LII,III emission, LIII absorption, Kβ5 emission, K absorption spectra of chromium from pure metal and nitrides with the electron microprobe

The characteristic L_{II, III} and Kβ₅ X-ray emission bands of chromium in the pure metal and the nitrides Cr₂N and CrN are investigated with an electron microprobe. Also presented are the chromium L_III and K absorption replicas obtained using the self-absorption method. The results are discussed with reference to the theories proposed in the literature.     

Quantum diffusion in solid H2?Ne solutions

Quantum diffusion in solid hydrogen containing 0.02–0.25 mol.% neon has been investigated by the calorimetric method in temperature range 1–3 K. The concentrations of orthohydrogen were 0.23; 0.5 and 1 mol. %. The parameter studied was characteristic configurational relaxation time τ. Heat capacity is very sensitive to space distribution of orthohydrogen molecules. Therefore, the determination of configuration relaxation rate has been performed by observing the time dependence of heat capacity. A neon impurity in the indicated concentration is observed to accelerate quantum diffusion in hydrogen. The magnitude of the effect diminishes as the temperature increases.     

Exciton mobility edge in CdS1−xSex solid solutions

Low temperature emission spectra of localized excitons in CdS_1?xSe_x solid solutions under the monochromatic excitation with tunable laser have been studied. It has been found that the luminescence of localized excitons has a high degree of linear polarization with respect to the polarization direction of exciting light. This polarization reflects the “hidden” anisotropy of macroscopically isotropic localized exciton system and strongly depends on the frequency of exciting light. Study of this dependence has permitted for the first time a determination of position of the “mobility edge” for exciton migration in disordered semiconductor solid solution.     

Dipolar dielectric relaxation in CeO2-YO1,5 solid solutions

The dielectric properties of yttrium oxide-doped cerium oxide solid solutions have been studied by using a.c. techniques. Frequency and temperature respectively range from 10 to 10⁵ Hz and from 70 to 200°C. Both a complex impedance plot (Z″ vs Z′) and a conductance plot (G at fixed frequency vs inverse of temperature T^?1) are shown to be complementary for an accurate determination of the bulk resistance and of the dielectric loss. For the three investigated concentrations of yttrium oxide (m/% YO_1,5:0.001, 0.01 and 0.1), the activation energies for conduction are equal to 0.86, 0.75 and 0.75 eV, while the activation energy for dipole reorientation is found to be concentration independent (0.75 eV; angular frequency preexponential factor: 6.0 × 10¹², 1.43 × 10¹³ and 3.05 × 10¹³ s^?1). Moreover, the dipolar relaxation rates are found to be of the same order of magnitude as that of the migration rate. Interpretation is given on the basis of Wachtman's model and of previous results obtained by Nowick et al. from ITC (ionic thermo-current) investigations. The observed dielectric peak appears to be due to the redistribution of oxyygen vacancies between charged (Y_Ce-V₀) pairs and fixed charged Y_Ce defects.     

K- and LII,III-Shell excitations in CS2 and COS by 2.5 keV electron impact

Energy loss spectra of 2.5 keV electrons, scattered by CS₂ and COS through small angles, have been studied in the regions of the respective oxygen K, carbon K and sulfur L_{II, III}(2p) edges. The carbon and oxygen K-shell spectra are dominated by the first discrete transition similar to the K-shell spectra of the “isoelectronic” molecules CO₂ and N₂O. However, the carbon K-shell spectra of CS₂ and COS have features which may indicate the possible existence of an effective potential barrier in these molecules.     

Superprotonic solid solutions between CsHSO4 and CsH2PO4

Solid solutions of (CsHSO₄)_1 − x(CsH₂PO₄)_x (x = 0.25-0.75) were synthesized by mechanical milling method over a wide range of compositions. Superprotonic cubic phase was confirmed for all these samples between 293 and 420 K depending on its composition. These superprotonic phases have primitive cubic structure similar to that of CsH₂PO₄. The kinetic stability of the supercooled cubic phase depends both on the composition x and the humidity of surrounding atmosphere. The most stable composition of the cubic phase was found around x = 0.67 and could be maintained for several days even under ambient atmosphere. The ionic conductivities of these superprotonic phases reached 10^− 2–10^− 3 S∙cm^− 1 at 450 K. With increasing x the ionic conductivity at the superprotonic phase decreased continuously associated with the increase of the activation energy. These findings suggest that the average number of the hydrogen bonds between XO₄ (X = S, P) units plays an important role on the stability of the cubic phase and also on the conductivity.     

