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Intracrystalline distribution of ferrous and ferric iron within pumpellyites (VII W 8VI X 4VI Y 8IV Z 12O56– n (OH) n , Z = 1) from low-grade metamorphic green rocks of the Kanogawa unit in the Northern Chichibu Belt, Hijikawa district, western Shikoku, Japan, was investigated using electron microprobe analysis, X-ray Rietveld refinement, and 57Fe Mössbauer spectroscopic analysis to verify the regularity of the distribution of Fe within the octahedral X and Y sites in pumpellyite and its effect on the pumpellyite structure. Two Fe-rich pumpellyite samples, labelled CLW and CHG, with average total Fe2O3 of 10.01±1.69 and 16.07±1.08 wt.%, respectively, were separated from the rock samples. The site occupancies at the X and Y sites in the CLW and CHG pumpellyites, refined using powder X-ray diffraction data, are X [Mg0.298Fe0.298(5)Al0.405] Y [Fe0.191Al0.809] and X [Mg0.244Fe0.42(1)Al0.34] Y [Fe0.32Al0.68], respectively. The Fe2+:Fe3+ ratio of the CLW pumpellyite, determined using Mössbauer spectroscopy, is 12(1):88(3). By combining the average chemical composition data, the site occupancies at the X and Y sites, and the Fe2+:Fe3+ ratio of the CLW pumpellyite, the chemical formulae of CLW and CHG pumpellyites are constructed as (Ca7.96K0.02Na0.01)Σ7.99(Mg1.19Mn2+0.09Fe2+0.39Fe3+0.71Al1.62)Σ4.00(Al6.47Fe3+1.50V0.02Ti0.01)Σ8.00Si12.26O43.33(OH)12.67 and (Ca8.01K0.01)Σ8.02(Mg0.97Mn2+0.02Fe2+0.63Fe3+1.03Al1.19)Σ4.01(Al5.44Fe3+2.55V0.01)Σ8.00Si12.02O42.69OH)13.31, respectively, implying that the proper name of both pumpellyites is pumpellyite-(Al). The intracrystalline distribution coefficients of Fe3+ versus Al between the X and Y sites, K D = (Fe3+/Al) X /(Fe3+/Al) Y , are 1.62 and 1.90 for the CLW and CHG pumpellyites, respectively, implying stronger X -site preference of Fe3+ than Al3+. In the CHG pumpellyite, where the Fe contents at the X and Y sites are higher than in the CLW pumpellyite, the mean < X –O> and < Y –O> distances are 2.06 and 1.98 Å, respectively, which are larger than < X –O> = 2.040 and < Y –O> = 1.944 Å in the CLW pumpellyite. The unit-cell parameters of the CHG pumpellyite are a = 8.8672(3), b = 5.9562(2), c = 19.1899(6) Å, β = 97.473(2)° with V = 1004.9(2) Å3 and are larger than those of the CLW pumpellyite, a = 8.8456(4), b = 5.9393(2), c = 19.1613(8) Å, β = 97.461(3)° with V = 998.14(7) Å3. [ABSTRACT FROM AUTHOR]

The distribution of Cr3+ ions in blue and green diopsides crystallised from a glass with the composition [CaMgSi2O6 (Di)]95[CaCrAlSiO6 (CrAlTs)]5 (mol.%) was determined using Rietveld refinement of X-ray diffraction data in order to evaluate published results by optical spectroscopic analysis, and to clarify the influence of Cr3+–Al3+ distribution between the octahedral M 1 and tetrahedral T sites on the crystal structure. The starting material was Di95CrAlTs5-diopside crystallised from glass at 800°C for 2 days. After another 19 days at 800°C and 1000°C for 7 days, the diopsides remained blue. The blue diopside gradually changed to bluish green by heating at 1200°C for 3 days and to green after 7 days. The stoichiometric compositions of the synthesised phases were confirmed by electron microprobe analysis. The Cr occupancies refined by the Rietveld method resulted in the site populations in the M 1 and T sites: M 1[Mg0.95Cr0.030(4)Al0.020] T [Si1.950Cr0.020Al0.030] and M 1[Mg0.95Cr0.037(4)Al0.013] T [Si1.950Cr0.013Al0.037] (per 6 oxygens) for the blue diopsides at 800 and 1000°C, respectively: M 1[Mg0.95Cr0.042(3)Al0.008] T [Si1.950Cr0.008Al0.042] for the bluish green diopside at 1200°C for 3 days; and M 1[Mg0.95Cr0.049(3)Al0.001] T [Si1.950Cr0.001Al0.049] for the green diopside at 1200°C for 7 days. Such Cr and Al distributions effect the volumes and site distortions of the octahedral and tetrahedral coordination polyhedra: the T O4 tetrahedron volumes of the blue diopsides (2.251–2.258 Å3) are larger than that of the green diopside (2.237 Å3); the M 1O6 octahedron volumes of the former (11.74–11.77 Å3) are smaller than that of the latter (11.86 Å3); the T O4 tetrahedra in the blue diopside (<λtet> =1.006; σθ(tet)2 = 24.37–24.69) are less distorted than that of the green diopside (<λtet> = 1.007; σθ(tet)2 = 27.94); the M 1O6 octahedra in the former (<λoct> =1.006; σθ(oct)2 = 20.39–21.13) are more distorted than that of the latter (<λoct> = 1.005; σθ(oct)2 = 17.58). [ABSTRACT FROM AUTHOR]

