Thermopower measuring technique

In the present section we focus on the various chemical and physical properties of the equiatomic YbTX compounds especially the physical properties, which have been intensively investigated in the last two decades. Besides detailed magnetic susceptibility and electrical resistivity measurements, various other techniques have been used to get deeper insight into the peculiar properties of these intermetallics " Sn and °Yb Mdssbauer spectroscopy, specific-heat data, thermopower measurements, solid-state NMR, photoemission studies, neutron dif action, muon spin relaxation, and a variety of high-pressure experiments. The diverse data are summarized in the following subsections. 

Thermopower measurements used the differential technique [48,49] two isolated copper blocks were alternately heated with the sample mounted between the copper blocks with pressure contacts. The heating current was accurately controlled by computer. The temperature difference between the two copper blocks was measured by a chromel-constantan thermocouple and did not exceed 0.5 K for each thermal cycle. The voltage difference across the sample was averaged for one complete cycle. Any temperature difference between sample and thermocouple was less than 10% of the temperature gradient across the sample the thermometry was carefully calibrated for the entire temperature range (5 K < T < 300 K). The absolute thermopower of the sample was obtained from the absolute scale for lead [48,49]. 

There are four experimental techniques that are commonly used to gain information about the electronic transport in a-Si H dc conductivity, the drift mobility, thermopower, and the Hall effect. Sections 7.1 and 7.2 describe these measurements and how the information about electronic conduction in Sections 7.3 and 7.4. 

In the following we describe the technique used at Jiilich for combined measurements of thermopower and dark- and photoconductivity. A cryostat is employed having two cold fingers that can be cooled independently by insertion of liquid nitrogen or by a flow of cool Nj or air. Each cold finger bears a 100-W resistance heater (HI and H2 in Fig. 5a). The heater mass... 

The PVC blend was prepared and investigated in two concentrations, 209 and Al%. Its composition corresponded in principle to a commercially available (though not commercially successful) blend, although an average concentration of 35% was planned for the industrial applications. For comparison purposes pure PAni powder was measured (as a molding made at room temperature and 10 kbar). The thermopower and conductivity and their temperature dependence were measured using standard techniques [78,80J. Conductivity as a function of temperature is shown in Fig. 19.61. 

---