Liquid Te Research Articles

Anomalous volume expansion in Hg1-xCdxTe melts: An analysis employing the inhomogeneous structure model.

New insights into anomalous volume expansion observed earlier in liquid HgTe are made possible if we assume that the liquid consists of a mixture of two kinds of domains and that the anomalous behavior arises from a continuous transformation of one kind into the other with increasing temperature. The analysis is consistent with some of the conclusions of the inhomogeneous structure model of Cohen and Jortner and is along the line of similar analyses carried out on liquid Te, ${\mathrm{In}}_{2}$${\mathrm{Te}}_{3}$, and ${\mathrm{Ga}}_{2}$${\mathrm{Te}}_{3}$ by various workers. Following a thermodynamic approach, we have used this model to interpret the negative thermal expansion below 750 \ifmmode^\circ\else\textdegree\fi{}C, indicating that the transformation of the liquid with heating to a structure of higher coordination number is for the most part completed when the minimum volume point is reached (at \ensuremath{\sim}750 \ifmmode^\circ\else\textdegree\fi{}C), even though appreciable heterogeneity persists above 800 \ifmmode^\circ\else\textdegree\fi{}C. The expansion at higher temperatures arises from normal volume expansion of the high-temperature phase. This description of a progressive transformation of the HgTe liquid into a high-coordination-number domain which may be more metallic is consistent with the rapid increase in the magnitude of experimental thermal diffusivity values of HgTe melts reported recently, though no direct determination of the liquid structure is available at this time. The analysis has been extended to pseudobinary ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Te melts, containing 5, 10, and 20 mol % solutions of CdTe in HgTe, respectively. For these melts, the volumes, which have been measured earlier, can be closely approximated as sums of volumes of two separate liquids---one HgTe and the other CdTe. The CdTe in the pseudobinary melt undergoes normal volume expansion consistent with the behavior reported for a pure CdTe melt by other workers.

CVD growth, thermodynamical study and electrical characterization of CuBTe 2 (B=A1, Ga, In) single crystals

CuAlTe 2, CuGaTe 2 and CuInTe 2 single crystals have been grown by the closed tube chemical vapor transport technique. The CuBTe 2 -I 2 system was considered and the optimization of thermodynamical growth parameters, necessary for avoiding the peritectoid decomposition and the formation of spurious species (i.e. liquid Te, solid TeI 4 and liquid CuI) was performed. The gap values and electrical characterization have also been reported.

The role of temperature on the structure of liquid Te 0.7Se 03. between

Raman scattering measurements are reported on liquid Te 0.7Se 0.3 between ∼400–600 C. In contrast to recent compositional studies which indicate a structural change from 3-fold to 2-fold bonding, the effect of temperature is not found to modify the 2-fold bonding in this alloy. This result differs from previous models that have related the nonmetal-metal transition to major changes in liquid network short range order. The Raman results imply, in contrast, increased intrachain disorder with temperature.

Magnetic Properties of Transition Metal Solutes in Liquid In, Sn, Sb and Te

The enhancement of the susceptibilities of liquid In, Sn and Sb by the addition of transition metal solutes decreases with increasing the valence electron number of solvent metals. That of Mn, Fe, Co and Ni solutes exhibits a rapid increase on going from liquid Sb to liquid Te solvent, while that of V and Cr solutes exhibits a slight decrease. On the basis of the Anderson model, the trend of the enhancement of susceptibilities is explained by the variation of ( U +4 J )/ Δ and N d .

Metal-nonmetal transitions in liquids under pressure

A brief review is presented on the aspects and mechanisms of the metal-nonmetal (M-NM) transition in the liquids under pressure. The correlations between the electronic and thermodynamic properties near the M-NM transition are discussed on expanded liquid Hg, liquid SeTe mixtures and liquid BiBiBr 3 mixtures. In expanded liquid Hg, the M-NM transition occurs at density near 9 g/cm 3 where anomalous behavior is found in the equation-of-state. In liquid SeTe mixtures, the transition from Se-like loosely packed to Te-like densely packed structure takes place by changing temperature, pressure and Te concentration. The M-NM transition is observed around 50 mole % Bi in the BiBiBr 3 mixture, which is caused by the rapture of Bi +Bi 3+ pairs in the mixed valence state. On the transition the sound velocity shows abrupt change.

