E. Kostiner

The crystal structure of NaMnPO4

Abstract NaMnPO 4 crystallizes in the space group Pmnb with a = 6.9041(1), b = 9.0882(1), and c = 5.1134(1)A. For Z = 4 the calculated density is 3.580 g/cm 3 ( V = 320.84A 3 ). Refinement ( R = 0.044, R w = 0.045) was carried out on hydrothermally grown crystals. NaMnPO 4 is isostructural to Na(Fe,Zn)PO 4 and the mineral maricite.

The crystal structure of cobalt orthophosphate Co3(PO4)2

Abstract The crystal structure of cobalt orthophosphate has been refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.039 (Rw = 0.058). The space group is P2 l c , with a = 5.063(1), b = 8.361(2), c = 8.788(2) A, and β = 121.00(2)°. Co3(PO4)2 is isotypic with the previously reported γ-Zn3(PO4)2 and Mg3(PO4)2. Cobalt ions occupy two distinct coordination polyhedra, one five and one six-coordinated, in a ratio of two to one. The structure is described in detail.

Structural analysis of metastable pseudobrookite ferrous titanium oxides with neutron diffraction and mossbauer spectroscopy

Abstract Four synthetic iron titanium oxides with the pseudobrookite (AB2O5, Cmcm, Z = 4) structure have been prepared and characterized by neutron diffraction and zero-field, natural abundance 57Fe Mossbauer effect spectroscopy (MES). The combination of the element specificity of MES with the different neutron scattering lengths of Ti and Fe (−0.33 and 0.95 × 10−12 cm, respectively) offers a unique opportunity to distinguish between cation distributions on the two (“A” and “B”) sites. Two of the samples have been prepared in low temperature experiments (quenched from 1200°C) and have the stoichiometry FeTi2O5, and Fe.6Mg.6Ti1.8O5. The third and fourth samples are commercial iron titanium oxides prepared by the reduction of ilmenite ore with carbon above 1700°C. The stoichiometries of these samples are Mn0.05Fe0.33Ti2.52O5 and Fe.33Mg.31Ti2.36O5. Results from these experiments indicate that for each of these samples the B site is predominantly (>65%) occupied by Ti, while the A site contains a mixture of Ti, Fe, and/or Mg. However, only at higher temperatures (>1700°C) is the B site devoid of ferrous cations. These results suggest that an “ordered” model for ferrous titanium-rich oxides of the pseudobrookite structure (100% Ti occupancy of the B site) is descriptive only at elevated temperatures, and that at lower temperatures a “disordered” model (partial iron occupation of the B site) is a more accurate representation of the structure. Because of this difference, it may be possible to predict the thermal history of naturally occurring samples based on cation distributions.

The crystal structure of Ca3Cu3(PO4)4

Abstract Single crystals of Ca3Cu3(PO4)4 synthesized hydrothermally at 420°C and 55 kpsi (3.8 kbar) were found to occur in the space group P2 1 a (No. 14) with a = = 17.619(2), b = 4.8995(4), c = 8.917(1)A, β = 124.08(1)°, and Z = 2. Full-matrix least-squares refinement of the structure using diffractometer data converged to a final anisotropic R = 0.037 (Rw = 0.046). The two calcium atoms are in six- and nine-coordination and the two copper-containing polyhedra (four- and five-coordinated) are similar to those previously found in Cu3(PO4)2.

The chemistry of the thermal decomposition of pseudobrookite ferrous titanium oxides

