Thermoelectric properties Seebeck coefficient

Ce[ 64Asi2 is probably a narrow gap semiconductor, but little low temperature data are available for this compound. The resistivity of a polycrystalline sample indicates a small gap on the order of 0.01 eV (Grandjean et al., 1984). The high temperature thermoelectric properties of this compound were investigated by Watcharapasorn et al. (2002). They found semimetallic behavior with a room temperature resistivity of 0.49 m 2 cm, a Seebeck coefficient of 40 pV/K, and a thermal conductivity of 3.8 W/mK. The maximum value for ZT, the thermoelectric figure of merit, was estimated to be 0.4 at 850 K. 

The thermoelectric properties were measured at room temperature along the direction perpendicular to the pressing direction. The samples with dimensions of 2 X 2 X15 mm and of 4x4x4 mm were cut out of the compound for the measurements of Seebeck coefficient a and thermal conductivity k and of the electrical resistivity p, respectively. Then, their surfaces were polished with a series of SiC polishing papers of up to 2000 and further polished on a polishing cloth impregnated with AI2O3 powders of 0.3 //m size. 

Thermocouple Materials. Thermoelectric properties of different materials can be represented by their respective Seebeck coefficients. Usually this is done with reference to Eq. 16.20, assuming a standard reference material (material B) and a standard reference temperature T0 (usually 0°C see Fig. 16.17). 

Hakim investigated the electrical properties of In203 and ITO films prepared by spray pyrolysis by measuring the electrical resistivity as a function of temperature [100], the Hall effect and the thermoelectric power [99]. He observed a very complicated dependency of the electrical resistivity on the temperature with an activation energy of about 0.07-0.1 eV for the temperature range of 70-190°C. These low values indicate shallow donor levels [124]. The Seebeck coefficients or the thermoelectric power of ITO films were in the range of 16 to 200 pV K . 

In summary, CPs offer numerous advantages over inorganic semiconductors for thermoelectric applications because of their unique properties. However, the poor electrical transport properties have impeded their practical application as TE materials in the past. Recent studies indicate that incorporating the inorganic nanoparticle into polymer matrix is an effective way to improve the electrical transport properties of CPs, including electrical conductivity and Seebeck coefficient, while keep the thermal conductivity at low level simultaneously. Consequently, the power factors of most CP-based nanocomposites are about 2 3 orders of magnitude higher than those of conventional pure CPs and the maximum ZT value is up to 0.1 at present. 

A summary of the common standardized thermocouples is given in Table 1. Besides the thermoelectric properties of the Seebeck coefficient, the thermal and electrical conductivities are important for the sensitivity and time response of the thermoelectric flow sensor. 

The more generalized parameters of the thermal conductance, G, and the temperature conductivity, C, are a function of the sensor geometry and the heat and temperature diffusiv-ity. The device parameters and characteristics are determined by the properties such as the thermal conductivity or the Seebeck coefficient of the thermoelectric materials as well as the geometric setup and fabrication method. The main sensor signal output is determined by the number of thermocouples n, the Seebeck coefficient, and the measured or applied temperature differences. With a higher temperature difference, the signal increases with the heat loss. Hence, the sensitivity of the sensor depends mainly on the properties of the thermocouple, as well as the thermal conductivity of the fluid and the substrate. For gas flow measurement and high temperature differences, the emissivities... 

Boron carbide is characterized by a relatively wide gap in its forbidden band, a low thermal conductivity, and a high thermoelectric power. These properties make it a potentially useful material for high-temperature thermoelectric energy conversion. Electrical conductivity and Seebeck coefficient as a function of temperature and composition are shown in Figs. 8.5 and 8.6. 

In line with this, the thermoelectric properties of pristine EuTiOs and Nb-substituted EuTio,98Nbo.o203 were investigated [62]. Here an anomalous large Seebeck coefficient present in EuTiOs below room temperature was found, while... 

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