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A series of bidentate, viz., 1,1'-(1,2-ethylene)-3,3'-dimethyldiimidazoline-2,2'-diylidene (L1), 1-methyl-3-(2-pyridylmethyl)-imidazoline-2-ylidene (L2) and tridentate, viz., 1,3-bis(2-pyridyl)-imidazoline-2-ylidene (L3) ligands have been obtained from their corresponding imidazolium salts through deprotonation reactions. Treatment of UO2Cl2(THF)3 with one equivalent L3 produces air-stable U(VI)-carbene complex 3, characterized by elemental analysis, FTIR, NMR spectroscopy as well as extended X-ray absorption fine structure (EXAFS) analysis. EXAFS result indicates that the ligand is bonded through one C and two N-atoms to the uranium atom. Attempts to synthesize uranyl complexes derived from L1 and L2 were also successful but these complexes are decomposed quickly within one hour at room temperature. 3 produces pure UO2 powder when heated under an argon atmosphere from room temperature to 600 °C with constant heating rate of 5 °C/min. The solid-state UV–Vis spectrum of the compound shows absorption peaks at 332 and 450 nm. The excitation spectrum of 3 (at λem = 520 nm) exhibits two almost symmetrical peaks at 273 and 368 nm. Density functional theory-based quantum mechanical calculations indicate that a partial covalent interaction exists between the carbene C and U while a weak non-covalent interaction exists between carbene N and U atoms. [ABSTRACT FROM AUTHOR]

Abstract: A dispersive extended X-ray absorption fine structure (EXAFS) beamline employing an elliptically bent crystal and a position-sensitive CCD detector has been developed at the BL-8 bending magnet port of INDUS-2 synchrotron source at RRCAT, Indore, India. The beamline enables simultaneous measurement of X-ray absorption spectra over the range of 5–20keV in a short span of time. The beamline performance has been investigated by measuring the absorption spectra of metal foils and oxide powders. The EXAFS measurements on crystalline Pb5Ge3O11 samples were performed for the first time in literature. The average Pb–O bond length obtained from these measurements is found to agree well with the theoretically estimated value. [Copyright &y& Elsevier]

Thermodynamic expression of the Gibbs free energy indicates existence of a miscibility gap in the α-solid solution of Ti-Zr system; with the apex of the miscibility gap at 308 K, X Zr = 0.5. Thermal aging and experimental observation of the phase separation is not possible due to the unfavorable kinetics. Ab-initio calculations confirm positive energy of formation as well as favors large Zr-Zr distance in the solution phase. Extended X-ray Absorption Fine Structure results suggest non-random solution structure in the HCP α-phase much above the critical temperature. Therefore, existence of a miscibility gap could be predicted from the non-random solid solution structure of the parent α-phase. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract We report the structural and optical properties of ternary α-(Ga x Cr (1- x)) 2 O 3 with 0 ≤ x ≤ 0.45 which is synthesized by solid state reaction method. Single phase with space group R-3c is obtained for the gallium composition range of 0 ≤ x ≤ 0.45 and further increase in Ga concentration results in appearance of secondary C 2/ m phase corresponds to Ga 2 O 3. Variations in the in-plane ’ a’ and out of plane ’ c’ lattice parameters shows a clear daviation from the Vegard's law with the bowing parameters of −0.0510 Å and 0.0305 Å respectively. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows larger values of Ga-O bond lengths, which elucidate the deviation in lattice parameters from the Vegard's law and immisibility of Ga in Cr 2 O 3 lattice. Diffuse reflectance spectroscopy (DRS) confirms a blue shift of 0.5 eV in the band gap of α-(Ga x Cr (1- x)) 2 O 3. It has also observed that Cr 3d level shifted towards the O 2p level in the valence band which has been reconfirmed by photo electron spectroscopy. The observed shift indicates enhancement of mixing between these levels which can leads to further delocalization of hole states in the valence band responsible for p-type conduction in the α-Cr 2 O 3. These results suggest that ternary α-(Ga x Cr (1- x)) 2 O 3 (0 ≤ x ≤ 0.45) can be useful in the field of UV transperant electronics and photodetectors. Highlights • Synthesis of α-(Ga x Cr (1- x)) 2 O 3 (0 ≤ x ≤ 0.45) by solid sate reaction method. • Deviation of lattice parameters from the Vegard's law and immiscibility of Ga is discussed. • Tunability of ∼0.5 eV in the bandgap of α-Cr 2 O 3 as a function of Ga composition. • Enhancement in the mixing of Cr d and O 2p states in the valance band. [ABSTRACT FROM AUTHOR]