Non-metallic Compounds Research Articles

Electronic structure of actinide compounds from LIII-edge x-ray absorption.

Double-peaked ${\mathrm{L}}_{\mathrm{III}}$-edge x-ray-absorption (XA) spectra are reported for various compounds of Np. Related high-pressure studies of ${\mathrm{UO}}_{3}$ support the idea that these peaks are due to core-ionized final states with different 5f occupancies reflecting the correlated electronic ground state. The weighted mean ${\mathrm{L}}_{\mathrm{III}}$-XA positions shift to higher energies with decreasing 5f occupancy and, for nonmetallic compounds, depend monotonically on the respective $^{237}\mathrm{Np}$ M\ossbauer isomer shifts. Deviations from this correlation are observed for metallic compounds due to conduction-electron contributions to the isomer shift.

L-edge X-ray absorption studies of neptunium compounds

The x-ray absorption near-edge structure (XANES) at the Np-L thresholds was investigated for Np compounds with formal valencies III to VII. At LIII, single and double-peaked white lines are observed corresponding to different final states that are populated through core excitation and 5f/ligand hybridization. For the non-metallic Np compounds studied, the weighted mean values of the LIII-XANES shifts relative to NpO2 exhibit a clear correlation with the isomer shifts of the 59-keV Mössbauer resonance of 237Np.

Structure and bonding in [M 6X 8] units of nonmetallic transition metal cluster compounds

A simple quantum mechanical method, based on the Wolfsberg-Helmholtz approximation, has been applied to some nonmetallic4 d and5 d transition metal cluster compounds containing M 6X 8 units. Our aim was to calculate bonding energies of M 6 clusters as a function of electronic configuration and symmetry. Energy sequences of clusters containing elements adjacent to each other in the periodic table are discussed, in particular, niobium and molybdenum as well as tungsten and rhenium. Compared with experimentally well-characterized compounds, the computional results show good qualitative agreement. So the occurrence of M 6 clusters with O h or lower symmetry can be explained by electronic effects.

Electronic excitation mechanism of sputtering and track formation by energetic ions in the electronic stopping regime

Atomic processes, such as sputtering and track formation, induced by electronic encounters of energetic heavy ions with nonmetallic compounds are discussed critically on the basis of electronic excitation mechanism. First, the behaviors of excitons in terms of electron-phonon coupling are surveyed and nonmetallic solids are divided into three categories. Possible atomic processes in each of these solids are discussed semi-quantitatively. It is pointed out that the electronic excitation mechanism can account for the observed yield of sputtering and of track formation, even though the mechanism differs from material to material depending on the type of nonmetallic compound according to the categorization given in the present paper. Some of the laser-induced processes that are not due to melting are also discussed.

The velocity distribution of sputtered atoms

Experimental methods for determining the velocity distribution of sputtered particles are reviewed. A critical comparison is made of the main classes: calorimetric, dynamometric, electromagnetic, kinematic and photonic. The main features of the observed distributions are described in the cases of polycrystalline metals, monocrystalline metals and nonmetallic compounds. The principal mechanisms of sputtering that operate in these systems are identified.

Crystal field parameters in a modified point charge model

A modification of the point charge model is proposed, taking into account the electronegatives of the metal and ligand atoms. On this basis empirical formulas for the effective ligand ( L) charge and its distance with respect to the metal ( M) origin have been set up. For a V M valent metal atom, surrounded by N L -nearest ligands at distance R 0, the respective relations q eff = v M (ϵ L /ϵ M − 1)/ N R 0ϵ L /(ϵ L + ϵ M ) are obtained. When applied to almost forty lanthanide and actinide non-metallic compounds the model shows reasonable agreement with the experimental data available.

Internal and External Oxidation of Nonmetallic Compounds and Solid Solutions (I)

AbstractA formal analysis is given treating the phenomenon of internal and external oxidation of oxide solid solutions. Theoretically, two situations can arise if those oxides are brought in an environment of higher oxygen potential. (1) Demixing and subsequently the formation of an outer layer of the reaction product occurs. (2) The reaction product forms internally; the two‐phase front advances into the interior of the solid solution. Some analogies with the phenomenon of internal alloy oxidation are discussed. Normally, a parabolic reaction kinetics prevails. Depending on the composition of, and the transport coefficients in the solid solution, a change from an internal to an external reaction may occur, and a criterion for this change is deduced. Internal oxidation (and reduction) is a means to disperse a second phase into an oxide matrix. This process may alter electrical, chemical and mechanical properties of the solid in question and thus could be of interest for materials science as well as geochemistry.