Abstract The thermal decomposition of two metastable ferrous titanium oxide compounds of commercial interest have been studied by in situ X-ray and neutron diffraction at elevated temperatures as well as by 57Fe Mossbauer effect spectroscopy. Thermal decomposition was monitored by collecting neutron diffraction data (taken at the Argonne National Laboratory Intense Pulsed Neutron Source (IPNS) powder diffractometers) at 30-min intervals at 900 and 1000°C. Previous work has shown that each of these materials (pseudobrookite structure, AB2O5), (Mn0.05Fe0.33Ti0.52)(Ti2.0)O5 and (Mg0.21Fe0.33Ti0.46)(Ti1.9Mg0.1)O5, has a significant amount of Ti in the +3 oxidation state and is completely ordered (no Fe located in the “B” site). The results of these “in situ” diffraction studies show that, prior to the thermal decomposition of the slags, there is a redistribution of cations within the pseudobrookite structure. Specifically, at temperatures in the range 600–700°C, iron cations move from the “A” sites to the “B” sites and Ti cations move from the “B” to the “A” sites. It is after this order-disorder transition that decomposition commences. At temperatures above 900°C, the neutron diffraction data show at least two modes of decomposition describing the high temperature chemistry of these disordered materials. The first mode produces iron metal and rutile (TiO2) and is modeled by the equation 2Fe0.5Ti2.5O5 → Fe + 5TiO2. The second mode of decomposition produces an iron-doped titanium oxide of the rutile structure and is modeled by the equation 4M0.3Ti2.7O5 → 2M0.5Ti2.5O5 + 5Fe0.04Ti1.16O2 (M = Fe2+, Mn2+, Mg2+).

The crystal structure of Na4Ni7(PO4)6

Abstract Na4Ni7(PO4)6 crystallizes in the space group Cm with a = 10.550(2), b = 13.985(5), and c = 6.398(2)A; β = 104.87(2)°. For Z = 2 the calculated density is 3.906 g/cm3 (V = 912.4 A3). Structure determination and refinement (R = 0.041, RW = 0.045) were carried out on flux (NaF) grown crystals. The structure consists of layers of nickel-containing octahedra and phosphorus-containing tetrahedra interconnected to form a pseudocentrosymmetric framework. A layer consisting of parallel tunnels which run along the a direction contains the sodium ions in a noncentrosymmetric arrangement.

The crystal structure of Cu4(PO4)2O

Abstract Cu4(PO4)2O crystallizes in the space group P 1 with a = 7.5393(8) A, b = 8.1021(9) A, c = 6.2764(8) A, α = 113.65(1)°, β = 98.42(1)° and γ = 74.19(1)°. The structure was refined by full-matrix least-squares techniques using automatic diffractometer data to R = 0.046 (Rw = 0.056). Four unique copper atoms are in six, five-, and four-coordinated polyhedra which are linked together to form a three-dimensional network. The structure is best described in terms of a cubic close-packed array of oxygen atoms with one-tenth of the possible anion sites vacant.

Disorder in the crystal structure of NaNi4(PO4)3

Abstract NaNi 4 (PO 4 ) 3 crystallizes in the space group Amam , a = 9.892(1), b = 14.842(2), and c = 6.3576(2) A. For Z = 4, the calculated density is 3.862 g/cm 3 ( V = 933.3A 3 ). The presence of several weak reflections (of the class 2 k 0 and 6 k 0) which should be systematically absent in this space group has been attributed to a partial disorder of one of the phosphate tetrahedra. Two half-occupied P (2) sites related by a mirror normal to the a axis result in a column of phosphate tetrahedra pointing either up or down in this direction. Nickel atoms occupy five- and six-coordinated sites while sodium is six-coordinated.

Determination of the structure of (VO)3(PO4)2 · 9H2O by powder X-ray diffraction analysis

Abstract The structure of a novel vanadyl (IV) orthophosphate hydrate (VO) 3 (PO 4 ) 2 · 9H 2 O has been solved and refined with the use of high resolution X-ray powder diffraction data taken on Beamline X7A at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL). The unit cell is monoclinic, P2 1 n , Z = 2, a = 7.4315(1), b = 16.6256(2), c = 6.2954(1) A, β = 92.388°(1)). The structure consists of large “squares” of (VO 6 PO 4 ) 4 moieties linked together by bridging PO 4 tetrahedra and VO 6 octahedra forming a corrugated layered structure in three dimensions with water molecules located within the open cells.

The preparation and characterization of the solid solution series CuFexGe1−xS2 (0.5 < x < 1.0)

Abstract Single crystals of the solid solution series CuFe x Ge 1− x S 2 (0.5 x x = 0.53 display antiferromagnetic behavior. The Neel temperature of 12°K and an effective moment of 5.0 BM is observed, which approaches the calculated spin-only moment of 4.92 BM. As x increases, deviations from spin-only behavior occur, indicating complex magnetic interactions.