Roméite-Group Minerals Review: New Crystal Chemical and Raman Data of Fluorcalcioroméite and Hydroxycalcioroméite

The roméite-group is part of the pyrochlore-supergroup and comprises cubic oxides of A2B2X6Y formula in which Sb5+ predominates in the B-site. The A and Y main occupants determine different minerals in the group and are important for the discovery of new mineral species. Two different roméite-group mineral samples were analysed by electron microprobe analysis (EMPA), Raman spectroscopy and single-crystal X-ray diffraction (XRD). The first sample is from Prabornaz Mine (locality of the original roméite), Saint Marcel, Valle d’Aosta, Italy, whereas the other one occurs in Kalugeri Hill, Babuna Valley, Jakupica Mountains, Nezilovo, Veles, Macedonia. Sample 1 was identified as fluorcalcioroméite, and sample 2 as hydroxycalcioroméite. Both samples belong to the cubic crystal system, space group Fd3¯m, Z = 8, where a = 10.2881(13) Å, V = 1088.9(4) Å3 for sample 1, and a = 10.2970(13) Å, V = 1091.8(4) Å3 for sample 2. The crystal structure refinements converged to (1) R1 = 0.016, wR2 = 0.042; and (2) R1 = 0.023, wR2 = 0.049. Bond-valence calculations validated the crystal structure refinements determining the correct valences at each crystallographic site. Discrepancies observed in the Sb5+ bond-valence calculations were solved with the use of the proper bond valence parameters. The resulting structural formulas are (Ca1.29Na0.55□0.11Pb0.05)Σ=2.00(Sb1.71Ti0.29)Σ=2.00[O5.73(OH)0.27]Σ=6.00[F0.77O0.21(OH)0.02]Σ=1.00 for sample 1, and (Ca1.30Ce0.51□0.19)Σ=2.00(Sb1.08Ti0.92)Σ=2.00O6.00[(OH)0.61O0.21F0.18]Σ=1.00 for sample 2. The Raman spectra of the samples exhibited the characteristic bands of roméite-group minerals, the most evident corresponding to the Sb-O stretching at around 510 cm−1.

Mid-IR Optical Property of Dy:CaF2-SrF2 Crystal Fabricated by Multicrucible Temperature Gradient Technology

Dy3+-doped CaF2-SrF2 crystals with various Dy3+ dopant concentrations were synthesized by multicrucible temperature gradient technology (MC-TGT). Dy:CaF2-SrF2 crystals were fluorite structured and crystallized in cubic Fm3¯m space group, as characterized by X-ray diffraction. The crystallographic site concentration was calculated from the measured density by Archimedes’ hydrostatic weighing principle. The optical transmission reached over 90% with a sample thickness of 1.0 mm. The Sellmeier dispersion formula was obtained following the measured refractive index in a mid-IR range of 1.7–11 μm. Absorption coefficients of 6.06 cm−1 and 12.71 cm−1 were obtained at 804 nm and 1094 nm in 15% Dy:CaF2-SrF2 crystal. The fluorescence spectra of 15 at.% Dy:CaF2-SrF2 showed the strongest wavelength peak at 2919 nm with a full width at half maximum (FWHM) of 267 nm under an excitation wavelength of 808 nm. The fluorescence lifetimes were illustrated for different Dy3+ dopant levels of 5%, 10% and 15%. The results indicate that the Dy:CaF2-SrF2 crystal is a promising candidate for compact mid-IR lasers.

New compound Sm2Ru3Sn5 with a structure derived from Ru3Sn7

Ternary intermetallic compound Sm2Ru3Sn5 was synthesized in the system Sm-Ru-Sn by arc-melting and annealing at 600 °C in the field with high content of Sn. Its crystal structure was determined using single crystal X-ray diffraction data (at 240 K). The compound crystallizes in cubic system with space group I 4 ‾ 3m (No. 217), unit cell parameter is a = 9.4606 (8) Å, Z = 4, Pearson symbol c/40. The intermetallic compound Sm2Ru3Sn5 represents an ordered version of the centrosymmetric Ru3Sn7 structure (space group Im 3 ‾ m), in which 16f Sn-filled crystallographic site is split into two 8c sites, each of which is solely occupied of one sort of atoms – Sn or Sm. The occupation of these two 8c sites leads to a reduction of symmetry due to the removal of the inversion center.

Dopant site-dependent luminescence from rare-earth doped dibarium octafluorohafnate Ba2HfF8 nanocubes for radiation detection

Rare-earth doped Ba2HfF8 nanocubes as a new scintillator host material with crystallographic site-dependent luminescence for radiation detection.

