Application of multi-edge HERFD-XAS to assess the uranium valence electronic structure in potassium uranate (KUO3)

The uranium valence electronic structure in the prototypical undistorted perovskite KUO3 is reported on the basis of a comprehensive experimental study using multi-edge HERFD-XAS and relativistic quantum chemistry calculations based on density functional theory. Very good agreement is obtained between theory and experiments, including the confirmation of previously reported Laporte forbidden f–f transitions and X-ray photoelectron spectroscopic measurements. Many spectral features are clearly identified in the probed U-f, U-p and U-d states and the contribution of the O-p states in those features could be assessed. The octahedral crystal field strength, 10Dq, was found to be 6.6 (1.5) eV and 6.9 (4) eV from experiment and calculations, respectively. Calculated electron binding energies down to U-4f states are also reported.

The unbiased diffusion Monte Carlo: a versatile tool for two-electron systems confined in different geometries

Computational codes based on the diffusion Monte Carlo method can be used to determine the quantum state of two-electron systems confined by external potentials of various natures and geometries. In this work, we show how the application of this technique in its simplest form, that does not employ complex analytic guess functions, allows to obtain satisfactory results and, at the same time, to write programs that are readily adaptable from one type of confinement to another. This adaptability allows an easy exploration of the many possibilities in terms of both geometry and structure of the system. To illustrate these results, we present calculations in the case of two-electron hydrogen-based species ($$\hbox {H}_{2}$$ H 2 and $$\hbox {H}_{3}^{+})$$ H 3 + ) and two different types of confinement, nanotube-like and octahedral crystal field. Graphic abstract

X-ray absorption linear dichroism at the Ti K-edge of rutile (001) TiO2 single crystal

X-ray absorption linear dichroism of rutile TiO2 at the Ti K-edge provides information about the electronic states involved in the pre-edge transitions. Here, linear dichroism with high energy resolution is analyzed in combination with ab initio finite difference method calculations and spherical tensor analysis. It provides an assignment of the three pre-edge peaks beyond the octahedral crystal field splitting approximation and estimates the spatial extension of the corresponding final states. It is then discussed for the first time the X-ray absorption (XAS) of pentacoordinated titanium atoms due to oxygen vacancies and it is found that, similarly to anatase TiO2, rutile is expected to exhibit a transition on the low-energy side of peak A3. Its apparent absence in the experiment is related to the degree of p–d orbital mixing which is small in rutile due to its centrosymmetric point group. A recent XAS linear dichroism study on anatase TiO2 single crystals has shown that peak A2 has an intrinsic origin and is due to a quadrupolar transition to the 3d energy levels. In rutile, due to its centrosymmetric point group, the corresponding peak A2 has a small dipole moment explaining the weak transition. The results are confronted with recent picosecond X-ray absorption spectroscopy on rutile TiO2 nanoparticles.

Fabrication and Optical Properties of Cr3+:YSAG Transparent Ceramics

Cr-doped Y3ScxAl(5-x)O12(Nd:YSAG) powder have been prepared with a combustion method. The powders are nanosized and a pure cubic phase when calcined at 900°C. Transparent Cr:YSAG ceramics were successfully fabricated by sintering the powder compact at 1800°C under H2 atmosphere. The optical properties were investigated in detail. It was found that after Sc substitute for Al, the The octahedral crystal-field parameter Dq and Dq/B was reduced, and that is why the absorption peak move to the longer wavelength side but the emission peak not moved.

The Studies of Geometrical Microstructure of Tetragonal Co2+-VO Centers in KNbO3 and KTaO3 Crystals from EPR Data

From the perturbation formulas for the EPR ɡ factors g|| and g⊥ of a 3d7 ion in tetragonal octahedral crystal field based on a cluster approach, the geometrical microstructures of tetragonal Co2+-VO centers in KNbO3 and KTaO3 crystals are obtained by fitting the calculated g|| and g⊥ to the observed values. It is found that the Co2+ ion in Co2+-VO centers is displaced away from the oxygen vacancy VO by 0.3 Å in KNbO3 and by 0.29 Å in KTaO3. These results are comparable with those of Fe3+-VO centers in ABO3 perovskite-type crystals obtained fromboth the shell-model simulations and the embedded-cluster calculations, and from theoretical studies of EPR data. The experimental values of g|| and g⊥ for the tetragonal Co2+-VO centers in both crystals are also explained reasonably.

Magnetic resonance in a cubic Ґ 3 (E) doublet system IV. Improved theory of the nuclear interactions

In previous papers of this series, a study has been made of the theory of magnetic resonance in a Ґ 3 doublet (paper I), together with experimental studies of Cs 2 NaHoCl 6 by n. m. r. (paper II) and by e. s. r. (paper III). In this substance the Ho 3+ ion, 4f 10 , 5 I 8 , is in an octahedral crystal field which gives a Ґ 3 doublet as the ground electronic state. The results, both from enhanced n. m. r. of the 165 Ho nucleus ( I = 7/2) and from e. s. r., provide evidence of fast motional averaging, ascribed to interactions between the ions. The measurements are in substantial agreement with the theory of I; however, though the theory is correct for the electronic levels and transitions, and for the nuclear electric quadrupole interaction in zero magnetic field, it needs improvement in the treatment of the nuclear terms when a field B is applied. In this paper a general theory is developed for the case when B is in an arbitrary direction, together with some special cases that are analytically simpler. These include B along [111], the spectrum of an isolated ion, and the spectrum of a concentrated compound where there are fast flip-flops between the electronic states.

Spektroskopische Untersuchungen in der Festkörperchemie, XII* Re-NQR-und 1H-Breitlinien-NMR -Studien an Rhenium(YII)- Sauerstoffverbindungen / Spectroscopic Investigations in Solid State Chemistry, XII* Re NQR and 1H Wideline NMR Studies on Rhenium(VII) Oxygen Compounds

The first Re NQR spectra of rhenium oxygen compounds with rhenium atoms in the pseudo-octahedral environment of Re2O7(H2O)2 and Re2O7(H2O)2 · 2(1,4)-dioxane were found. The values of the Re NQR coupling constants of these rhenium atoms are the highest measured until now. They show, that the gradient of the electrical field is much more sensitive to distortions of an octahedral crystal field than to distortions of a tetrahedral field.