Medium-range fluctuations accompanying the metal-nonmetal transition in expanded fluid hg

We have carried out small angle x-ray scattering experiments of expanded fluid Hg in the metal-nonmetal (M-NM) transition region around 9.0 g cm(-3). Increase of small angle scattering intensity following the Ornstein-Zernike equation is clearly observed in the M-NM transition region as well as near the liquid-vapor critical point at 5.8 g cm(-3). The short-range correlation length, R, becomes twice as large in the M-NM transition region as in the critical region. The enhancement of R in expanded fluid Hg suggests a new type of fluctuations reflecting a first-order M-NM transition.     

Observation of fast sound in metal-nonmetal transition in liquid Hg

Liquid Hg undergoes the metal-nonmetal (M-NM) transition when it is expanded from 13.6 g cm⁻³ at ambient conditions to 9 g cm⁻³ at high temperature and high pressure. To investigate collective and single particle motions in expanded fluid Hg, we have made inelastic X-ray scattering experiments and obtained the dynamic structure factor, S(Q,ω), of fluid Hg. We analyzed S(Q,ω) within the framework of generalized hydrodynamics and found that the excitation energies of collective modes disperse three times as fast as the hydrodynamic sound velocity in the M-NM transition region at 9 g cm⁻³. The results indicate the existence of fast sound in expanded fluid Hg accompanying the metal-non-metal transition and strongly hint that fluctuations intrinsic to the M-NM transition are induced on atomic length scale and sub-picosecond time scale.     

Static, dynamic and electronic properties of expanded fluid mercury in the metal-nonmetal transition range. An ab initio study

Fluid Hg undergoes a metal-nonmetal (M-NM) transition when expanded toward a density of around 9 g cm(-3). We have performed ab initio molecular dynamics simulations for several thermodynamic states around the M-NM transition range and the associated static, dynamic and electronic properties have been analyzed. The calculated static structure shows a good agreement with the available experimental data. It is found that the volume expansion decreases the number of nearest neighbors from 10 (near the triple point) to around 8 at the M-NM transition region. Moreover, these neighbors are arranged into two subshells and the decrease in the number of neighbors occurs in the inner subshell. The calculated dynamic structure factors agree fairly well with their experimental counterparts obtained by inelastic x-ray scattering experiments, which display inelastic side peaks. The derived dispersion relation exhibits some positive dispersion for all the states, although its value around the M-NM transition region is not as marked as suggested by the experiment. We have also calculated the electronic density of states, which shows the appearance of a gap at a density of around 8.3 g cm(-3).     

Expanded fluid mercury in the metal-nonmetal transition range. An ab-initio MD study

Fluid Hg undergoes a metal-nonmetal (M-NM) transition when is expanded from the triple point towards a density of around 9 gr/cm³ at high temperature and high pressure. To investigate the related changes in the static and dynamic properties, we have performed ab-initio molecular dynamics simulations for some states close to the M-NM transition range. The calculated static and dynamic structure factors show a good agreement with the available experimental data. It is found that the volume expansion reduces the number of nearest neighbors at the expense of the inner ones. The dispersion relation exhibits a positive dispersion which is not so marked as that deduced from experimental data. The total electronic density of states shows the appearance of a band gap at a density somewhat smaller than 9 gr/cm³.     

NMR studies of metal-nonmetal transition in lithium-methylamine solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li and ¹H have been measured in Li-methylamine solutions, in which a transition from the metallic to the nonmetallic states occurs.     

Anomalous pressure dependence of the metal-nonmetal transition of NiS

The pressure dependence of the metal—nonmetal transition in the hexagonal form of NiS has been measured to 13.7 kbar. An anomalous pressure dependence in the transition temperature was observed near 4.5 kbar. We associate this with the unusual lattice parameter behaviour previously reported for this region.     

Temperature dependent energy bands and the metal-nonmetal transition in NiS

The LCMTO (linear combination of muffin-tin orbitals) technique has been used to calculate the first temperature dependent energy bands for a transtion metal compound. The particular compound studied was hexagonal NiS which undergoes a first-order metal-to-nonmetal transition as the temperature is lowered below 264K. We find the bands to agree well with XPS data and that the Sp bands overlap the bottom of the d bands as predicted by White and Mott. This p-d overlap, which reduces the correlation energy, is found to increase with temperature as a result of lattice vibrations whereas the lattice distortion accompanying the transition has very little effect on the energy bands. This suggests that the Mott-Hubbard transition in NiS is driven by the Debye-Waller modification of the potential and not the lattice distortion as suggested by White and Mott.     

Hall-effect and metal-nonmetal transition in copper-argon and lead-argon systems

Summary Hall-effect measurements have been made to find out the type of transition from metal to nonmetal in copper-argon and lead-argon films prepared at helium temperature. The Hall measurements indicate that the transition from metal to nonmetal is a new-type transition. Such a metal-nonmetal transition in metal-argon systems may be attributed to the combined effect of electron correlation intermediated by phase transition. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Doping density striation effects in studies of the metal-nonmetal transition in heavily doped semiconductors

Significant oscillatory doping density inhomogeneities - striations - are reportedly a commonplace phenomenon in germanium and silicon crystals. Schottky barrier tunneling data on heavily doped and irradiation compensated silicon are presented which are consistent with the presence of such striations. The need for considering striations in studies of the metal-nonmetal transition is emphasized.     

