Table of contents

The universality of both the Birch equation and the equation of Vinet et al. (1989) is tested and discussed using the compressibility data for the 15 transition metals and 22 compounds.

The valence states of europium in EuPd₃B are studied in connection with the distribution of boron atoms in the neighbourhood of the Eu ion. The temperature dependence of this distribution, which determines the populations of the Eu³⁺ and Eu²⁺ states, is analysed. The results are compared with the experimental intensity ratios of the Mossbauer lines. Fairly satisfactory agreement is obtained.

This paper presents the de Haas-van Alphen (DHVA) effect of the stage-3 SbF₅-graphite intercalation compound (GIC). Three groups of DHVA frequencies and carrier cyclotron masses are explained by the Blinowski band structure model with a Fermi energy of -0.73 eV. The highly anisotropic Fermi surface of the compound is measured with the angular dependence of the DHVA frequencies. It is also found that the energy bands and the charge distribution over the graphite layers are similar in the stage-3 SbF₅-GIC and the stage-3 SbCl₅-GIC.

Reflectivity measurements over the energy range 0.5-12 eV have been made for the amorphous alloy system a-Si_1-yNi_y:H with y=0.0, 0.11, 0.28, 0.45. The infrared region of the reflectivity shows evidence of a semiconductor-to-metal transition as y is increased, whilst the visible/ultraviolet regions show a systematic shift in energy of prominent features. Using suitable extrapolations to the reflectivity data, Kramers-Kronig analysis has enabled the determination of in ₁, in ₂ and hence the OJDOS (optical joint density of states) for the system. A schematic valence and conduction band DOS has been deduced from these data in conjunction with the previously determined variation of optical bandgap with composition.

The authors consider Shockley-type surface states (SSS) in substitutionally disordered alloys. For this purpose the Green function for the semi-infinite system is obtained by matching the bulk Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) Green function with the free-electron Green function on the bounding surface.The formalism is applied to calculate binding energies and disorder induced smearings of the Y-centred SSS on the (110) surface and the Gamma -centred SSS on the (111) surfaces of Cu, Cu₉₀Al₁₀, Cu₇₀Zn₃₀, and Cu₉₀Ge₁₀. Their theoretical predictions with regard to changes in the binding energy and the disorder induced smearing in Cu₉₀Al₁₀ where corresponding angle-resolved photoemission experiments are available for comparison are in reasonable accord with measurements. Their computations indicate that the binding energy of the SSS in Cu-based alloys will generally increase with increasing electron/atom (e/a) ratio.

The unoccupied electronic states of the group Vb transition metal dichalcogenide compound vanadium diselenide have been measured up to about 10 eV above the Fermi level using isochromat momentum-resolved inverse photoemission. Bands along the Gamma A direction of the Brillouin zone were probed by recording normal-incidence spectra at photon energies between 17 and 28 eV. Band dispersions in the two principal symmetry planes of the Brillouin zone, Gamma ALM and Gamma AHK, were determined from off-normal-incidence spectra recorded at a photon energy of 20 eV. Strong features resulting from transitions into the unoccupied V 3d-derived bands are seen at about 1 eV and about 3 eV above the Fermi level; the variation of the intensity of these features with the azimuthal angle of electron incidence reflects the three-fold symmetry of the 1T crystal structure adopted by VSe₂. A broad feature centred at about 8 eV, and showing an onset at about 6 eV, is associated with higher-lying s/p bands while a weak peak at about 5 eV, which shows no dispersion along Gamma A, is tentatively identified as a surface resonance. The results are compared with published band-structure calculations.

The structures of expanded liquid alkali metals, Na, K, Rb and Cs, along the liquid-vapour coexistence curve are investigated theoretically by employing the integral equation method in the modified hypernetted-chain (MHNC) approximation and the molecular dynamics (MD) simulation. Excellent agreement is obtained between the MHNC and the MD results, which also agree well with the experimental results. It is shown from these systematic investigations that the characteristic features of the density dependence of the structure along the liquid-vapour coexistence curve observed for expanded liquid Rb (Franz et al. 1980) and Cs (Winter et al. 1987) are common features for expanded liquid alkali metals.

The method of X-ray diffraction with isomorphic substitution has been extended to aqueous solutions containing complex ions. In a study of isomorphism between NO₃^-(aq), BrO₃^-(aq) and ClO₃^-(aq), it is found that the NO₃^- and BrO₃^- ions are isomorphic up to the level of the first-order difference indicating a similarity in their anion-hydration structure. Based on the isomorphism of these two ions, and because the water molecules are only weakly perturbed from their structure in pure water, a second-order difference calculation was made and the ion-ion pair correlation function of these two ions obtained. The results show that the most probable ion-ion separation is between 5 AA and 11 AA and the distance of closest approach is 4.8 AA. NO₃^- and BrO₃^- are found, however, not to be isomorphic with ClO₃^-.

Medium- ( Delta E=50 mu eV) and high-resolution ( Delta E=15 mu eV) neutron quasi-elastic scattering spectra of liquid CCl₄ at two temperatures within the liquid range are reported. The (mostly coherent) dynamical structure factors are analysed in terms of a model which takes into account the effects of the liquid structure on the single-particle dynamics, and extends the usual rotational diffusion approximations. Such an extension was found to be necessary in order to reconcile the measured dynamical parameters with those available from NMR relaxation.

In the present paper changes in the percolation threshold of AOT-isooctane-water droplets by solubilizing a protein such as cytochrome c are reported. It is demonstrated that the critical percolation factors (volume fraction, temperature, water content) change by cytochrome c addition. This is attributed to the increase in the attractive interactions between droplets by solubilizing cytochrome c in water droplets.

The authors have investigated the electronic structure of the recently synthesized hydride Na₂PdH₂ by means of a calculation of the energy bands and densities of states using the linear muffin-tin orbital method. The metal-hydrogen bonding features, the Fermi-energy-related properties and the maximum hydrogen content of the system are discussed.

Ground state energies of shallow states of donor impurities on cosine-shaped periodically rough interfaces formed by two isotropic semiconductors, such as GaAs/Ga_1-xAl_xAs or GaAs/vacuum are calculated variationally with the approximation that interfaces represent infinitely high potential barriers. The results show that changes in the ground state energies of interface impurity states caused by rough interface are not negligible especially for GaAs/Ga_1-xAl_xAs interfaces with sharp defects.

The authors report on the effect of thermal equilibration on the dark conductivity of undoped optimized a-Ge:H with an optical gap of 1.03 eV. The freeze-in temperature T_E is about 160 degrees C. The isothermal relaxation of the conductivity follows a stretched exponential function. The inverse equilibration time tau ^-1 is thermally activated with an energy E_tau of 1.4-1.5 eV. It is then shown that, as compared with the values for a-Si:H T_E, tau and E_tau are only slightly different. The results are fully consistent with the model of dispersive diffusion of hydrogen.