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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)Å, b = 11.725(2)Å, c = 4.971(1)Å, V = 330.4Å3, Z = 4, dcalc. = 7.726, dobs. = 7.17-7.56g/cm3, F(000) = 614, R = 0.025 for 8...
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Context 1
... environment around Bi -atoms in bismutocolumbite is highly asymmetric with four shorter and two longer distances Bi -O similar to Sb 3 + in LT -and HT -SbNbO 4 ( Ponomarev et al. 1981), to Bi 3 + in a -BiNbO 4 (Subramanian & Calabrese 1993) and to Sn 2 + in a -SnWO 4 (Jeitschko & Sleight 1974) (Table 7). Sb 3 + cations in stibiocolumbite ex- hibite the same tendency to form the irregular coordination polyhedra: four Sb 3 + -O bonds 2.008 -2.338 Å are significantly shorter in respect to two (Table 8) indicates that the latter ligand does not participate in Sb 3 + polyhedron. This one-sided arrangement of four shorter ligands with distances on the opposite side of the lone-pair makes allowance for the space requirements of the stereoactivity of the 6s 2 lone-pair elec- trons of the Bi 3 + cations and of the 5s 2 lone-pair electrons of Sn 2 + and Sb 3 + cations. ...
Citations
... Structurally related Bi and Sb minerals: unit-cell parameters, space group (s.g.) symmetry, volume variation (ΔV) and CPI value.Zubkova et al. (2002); 2Galliski et al. (2001); 3Dihlström (1938); 4 ...
The new mineral species tavagnascoite, Bi4O4(SO4)(OH)2, has been discovered in the Pb-Bi-Zn-As- Fe-Cu ore district from Tavagnasco, Turin, Piedmont, Italy. It occurs as blocky colourless crystals, up to 40 micron in size, with a silky lustre. In the studied specimen, tavagnascoite is associated with other uncharacterized secondary Bi-minerals originating from the alteration of a bismuthinite ± Bi sulfosalts assemblage. Electron microprobe analysis gave (average of 3 spot analyses – in wt%): Bi2O3 85.32, Sb2O3 0.58, PbO 2.18, SO3 8.46, H2Ocalc 1.77, sum 98.31. On the basis of 10 O atoms per formula unit, the chemical formula is (Bi3.74Pb0.10Sb0.04)somma=3.88O3.68(SO4)1.08(OH)2, with rounding errors. Main calculated diffraction lines are [d in Å (relative intensity) hkl]: 6.39 (29) 012, 4.95 (19) 111, 4.019 (32) 121, 3.604 (28) 014, and 3.213 (100) 123. Unit-cell parameters are a = 5.831(1), b = 11.925(2), c = 15.123(1) Å, V = 1051.6(3) Å3, Z = 4, space group Pca21. The crystal structure has been solved and refined from single-crystal X-ray diffraction data to R1 = 0.037 on the basis of 1269 observed reflections. It consists of Bi–O polyhedra and SO4 tetrahedra. Bismuth polyhedra are connected each to other to form Bi–O sheets parallel to (001). Successive sheets are linked together by SO4 groups and hydrogen bonds. Tavagnascoite is the Bi-analogue of klebelsbergite, Sb4O4(SO4)(OH)2, and it is the fifth natural known bismuth sulfate without additional cations. The mineral and its name have been approved by the IMA CNMNC (2014-099).
Stibiotantalite, SbTaO4, from the Nanyangshan LCT pegmatite, North Qinling Orogen, Central China is described. The mineral is associated with oxystibiomicrolite, oxycalcioroméite, hydrokenomicrolite, hydroxynatromicrolite, hydromicrolite, stibnite, bismuthinite, tantalite-(Mn), columbite-(Mn), spodumene, polylithionite, trilithionite, luanshiweiite, fluorluanshiweiite, elbaite, albite, and quartz. Results from electron microprobe data analysis (n = 4) yield the average empirical formula (based on O = 4): (Sb0.96Bi0.04)Σ1.00(Ta0.85Nb0.15)Σ1.00O4. The seven strongest X-ray powder diffraction lines are [d in Å (I)(hkl)] 3.126(100)(121), 2.964(81)(040), 5.976(27)(020), 3.515(22)(111), 1.891(22)(240), 1.736(19)(161), and 2.693(16)(131). Single-crystal X-ray diffraction (SXRD) patterns show strong reflections consistent with space group Pna21. The refined unit-cell parameters from the SXRD data are a 5.5419(2) Å, b 4.9200(2) Å, c 11.8003(5) Å, and V 321.75(2) Å3 with Z = 4. The structure has been refined to a final R1 = 0.0173 on the basis of 766 reflections with Fo > 4σ(Fo). In the previous study, the AO6 octahedron of stibiotantalite was close to an ideal octahedron. The new structure refinement of stibiotantalite from the Nanyangshan pegmatite indicates that the AO6 octahedron has a larger distortion due to the lone-pair effect of Sb3+. The high-quality structural data presented in this study gives a more accurate portrayal of the crystal structure of stibiotantalite than provided in the original description of the mineral.
