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DOE OSTI2011

The crystal structure of Yb{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O and its decomposition product, {beta}-Yb{sub 2}(SO{sub 4}){sub 3}

Yb{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O, synthesised by hydrothermal methods at 220(2) deg. C, has been investigated by single crystal X-ray diffraction. Yb{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O crystallises in space group Cmc2{sub 1} and is isostructural with Lu{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O. The crystal structure has been refined to R{sub 1}=0.0145 for 3412 reflections [F{sub o}>3{sigma}(F)], and 0.0150 for all 3472 reflections. The structure of Yb{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O is a complex framework of YbO{sub 6} octahedra, YbO{sub 8} and YbO{sub 5}(H{sub 2}O){sub 3} polyhedra and SO{sub 4} tetrahedra. Thermal data shows that Yb{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O decomposes between 120 and 190 deg. C to form {beta}-Yb{sub 2}(SO{sub 4}){sub 3}. The structure of a twinned crystal of {beta}-Yb{sub 2}(SO{sub 4}){sub 3} was solved and refined using an amplimode refinement in R3c with an R{sub 1}=0.0755 for 8944 reflections [F{sub o}>3{sigma}(F)], and 0.1483 for all 16,361 reflections. {beta}-Yb{sub 2}(SO{sub 4}){sub 3} has a unique structural topology based on a 3D network of pinwheels. - Graphical abstract: Octahedral-tetrahedral linkages found in Y{sub 2}(SO{sub 4}){sub 3} [and Er{sub 2}(SO{sub 4}){sub 3}] and ss-Yb{sub 2}(SO{sub 4}){sub 3}. Highlights: > The crystal structure and decomposition reactions of Yb{sub 2}(SO{sub 4}){sub 3}.3H{sub 2}O. > The crystal structure of a twinned crystal of {beta}-Yb{sub 2}(SO{sub 4}){sub 3}. > Comparison of the structures of {beta}-Yb{sub 2}(SO{sub 4}){sub 3} and Y{sub 2}(SO{sub 4}){sub 3}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2010

Kapundaite, (Na,Ca)[subscript 2]Fe[subscript 4][superscript 3+](PO[subscript 4])[subscript 4](OH)[subscript 3]·5H[subscript 2]O, a new phosphate species from Toms quarry, South Australia: Description and structural relationship to mélonjosephite

Kapundaite, ideally (Na,Ca){sub 2}Fe{sub 4}{sup 3+}(PO{sub 4}){sub 4}(OH){sub 3}{center_dot}5H{sub 2}O, is a new mineral (IMA2009-047) from Toms phosphate quarry, Kapunda, South Australia, Australia. The new mineral occurs as cavernous aggregates of fibers up to several centimeters across, associated with leucophosphite, natrodufrenite, and meurigite-Na crystals and amorphous brown, black, and/or greenish coatings. Individual kapundaite crystals are very thin flattened fibers up to a few millimeters in length, but typically no more than a few micrometers in thickness. The main form observed is {l_brace}100{r_brace}; other forms in the [010] zone are present, but cannot be measured. Crystals of kapundaite are pale to golden yellow, transparent to translucent, have a yellow streak and silky luster, and are non-fluorescent. Mohs hardness is estimated to be about 3; no twinning or cleavage was observed. Kapundaite is biaxial (+), with indices of refraction = 1.717(3), {beta} = 1.737(3), and {gamma} = 1.790(3). 2V could not be measured; 2V{sub calc} is 64.7{sup o}. The optical orientation is Z = b, Y {approx} c with weak pleochroism: X = nearly colorless, Y = light brown, Z = pale brown; absorption: Y > Z > X. No dispersion was observed. The empirical chemical formula (mean of seven electron microprobe analyses) calculated on the basis of 24 O is (Ca{sub 1.13}Na{sub 0.95}){sub {Sigma}2.08}(Fe{sub 3.83}{sup 3+}Mn{sub 0.03}Al{sub 0.02}Mg{sub 0.01}){sub {Sigma}3.89}P{sub 3.92}O{sub 16}(OH){sub 3}{center_dot}5H{sub 2.11}O. Kapundaite is triclinic, space group P{sub {bar 1}}, a = 6.317(5), b = 7.698(6), c = 9.768(7) {angstrom}, {alpha} = 105.53(1){sup o}, {beta} = 99.24(2){sup o}, {gamma} = 90.09(2){sup o}, V = 451.2(6) {angstrom}{sup 3}, and Z = 1. The five strongest lines in the powder X-ray diffraction pattern are [d{sub obs} in {angstrom} (I) (hkl)]: 9.338 (100) (001), 2.753 (64) (2{sub {bar 1}}1), 5.173 (52) (011), 2.417 (48) ({sub {ovr 21}}3, 202, 0{sub {bar 1}}4), and 3.828 (45) (0{sub {bar 2}}1). The crystal structure was solved from single-crystal X-ray diffraction data using synchrotron radiation and refined to R{sub 1} = 0.1382 on the basis of 816 unique reflections with F{sub o} > 4{sub {sigma}}F. The structure of kapundaite is based on a unique corrugated octahedral-tetrahedral sheet, which is composed of two types of chains parallel to a. Kapundaite is structurally related to melonjosephite. The mineral is named for the nearest town to the quarry.

36 MATERIALS SCIENCE↗