Perturbation of magnetization of a magnetic fluid by ultralow thermal fluctuations accompanying a sound wave

The paper presents the results of theoretical and experimental research of the the effect of perturbation of the magnetization of a magnetic fluid caused by thermal fluctuations in an adiabatic sound wave in the initial area of the magnetization curve. Measurements are conducted on samples of a magnetic colloid with various viscosity of the dispersion medium in the frequency range of 20–60 kHz. In this frequency range, the studied samples are characterized by the absence of thermal relaxation of magnetization. Comparison of the conclusions of the thermal magnetization relaxation model with the results of experiment make it possible to obtain information on the rheological features of the neareast molecular environment of a particle, i.e., nanorheology.     

Shear-excited sound in magnetic fluid

Perceptible sound is shown to be excited in ferrofluids by the shear motion of a rigid plate, if the fluid is exposed to a magnetic field oblique both to the plate and to the direction of propagation. This is in contrast to other fluids, including anisotropic ones such as nematic liquids.     

Electronic structure and metal-nonmetal transition in liquid Cs−Sb and Cs−I systems

The electronic structures of liquid Cs–Sb and liquid Cs–I systems have been calculated using the self-consistent semirelativistic APW method within the superlattive model. We have investigated the nature of chemical bonding in connection with the composition dependent metal-nonmetal transition in these systems. It is found that Cs–Sb system is principally ionic as well as Cs–I system, but appreciable admixture of the metallic bonding is observed; this explains the different behavior between the two systems in their composition-induced metal-nonmetal transitions.     

On the molecular sound absorption in fluid mixtures

Measurements of sound absorption in binary mixtures of gases in which two relaxation processes can occur due to the specific heats of the molecular vibrations, have hitherto been evaluated by using a theory based mainly on gaskinetic considerations. The theory presented here, uses the thermodynamics of irreversible processes as developed byMeixner for sound absorption in fluid systems due to interior reactions of arbitrary kind and number. This treatment permits a concise derivation of the final formulas which are also valid for mixtures of real gases and fluids. According to which set of independent thermodynamical variables for the derivation is used, the final formulas seem to differ considerably. It is pointed out that these differences arise from introducing two types of relaxation times and may be eliminated by means of the relationship between these relaxation times.     

Charge transfer transition accompanying x-ray photoionization in transition-metal compounds

Satellites, 5 to 10 eV below the main peaks, have been observed in the x-ray photoelectron spectra of the 2s, 2p, 3s, 3p and valence shells of the 3d transition-metal ions of nickel and copper oxides. They are believed to be the result of electron shake-up. Since shake-up satellites are present in ions with partially filled 3d shell but absent in ions with completely filled 3d shell, they may be attributed to monopole charge transfer transitions (ligand → metal 3d) using the sudden approximation (monopole selection rules) and the ligand field theory.     

The metal-nonmetal transition in NiS studied by the Mössbauer effect of 57Fe

Mössbauer spectra of ⁵⁷Fe impurities in α NiS show an abrupt collapse of the hyperfine splitting at T_t = 260 K, the nonmetal-metal transition; the extrapolated Néel point is ～420 K. Below T_t, it appears that iron adjacent to a vacancy is low-spin. There us evidence of substantial d-electrons delocalisation above T_t. β NiS does not order magnetically down to 4 K.     

Metal-insulator transition in hydrogen and in expanded alkali metals

Two methods are considered for testing the stability of an electron gas to formation of bound states round a pair of protons. In the first, the screened potential for the two protons is set up as a superposition, which is appropriate in a very high density electron gas. The condition for bound state formation is then examined in the two-centre problem. The density thus obtained is in the right density range to accord with the experiment of Hawke et al. for producing cold metallic hydrogen.This has encouraged us to attempt a more ambitious calculation, namely the investigation of the Heitler-London energy of a model H₂ molecule with screened electron-nuclear and electron-electron interactions, the screening being again through appropriate introduction of the Thomas-Fermi screening radius. The merit of this second model is that the theory contains the Heitler-London value of the dissociation energy of the free H₂ molecule in the limit when the density of the electron gas tends to zero. This feature, the binding energy of the diatomic and its importance in distinguishing the metal-insulator transition in hydrogen from those expected to occur in expanded alkali metals is stressed. The second point we stress is that, in both the models discussed above, there is a close connection with the one-centre criterion for bound state formation. Though we have not carried out detailed two-centre calculations for expanded alkali metals, nevertheless some discussion is given of the one-centre bound state criterion in these metals.Some remarks are also made on the dielectric function of molecular crystals, in relation to the insulator-metal transition.