We have studied the effects of structural symmetry related distortions on the band gaps and overall energetics of SbMO4 compounds (M = Ta, Nb). Evolution of the electronic structures was studied as one transitions gradually from a system of 4d bands to 5d bands, and whether this has any effect on the Sb oxidation state or its lone pair s electrons. From the atomic point of view, electronic correlation energy is higher in Ta 5d than in Nb 4d, and Nb 4d bands are higher in energy than Ta 5d. These were examined in terms of oxidation states in their respective solids and mixed alloys. We look at the effects of increasing Nb concentration on the electronic structures of SbTa1-xNbxO4 alloys with emphasis on polyhedral interactions and overall cell distortions. We decouple the effects caused by the presence of different nd cations from those caused by distortions and reorientation of various polyhedra.
Thermal behavior of the orthorhombic (α) and triclinic (β) polymorphs of BiNbO4 was studied by the methods of high-temperature powder X-ray diffraction (HTPXRD) and differential scanning calorimetry (DCS) in the temperature range 25-1200 °C. The study revealed the sequence of thermal phase transformations and the new high-temperature modification, γ-BiNbO4, which was formed above 1001 °C and existed up to the melting temperature of BiNbO4. The incongruent melting of BiNbO4 was characterized by the formation of the cubic phase with the approximate composition Bi3NbO7. The HTPXRD method was used in this study to evaluate thermal deformations and to calculate thermal-expansion coefficients (TEC) of the three modifications of BiNbO4 (α, β, and γ). The average volumetric TECs of these three modifications were in the range 19-36 × 10⁻⁶ °C⁻¹. The triclinic phase β-BiNbO4 demonstrated the highest anisotropy of thermal expansion. α-BiNbO4 was characterized by the minimal TEC and anisotropy, which indicated its greatest stability. The crystal structure of γ-BiNbO4 was determined at 1100 °C using powder data and was refined using the Rietveld method (the α-LaTaO4 structural type, the space group Cmc21, a = 3.95440(3) Å, b = 15.0899(1) Å, c = 5.65524(5) Å, V = 337.458(5) ų, Rwp = 4.82, RBragg = 3.61%). The methods of thermal analysis and high-temperature powder X-ray diffraction revealed that, during the heating, bismuth orthoniobate underwent the following sequence of phase transitions: α-BiNbO4 → γ-BiNbO4 → β-BiNbO4 and β-BiNbO4 → γ-BiNbO4 → β-BiNbO4 or, at slow heating, β-BiNbO4 → (α-BiNbO4) → γ-BiNbO4 → β-BiNbO4, where γ-BiNbO4 is the high-temperature phase of bismuth orthoniobate.
The crystal structure of bismutocolumbite, Bi(Nb0.79Ta0.21)O-4 with orthorhombic (sp. gr. Pnna) stibio-tantalite structure type at ambient conditions has been determined at 2.59 and 9.56 GPa, and 23 degreesC. Crystal data and results of structure refinement using powder X-ray diffraction and Rietveld analysis for Bi-rich stibiocolumbite, (Sb0.52Bi0.48)(Nb0.71Ta0.29)O-4, are reported. At the pressure similar to2.9 GPa bismutocolumbite exhibits phase transition which is accompanied by the change of its symmetry: sp. gr. Pnna is replaced by the sp. gr. Pn2(1)a. This kind of transformation is anticipated at ambient pressure in bismutocolumbite- stibiocolumbite solid solution series in the compounds with Sb/(Bi + Sb) ratio higher than 0.52 which characterises the studied crystals of stibiotantalite. Similarly with scheelite-like BiVO4, in bismutocolumbite the reduction of the unit cell volume under HP is mainly a result of Bi-O polyhedral compression, which is accompanied by a rearrangement of (Nb,Ta)O-6 octahedra within octahedral sheets parallel to (010). (Nb,Ta)O-6 octahedra remain rigid with smaller change in size at high pressure.
