Temperature dependence of the absorption edge of liquid sulfur

The absorption coefficient of liquid sulfur was measured in the energy range of 1.2–2.6 eV. No discontinuous behavior in the temperature dependence of the optical edge was observed at the polymerization temperature if the increase in light scattering occurring at the onset of the polymerization process is taken into account. Therefore, the electronic states that determine the optical edge appear to be insensitive to higher-order structural correlations.     

High precision measurements of the temperature dependence of the sound velocity in selected liquid metals

The temperature dependence of the sound velocity in liquid lead, tin, bismuth and antimony has been measured with high precision (errors of less than 0.35%) by the ultrasonic pulse transmission technique. The measurements were performed from the melting temperature to approximately 1000 °C. A smooth temperature dependence of the sound velocity was found in liquid lead and antimony. In liquid lead, a linear dependence with a negative temperature coefficient was observed whereas for liquid antimony the sound velocity displays a distinct maximum. The high precision of the measurements enabled uncovering localized features in the temperature dependence of the sound velocity in liquid tin and bismuth. The measurements provide some information on the temperature dependent structure of the molten state of these four elements.     

Temperature dependence of the density of some liquid crystals in the alkyl cyanobiphenyl series

Experimental results for the temperature dependence of the density of propyl – cyanobiphenyl (3CB), butyl – cyanobiphenyl (4CB) and hexyl – cyanobiphenyl (6CB) are presented. The results are compared with previous results for temperature dependence of other members of the alkyl cyanobiphenyl series (nCB). The deviation of the density from linear temperature dependence is discussed in terms of the recently discovered corresponding rule for nematic liquid crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Atomistic simulation of self-diffusion and interfacial diffusion of liquid lead

A liquid metal cooled nuclear reactor, liquid metal fast reactor is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal has safety advantages and it allows a much higher power density than traditional coolants. Disadvantages include difficulties associated with inspection and corrosion problems. For a clear understanding of those phenomena related to diffusion, a study of self-diffusion and mutual diffusion in liquid metals is of critical importance. The molecular dynamics (MD) computer simulation technique has been used to study the self-diffusion and mutual diffusion processes of liquid lead. The diffusion coefficients and activation energy of liquid lead self-diffusion are calculated and the values are consistent with those in experimental results. The mutual diffusion relationship between the activation energy for liquid lead and solid iron is similar to previous results.     

Temperature coefficient of electronic polarizability in optical glasses

The temperature coefficient of refractive index dn/dT and that of volume expansion β have been measured by an interferometric procedure designed to determine the coefficients simultaneously, with one sample. The temperature coefficient of electronic polarizability φ have been calculated from dn/dT and β. φ is expressed as the sum of the contributions of each glass component, φ_i·φ_i is expressed as follows: φ_i = ß_iγ_i, where ß_i is the thermal change in cation-oxygen distance and γ_i is the change in electronic polarizability due to the inter-ionic distance change. φ_i decreases as the ionic field strength z/a² of the cation increases, which is the same tendency as that of ß_i. γ_i, calculated from φ_i and ß_i, gradually increases as z/a² increases. This means that φ_i is mainly determined by the elongation of the inter-ionic distance, and it also suggests that the deformation of the electron cloud of oxygen ion due to the inter-ionic distance change, γ_i becomes larger, as the electronic polarizing power of the cation increases.     

Short range order in anomalous liquid metals

Liquid metals with anomalous physical properties such as increasing sound velocity with temperature or density anomalies, exhibit a complex structure in their one dimensional experimental diffraction patterns. Typically, their radial distribution functions are characterized by an asymmetric first peak and a subsidiary peak or shoulder on the right hand side of the first main peak. It has been hypothesized that the complex structure is associated with short range ordering the liquid. Specifically in the liquid pnictides, it has been proposed that such order may be associated with the underlying solid A7 structure. We present an analysis of the short range order in liquids using a modified quasi-crystalline model of liquid structure. This model is shown to fit the experimental radial distribution function very well and to reproduce the experimentally observed structure factor. Using this model we find that the short range order in the liquid pnictides is dominated by an A7-like structure with two types of bonds, in close agreement with the underlying solid phase. The existence of two bond lengths is necessary within this model to explain the asymmetry in the first peak as well as the change in coordination number along the pnictide series. The quasi-crystalline model is discussed and shown to correlate with the Lindemann melting criterion.     

Temperature dependence of dielectric losses in chalcogenide glasses

The frequency (2 × 10⁴?2 × 10⁷ Hz) and temperature (250–600 K) dependence of the imaginary part of the permittivity, ?′', of As₂Se₃ and Tl₂SnSe_8.61 is explained within a theoretical model. The dielectric premittivities of these compounds are correctly explained by means of a model of a hopping process over a potential barrier between localized sites.We have found that the glassy system of chalcogenide can exist in the form of dipoles. The theory shows, in agreement with the experimental results, that ?′' = Aω^m, where m is a function of temperature.     

Temperature dependence of hopping transport in polymeric semiconductors

We report the results of measurement and analysis of the electrical conductivity of two synthetic highly purified copolymers of the polyacene quinone radical (PAQR) type. The dc conductivity was examined as a function of temperature and pressure. The conductivity-pressure relation is observed to go as log σ versus $\text{P}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The conductivities under moderate pressure (400–5000 atm) show linear relationships on log σ versus $\text{T}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>4</mtext>}}$ plots in the temperature range 70 K < T < 300 K. The possible interpretations as variable range hopping or as nearest neighbour hopping with distributions of activation energies are discussed.     

