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High temperature shape memory alloys RuNb and RuTa were investigated by X-ray diffraction in order to determine the structure of the low temperature β” martensite. Powder X-ray diffraction and Rietveld analysis confirm the monoclinic symmetry and allow a precise determination of the atom positions. The low temperature microstructure is the result of a martensitic transformation from a tetragonal β′ martensite. The analysis of how it is controlled by the space groups of the two phases and by their relative orientation is performed by transmission electron microscopy. A three level twinned microstructure is recognized in the β” phase. The investigation at the smallest scale twins reveals the presence of wavy contrast boundaries which are typical for translation interfaces. High resolution transmission electron microscopy images, accompanied by phase contrast imaging analysis, have been used to determine the translation vectors associated to the interfaces. These displacements are the translations of the tetragonal β′ phase which are lost during the transformation. The combination of X-ray diffraction and transmission electron microscopy investigation allows the suggestion of a global distortion mechanism that explains the atomic displacements in the β” form. [ABSTRACT FROM AUTHOR]

Abstract: The preparation of thorium phosphate-diphosphate (Th4(PO4)4P2O7, TPD) was developed through the precipitation of thorium phosphate-hydrogenphosphate hydrate (Th2(PO4)2(HPO4)·H2O, TPHPH) at 150–160°C in closed PTFE container or in autoclaves. From EPMA analyses and SEM observations, the initial precipitate was single phase and multilayered. The behaviour of TPHPH (orthorhombic system with a =21.368(2)Å, b =6.695(1)Å and c =7.023(1)Å) was followed when heating up to 1250°C. It was first dehydrated leading to the anhydrous thorium phosphate-hydrogenphosphate (TPHP, orthorhombic system with a =21.229(2)Å, b =6.661(1)Å and c =7.031(1)Å at 220°C) after heating between 180 and 200°C. This one turned progressively into the new low-temperature variety of TPD (called α-TPD, orthorhombic system with a =21.206(2)Å, b =6.657(1)Å and c =7.057(1)Å at 300°C) correlatively to the condensation of hydrogenphosphate groups into diphosphate entities. These three phases (TPHPH, TPHP and α-TPD) exhibit closely related 2D layered structures, therefore different from the 3D structure of the thorium phosphate-diphosphate (high-temperature variety). This latter compound, now called β-TPD, was obtained by heating α-TPD above 950°C. All the techniques involved in this study (XRD, Raman and IR spectroscopy, 1H and 31P NMR) confirmed the successive chemical reactions proposed. [Copyright &y& Elsevier]

Abstract: Materials with red long-lasting phosphorescence, such as MnII-doped diopsides, can be used for small animal in vivo imaging. CaMgSi2O6:Mn powders with various amounts of Mn were prepared by sol–gel to investigate their long-lasting phosphorescence mechanism. X-ray diffraction, X-ray absorption fine and near-edge structure and electron paramagnetic resonance showed that manganese is quantitatively introduced in the structure as MnII. Most of the Mn doping ions substitute Mg and possess a highly elongated octahedral environment. While photoluminescence and X-ray excited optical luminescence spectra show both orange (585nm) and red (685nm) 4T1 (4G)→ 6A1 (6S) emission of MnII Ca and MnII Mg, respectively, MnII Mg red emission dominates long-lasting phosphorescence and thermally stimulated luminescence spectra. These results point to MnII Mg as the preferential hole trap and recombination center in the long-lasting phosphorescence mechanism. An intense persistent red emission suitable for in vivo imaging probes is obtained for the highest nominal Mn content (7.5%). [Copyright &y& Elsevier]

Abstract: Physical and electrochemical investigations of vanadium phosphates, Li2x VO(H2−x PO4)2 (0< x <2), have been undertaken. H+/Li+ ionic exchange from VO(H2PO4)2 to Li2VO(HPO4)2 leads to grain decrepitation. Further ionic exchange toward formation of Li4VO(PO4)2 lowers the symmetry. As inferred from potentiodynamic cycling correlated to ex situ and in situ X-ray diffraction (XRD), the system Li/Li4VO(PO4)2 shows several phase transformations that are associated with thermodynamical potential hysteresis that span from roughly 15mV to more than 1.8V. Small hysteresis are associated with topotactic reactions and with VV/VIV and VIII/VII redox couples. Large potential hysteresis values (>1V) were observed when oxidation of VIII to VIV is involved. [Copyright &y& Elsevier]

This work presents the crystal structure and luminescent properties of TlSrLa(AsO4)2. In this phase Tl+ ions are located in large tunnels delimited by chains of alternating (AsO4) and (Sr,La)O8 polyhedra. Thallium atoms are eightfold coordinated with C1 symmetry. Large Tl&z.sbnd;O distances are observed revealing a low stereochemical activity of the 6s2 lone pair. Excitation and emission spectra of Tl+ in TlSrLa(AsO4)2 showed broad bands at lower energy than those observed in previous works. Excitation spectra are decomposed into multiple Gaussian bands and a theoretical analysis is made to explain the number of observed components. Two Gaussian components are revealed for emission spectra. [Copyright &y& Elsevier]