Magnetic properties of transition metal solutes in liquid In, Sn, Sb, Te and Se-Te alloy solvents

The enhancement of the susceptibilities of liquid In, Sn and Sb solvents by the addition of transition metal solutes decreases with increasing the valence electron number of solvent metals. That of Mn, Fe, Co and Ni solutes exhibits a rapid increase on going from liquid Sb to liquid Te and Se-Te alloy solvents, while that of Cr and V solutes exhibits a slight decrease from liquid Sb to liquid Te. The different relationship between the additional susceptibilities χd of transition metal solutes was found, that is, χd(Fe) >χd(Cr) and χd(Co) >χd(V) in liquid Te and Se-Te alloy solvents. According to the Anderson model, their trend of χd is explained by the decreasing effect of Nd and the increasing effect of (U + 4J)/Δ.

Vibrational dynamics and structure of liquid Te

Polarized and depolarized Raman spectra are reported for liquid Te near the melting point. The spectra differ significantly from liquid Se indicating that 2-fold coordinated chains are not present in substantial numbers. The three peaked nature and polarization properties of the Raman spectra are consistent with the Cabane-Friedel picture of As-like short range order. The Raman scattering and diffraction studies suggest a 3-fold coordinated, random network model.

Electronic and thermodynamic properties of liquid chalcogenides

Recent measurements of various physical properties such as compressibility, electrical conductivity, optical reflectivity and nuclear magnetic resonance shift over wide temperature and pressure range are reported for liquid Se and SeTe mixtures. The observed semiconductor to metal transition for liquid Se and SeTe mixtures is accompanied by a substantial modification of the chain structure. A simple model of the transition to metallic state is proposed. The effect of charged additives on the transport properties of liquid Se is also discussed in connection with the change of the bonding configuration.

Vapor growth, thermodynamical study and characterization of CuInTe2 and CuGaTe2 single crystals

CuInTe2 and CuGaTe2 single crystals have been grown by the closed tube chemical vapor transport technique. In order to define the growth conditions, a thermodynamical study of the CuInTe2/CuGaTe2-I2 system was undertaken. The behavior of all gaseous species, the formation of spurious phases, i.e. liquid Te and solid TeI4, and transport conditions were discussed. Resistivity, carrier mobility and carrier concentration were determined by resistivity and Hall effect measurements using the Van der Pauw method.

Positron lifetimes in liquid SeTe alloys

Measurements of positron lifetime in Se xTe 1−x alloys with x = 0, 0.2, 0.4 and 0.6 have been carried out in the solid and liquid states. The temperature dependence of lifetime is closely related to the change in the density. The lifetime reflects the structural modification and the associated change in the electronic structure with temperature. The dependence of lifetime on temperature and concentration is qualitatively explained provided the two kinds of trapping sites are taken into account in the liquid SeTe alloy.

Hall Coefficients of Liquid Se–Te Alloys

The Hall coefficients of liquid Se–Te alloys have been measured by an alternating current and a direct current magnetic field for operation temperature from their melting point to about 750°C. The signs are negative for liquid Te and liquid Se x Te 1- x , alloys with x =0.2, 0.3, 0.4 and 0.5. The absolute values of Hall coefficient for liquid Se–Te alloys exhibit the negative temperature coefficients and increase with increasing Se concentration. The Hall mobilities of these alloys have small negative temperature coefficients. The relationship between the Hall coefficient and the density of states at the Fermi level has been discussed on the basis of his formula given by Friedman.

The liquid alloy system Mn x Te1-x

Abstract The electrical conductivity of liquid Mn x Te1-x (0≤x£0·5) has been measured as a function of x. It is shown that the semi-metallic nature of liquid Te is gradually eliminated as x is increased and that at stoichiometry (x = 0·5) MnTe is a liquid semiconductor. This behaviour is contrasted with that for liquid Ni x Te1-x which becomes increasingly metallic. Neutron diffraction data are used to show that Mn x Te1-x and Ni x Te1-x are structurally similar. The differences in electrical behaviour are discussed in terms of the Mott—Hubbard model of magnetic insulators.

The segregation of impurities and the self-compensation problem in II-VI compounds

The electrical and optical properties of ZnTe or CdTe crystals are generally inhomogeneous after annealing. This is shown to be due to the redistribution of preexisting impurities. Indeed, after growth, these crystals contain some excess tellurium which must precipitate since the solidus line has a retrograde shape. The liquid Te droplets are then able to purify the surrounding materials by a solid-liquid segregation mechanism. On annealing, the tellurium excess can disappear more or less rapidly: the Te precipitates and the small inclusions shrink progressively while the impurities are released into the crystal. This mechanism explains the bright dots observed in the scanning electron microscope (cathodoluminescence mode) and due to the high lithium concentration. Under other conditions, dark dots are obtained and the role of copper is suspected. This model is discussed on the basis of the available data (segregation and diffusion coefficients). Further confirmation is obtained from direct chemical analysis of the crystal and of the inclusions itself. The consequences of the segregation of impurities on the interpretation of the self-compensation problem are analyzed. A fully satisfactory interpretation of conductivity variation with zinc pressure previously attributed to the zinc vacancy, can be derived with the single hypothesis that acceptor and donor impurities in sufficient amount are stored in the crystal. The dominant role of residual impurities in the close control of the II-VI materials is particularly emphasized.