X-ray absorption near edge structure in solid Kr and KrF2

X-ray absorption near edge structure (XANES) spectra of gaseous Kr, solid Kr and solid KrF₂ have been obtained and compared to differentiate between continuum resonances near the edge and bound state transitions. By comparing experimental and ab initio (MSW-Xα) calculated spectra the influence of environment as well as molecular bonding on XANES is demonstrated.     

Electronic structure of SixGe1−x semiconductor solid solutions

The electronic structure of Si_xGe_1?x solid solutions is studied by means of a semi-ab initio method without involving the virtual crystal approximation. The calculations are performed on large cubic cells of the diamond lattice which contain a total of 64 Si and Ge atoms homogeneously distributed in different compositional ratios. The basis functions and the potentials used in the calculation give good band structures of elemental Si and Ge respectively. The calculated variation of band gap with x is in agreement with optical experiment: the two linear curves of gap vs concentration have different slopes at high and low x values with a crossing-over at about x=0.28. The band gaps are direct for xε (0, 0.28) and indirect for x ≥ 0.28. The density of states (DOS) of the solid solution can be very well approximated by the weighted average of the bulk Si and Ge DOS. There is a very slight charge transfer of about 0.05 electron per atom from Si to Ge.     

Exciton luminescence of AgBr1−x Cl x solid solutions

Institute of Solid-State Physics, 8, Kengaraga St., Riga, LV 1063, Latvia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 3, pp. 174–177, May–June, 1995.     

Comments on the microwave absorption spectrum of solid H2

Recent theories by Luryi et al. and by Harris et al. for the energy levels of an isolated pair of ortho-H₂ molecules in nearly pure solid para hydrogen are compared.     

High temperature thermodynamics of H2 and D2 in titanium,and in dilute titanium oxygen solid solutions

The Tian Calvet microcalorimetric method has been improved in order to determine Δ$\text{H}$_H(D), the partial molar enthalpy of mixing of hydrogen (deuterium) in the Ti-H₂(D₂) solid systems for compositions 0 < (H/Ti) < 1.85, at 713 K and in the α TiO_y + H₂ solid solutions (y = (O/Ti)) at 745 K. The combined calorimetric and equilibrium method allows a precise evaluation of the partial molar entropies. The results of this study differ substantially from earlier published data.     

Investigation on the magnetocaloric effect in (Gd,Pr)Al2 solid solutions

A theoretical and experimental investigation on the magnetocaloric properties of the rare earth pseudo-binary compounds Gd_1−nPr_nAl₂ is presented. The calculated isothermal entropy and adiabatic temperature changes under magnetic field variations from 0 to 2 T and from 0 to 5 T are in good agreement with the experimental data. For the Pr-concentrations n=0.25, 0.5 and 0.75 the experimental data present an inverse magnetocaloric effect which was theoretically predicted and associated with the competition between the opposite magnetizations of the Gd and Pr sublattices. The two-sublattice Hamiltonian used in the calculations takes into account the crystal field, exchange and Zeeman interactions.     

Study of amorphous thin films of (Ti, Nb)O2 solid solutions by X-ray absorption at the Ti K edge

As the (Ti, Nb)O₂ amorphous thin films cannot be prepared under a self-supported form, we have recorded the X-ray reflectivity. A new program which allows extraction of the X-ray absorption from the reflectivity is briefly described. The correction of the anomalous dispersion effect is effective, particularly near the edge within 200 eV. Hence, it has allowed a comparison between the amorphous layers and the crystalline analogues for which the X-ray absorption has been recorded by transmission. In the amorphous state, the TiO₆ group is smaller than in the crystalline state because of the relaxation of the crystallographic constraints. The oxygen coordination octahedron is almost regular in the films. On the other hand, in both cases, an electron transfer takes place from Nb to Ti.     

