XANES study of rare-earth valency in LRu4P12 (L = Ce and Pr)

Valency of Ce and Pr in LRu4P12 (L = Ce and Pr) was studied by L2,3-edge x-ray absorption near-edge structure (XANES) spectroscopy. The Ce-L3 XANES spectrum suggests that Ce is mainly trivalent, but the 4f state strongly hybridizes with ligand orbitals. The band gap of CeRu4P12 seems to be formed by strong hybridization of 4f electrons. Pr-L2 XANES spectra indicate that Pr exists in trivalent state over a wide range in temperature, 20 < T < 300 K. We find that the metal-insulator (MI) transition at TMI = 60 K in PrRu4P12 does not originate from Pr valence fluctuation.Comment: 4 page

Synthesis of zirconolite-2M ceramics for immobilisation of neptunium

Praseodymium-doped zirconolite ceramics targeting nominal composition Ca1-xPrxZrTi2-5x/3Al5x/3O7 (x ≤ 0.20, Δx = 0.05) were fabricated by a mixed oxide solid state reaction, at 1350 °C in air for 20 h. Praseodymium (Pr) was employed as a surrogate for neptunium (Np), with Al3+ co-accommodated to provide charge balance. High-resolution transmission electron microscopy and electron diffraction analyses confirmed that zirconolite crystallised as the 2 M monoclinic polytype throughout the phase evolution, with no evidence of transformation to other polytype structures. Phase assemblage and microstructural data were consistent with zirconolite occupying a high fraction of the phase assemblage (>ca. 93 wt %), alongside a minor secondary perovskite phase at all levels of targeted Pr incorporation. Despite this, it was demonstrated near theoretical density formed through a solid-state fabrication route, and we therefore propose that, through analogy with the corresponding Pr solid solution, zirconolite may be a suitable candidate for the immobilisation of Np-bearing wastes

LII,III\mathrm{L_{II,III}} near-edge study of tetravalent Pr-oxides: PrBaO3\mathrm{PrBaO_3} and PrO2\mathrm{PrO_2}

The X-ray absorption near-edge structure (XANES) at the PrLII,III thresholds was studied for tetravalent PrBaO3 and PrO2. The XANES spectra of both systems exhibit typical double-peaked “white-line” structures with substructures reflecting the different oxygen coordination in PrBaO3 and PrO2. These substructures are best visualized by the second derivative of the XANES spectra. We observe also characteristic differences between the respective LII- and LIII-edge spectra

Temperature and Pressure Induced Valence Transitions in YbCu5-xGax Studied by Yb-LIII XANES

Employing the Yb-LIII XANES, YbCu5, YbCu4Ga, YbCu3Ga2 and YbCu3.5Ga1.5 were studied in the temperature range 25 K to 300 K. YbCu5 and YbCu4Ga were studied at 300 K at pressures up to 175 kbar

Temperature and Pressure Induced Valence Transitions in YbCu5−xGax\mathrm{YbCu_{5-x} Ga_x} Studied by Yb−LIII\mathrm{Yb-L_{III}} XANES

Employing the Yb-LIII XANES, YbCu5, YbCu4Ga, YbCu3Ga2 and YbCu3.5Ga1.5 were studied in the temperature range 25 K to 300 K. YbCu5 and YbCu4Ga were studied at 300 K at pressures up to 175 kbar

EXAFS Study of Oxygen Distortions in Gd2CuO4 as Function of Temperature and Pressure

We studied the temperature and pressure dependence of the oxygen distortion in the Cu-O planes of the Gd2CuO4 T-phase, employing the Gd-LIII EXAFS

Magnetic ordering and spin fluctuation behavior in compounds of the type, Ce<SUB>2</SUB>(Pd,Rh)<SUB>2</SUB>In

The results of heat capacity (C), electrical resistivity and Ce L<SUB>III</SUB>-edge measurements on the alloys, Ce<SUB>2</SUB>Pd<SUB>2</SUB>In, Ce<SUB>2</SUB>Rh<SUB>2</SUB>In and some of their derivatives, are reported. The temperature dependence of C data of Ce<SUB>2</SUB>Pd<SUB>2</SUB>In exhibits features attributable to short range magnetic correlations preceding a sharp upturn at 4 K arising from long range magnetic ordering. An increase in Pd/In ratio apparently diminishes the magnetic transition temperature and the features due to spin fluctuation effects. The low temperature values of C/T of Y<SUB>1.6</SUB>Ce<SUB>0.4</SUB>Pd<SUB>2</SUB>In and Lu<SUB>1.6</SUB>Ce<SUB>0.4</SUB>Pd<SUB>2</SUB>In are large, attributable to heavy fermion behavior. In the compound Ce<SUB>2</SUB>Rh<SUB>2</SUB>In, Ce is found to be strongly mixed valent, with a large spin fluctuation temperature

X-Ray Absorption Study of the Local Structure At Potassium and Rubidium in K3−xRbxC60K_{3-x}Rb_xC_{60}

X-ray absorption fine structure (EXAFS and XANES) studies of the K-edges of potassium and rubidium in K3C60, K2RbC60 and Rb3C60 reveal the local structure and site preferences of the alkali metals. Both K and Rb ions on tetrahedral interstices exhibit regular positions with respect to the C60 neighbours in agreement with crystallographic data, while for Rb ions located on octahedral interstices an off-center position is found. The K2RbC60 sample exhibits a clear preferential site occupation of the octahedral site by Rb, which is also reflected by the lattice constant, and indications for structural rearrangement of the Rb ions on octahedral sites around 50 K

EXAFS Study of Oxygen Distortions in Gd2CuO4\mathrm{Gd_2 CuO_4} as Function of Temperature and Pressure

We studied the temperature and pressure dependence of the oxygen distortion in the Cu-O planes of the Gd2CuO4 T-phase, employing the Gd-LIII EXAFS

(Tb, Ce)-LIII XAS High Pressure Study of Tetravalent BaTbO3 and SrCeO3

We have studied the Tb- and Ce-LIII XAS of distorted-perovskite type BaTbO3 and SrCeO3 at pressure up to 20 GPa using a diamond anvil cell. While the XANES spectra of both tetravalent systems monitor an increase of hybridization and crystalfield splitting with pressure, the EXAFS spectra indicate an approach towards an undistorted perovskite structure with pressure