Specific heat of liquid In-Te alloys

The temperature and composition dependence of the specific heat in liquid In-Te alloys, measured with adiabatic calorimeter, are reported. The specific heat isotherms around the composition of In2Te3 are anomalously large above the liquidus temperature and they tend to be small at very high temperatures. The large specific heats and their temperature dependences are satisfactorily explained in terms of the partial dissociation of compound formation with increasing temperature. The required molar energy for the dissociation from semiconducting to metallic states in liquid Te is about 3.31 kcal mol-1 and that in liquid In2Te3 is 4.21 kcal mol-1.

The structure and electrical properties of liquid semiconductors. II. Electron transport in liquid Ni-Te alloys

For pt.I see ibid., vol.15, p.4627 (1982). The resistivity and thermoelectric power of liquid Ni-Te alloys have been measured as a function of temperature over a wide range of compositions. It is shown that the resistivity of liquid Te can be halved by the addition of less than 10 at.%Ni. Comparison with other liquid alloys containing Te is made and a unified model for the atomic and electronic structure is proposed.

Electrical transport and structural properties of Se−Te semiconductors

De conductivity of different TeSex semiconducting alloys, withx=50, 30, 20, 15, 10 and 5, are studied in both the liquid and the crystallized phases. The composition dependence of σ0 (temperature independent pre-exponent) andEσ (activation energy of conduction) in liquid Se−Te mixtures has been correlated with the electronic features and ability of the Te atoms to dissociate the Se chains. The conductivity dependence on time (t) in supercooled liquid Te−Se alloys is investigated in the temperature range of 90−180 °C. The data obtained are used to calculate the crystallization kinetic parametersK andn of anAvrami equation in the form, α(t)=1−Exp (−Ktn). The activation energy of the crystallization process shows a certain compositional dependence with a minimum value 0.37 eV at the composition of TeSe30.

Densities and electrical conductivities of liquid TlTe, InTe and GaTe systems

The densities of the liquid InTe and GaTe alloy systems were measured over the entire composition ranges, using fused silica pycnometers. The isothermal density results show a negative deviation from linear mixing, with the minimum relative density at 60 at.% Te for both systems. The density of alloys near the composition In 0.4Te 0.6 rises immediately above the melting point, passes through a maximum and then falls with increasing temperature. For alloys with compositions near Ga 0.4Te 0.6, the density shows only a very small temperature dependence. The electrical conductivities of the liquid TlTe, InTe and GaTe systems were measured by the inductive coupling method. The results show positive temperature coefficients for most compositions and minima in the conductivity isotherms occurring at Tl 0.67Te 0.33, In 0.4Te 0.6 and Ga 0.4Te 0.6. The results are analyzed and discussed in relation to theories and models of liquid metallic, semimetallic and semiconducting systems.

The Soret Effect in Molten Ag‐Te Solutions

The Soret effect was studied in liquid Te solutions containing 17.5 to 69 a/o Ag. The measurements extended from close to the liquidus temperatures to 1100–1200 K. The factors affecting the experimental uncertainty were examined and used to estimate the accuracy of the data. Thermodynamic data for the liquid solutions and solid were compiled and used to calculate experimental heat of transport, , values. These values were found to have strong negative temperature coefficients; this observation can be explained on the basis of a correlation between the Soret segregation and the thermoelectric properties of the melts.

Electronic Behaviour of Dilute Liquid Te Alloys

The electrical conductivity and the magnetic susceptibility of dilute liquid Te alloys containing the solute atom Ag, Cd, In, Sn or Sb have been measured from the melting point to about 900°C. The additional conductivity and the additional susceptibility are in good agreement with the simple relationship where Δ σ/σ=2 Δ χ e /χ e . This result suggests that the density of states at the Fermi level plays an essential role in determining the change of the electronic structure in these liquid alloys.

Electrical Properties of Semiconducting Liquid Te with Transition Metal Solutes

The effect of localized d electrons in liquid Te has been examined. The change of electrical resistivity by addition of solute into liquid Te is positive for the “less than half” transition metal solutes and is negative for the “more than half” ones. The additional resistivity is sufficiently explained from the effects due to the s-d resonant scattering and the change of density of states at the Fermi level. This pattern of additional resistivities in the series of transition metal solutes agrees roughly with a sine function of the number of the localized d electrons.