Conductivity of crystals

This idea that the heat was transfered by a random walk was used early on by Einstein [21] to calculate the thermal conductance of crystals, but, of course, he obtained numbers much lower than those measured in the experiment. As we now know, crystals at low enough T support well-defined quasiparticles—the phonons—which happen to carry heat at these temperatures. Ironically, Einstein never tried his model on the amorphous solids, where it would be applicable in the / fp/X I regime. 

Referring to results obtained in study [16], we can assume that the conductivity of crystals in sintered ZnO film increases due to increase in number of conductivity electrons in the surface layer. Taking the sample mobility of electrons fd as 10 cm -s -V the temperature dependence being T (the data borrowed from [21]) one estimate the value A[e] from the following expression Acr = A[e, where Acr is the con-... 

MSN.ll. R. Brout and I. Prigogine, Statistical mechanics of irreversible processes. Part VI Thermal conductivity of crystals, Physica 22, 263-272 (1956). 

Riehl, N. The electrical conductivity of crystals of polycyclic compounds and other organic insulators, II. Zhur. Fiz. Chem. 29, 1152 (1955). 

The conference was opened with a speech by Lorentz on the theory of electrons he had developed about 20 years before, followed by papers by Joffe on the electrical conductivity of crystals, Kamerlingh Onnes on superconductivity, and Hall on the metallic conduction and the transversal effects of the magnetic field. This last speech was followed by a discussion in which Langevin and Bridgman injected a few interesting remarks. 

This can only be decided by experiment, or, failing that, by a suitable hypothesis whose consequences are in agreement with experiment. Properties which appear to approach infinity at the absolute zero are, for example, the electrical and thermal conductivity of metals and the thermal conductivity of crystals (Eucken ), while the thermal conductivity of amorphous bodies, the specific heat, and the coefficient of expansion appear to approach zero. 

The thermal conductivity of solids varies considerably (Table 15.2). Metals have a high thermal conductivity, with silver having the highest room-temperature thermal conductivity, at 430 W m K . Alloys have lower thermal conductivities than pure metals. Ceramics are even lower, especially porous porcelains or fired clay products (Figure 15.3). The lowest thermal conductivities are shown by plastic foams such as foamed polystyrene. As would be expected, the thermal conductivity of crystals varies with direction. For example, the thermal conductivity of the hexagonal metal cadmium Cd, (A3 structure), is 83Wm K parallel to the c axis and 104 W m parallel to the a axis. At 25 °C, the oxide quartz, which has a hexagonal unit cell, has a thermal conductivity parallel to the c axis of 11 W m K , and 6.5 W m K paraUel to the a axis. 

A SIMPLE APPARATUS FOR THE DETERMINATION OF THERMAL CONDUCTIVITY OF CRYSTALS. 

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