Abstract 10 mol% Fe- and Ni-substituted Li 2 MnO 3 (Li 1+x (Fe 0.1 Ni 0.1 Mn 0.8) 1-x O 2 , 0 < x < 1/3) samples were prepared under different calcination atmospheres (in air or flowing N 2). The N 2 calcined sample (sample N) exhibited better cycle performance because sample N had a more homogeneous transition metal (TM) distribution. Through X-ray Rietveld analysis, highly TM-deficient spinel phases were detected with layered rock-salt phase after charging. The highly TM-deficient spinel had unusually low TM occupancy on the 16 d site (<40%). At the end of discharging, the spinel phase was diminished. Only TM-disordered layered rock-salt phase was observed. At 34th discharged state, the highly TM-deficient spinel phase appeared as a minor phase because of layer to spinel conversion when upper cut-off voltage was set to 4.6 V. However, the highly TM-deficient spinel phase converted to a normal LiMn 2 O 4 -like phase when the upper cut-off voltage was set to 4.8 V. The spinel content after cycling can be reduced by synthesizing homogeneous TM distributed samples. Highlights • Two 10% Fe- and Ni-substituted Li 2 MnO 3 samples were prepared for characterization. • The sample calcined in N 2 atmosphere had better electrochemical performance. • Structural change was examined during electrochemical activation and cycles. • Spinel phases of two kinds were detected after cycling. [ABSTRACT FROM AUTHOR]

Abstract Three mixed pyrochlores, A 2 GaSbO 7 (A3+ = Y, Dy, Gd) were synthesized using the solid-state reaction technique and characterized systematically through powder X-ray diffraction and its Rietveld analysis, SEM-EDAX, UV–Visible absorption spectra, Fourier-transform infrared and Raman spectroscopy. Scherrer analysis of the XRD pattern and SEM-image were used to estimate size of the nano-structured particles of the polycrystalline samples to be ∼40–50 nm. From the UV–Vis absorbance data, absorption band edge and optical band gap were determined, and found to be ∼350 ± 8 nm and 2–2.5 eV, respectively, for these compounds. Four F 1 u bands were only observed in the infrared spectra within the phonon wave numbers range of 400–800 cm−1 for these samples. The highest wave number infrared mode arises due to the interaction between bending and stretching of A−O and B−O bonds. A mode-splitting caused by the mass-difference of B-site ions was found in the other three infrared modes. The Raman spectra of these compounds exhibit six Raman modes, e.g., A 1 g , E g , and 4 F 2 g , within the experimental range of 50–1000 cm−1, with few extra bands in the higher (>700 cm−1) and lower (<200 cm−1) wave numbers range. A normal coordinate analysis using a generalized valence force-field model has been performed to assign and evaluate the vibration modes in these compounds. Five stretching and four bending force constants were considered to construct the force-field matrix. Comparison of the calculated phonon wave numbers with experimental values obtained in infrared and Raman excitation zones describes excellent agreement for all these isomorphous compounds. Highlights • A 2 GaSbO 7 pyrochlores are synthesized. • Optical band gap is determined. • Four IR and thirteen Raman vibration modes are observed. • Valence force-field model using GF-matrix method is applied to phonon spectra. [ABSTRACT FROM AUTHOR]