Effect of zirconium, cerium, and nitrogen on the properties of a cast chromium-base dispersion-strengthened alloy

An analysis of the chemical inertness and wettability of various nonmetallic compounds has shown zirconium nitride to be the most suitable strengthening phase for a chromium-base alloy. Endogeneously strengthened alloys have been produced having values of high-temperature strengthσ t 900 of between 270 and 340 MPa and of room-temperature ductilityδ 20 of between 5 and 44%. The properties of such an alloy are determined by the size and uniformity of distribution of its strengthening particles, while these in turn depend on the zirconium-tonitrogen ratio in the alloy.

Solution and Precipitation Hardening in (Ca, Mn) Sulfides and Selenides

The deformable sulfides and selenides of calcium and manganese develop extensive, but not complete, solid solubility. It was thus possible to use them to study both solution hardening and precipitation hardening in inorganic, nonmetallic compounds. Samples were first solution treated and quenched. Since phase separation was reasonably slow during cooling, it was possible to determine the amount of solution hardening over a wide temperature and composition range. It was also possible to precipitation harden and over-age these materials. Solution hardening and precipitation hardening are parallel to those found in metals. Cation substitution, as with anion substitution, leads to a harder compound when substituting species are more ionic,i.e., Ca2+-rich compounds are harder than Mn2+-rich compounds, and S2--rich compunds are harder than Se2--rich compounds. Precipitation hardening (and over-aging) occurs more rapidly with greater supercooling and with the lower-melting selenides.

Semiempirical Relation between Hyperfine Constant and Charge Amount of Doped Mn2+ Ion in Non-Metallic Compounds

A semiempirical relation is given between the number of electrons transferred to the empty orbits and the hyperfine constant of the doped Mn 2+ ion in various compounds, on the basis of the empirical relation between the Szigeti charge and the hyperfine constant of the doped Mn 2+ ion in the divalent metal compounds and of an assumption that the charge of the impurity ion is equalized to that of the host cation when the impurity replaced the host cation having the same valence as the impurity. The derived semiempirical relation is applied to a problem of the degree of the localization of the bound hole to the doped Mn 2+ ion in the III V semiconductors. The bound hole is shown to be almost completely localized on the Mn orbits.

NMR and spin/charge fluctuations in intermediate-valent SmB6

Information on spin and charge fluctuations in the non-metallic intermediate-valent compound SmB6 has been obtained via 10B and 11B NMR between 2 and 300 K. Both the isotropic shift and the quadrupole coupling constant are temperature independent over this range, as expected if the fractional valence mixing is also temperature independent. Below 4.2 K the boron spin-lattice relaxation rate T1−1 varies linearly with temperature, and yields a spin fluctuation rate τs−f1∼1013 sec−1, which corresponds to a spin fluctuation temperature Tsf∼ 50 K if characteristic of the stoichiometric compound. An increase of T1−1 above 20 K indicates the onset of Sm-spin relaxation by thermal excitations. The results are also consistent with relaxation by impurity-band states associated with vacancies, but the Korringa constant obtained on this assumption is unrealistically small. Comparison between data obtained from 10B and 11B resonances yields no indication of a contribution from electric field gradient fluctuations to the relaxation; an upper bound on the charge fluctuation time τcf≲3τsf is obtained. It is shown that correlations between Sm spin and charge fluctuations, if present, do not affect the nuclear relaxation in the extreme narrowing limit.

Handbook on the physics and chemistry of rare earths. Vols. III and IV. Non-metallic compounds edited by K. A. Gschneidner Jr and L. Eyring

<i>Handbook on the physics and chemistry of rare earths. Vols. III and IV. Non-metallic compounds</i> edited by K. A. Gschneidner Jr and L. Eyring

Comment on two models for indirect spin-spin coupling in nonmetallic compounds

We discuss two previously proposed models for indirect coupling between $4f$ moments in nonmetallic rare-earth compounds. We show that the derivations of the final expressions are erroneous despite the fact that they are currently referred to in the literature. We propose convenient derivations and expressions in both cases. They may be extended to nuclear spin-spin coupling in nonmetals.

