals-with-stibiotantalite-sbtao4-structure(df43d5d1-3529-4299-b8dd-e7f388bc281b).html

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