Masahiro Susa

Thermal conductivities of silicon and germanium in solid and liquid states measured by non-stationary hot wire method with silica coated probe

The thermal conductivities of silicon and germanium have been determined using the non-stationary hot wire method. Measurements were carried out over the temperature range 293–1724 K on solid and liquid silicon and on liquid germanium in alumina tube. For solid silicon, the thermal conductivities were about 139 W/mK at 293 K and 19 W/mK at 1573 K and displayed temperature dependence steeper than T � 1 ; where T is the temperature. Calculation of thermal conductivities for solid silicon based upon isotope, three-phonon and four-phonon scatterings indicates that phonon conduction dominates heat conduction at temperatures below 1000 K. At temperatures above 1000 K, on the contrary, contributions from electron, hole and electron–hole pair to heat conduction became greater progressively with a temperature rise. For liquid silicon, the thermal conductivity was about 57 W/mK at 1700 K and exhibited a slight increase with an increase in temperature. The thermal conductivity of liquid germanium was about 43 W/mK at 1273 K and slightly increased with increasing temperature. In both liquids, temperature dependency of thermal conductivity values was discussed from the view point of the Wiedemann–Franz law. r 2002 Elsevier Science B.V. All rights reserved.

Degradation of electrochromic amorphous WO sub 3 film in lithium-salt electrolyte

The electrochromic behavior of amorphous WO{sub 3} films prepared by electron-beam deposition has been studied. SIMS analysis has revealed the lithium accumulates in amorphous WO{sub 3} films during reversible coloring and bleaching in propylene carbonate solution of LiClO{sub 4}. When a large quantity of lithium has been injected into WO{sub 3} films, an absorption spectrum different from tungsten bronze is observed. In these films, lithium tungstate has been observed using x-ray photoelectron spectroscopy and x-ray diffraction analysis. It has been concluded that the degradation of electrochromism of amorphous WO{sub 3} is caused by the formation of stable lithium tungstate.

Phase (Liquid/Solid) Dependence of the Normal Spectral Emissivity for Iron, Cobalt, and Nickel at Melting Points

Normal spectral emissivities of liquid and solid Fe, Co, and Ni have been determined at their melting points at wavelengths from 650 to 800 nm and from 1000 to 1900 nm using an apparatus that consists of a cold crucible and diffraction grating spectroscopes. For all three metals, the emissivities of the liquid phases are slightly larger than those of the solid phases both in the visible and near-infrared regions. For iron, the near-infrared emissivities decreased progressively with each additional measurement series and settled down after three series. A possible explanation to this behavior is offered. The present results for iron were assessed by comparisons with previously reported results and with predictions based upon the Hagen–Rubens relation for the ratio of the emissivity of the liquid to that of the solid (εLiquid/εSolid). The measured emissivities for all three metals are in good agreement with previous results at and near the melting point. The results for εLiquid/εSolid in the near-infrared region demonstrate that the phase (liquid/solid) dependence of the infrared emissivity is consistent with that of the dc resistivity for all the metals at their melting points.

Deviation from Wiedemann–Franz Law for the Thermal Conductivity of Liquid Tin and Lead at Elevated Temperature

The thermal conductivities of tin and lead in solid and liquid states have been determined using a nonstationary hot wire method. Measurements on tin and lead were carried out over temperature ranges of 293 to 1473 K and 293 to 1373 K, respectively. The thermal conductivity of solid tin is 63.9±1.3 W⋅m−1⋅K−1 at 293 K and decreases with an increase in temperature, with a value of 56.6±0.9 W⋅m−1⋅K−1 at 473 K. For solid lead, the thermal conductivity is 36.1±0.6 W⋅m−1⋅K−1 at 293 K, decreases with an increase in temperature, and has a value of 29.1±1.1 W⋅m−1⋅K−1 at 573 K. The temperature dependences for solid tin and lead are in good agreement with those estimated from the Wiedemann–Franz law using electrical conductivity values. The thermal conductivities of liquid tin displayed a value of 25.7±1.0 W⋅m−1⋅K−1 at 573 K, and then increased, showing a maximum value of about 30.1 W⋅m−1⋅K−1 at 673 K. Subsequently, the thermal conductivities gradually decreased with increasing temperature and the thermal conductivity was 10.1±1.0 W⋅m−1⋅K−1 at 1473 K. In the case of liquid lead, the same tendency, as was the case of tin, was observed. The thermal conductivities of liquid lead displayed a value of 15.4±1.2 W⋅m−1⋅K−1 at 673 K, with a maximum value of about 15.6 W⋅m−1⋅K−1 at 773 K and a minimum value of about 11.4±0.6 W⋅m−1⋅K−1 at 1373 K. The temperature dependence of thermal conductivity values in both liquids is discussed from the viewpoint of the Wiedemann–Franz law. The thermal conductivities for Group 14 elements at each temperature were compared.