特徴的な電解反応の有機合成への応用

This review is organized under the following headings with 440 references.1. Generation and reactions of reactive intermediates.1.1. Carbon species. 1.2. Nitrogen species. 1.3. Oxygen species. 1.4. Others.2. Reactions of organic hetero atoms.2.1. Nitrogen. 2.2. Sulfur. 2.3. Phosphorus and others.3. Formation and reactions of organometallic compounds.3.1. Formation of metallic compounds employing electrodes as a metal source.3.2. Conversion of metallic compounds to other metallic compounds. 3.3. Formation of nonmetallic compounds from metallic compounds.4. Bimolecular reactions.4.1. Dimerization. 4.2. Cyclization. 4.3. Ring expansion and contraction.5. Stereochemistry.5.1. Stereoselective and stereospecific reactions. 5.2. Asymmetric reactions and asymmetric syntheses.6. New type reactions.

Modified Lytle's potential for the extended fine structure of the X-ray absorption edge

In Lytle's theory the observed absorption maxima correspond to the allowed energy states E of the ejected electron in a spherical well of infinite depth; E=const Q, where Q are the zero roots of the spherical Bessel function. The observed plot of E against Q fails to pass through the origin of the non-metallic compounds. This departure is accounted for by modifying the Lytle potential to include the effect of coulomb attraction felt by the escaping electron in the vicinity of the absorbing atom bound in a molecule. The depth of the appended spherical well, representing the effective coulomb force, is correlated with the bonding energy through electronegativity considerations.

X-ray TiKspectra and band structures of oxides of titanium

The Ti $K$ emission and absorption spectra of the titanium oxides $\mathrm{Ti}{\mathrm{O}}_{x}$ ($x=0, 0.4, 0.84, 0.9, 1.0, 1.12, 1.25, \mathrm{and} 2$) have been measured with a two-crystal spectrometer by means of a step scanning method. The emission spectra were obtained by the fluorescent excitation method. Results are compared with the calculated density of states proposed till now with emphasis on the effect of the oxygen concentration on the electronic structure. The calculated density of states of $\mathrm{Ti}{\mathrm{O}}_{x}$($x=0.80, 0.91, 1.0, 1.08, \mathrm{and} 1.22$) crystallizing in the rocksalt structure explains qualitatively the observed profiles of the $K$ spectra of these substances, both the emission and absorption spectra. However, in detail there exist several discrepancies between the experimental results and the calculation with respect to the forbidden energy gap and the detailed structure of the oxygen $2p$ band and so on. The molecular-orbital theory provides a suitable interpretation for the $K$ spectra of the nonmetallic compound Ti${\mathrm{O}}_{2}$.

High-temperature catalyst supports based on nonmetallic refractory compounds

A study was made of conditions of preparation of supports based on MgO-Si3N4 and Si3N4-SiC composites for catalysts intended for high-temperature processes. It is shown that synthesized supports of these compositions surpass GIAP-3 industrial catalyst in thermal fatigue resistance and mechanical strength.

Subshell photoionization cross sections of the elements for AlKαradiation

Relative subshell photoionization cross sections for the elements have been derived from published data on the relative strength of lines observed in a photoelectron spectrometer and the results converted to an absolute scale based on a value for the $\mathrm{Na}(1s)$ cross section. Values obtained have been found to be in substantial agreement with the predictions of a recent theoretical study for the stronger transitions in elements with $Z&lt;56$. Final-state effects have been demonstrated to be particularly significant in the photoionization of the $3d$ and $4d$ subshells in the lanthanides and actinides. The data derived in the present study strongly suggest that electron attenuation in inorganic (nonmetallic) compounds follows a functional dependence on kinetic energy which does not vary by more than 15% from compound to compound.

Observation of non-metallic compounds in aluminum and its alloys

Observation of non-metallic compounds in aluminum and its alloys

Valence-electron concentration rules and diagrams for diamagnetic, non-metallic iono-covalent compounds with tetrahedrally coordinated anions

Valence-electron concentration rules and diagrams for diamagnetic, non-metallic iono-covalent compounds with tetrahedrally coordinated anions