A few iron-antimonate pyrochlores R 2 FeSbO 7 (R 3+ = Y, Dy, Gd, Bi) were synthesized using the solid state reaction technique and characterized systematically through powder X-ray diffraction and its Rietveld analysis, SEM-EDAX, Fourier-transform infrared and Fe 57 Mössbauer spectroscopy. Scherrer's analysis of the XRD pattern and SEM-EDAX analysis estimate particle size of the polycrystalline powder to be in the range of 30–40 nm. Using the Rietveld fitting of the XRD profile, a model for unit Bravais cell is constructed suitably choosing 4 R ions, 4 Fe/Sb ions, 12 O ions and 2 O′ ions. A very strong and broad band at high wavenumber end at 642.0 cm −1 followed by some low intensity bands at 490, 465, 447 and 432 cm −1 are observed in the mid-infrared region of 400–1000 cm −1 in FT-IR spectra of Y 2 FeSbO 7 . The bands at 642 and 490 cm −1 can be ascribed to the stretching vibrations of the smallest inter-atomic bond M(Fe/Sb)–O in MO 6 octahedron and Y–O′ bond, respectively. Mössbauer spectra exhibit paramagnetic doublet and sextet magnetic splitting at 300 K and 9 K, respectively. Quadrupole splitting measured at 300 K decreases linearly with the decrease of the x -coordinate of the 48 f oxygens, which measures the distortion of the FeO 6 octahedron. The quadrupole splitting arises due to the electric field gradient at Fe 3+ nucleus site, which is nearly one-half of the value found for high-spin Fe 2+ nucleus. Quadrupole splitting in the magnetic ordered spectra taken at 9 K is reduced from its 300 K value due to random distribution of the hyperfine fields at Fe site with regard to the electric field gradient axis. The larger effective magnetic moment of cations causes higher hyperfine field at Fe nucleus and vice-versa in these compounds. [ABSTRACT FROM AUTHOR]

Only the orthorhombic form of lead meta-niobate (PbNb2O6 or PNO) is ferroelectric, allowing high temperature piezoelectric applications. Quenching from a high temperature like 1270°C appears essential to get the orthorhombic phase. But such quenching is risky and can generate defects in the sample. Here, differential scanning calorimetry (DSC) and XRD characterizations show that on using suitably pre-fired Nb2O5 or monoclinic Nb2O5 as starting reactant, slow cooling as well as quenching leads to orthorhombic PbNb2O6 as the product. Present work is the first detailed report of the preparation of orthorhombic PbNb2O6 without quenching. All starting materials, tried here, and resulting products have been thermally characterized along with necessary XRD characterizations. [ABSTRACT FROM AUTHOR]

Homologous series of ZnkIn2Ok+3 (k=3, 5, 7) and ZnkInGaOk+3 (k=1, 3, 5) were prepared by solid state reaction method and the crystal structures were analysed by X-ray Rietveld analysis in order to clarify the relationship between their crystal structure and thermoelectric properties. For both the series, the lattice parameter a and the In-O distance in InO6 octahedra in the InO-2 layer gradually increased as k decreased. Electrical conductivity increased as k decreased, while trend in k dependence of Seebeck coefficient was entirely opposite to that of the electrical conductivity for both the series. The increased In-O distance was found to be associated with the enhancement of electrical conductivity as k decreased. The dimensionless figure-of-merit ZT of 0·04 was obtained at 773 K for ZnInGaO4 which has the longest In-O distance in the homologous compounds examined in this experiment. [ABSTRACT FROM AUTHOR]

Abstract: Completely reduced CoCrxFe2 − xO4 can be used to decompose CO2. It was found that for pure CoFe2O4 there is no FeO formation in the first step while there is formation in the second step. For CoCr0.08Fe2−0.08O4, there is no FeO formed in all the oxidation process, because of effect of Cr3+. Pure CoFe2O4 was destroyed at the first reaction cycle of H2 reduction and CO2 oxidation, while doped Cr3+ spinel CoCr0.08Fe1.92O4 showed good stability. The results from H2-TG, CO2-TG and XRD show that the addition of Cr3+ to CoFe2O4 can inhibit the increasing of crystallite size and the sintering of alloy. Most importantly, the CoCr0.08Fe1.92O4 can be used to decompose CO2 repeatedly, implying that it is a potential catalyst for dealing with the CO2 as a ‘green house effect’ gas. [Copyright &y& Elsevier]