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We report the discovery of a low-temperature spin-flop transition in 5C pyrrhotite at ~155 K that is similar to those seen in hematite at 260 K and FeS (troilite) at 440 K. The 5C crystal was produced by annealing a 4C pyrrhotite crystal at 875 K to produce a change in the vacancy-ordering scheme that developed during cooling. The 5C structure is confirmed by single-crystal X‑ray diffraction and the stoichiometry and homogeneity by electron microprobe and SEM BSE mapping. Resonant ultrasound spectroscopy (RUS), heat capacity, and magnetization measurements from room temperature down to 2 K are reported. The transition is marked by a steep change in elastic properties at the transition temperature, a peak in the heat capacity, and weak anomalies in measurements of magnetization. Magnetic hysteresis loops and comparison with the magnetic properties of 4C pyrrhotite suggest that the transition involves a change in orientation of moments between two different antiferromagnetic structures, perpendicular to the crystallographic c-axis at high temperatures and parallel to the crystallographic c-axis at low temperatures. The proposed structures are consistent with a group theoretical treatment that also predicts a first-order transition between the magnetic structures. [ABSTRACT FROM AUTHOR]

Valence and spin states of Fe were investigated in a glass of almandine (Fe3Al2Si3O12) composition to 91 GPa by X-ray emission spectroscopy and energy- and time-domain synchrotron Mössbauer spectroscopy in the diamond-anvil cell. Changes in optical properties, total spin moment and Mössbauer parameters all occur predominantly between 1 bar and ~30 GPa. Over this pressure range, the glass changes from translucent brown to opaque and black. The total spin moment of the glass derived from X-ray emission spectroscopy decreases by ~20%. The complementary Mössbauer spectroscopy approaches reveal consistent changes in sites corresponding to 80–90% Fe2+ and 10–20% Fe3+. The high-spin Fe2+ doublet exhibits a continuous decrease in isomer shift and increase in line width and asymmetry. A high-spin Fe3+ doublet with quadrupole splitting of ~1.2 mm/s is replaced by a doublet with quadrupole splitting of ~1.9 mm/s, a value higher than all previous measurements of high-spin Fe3+ and consistent with low-spin Fe3+. These observations suggest that Fe3+ in the glass undergoes a continual transition from a high-spin to a low-spin state between 1 bar and ~30 GPa. Almandine glass is not expected to undergo any abrupt transitions in electronic state at deep mantle pressures. [ABSTRACT FROM AUTHOR]

Polycrystatine samples of Ln18Li8Rh5-xFexO39 (Ln = La, Nd; 0.5 ⩽ x ⩽5) have been synthesized by a solid-state method and studied by a combination of dc and ac magnetometry, neutron diffraction, and Mössbauer spectroscopy. All compositions adopt a cubic structure (space group Prn3n, ao ∼ 12 A) based on intersecting (111> chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Ln-O framework. At low values of x, iron preferentially occupies the smaller (2a) of the two distinct octahedral sites as tow- spin Fe(IV). The Rh(lll) on the larger (8e) octahedral site is replaced by high-spin Fe(lll). Nd-containing compositions having x> 1 show spin-glass-like behavior below ∼5 K. La-containing compositions having x> 1 show evidence of a magnetic transition at ∼8 K, but the nature of the transition is unclear. This contrasting behavior demonstrates that, although the structural chemistry of the two systems is essentially the same, the magnetic character of the Ln cations plays an important role in determining the properties of these compounds. [ABSTRACT FROM AUTHOR]

The structure proposed for Li11Nd18Fe4O39-δ (Chen et al. Inorg. Chem. 2012, SI, 8073) on the basis of diffraction and Mossbauer spectral data is compared to that determined previously for Nd18Li8Fe5O39 (Dutton et al. Inorg. Chem. 2008 47, 11212) using the same techniques. The Mössbauer spectrum reported by Chen et al. has been reinterpreted. The newly refined spectral parameters differ significantly from die published values but are similar to those reported for Nd18Li8Fe5O39). The relative areas of the three components indicate that iron cations occupy the 2a, 8e, and 16i sites in space group ...Pm3n, in disagreement with the model determined from neutron diffraction by Chen et al. in which only the 2a and 8e sites are so occupied. The relationship between Li11Nd18Fe4O39-δ and Ndl8Li8Fe5O39 is discussed, and it is proposed that the sample prepared by Dutton et aL is a kinetic product whereas the sample prepared by Chen et al. is the therrnodynamicalry preferred product. [ABSTRACT FROM AUTHOR]

ABX 3 -type hybrid organic-inorganic structures have recently emerged as a new class of meltable materials. Here, by the use of phenylphosphonium derivatives as A cation, we study liquid- and glass-forming behavior of a new family of hybrid structures, (RPh 3 P)[Mn(dca) 3 ] (R = Me, Et, Ph; dca = dicyanamide). These new compounds melt at 196-237 °C ( T m ) and then vitrify upon cooling to room temperature, forming glasses. In situ glass formation of this new family of materials was probed on a large scale using a variable-temperature PXRD experiment. Structure analyses of the crystalline and the glasses were carried out by solid-state nuclear magnetic resonance spectroscopy and synchrotron X-ray total scattering techniques for using the pair distribution function. The mechanical properties of the glasses produced were evaluated showing promising durability. Thermal and electrical conductivities showed low thermal conductivities (κ ∼ 0.07-0.09 W m -1 K -1 ) and moderate electrical conductivities (σ ∼ 10 -4 -10 -6 ) at room temperature, suggesting that by the precise control of the A cation, we can tune meltable hybrid structures from moderate conductors to efficient thermal insulators. Our results raise attention on the practical use of this new hybrid material in applications including, e.g., photovoltaic devices to prevent light-deposited heat (owing to low κ -1 ) at room temperature, suggesting that by the precise control of the A cation, we can tune meltable hybrid structures from moderate conductors to efficient thermal insulators. Our results raise attention on the practical use of this new hybrid material in applications including, e.g., photovoltaic devices to prevent light-deposited heat (owing to low κ RT ), energy harvesting thermoelectric, etc., and advance the structure-property understanding.