Thermoelectric power conductor

The main drawback in this type of thermometry is the presence of spurious thermoelectric powers due to chemical inhomogeneity, stress in conductors, contact effects in switches if present, etc. 

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. 

If the thermal gradient at the electrodes is weak, which is usually the case, the terms a(T, -T2) and a (T3 -T4) ate neghgible. Moreover, since the conductor connecting the two sohds R and S is metalhc, its thermoelectric power a is weak and the term a (Tj — T3) is small. This electromotive force, for systems at a temperature lower than 360°C, was estimated at a few mV by J.P. Beaufils. 

In practice, the thermoelectric power of a conductor A is usually reported for a temperature difference of 100 C between hot and cold junction and by fixing the second material B. The second material used as the standard is most of the time pure platinum and, less frequently, copper or even lead. Hence, the thermoelectric power is reported in modern tables in mV versus Pt or mV versus Cu, respectively. Therefore to convert a thermoelectric power measured with a given scale into another scale, the following simple equation can be used ... 

The order of magnitude for thermoelectric power is commonly in the range of several mV/K for semiconductors and of several gV/K for most metals and alloys (Table 9.1). On the other hand, for semiconductors, the theoretical thermoelectric power can be assessed using the following equation, where is the electronic density in the conductor and C the molar heat capacity at constant volume ... 

LaTer-LaSbj system. A large solid solution exists from LaTe2 to the composition limit LaSbi sTeos, in which the substitution of Te by Sb creates an orthorhombic distortion of the tetragonal structure of LaTc2 (Wang et al., 1967). This substitution decreases the resistivity, and degenerate p-type semi-conductors are obtained. The thermoelectric power first increases then decreases as the material becomes more metallic (Narasimhan et al., 1968). 

IX. Thermoelectric Power of Cells with Mixed Conductors... 

IX. THERMOELECTRIC POWER OF CELLS WITH MIXED CONDUCTORS... 

The temperature dependence of the magnetic susceptibility x from 80 to 800 K is linear, showing that the Curie-Weiss law is obeyed, x is 19700x10 cm /mol Eu at 293 K. The paramagnetic Curie temperature is 0p=-21K. The effective moment e = 7.04pB differs considerably from the 7.94 iq expected for Eu ". This may be due to a certain amount of Eu or a partially frozen orbital moment. Electrical measurements from 300 to 1000 K in He atmosphere show Eu4Se7 to be a p-type conductor. An electrical conductivity of 45 cm and a thermoelectric power of 355 xV/K are obtained at room temperature, Butusov et al. [1]. 

The distinguishing featme of space power systems is that they operate at high temperatures because excess heat can only be removed into the environment by radiation. As tbe radiator surface (and weight) is limited, the temperature level of the whole system gets high. Therefore, high-temperature semi-conductors, silicon and germanium, are the elements of the thermoelectric converter. 

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