Polyacrylonitrile–sulfolane–CuX2 (X=Cl, Br, CF3SO3) solid polymer electrolyte

A series of polyacrylonitrile–sulfolane–CuX₂ (PAN–TMS–CuX₂, where X=Cl, Br, CF₃SO₃) polymer electrolytes, of thickness between 0.03 and 0.07 cm, were prepared by means of the solution cast technique. The solvent content was as high as 60–70 wt.%. Conductivities of the foils obtained from impedance measurements were of the order of 10⁻³ Ω⁻¹ cm⁻¹. Temperature variation of the conductivity for all the systems studied was of the Arrhenius type. Exchange current density at the Cuelectrolyte interface, determined from the Tafel plot, was of the order of milliampere (mA). Cyclic voltammetry showed the irreversible character of the copper plating–stripping process.     

Fine structure in the absorption edge spectrum of NbS2Y2 (Y = Cl,Br, I)

High resolution absorption spectra of single crystals of NbS₂Y₂ (Y = Cl, Br, I), obtained at temperatures between 4.2 and 300 K revealed extensive fine structure in the absorption edge. This structure has been analysed and interpreted in terms of allowed indirect interband transitions, involving phonons corresponding to SS and NbS vibrations, followed by forbidden and by allowed direct transitions. From the shape of the absorption curve associated with the phonon branches of the indirect transitions a binding energy of 23 cm^? for indirect excitons is obtained. A binding energy of 28 cm^? for direct excitons is deduced from the exciton lines observed at the long-wavelength side of the direct transitions. A detailed interpretation of the optical transitions is given in terms of a molecular orbital diagram for the Nb₂S₄ clusters, present in these crystals.     

Electron spin resonance of diluted solid solutions of MnO2 in Y2O3

Electron spin resonance spectra of Mn²⁺ in diluted solid solutions of MnO₂ in Y₂O₃ have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn²⁺ ions in sites with two different symmetries were observed, as well as Mn²⁺ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn²⁺ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C₂ symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn²⁺ ions of 0.53 nm, of the same order as that of Mn²⁺ ions in CaO.     

Magnetic properties of Ni0.8Cu0.2−xGex solid solutions

The results of magnetic measurements performed on Ni_0.8Cu_0.2-xGe_x solid solutions, with x ? 0.10 are reported. The saturation magnetization, Curie temperature and effective nickel moments decrease nearly linear when substituting Cu by Ge. The ferromagnetic resonance measurements show that the g values are not dependent on composition. Finally, the magnetic behaviour of nickel in these solid solutions is analysed.     

Emission spectra of iron doped ZnSxSe1-x solid solutions

The photoluminescence of ZnS_xSe_1?x:Fe has been investigated in the visible and near infrared (λ ? 1.2 μm) region. The doping dependence shows, that the incorporation of iron in ZnS produces, in addition to the well-known red luminescence (λ_max = 660 nm), another emission band at 980 nm, which was hitherto unknown for ZnS: Fe. The energetic position of this new band is proved to be independent of composition of the ZnS_xSe_1?x solid solution. Therefore, it is interpreted as an internal transition in iron centres. On the other hand, the red Fe-band shifts to lower energy with increasing selenium concentration. This result shows clearly, that the red Fe-band of zincsulfide cannot be interpreted by an internal transition in iron centres [3], but favors the donor-acceptor model, which was already suggested by other authors [4].     

Dielectric response function of GaPAs solid solutions in the vibrational absorption region

By taking spectra of IR transmission and reflection, attenuated total reflection, and Raman scattering, different models of the dielectric response function of GaPAs solid solutions are tested. It is demonstrated that the models accounting for the difference in the times of transverse and longitudinal vibrational relaxations, as well as the frequency distribution of TO phonons, make possible the prediction of the experimental spectra with a reasonable accuracy.