Search results for "Valence"
showing 10 items of 2732 documents
Physical properties of (1−x)Ba0.95Pb0.05TiO3+xCo2O3 (x=0, 0.1, 0.3, 0.5, 1.0, 2.0wt%) ceramics
2015
The paper reports studies of the (1−x)Ba0.95Pb0.05TiO3 – xCo2O3 (x≤0.02) ceramics. Results of X-ray powder diffraction, dielectric, magnetic and IR measurements, as well as ab initio simulations are presented. The Co-doping induces small decrease of the (c/a) tetragonality of the perovskite lattice and leads to the gradual shift of the ferroelectric transition temperature from 398 K for x=0 down to 357 K for x=0.02. The conductivity activation energies are in the range 0.8–0.9 eV in agreement with the calculations. The high-temperature conductivity can be ascribed by the migration of oxygen vacancies introduced to compensate the charge deficiency due to Co3+ valence at the B-site of the per…
Electronic structure of EuO spin filter tunnel contacts directly on silicon
2011
We present an electronic structure study of a magnetic oxide/ semiconductor model system, EuO on silicon, which is dedicated for efficient spin injection and spin detection in silicon-based spintronics devices. A combined electronic structure analysis of Eu core levels and valence bands using hard X-ray photoemission spectroscopy was performed to quantify the nearly ideal stoichiometry of EuO “spin filter” tunnel barriers directly on silicon, and the absence of silicon oxide at the EuO/Si interface. These results provide evidence for the successful integration of a magnetic oxide tunnel barrier with silicon, paving the way for the future integration of magnetic oxides into functional spintr…
Understanding the trend in the Curie temperatures ofCo2-based Heusler compounds:Ab initiocalculations
2007
The Curie temperatures for the Heusler compounds Co{sub 2}TiAl, Co{sub 2}VGa, Co{sub 2}VSn, Co{sub 2}CrGa, Co{sub 2}CrAl, Co{sub 2}MnAl, Co{sub 2}MnSn, Co{sub 2}MnSi, and Co{sub 2}FeSi are determined ab initio from the electronic structure obtained with the local-density functional approximation and/or the generalized gradient approximation. Frozen spin spirals are used to model the excited states needed to evaluate the spherical approximation for the Curie temperature. The spherical approximation is found to describe the experimental Curie temperatures very well which, for the compounds selected, extend over the range from 95 to 1100 K; as a function of the valence electron count, they sho…
Slow magnetic relaxation and water oxidation activity of dinuclear CoIICoIII and unique triangular CoIICoIICoIII mixed-valence complexes
2020
Construction of efficient multifunctional materials is one of the greatest challenges of our time. We herein report the magnetic and catalytic characterization of dinuclear [CoIIICoII(HL1)2(EtOH)(H2O)]Cl·2H2O (1) and trinuclear [CoIIICoII2(HL2)2(L2)Cl2]·3H2O (2) mixed valence complexes. Relevant structural features of the complexes have been mentioned to correlate with their magnetic and catalytic properties. Unique structural features, especially in terms of significant distortions around the CoII centre(s), prompted us to test both spin–orbit coupling (SOC) and zero field splitting (ZFS) methodologies for the systems. The positive sign of D values has been established from X-band EPR spec…
Rydberg, valence and mixed states in the vertical spectrum of HF
2009
Abstract Size-consistent self-consistent multireference singles and doubles configuration interaction (SC)2–MR–SDCI, and linear response coupled cluster of singles and doubles including triples LR–CCSDR(3) methods, with a basis set of ANO’s augmented with a single series of molecular Rydberg functions, have been applied to the calculation of vertical excitation energies of HF in the 10–16 eV region. Special care has been put in the description of the valence, Rydberg and mixed states. Some advantage has been taken from the different physical contents of the methods to discuss some assignments. The (4,5) f Rydberg states of HF are predicted at 15.2 and 15.5 eV.
Comparative Mössbauer spectroscopic study of iron impurities in ZnSe
2001
Abstract An anomalous spectral doublet attributed to Fe 2+ impurity pairs is observed in Mossbauer absorption spectra of 57 Fe 0.01 Zn 0.99 Se below room temperature. In Mossbauer emission experiments, ZnSe: 57 Co polycrystal and powder sources exhibit below 45 K the nucleogenic Fe 1+ valence state born as an after effect of the electron-capture decay of 57 Co. Above 8 K, the proportion of the nucleogenic Fe 1+ decreases under the effect of the thermally activated Fe 1+ →Fe 2+ relaxation. The activation energy is estimated to 0.004 eV. While nucleogenic Fe 1+ is absent in ZnSe: 57 Co single crystal spectra, increasing proportions are detected in samples with an enhanced specific surface. Th…
Surface versus bulk composition of a phosphate glass
1994
Transmission and conversion electron Mossbauer spectroscopy as well as photoelectron spectroscopy were applied to study alterations of the surface layer of an iron containing industrial phosphate glass as compared with its bulk. In the surface layer, after polishing and exposure to ambient atmosphere, Fe 2+ is partially oxidized to Fe 3+ . This oxidation, however, does not increase the O/P ratio in this layer, because it goes along with a strong leaching of network modifiers. This leaching leads to a net decrease of the O/P ratio because it overcompensates the relative oxygen increase by Fe 2+ oxidation and by uptake of water
Heat-induced charge transfer in cobalt iron cyanide
2006
The heating of Co(2+) ferricyanide above 801C induces an inner charge transfer from Co(2+) towards Fe(III) to form the mixed valence system Co(2+)Co(III) ferri- ferro-cyanide. This charge transfer takes place preserving the material framework and forming a solid solution of the initial and final species. The cell edge of the cubic cell (Fm-3m) of this solid solution follows a regular variation with
Electronic structure of large disc-type donors and acceptors
2010
Searching for new pi-conjugated charge-transfer systems, the electronic structure of a new acceptor-donor pair derived from coronene (C(24)H(12)) was investigated by ultraviolet photoelectron spectroscopy (UPS). The acceptor coronene-hexaone (C(24)H(6)O(6), in the following abbreviated as COHON) and the donor hexamethoxycoronene (C(30)H(24)O(6), abbreviated as HMC) were adsorbed as pure and mixed phases on gold substrates. At low coverage, COHON adsorption leads to the appearance of a charge-transfer induced interface state 1.75 eV below the Fermi energy. At multilayer coverage the photoemission intensity of the interface state drops and the valence spectrum of neutral COHON appears. The sa…
Theoretical characterization of the lowest-energy absorption band of pyrrole
2002
The lowest-energy band of the electronic spectrum of pyrrole has been studied with vibrational resolution by using multiconfigurational second-order perturbation theory (CASPT2) and its multistate extension (MS–CASPT2) in conjunction with large atomic natural orbital-type basis sets including Rydberg functions. The obtained results provide a consistent picture of the recorded spectrum in the energy region 5.5–6.5 eV and confirm that the bulk of the intensity of the band arises from a ππ∗ intravalence transition, in contradiction to recent theoretical claims. Computed band origins for the 3s,3p Rydberg electronic transitions are in agreement with the available experimental data, although new…