New sodium-rich mixed Mn/In chalcogenido metallates Na12MnIn2Q10 (Q = S, Se)

The sodium-rich sulfido and selenido metallates Na12MnIn2Q10 (Q = S/Se) were synthesized in pure phase from melts composed of stoichiometric quantities of the manganese monochalcogenides MnQ, elemental indium and the chalcogens together with either Na2S (Q = S) or elemental sodium (Q = Se) as starting material. The samples were heated up to maximum temperatures of 1000/900 °C under an argon atmosphere; crystallization was achieved by slow cooling rates of 10 K h−1. The two isotypic compounds (monoclinic, space group P21/m, a = 678.26(2)/698.85(10), b = 2202.77(7)/2298.7(3), c = 766.39(3)/800.59(13) pm, β = 90.232(2)/90.147(5)°, Z = 2, R1 = 0.0516/0.0575) crystallize in a new structure type. According to the division of the formula as Na12[InQ4][MnInQ6] the salts contain ortho indate anions [InIIIQ4]5− besides hetero-bimetallic dimers [MnIIInIIIQ6]7−, which consist of two edge-sharing [MQ4] tetrahedra. The seven crystallographically different sodium cations exhibit an either tetrahedral or octahedral coordination by the chalcogen atoms. Thus, the overall structure of the salt is best described by a hexagonal close packing of the sulfide/selenide anions, in which the octahedral voids of every second interlayer section are fully occupied by the (overall 5/f.u.) Na+ positions with CN = 6. In the other half of the interlayer sheets, all tetrahedral voids (overall 10/f.u.) are occupied by the seven CN = 4 Na+ cations, one In3+ of the ortho anion and the two Mn2+/In3+ cations (which statistically occupy one crystallographic site). This structure relation is also verified by a Bärnighausen group-subgroup tree connecting the h.c.p. (Mg type) aristotype (with its tetrahedral and octahedral voids) by an overall index of 60 with the structure of the two title compounds.

The High-Pressure Structural Evolution of Olivine along the Forsterite–Fayalite Join

Structural refinements from single-crystal X-ray diffraction data are reported for olivine with a composition of Fo100 (forsterite Mg2SiO4, synthetic), Fo80 and Fo62 (~Mg1.6Fe0.4SiO4 and ~Mg1.24Fe0.76SiO4, both natural) at room temperature and high pressure to ~8 GPa. The new results, along with data from the literature on Fo0 (fayalite Fe2SiO4), were used to investigate the previously reported structural mechanisms which caused small variations of olivine bulk modulus with increasing Fe content. For all the investigated compositions, the M2 crystallographic site, with its bonding configuration and its larger polyhedral volume, was observed to control the compression mechanisms in olivine. From Fo100 to Fo0, the compression rates for M2–O and M1–O bond lengths were observed to control the relative polyhedral volumes, resulting in a less-compressible M1O6 polyhedral volume, likely causing the slight increase in bulk modulus with increasing Fe content.

Crystal structure and magnetic properties of the ternary rare earth metal-rich transition metallides RE14T3Al3 (RE = Y, Gd–Tm, Lu; T = Co, Ni)

The rare earth metal-rich RE14T3Al3 series (RE=Y, Gd–Tm, Lu; T=Co, Ni) have been prepared by arc-melting the rare earth metals with appropriate amounts of TAl precursors. All compounds crystallize in the tetragonal crystal system with space group P42/nmc in the Gd14Co3In2.7-type structure. Two structures (Y14Co2.78(1)Al3.22(1): a=952.99(4), c=2292.98(10) pm, wR2=0.0423, 2225 F2 values, 63 variables; Y14Ni3.07(2)Al2.93(2): a=955.06(5), c=2298.77(10) pm, wR2=0.0416, 2225 F2 values, 63 variables) have been refined from single-crystal data, indicating T/Al mixing on one crystallographic site. The lattice parameters of all members have been refined from powder X-ray diffraction experiments. The Y and Lu containing compounds for T=Co and Ni exhibit Pauli paramagnetic behavior, indicating that the Co and Ni atoms exhibit no localized magnetic moment in line with a filled 3d band. The other compounds show paramagnetism, in line with the rare earth atoms in the trivalent oxidation state. Detailed magnetic investigations, however, were impossible due to the presence of e.g. RE3T trace impurities.

Anion Influence on Spin State in Two Novel Fe(III) Compounds: [Fe(5F-sal2333)]X

Structural and magnetic data on two iron (III) complexes with a hexadentate Schiff base chelating ligand and Cl− or BPh4− counterions are reported. In the solid state, the Cl− complex [Fe(5F-sal2333)]Cl, 1, is high spin between 5–300 K while the BPh4− analogue [Fe(5F-sal2333)]BPh4, 2, is low spin between 5–250 K, with onset of a gradual and incomplete spin crossover on warming to room temperature. Structural investigation reveals different orientations of the hydrogen atoms on the secondary amine donors in the two salts of the [Fe(5F-sal2333)]+ cation: high spin complex [Fe(5F-sal2333)]Cl, 1, crystallizes with non-meso orientations while the spin crossover complex [Fe(5F-sal2333)]BPh4, 2, crystallizes with a combination of meso and non-meso orientations disordered over one crystallographic site. Variable temperature electronic absorption spectroscopy of methanolic solutions of 1 and 2 suggests that both are capable of spin state switching in the solution.