Thermoelectric power, temperature dependence

For the famous (TMTSF)2X salt series (a 500 cm- at 300 K), we observe a coherent regime along the staddng direction at low temperature (A a) (the thermoelectric power T dependence is also a good indicator of this regime change), but also a change in... 

Fig. 6. Temperature dependence of the thermoelectric power of three SWCNT samples [11].

At relatively high temperatures thermocouple thermometers are most commonly used to measure temperature. The thermoelectric power of three frequently used thermocouples is compared in Figure 10.2. The choice of thermocouple depends on the temperature range, the chemistry of the problem in question, sensitivity requirements and resistance towards thermal cycling. The temperature range and typical uncertainty of some of the most commonly used thermocouple thermometers are given in Table 10.2. 

Figure 19 Temperature dependence of the thermoelectric power for the La-Ba-Cu-O material with the fraction of Ba either x =0.15 (a) or x = 0 (b). Ref. 71.

The compositional dependence of the structural O -O transition at 7jt and the 0 -R transition at Tor can be clearly followed by monitoring the temperature dependence of the resistance (Mandal et al., 2001) monitoring the variation with x of the higher-order transition at T from the resistance curve R(T) is more subtle and has been accomplished with further aid from the thermoelectric power a(T) measured on single crystals (Zhou and Goodenough, 2000). The transition from polaronic to itinerant electronic behavior in the paramagnetic R-rhombohedral phase has not been studied. 

Fig. 55. Effects of hydrostatic pressure on the temperature dependence of the thermoelectric power a(T) for Pro.5(Cao.9Sro.i)o.5Mn03, after Rivadulla et al. (2002).

The pressure-dependent electrical resistivity of the heavy-fermion compound YbNi2B2C (see also Section 4.12) could be explained by competing contributions from crystal-electric-field splitting and Kondo effect (Oomi et al., 2006). The pressure-dependent room-temperature thermoelectric power of YNi2B2C exhibits a peak around 2 GPa, which was explained by changes in the Fermi-surface topology (Meenakshi et al., 1998). A possible correlation with a small peak in the temperature-dependent thermopower around 200 K (Fisher et al., 1995 Section 3.4.3) needs further investigation. 

Dc, ac, impedance, and thermoelectric power of the compounds 33-38 in Fig. 9 have been investigated in detail. The measured temperature dependence of the thermoelectric power of 33-38 in thin film varied approximately exponentially with temperature. Compared to 38, the absolute value of the thermopower for the film of 34 is larger by nearly a factor of 3. The positive sign of Seebeck coefficient confirms that thin films of the compounds behave as a p-type semiconductor [46],... 

The thermoelectric power, or thermopower, of the thermocouple is of the order of 2 to 50 iV/°C, depending on the metals and the temperature. In general, the thermopower decreases with decreasing temperature. Typically, in a thermocouple, the first junction is at Th, and the second, or reference junction, is held at the ice point of water (Tc = 0°C) (Fig. 10.21), or its electrical equivalent ("cold junction compensation"). 

The temperature dependence of the thermoelectric power in the range 300 to 4 K is shown in Fig. 12. The thermoelectric power decreases gradually with decreasing temperature, and no anomaly corresponding to the maximum in conductivity is seen, which suggests that the maximum in conductivity is not of the Peierls type but is attributable to the strong carrier... 

Fig. 7.22. Calculated temperature dependence of (a) the conductance and (b) thermoelectric power (lower) of a network containing potential fluctuations. The curves give results for difierent charge densities (Overhof and Beyer 1981).

Thermoelectric effects. A temperature gradient generates in tungsten a small potential difference (the Thomson effect). This difference, called the thermoelectric power S (pV/K), drops with increasing temperature. Its temperature dependence is tabulated in Table 1.17. 

TABLE 1.17. Temperature Dependence of Thermoelectric Power of Tlmgsten [1.35]... 

It should be noted that in situ conductivity measurements of ECP films allow for an estimation of the absolute values ofconductivity, although high values of conductivity are not the only feature of a metallic state. Ex situ direct current electronic conductivity measurements of the films should be carried out in order to examine any temperature dependence of the conductivity and thermoelectric power over a wide range of temperatures, starting with very low values (of a few K) [30]. Typical metals have negative temperature coefficients for their electronic conductivity, and positive temperature coefficients for their thermopower, which contrasts with... 

Temperature dependence of the thermoelectric power tensor components. 

The observed temperature dependence of the anisotropic thermoelectric power is shown in Fig. 3. The anisotropy was negligible below 200 K, while above 200 K the anisotropy increased with temperature. 

Fig.3 Temperature dependence of thermoelectric power for 2-stage FGM of PbTe shown with those for component (1) and (2) with different electron concentration listed in Table 1...

The temperature dependence of thermoelectric properties such as the Seebeck coefl dent, electrical resistivity and power factor for two kinds of Ge dopant levels were clarified to shift the temperature ofthemaximmn power factor due to the dopant levels and sintered condition. The power factor at the maximmn for the sinteredMn-Si element was obtained 1.05-l.lxlft (W/mK2) as the promising thermoelectric element for hi and middle temperature range. 

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 . 

Another electrical property of fundamental importance is the thermoelectric power, or Seebeck effect. Its sign, magnitude, and temperature dependence can provide information about the sign of the charge carriers... 

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