Electric Resistivity Measurements of Sb2Te3 and Ge2Sb2Te5 Melts Using Four-Terminal Method

In this work, we aim to determine the electric resistivities of liquid Sb2Te3 and Ge2Sb2Te5. Electric resistivities were measured using the four-terminal method. First, the electric resistivities of liquid Ga and Sn were measured to establish this method. Second, the electric resistivities of Sb2Te3 and Ge1.6Sb2.0Te5.0 were measured over temperature ranges between the respective melting temperatures of samples and 1020 K. The electric resistivity of Sb2Te3 has been determined to be 4.36±0.14 µΩ m at 992 K. The uncertainty was determined on the basis of the guide to the expression of uncertainty in measurement. The electric resistivity of Ge1.6Sb2.0Te5.0 is smaller than that of Sb2Te3. It is also found that both resistivities decrease with an increase in temperature; which indicates that both liquid materials behave as a semiconductor. Therefore, the pseudogap model was applied to derive the electrical activation energies.

Determination of refractive index and electronic polarisability of oxygen for lithium-silicate melts using ellipsometry

The refractive index of Li2O–SiO2 melts has been measured using the ellipsometer constructed for high-temperature use. Measurements were carried out on four samples having different compositions over a wide temperature range (1300–1800 K). The standard deviation for the values measured was within ±0.0005. Additions of Li2O were found to cause increases of refractive index in the temperature range investigated. At Li2O concentrations <25 mol% the refractive indices of the melts increased with increasing temperature, similar to SiO2. However, this temperature dependence became smaller with additions of Li2O and at Li2O concentrations more than 30 mol% the refractive indices of the melts decreased with increasing temperature. The temperature dependence of the refractive indices has been discussed from those of the density and the molar electronic polarisability on the basis of the Lorentz–Lorenz equation. In addition, the electronic polarisability of oxygen derived from the molar electronic polarisability increased with increasing temperature in each melt, suggesting that the ionicity of oxygen increases as temperature increases. Furthermore, additions of Li2O were found to cause increases in the electronic polarisability of oxygen, due to the formation of non-bridging oxygen ions.

Thermal Conductivity Measurements of Solid Sb2Te3 by Hot-Strip Method

The thermal conductivity of solid Sb2Te3 has been measured by the hot strip method from room temperature to 789 K. The thermal conductivity of solid Sb2Te3 decreases with an increase in temperature up to approximately 500 K and then increases. It is proposed that phonon thermal conduction dominates the heat transport around room temperature although other mechanisms such as electron and ambipolar diffusion are also in operation. Ambipolar diffusion is thought to be more dominant at higher temperature and contributes to the increase in the thermal conductivity.

MAGNETIC STRUCTURE OF AS-QUENCHED SILICATE GLASSES CONTAINING IRON OXIDES

The effect of valence states of iron on the magnetic structure of as-quenched silicate glasses containing iron oxides has been investigated. The glasses, all having the same compositions, are melted in various oxygen pressures to control the ratios of Fe3+ ions to the total number of iron ions and quenched at the same speed, and the magnetic properties are measured. There are only a few reports which focus particularly on the relation between valence states of iron and the magnetic properties of the glasses. Here, the dc magnetizations and ac susceptibilities of the glasses are explained based upon a proposed magnetic structure model in which both microcrystalline clusters and free iron ions in the glass matrix bear magnetism. (In this article free iron ions mean iron ions which are distributed in the glass matrix.) The number density of microcrystalline clusters is highest in a sample of x=0.73 (x: the ratio of Fe3+ ions to the total number of iron ions) and it becomes smaller as the value of x becomes s...

Phase Dependence (Liquid/Solid) of Normal Spectral Emissivities of Noble Metals at Melting Points

Normal spectral emissivities of liquid and solid Cu, Ag, and Au have been determined at their melting (freezing) points in the visible region using a cold crucible as the heating method. The use of the cold crucible enables the solidification front to be moved on the molten metal surface slowly enough to measure the emissivities of liquid and solid phases separately at the freezing point. Combined standard uncertainties of the spectral emissivities and wavelengths have been estimated. In silver, the spectral emissivity obtained for the liquid is systematically larger than that for the solid over the visible region, which is consistent with the prediction from a classical free-electron model. In copper and gold, the spectral emissivities at wavelengths around their absorption edges do not change for the solid-to-liquid transition. The wavelength range where the emissivity of copper is independent of the phase is unexpectedly broad (the width is greater than 40 nm), which differs significantly from classical experimental studies on the so-called X-point in the emissivity of copper. A qualitative explanation is provided for the difference in the phase dependence (liquid/solid) of the emissivity between copper and gold.

Electrical and heat conduction mechanisms of GeTe alloy for phase change memory application

GeTe alloy has drawn much attention as one of the promising candidates for phase change memory application. In this work, the electrical resistivities and thermal conductivities of GeTe alloy have been determined as functions of temperature by the four-terminal method and hot strip method, respectively. The electrical resistivity increases and the thermal conductivity decreases monotonically with increasing temperature, and thus it is likely that free electron dominates the thermal conduction. The electrical resistivity increases slowly with time during holding at 773 K, and the thermal conductivity decreases corresponding to the change of the electrical resistivity, which suggests that small amount of high temperature phase might exist in the samples.