Electronic structure calculations in liquid and amorphous metals

We review the theoretical methods employed to describe electronic states in structurally disordered metallic systems. Substantial progress has been made in this area using techniques based on multiple scattering theory. We focus on the way in which X-ray and neutron scattering data enter the calculation of the average electronic spectrum. Applications to molten Cu and amorphous NiP alloys are discussed.     

Control of impurity concentration in liquid metals by neutron scattering

A technique is proposed for determining the impurity concentration in liquid metal-impurity systems. This technique does not require special measurements or geometry: information about the impurity concentration can be obtained directly from the data collected during the diffraction experiment. The impurity concentrations in a lead melt with a potassium impurity and in a sodium melt with a lead impurity are determined.     

The incorporation of phosphorus in silicon; The temperature dependence of the segregation coefficient

An analysis is given of the temperature dependence of the segregation of phosphorous during chemical vapour deposition. The observed temperature dependence is compared with a theoretical expression which takes into account the ionization of P in the solid. From both expressions the differential heat of solution of P in Si can be calculated to be –14.9± 2.3 kcal, the uncertainty being mainly due to the unknown value of the bandgap of silicon at high temperatures. The heat of solution can be broken down - amongst others - into a binding part and a strain part for the incorporation of P in Si. The strain energy can be calculated to be 2.2 kcal, which gives an energy of 50.2 ± 0.6 kcal for the binding energy of the P-Si bond, close to the value of the Si-Si bond itself being 53.25 kcal.     

Temperature dependence of lattice parameters of langasite single crystals

To determine the coefficient of thermal expansion of trigonal langasite (La₃Ga₅SiO₁₄) the two independent lattice parameters a and c are measured over a temperature range of 800 °C using X‐ray diffraction on single crystal samples. From the given nonlinear temperature dependence the linear and quadratic thermal coefficients of expansion α₁₁, β₁₁ and α₃₃, β₃₃ for the two lattice parameters a and c could be deduced. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of biased hysteresis loops in hard-soft nanocrystalline Co-based ribbons

The low field hysteresis loops of hard-soft magnetic materials can be biased as a consequence of the magnetic coupling of both phases. In hard-soft nanocrystalline materials, magnetostatic and exchange interactions between the hard crystalline phase and the much softer embedding amorphous matrix coexist and the relevance of their effect on the hysteresis is difficult to distinguish. In this work, the thermal evolution of the biased magnetic hysteresis loops of hardsoft devitrified Co₆₆Fe₄Mo₂Si₁₆B₁₂ ribbons has been studied between room and Curie temperature. The nature of the coupling between the two magnetic phases is discussed in terms of the influence of the temperature on the magnetic properties of the soft phase, mainly on its saturation magnetization and exchange constant, and on the switching field distribution of the hard phase. The results allow to conclude that the effect of the exchange interaction predominates over the magnetostatic one.     

Relationship between excess entropy and microstructure of undercooled liquid metals

Molecular dynamics simulations were performed for stable and undercooled liquid metals. The inherent structures formalism was used to explore the potential energy landscape, showing a competition between crystalline (fcc and bcc) and icosahedral (regular and distorted) order. The two-body approximation of the excess entropy is used to study the interplay between the microstructural ordering and the entropy of undercooled liquid metals. A strong correlation between the excess entropy and the relative changes in the crystalline and icosahedral order is obtained, indicating that entropic effects are coupled to the microstructural changes of undercooled liquid metals. Thermal entropy behavior was obtained by using structural information of both inherent structures and atomic configurations.     

Temperature dependence of photoluminescence from ordered GaInP2 epitaxial layers

The temperature behavior of the integrated intensity of photoluminescence (PL) emission from ordered GaInP₂ epitaxial layer was measured at temperatures of 10 ‐ 300 K. Within this temperature range the PL emission is dominated by band‐to‐band radiative recombination. The PL intensity temperature dependence has two regions: at low temperatures it quenches rapidly as the temperature increases, and above 100 K it reduces slowly. This temperature behavior is compared with that of disordered GaInP₂ layer. The specter of the PL emission of the disordered layer has two peaks, which are identified as due to donor‐accepter (D‐A) and band‐to‐band recombination. The PL intensity quenching of these spectral bands is very different: With increasing temperature, the D‐A peak intensity remains almost unchanged at low temperatures and then decreases at a higher rate. The intensity of the band‐to‐band recombination peak decays gradually, having a higher rate at low temperatures than at higher temperatures. Comparing these temperature dependencies of these PL peaks of ordered and disordered alloys and the temperature behavior of their full width at half maximum (FWHM), we conclude that the different morphology of these alloys causes their different temperature behavior. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of secondary electron emission from SiO2-layers

By means of a “random walk model” the escape depths of secondary electrons (SE) can be obtained as a consequence of interaction with LO-phonons. The measured temperature dependence of the SE-yield leads to a high energetic LO-mode with ħω ⋍ 140 meV in amorphous SiO₂ influencing dominantly the electronic slowing down process.