Thermoelectric power of liquids

Fig. 7.36. The thermoelectric power of liquid Mg-Bi as a function of composition at temperatures 100°C above the liquidus temperature.

Fig. 7.50. Thermoelectric power of liquid Tei x Se alloys (after Perron (1967)).

Enderby, J.E., 1985, Diffraction Studies of Liquids, in Amorphous Solids and the Liquid State, eds N.H. March, R.A. Street and M. Tosi (Plenum, New York) pp. 3-30. Enderby, J.E., and R.A. Howe, 1973, The Thermoelectric Power of Liquid Metals and Alloys, in The Properties of Liquid Metals, ed. S. Takeuchi (Taylor and Francis, London) pp. 283-287. 

The Experimental Determination of the Thermoelectric Power in Liquid metals and alloys. Phil. Mag. 7, 1337—1347 (1962). 

Thermocouples are unsurpassed for making temperature-difference measurements. The thermoelectric power of thermocouple materials makes them adequate for use at liquid-air temperatures and above. At 20 K and below, the thermoelectric power drops to a few pV/K, and their use in this range is as much art as science. 

Fig. 7.29. The thermoelectric power of (a) sohd Cu, (b) liquid CdSb, (c) liquid InSb, (d) liquid ZnSb, (e) liquid SbjTCg. (Enderby and Walsh 1966).

Fig. 10.22 Electrical conductivity (a) and thermoelectric power (b) of liquid Se J x alloys as functions of reciprocal temperature. 

The electrical resistivity data on crystals of indium(III) oxyfluoride indicate a nearly temperature independent conductor (3.6 X 10 2 fl-cm. at room temperature and 1.8 X 10-2 fl-cm. at liquid-helium temperature) with high negative thermoelectric power (—230 juV./°C.). These properties are similar to those observed for some conductive forms of indium(III) oxide. 

The metallic nature of concentrated metal-ammonia solutions is usually called "well known." However, few detailed studies of this system have been aimed at correlating the properties of the solution with theories of the liquid metallic state. The role of the solvated electron in the metallic conduction processes is not yet established. Recent measurements of optical reflectivity and Hall coefficient provide direct determinations of electron density and mobility. Electronic properties of the solution, including electrical and thermal conductivities, Hall effect, thermoelectric power, and magnetic susceptibility, can be compared with recent models of the metallic state. 

Sundstrom, L. J. A Theorie of the Electrical Properties of Liquid Metals IY. Quantitative Calculations of Resistivity and Thermoelectric Power. Phil. Mag. 11, 657 (1965). 

We now outline the techniques which have been developed to measure the principal electron transport parameters of liquid semiconductors. The three parameters which are most commonly investigated are the conductivity (a), the Hall coefficient (R) and the thermoelectric power (S). 

Liquid Si and Ge are metallic in character. The optical properties, Hall coefficient, thermoelectric power and conductivity are, (where measured), similar to those for other quadrivalent liquid metals like Sn and Pb (Hodgson (1961) Busche and Tieche (1962)). A selection of experimental data for liquid Si Ge, Sn and Pb is presented in Table 7.1. 

The electrical properties of liquid alloys vary with composition in two distinctive ways. In some cases the Hall coefficient, thermoelectric power... 

The most comprehensive attack on the theoretical problems posed by the existence of liquid semiconductors has been made by Mott (1966, 1967, 1970, 1971). TTie essential features of his model are shown in Figure 7.53 and have been described in detail by Cohen, Fritzsche and Ovshinsky (1969) and by Davies and Mott (1970). and separate the extended from the localized states (shown shaded) and mark the energy at which a substantial drop in the mobility occurs. An additional hypothesis is that the energy range of localised states is somewhat greater in the conduction band than in the valence band, thereby explaining the tendency for liquid semiconductors to exhibit positive thermoelectric powers. All the liquids... 

From the observed Hall coefficients and within the free electron theory kp and Ep may be calculated and are given for Tl-Te in Table 7.6 we note that the condition Ep > kT is satisfied so that liquid Tl-Te is degenerate at all compositions, except, possibly, at compositions very close to Tl Te where the measurements are not yet sufficiently accurate to decide. The thermoelectric power data of Cutler and Mallon (1966) may, therefore, be expressed in terms of the dimensionless parameter with the result shown... 

Best estimates of the experimental values for the electrical resistivity in the liquid, Pl> solid, and of dpJdT for the R s at their melting points, are shown in table 9. Similar values for the thermoelectric power, Q Q, dQJdT, and (<2l Gs) displayed in table 10. Considerable difficulties have been encountered in containing these highly reactive liquid metals, and in maintaining their purity while their electronic properties are measured. For discussions of the ways these difficulties have been addressed, the reader is referred to the literature references cited. 

A K), which we encountered earlier in our discussion of liquid structure (section 2.2). Similarly, the thermoelectric power (thermopower), Q, takes the form... 

The thermoelectric power a(T) is a transport property that is not affected by the grain boundaries of a polycrystalline sample, and the pressure variation of its magnitude at room temperature, d a(300 K) /dP, shows the sign of the variation of m with pressure for a Fermi liquid. Figure 4 compares the a(T) data under hydrostatic pressure P for CaV03 and Pt. 

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