Billwiseite ideally Sb-5(3+)(Nb,Ta)(3)WO18, is an oxide mineral from a granitic pegmatite on the eastern margin of the Nanga Parbat - Haramosh massif at Stak Nala, 70 km east of Gilgit, Pakistan. It is transparent, pale yellow (with a tinge of green), has a colorless to very pale-yellow streak, a vitreous luster, and is inert to ultraviolet radiation. Crystals are euhedral with a maximum size of similar to 0.5 x 0.25 x 0.15 mm and show the following forms: {100} pinacoid approximate to {011} pinacoid approximate to {410} prism; contact twins on (100) are common. Cleavage is {100} indistinct, Mohs hardness is 5, and billwiseite is brittle with a hackly fracture. The calculated density is 6.330 g/cm(3). The indices of refraction were not measured; the calculated index of refraction is 2.3, 2V(obs) = 76(2)degrees. Billwiseite is colorless in transmitted light, non-pleochroic, and the optic orientation is as follows: X parallel to b, Y boolean AND c = 72.8 degrees (in beta acute). It occurs scattered across the surface of a large (similar to 5 x 2.5 x 1.3 cm) crystal of lepidolite from a miarolitic cavity. The most abundant minerals in the cavities at Stak Nala are albite, quartz, K-feldspar, tourmaline, muscovite or lepidolite, topaz and fluorite, and billwiseite can be partly mantled by B-rich muscovite. Billwiseite is monoclinic, space group C2/c, a 54.116(5), b 4.9143(5), c 5.5482(5) angstrom, beta 90.425(2)degrees, V 1475.5(2) angstrom(3), Z = 4, a:b:c = 11.012 : 1 : 1.131. The strongest seven lines in the X-ray powder-diffraction pattern [d in angstrom(I)hkl] are as follows: 3.147(100)(91 (1) over bar, 911), 3.500(55) (51 (1) over bar, 511), 1.662(53)((14) under bar2 (2) over bar), 3.017(48)((18) under bar 00), 1.906(47)((18) under bar 20), 1.735(30)(11 (3) over bar, 113), 1.762(25)((27) under bar1 (1) over bar, (27) under bar 11). Chemical analysis by electron microprobe gave Nb2O5 12.03, Ta2O5 19.31, Sb2O3 48.34, TiO2 0.99, WO3 19.96, sum 100.63 wt.% where the valence state of Sb was determined by crystal-structure analysis. The resulting empirical formula on the basis of 18 O anions is Sb-4.87(3+)(Nb1.33Ta1.28Ti0.18W1.26)(Sigma 4.05)O-18. The crystal structure of billwiseite was solved by direct methods and refined to an R-1 index of 4.71% based on 2122 observed reflections collected on a three-circle diffractometer with MoK alpha X-radiation. The structure consists of two distinct sheets of M (= Ta, Nb, W) octahedra and three distinct sheets of Sb3+ polyhedra parallel to (100). These sheets alternate in the a direction to form a continuous structure.
Bismutotantalite-stibiotantalite-stibiocolumbite (BSS) aggregates occur exclusively in pockets of the elbaite subtype pegmatites cutting serpentinized peridotite at Khetchel village, Molo quarter near Momeik Township, northeast of Mogok, Shan State, Myanmar (Burma). The pegmatites exhibit simple zoning with common pockets lined with K-feldspar, "mushroom-like" pink to red elbaite, beryl (aquamarine, morganite), petalite, phenakite, quartz, saccharoidal albite, adularia, hambergite and cookeite(?). The BSS aggregates consist of prismatic crystals of bismutotantalite-stibiotantalite (Bi/(Bi+Sb) = 0.47-0.51; Ta/(Ta+Nb) = 0.64-0.67; a = 5.6017(3), b = 11.7802(3), c = 4.9497(3) Å and V = 326.63(2) Å3), up to about 5 mm in size, and their aggregates, up to 3 cm in diameter, forming ∼95 vol.% of the overall BSS aggregate. Oval to irregular grains blebs of stibiotantalite (Bi/(Bi+Sb) = 0.04-0.08; Ta/(Ta+Nb) = 0.62-0.68), up to 100 μm in diameter, scarcely occur in bismutotantalite-stibiotantalite. Thin veinlets of stibiocolumbite (Bi/(Bi+Sb) = 0.01-0.05; Ta/(Ta+Nb) = 0.40-0.49) with brecciated textures, up to 30 μm thick, cut bismutotantalite-stibiotantalite and rarely also stibiotantalite blebs. Two distinct compositions were found in the stibiocolumbite veinlets, W-poor and rare W-rich (up to 19.34 wt.% WO3). Late stibiocolumbite overgrowths (Bi/(Bi+Sb) = 0.01-0.03; Ta/(Ta+Nb) = 0.17-0.33) on crystals of bismutotantalite-stibiotantalite reach up to 20 μm in size. Bismutotantalite-stibiotantalite + stibiotantalite blebs → stibiocolumbite veinlets → stibiocolumbite overgrowths - is the succession of crystallization. All phases contain along with dominant Bi, Sb, Nb and Ta also low to moderate concentrations of some cations (W6+ ≤ 0.275 apfu in stibiocolumbite veinlets, Pb2+ ≤ 0.052 apfu, Sn4+ ≤ 0.010 apfu, As3+ ≤ 0.032 apfu; Ti ≤ 0.045 apfu and U ≤ 0.005 apfu, the latter two only in the stibiocolumbite overgrowths). High amounts of W in the stibiocolumbite veinlets change slightly ABO4 stoichiometry from A/B ∼1 to ΣA-site cations up to 1.216 apfu with ΣA+B = 2.000. The simple exchange vectors Sb1 Bi−1 and Nb1 Ta−1 are dominant in all phases examined, but the minor substitution Pb2+1 W6+1 Sb3+−1 Nb5+−1 also was encountered in W-poor compositions. Fractionation in the BSS assemblage expressed by the Bi/(Bi+Sb) and Ta/(Ta+Nb) is asynchronous; the Bi/(Bi+Sb) value significantly drops down in the stibiotantalite blebs and it is very low in stibiocolumbite. Ta/(Ta+Nb) is constant in the bismutotantalite-stibiotantalite and stibiotantalite blebs, and then it decreases in the stibiocolumbite veinlets and particularly in the stibiocolumbite overgrowths.
