Crystal resistivity measurements

Resistivity measurements of doped, alpha-siUcon carbide single crystals from —195 to 725°C showed a negative coefficient of resistivity below room temperature, which gradually changed to positive above room temperature (45). The temperature at which the changeover occurred increased as the ionization of the donor impurity increased. This is beUeved to be caused by a change in conduction mechanism. 

Resistivity measurements on single crystals of AuTe2l and AuTe2Br established the metallic character of the conductivity. Single crystals... 

In reference to the latter question, we have obtained UPS data on polycrystalline samples of NaMo406, but not on single crystals. These measurements indicate a relatively high density of states at the Fermi level, which is in agreement with the low resistivity and metallic character of the material. 

Barrer, R.M. and James, S.D. (1960) Electrochemistry of crystal—polymer membranes. Part I. Resistance measurements. J. Phys. Chem., 64 (4), 417-421. 

Figure 6.30. Resistivity measurements using the four-probe technique performed on a /u. -(TMTTF)2Re04 thin single crystal. Reprinted with permission from Perruchas et al, 2005.

Manufactured graphite is semimetallic in character with the valence and conduction bands ovedapping slighdy (4—6). Conduction is by means of an approximately equal number of electrons and holes that move along the basal planes. The resistivity of single crystals as measured in the basal plane is approximately 0.40 this is several orders of magnitude lower than the resistivity across the layer planes (7—9). Thus the electrical conductivity of... 

The DC conductivity of single crystals and the pressed powder of the synthesized salts has been measured in the temperature range of 77-300 K by four-contact technique. Table 1 presents the values of specific electrical conductivity at room temperature aRT and of conductivity activation energy A calculated on the basis of resistive measurements at various temperatures. Conductivity models applied for the calculation of the A value in each compound are presented and discussed in the next section. 

For all the studied compounds, values of conductivity activation energy A calculated from the data of resistive measurements (Table 1) exceed those estimated in the analysis of IR absorption spectra. This difference may be due to the quality of crystals and to that of the electric contacts used for conductivity measurements. 

Resistivity Measurements. The measurements by the Cornell group have all been made on single crystals by a potential-probe method, the details of which have been reported (32). Typical results are presented graphically in Figure 3. 

Irradiation techniques are more and more widely utilized for industrial applications for instance, for food preservation, medical sterilization, and polymer processing. Such techniques require specific rules of control by means of accurate dosimetry [89]. In this context, new promising dosimeters based on resistance measurements of organic conducting crystals have been reviewed by Zuppiroli et al. [89]. The crystals utilized as dosimeters are either small needles (0.01 x 0.01 x 3 mm3) or larger plates (0.1 x 0.5 x 3 mm3), and their electrical resistances ( 1 kfl in the first case, 1 H in the second) increase exponentially with the adsorbed radiation dose, up to quite high doses. 

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