Search

A mineral with the composition Pd(Bi0.53Sb0.47), intermediate between sobolevskite, ideally PdBi, and sudburyite, PdSb, from the Chineiskii Deposit (Transbaikal region, Russia), was studied by the SEM and XRD methods. Its crystal structure was solved and refined (R = 3.02%) based on single crystal X-ray diffraction data. The structure is orthorhombic, and the space group is Cmcm. The unit-cell parameters are a = 4.1465(4) Å, b = 7.1782(6) Å, c = 5.6843(4) Å, V = 169.19(2) Å3, Z = 2. The series of the structures β-PdBi–Pd(Bi0.53Sb0.47)–PdSb and sobolevskite–sudburyite are discussed. [ABSTRACT FROM AUTHOR]

The polytypic structure of Pd8T3 (T = As, Sb) compounds was revealed using the graph method. The topology of the layers and the regular sequence of their alternation are analyzed. The ordering of antimony and arsenic atoms by the positions at the nodes of layer-networks and the positional disorder in the sequence of alternating layers, which lead to the formation of different structural polytypes, are considered. [ABSTRACT FROM AUTHOR]

High-temperature transformation of β-PtBi2, a synthetic analogue of insizwaite, was studied under oxidizing conditions (on air). The behavior of the sample upon heating up to 660°C and cooling was studied by differential thermal analysis (DTA) and high-temperature X-ray powder diffraction. It was shown that polymorphic transitions of β-PtBi2 into high-temperature γ- and δ-polymorphs do not occur under thermal treatment in the oxidizing conditions (on air). The DTA curve shows two exothermic peaks at 318 and 620°C. The total weight change in the temperature range studied is +10.5%. No thermal reactions or weight changes were recorded upon cooling of the sample. According to the high-temperature diffraction experiment in situ, the decomposition of the synthesized phase into Pt and Bi was recorded with their subsequent oxidation to bismuth oxide Bi2O3 with the bismite-type structure and double platinum and bismuth oxide with the pyrochlore-type structure Bi2Pt2O7. The study by electron microprobe analysis showed that the grains of the transformed insizwaite are a finely dispersed mixture of two oxides. [ABSTRACT FROM AUTHOR]

The article presents investigation of polymorphic transformations of the PtBi2 phases that occur during heating in inert atmosphere and in vacuum. A synthetic medium-temperature β-PtBi2 modification corresponding to the mineral insizwaite was studied by high-temperature X-ray diffraction and differential thermal analysis in the temperature range of 20–640°C. Two phase transitions are established by in situ X‑ray powder diffraction: from β into γ-PtBi2, and then into δ-PtBi2. Two endothermic peaks are recorded on the DTA curve, which correspond to the phase transitions. High-temperature X-ray powder diffraction data determined γ- and δ-PtBi2 formation at high temperature in inert atmosphere and in vacuum. Reverse polymorphic transformation were not observed by X-ray powder diffraction during cooling. It is suggested that insizwaite is a mineral geothermometer and its presence in the geological system implies certain temperature ranges of mineral formation environments. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060065 [ABSTRACT FROM AUTHOR]

The crystal structure of the mineral mertieite-II from the Kaarreoja River, Inari commune, Finnish Lapland, Finland, was refined to R1 = 0.0222 (I) and 0.0228 (II) on the basis of X-ray diffraction data collected from two single crystals. The mineral is trigonal, space group is R-3c. The unit-cell parameters for the two crystals are determined as: a = 7.5172(3), c = 43.037(2) Å, V = 2106.1(2) ų (I); a = 7.5135(4), c = 43.003(3) Å, V = 2102.4(3) ų (II) with Z = 12. The occupancies of the Sb and As position in the structure were refined according to the Sb:As ratio of each crystal. The position As1 (Wyckoff 6b) is completely filled by As atoms. Any excess of As is distributed together with Sb on structural positionM1 (Wyckoff 12c). The crystal chemical formulae are defined as Pd8Sb1.5(Sb0.94As0.06)As0.5 (crystal I) and Pd8Sb1.5(Sb0.88As0.12)As0.5 (crystal II). As-Sb substitution of up to 4.50 wt% of As does not affect the main structural topology of mertieite-II. Mertieite-II, Pd8Sb2.5As0.5 and synthetic Pd8Sb3 are isotypic compounds. The crystal structures of synthetic Pd8Sb3 and natural mertieite-II, Pd8Sb2.5As0.5, can be derived from the hexagonal close packing by filling additional layers between the close-packed 36 layers. The structure consists of Sb and (Sb,As) triangular 36, Pd triangular 36 and Pd pentagonal-triangular 5.33 layers. Stacking of Sb-, (Sb,As)- and Pdnets along the z axis caused extension of the unit cell. It contains a total of 36 layers: six Sb1-nets, six (M1, As1)-nets, 12 Pd1-nets and 12 (Pd1,Pd3,Pd4)-nets. [ABSTRACT FROM AUTHOR]

The crystal structure of the fibrous mineral arangasite, Al2F(PO4)(SO4)·9H2O from the Alyaskitovoje deposit, Eastern Yakutiya, Russia, was solved using low-temperature single-crystal data from synchrotron radiation and refined against F2 to R = 9.8%. Arangasite crystallizes in the monoclinic space group P2/a, with unit-cell parameters a = 7.073(1), b = 9.634(2), c = 10.827(2) Å, β = 100.40(1)º, V = 725.7(7) Å3 and Z = 2. The positions of all the independent H atoms were obtained by difference- Fourier techniques and refined in an isotropic approximation. The arangasite crystal structure is built from one-dimensional chains of Al octahedra and PO4 tetrahedra sharing vertices, quasi-isolated SO4 tetrahedra and H2O molecules. All O atoms are involved in the system of H bonding, acting as donors and/or acceptors. Hydrogen bonding serves as the only mechanism providing linkage between the main structural fragments, thus maintaining the framework. Chains of corner-sharing Al octahedra and P tetrahedra in the arangasite structure are topologically identical to the chains built from (Fe, Al) octahedra and P tetrahedra in the crystal structure of destinezite, Fe2(OH)(PO4)(SO4)·6H2O. It has been shown that in spite of very similar chemical formulae, arangasite and sanjuanite, Al2(OH)(PO4)(SO4)·9H2O, are not isotypic. [ABSTRACT FROM AUTHOR]