Hall coefficient, oxides

The variation of the Hall coefficient and the conductivity of zinc oxide as a function of oxygen pressure has been studied by many workers (27,32,40-42). The conclusions reached are that the number of carriers varies with oxygen pressure approximately according to the equation... 

This evidently does not apply to sintered zinc oxide, since at low temperature its conductivity shows an activation energy of a few hundredths of an electron volt, the same as is shown by the Hall coefficient (26), independent of the previous treatment of the sample. This, then, indicates that the grains of sintered zinc oxide are actually fused, rather than merely touching. 

It is risky, of course, to generalize from one oxide to another, but in the absence of adequately completed studies with anyone of the oxides, the assumption concerning the density of carriers seems justified. All of the superconducting oxides display R(T)fs similar to those cited above. In the case of strontium titanate, SrTiOg.., Schooley et al. (15) have shown that the critical superconducting temperature determined from the midpoints of the abrupt decreases in the resistance vs temperature and the magnetic susceptibility vs temperature depend on the density of carriers determined from measurements of Hall coefficients. Thus the results of Tc vs density of carriers is shown in Figure 4. Therein, one observes that the Tc s from both R(T) and x(T) increase to maxima near 10 carriers cm 3 and thereafter they decrease. 

W. M. Latimer, The Oxidation States of the Elements and their Potentials in Aqueous Solutions, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1952. Although a useful source in its time, this book is now outdated. Unfortunately, no comprehensive compilation of electrochemical thermodynamic data has entirely replaced it. However, useful data sources include A. 1. de Be-thune, N. A. S. Loud, Standard Aqueous Electrode Potentials and Temperature Coefficients at 2S°C, C. A. Hampel, Skokie, IL, 1964 A. J. Bard, ed.. Encyclopedia of Electrochemistry of the Elements, Vols. 1-10, Marcel Dekker, New York, 1973-1976. 

In general, the oxidation rate of pure dry oils was approximately doubled by a 10 C. (18° F.) rise in temperature in the absence of catalysts. In the presence of light or metal catalysts the coefficient was much smaller. There is no published information on the temperature coefficient of the coupled reaction between hemoglobin and unsaturated fat. Numerous more recent studies on frozen meats and poultry have emphasized the importance of low storage temperatures in retarding rancidity (Cook and White, 1939, 1941 Ramsbottom, 1947 Atkinson et al., 1947 Hall et al., 1949 Klose et al., 1950 Palmer et al., 1953). 

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