Conductivity of solids

The conductivity of solid dielectrics is roughly independent of temperature below about 20°C but increases according to an Arrhenius function at higher temperatures as processes with different activation energies dominate [ 133 ]. In the case of liquids, the conductivity continues to fall at temperatures less than 20°C and at low ambient temperatures the conductivity is only a fraction of the value measured in the laboratory (3-5.5). The conductivity of liquids can decrease by orders of magnitude if they solidify (5-2.5.5). 

The thermal conductivity of solids has a wide range of numerical values, depending upon whether the solid is a relatively good conductor of heat, such as metal, or a poor conductor, such as glass-fiber or calcium silicalc. The laUer serves as insulation. 

The great variations among solids make it desirable to And useful classification schemes. Though this topic is taken up much later in the course (Chapter 17), a beginning is provided by a look at the electrical conductivity of solids. 

This relationship makes it possible to calculate the maximum ionic conductivity of solid electrolytes. Assuming that the mobile ions are moving with thermal velocity v without resting and oscillating at any lattice site, this results in a jump frequency... 

Another way of looking at high ionic conductivities of solid electrolytes is to consider the activation enthalpy as illustrated in Fig. 8. Generally, the activation enthalpy is strongly correlated with the room-temperature ionic conductivity the higher the room-temperature ionic conductivity, the lower the activation enthalpy. The straight lines in the Arrhenius... 

Detailed information about the conductivity of solid electrolytes can be found elsewhere.2,3,6 8,10,11 As shown in Fig. 3.1, the temperature dependence of the ionic conductivity o can, in general, be described by the semiempirical equation ... 

The conductivity of solid salts and oxides was first investigated by M. Faraday in 1833. It was not yet known at that time that the nature of conduction in solid salts is different from that in metals. A number of fundamental studies were performed between 1914 and 1927 by Carl Tubandt in Germany and from 1923 onward by Abram Ioffe and co-workers in Russia. These studies demonstrated that a mechanism of ionic migration in the lattice over macroscopic distances is involved. It was shown that during current flow in such a solid electrolyte, electrochemical changes obeying Faraday s laws occur at the metal-electrolyte interface. 

G.E. Childs, R.L. Ericks, R.L. Powell Thermal Conductivity of Solids, NBS Monograph 131, US Govt. Print. Office, Washington, DC (1973)... 

Although the free electron model leads to a simple understanding of electrochemical phenomena, even in solution, it offers no explanation of the different conduction properties of different types of solid. In order to understand the conduction of solids it is necessary to extend the free electron model to take account of the periodic lattice of a solid. 

Figure 5.17 Heat conductivities of solids modeled by the series, the parallel, and the Maxwell formulation of spheres embedded in a matrix...

Nakahara Y, Kimura K, friokuchi H, Yagi T (1979) Electrical conductivity of solid state proteins simple proteins and cytochrome C3 as anhydrous film. Chem Lett 8 877-880... 

Among the different possible methods to study the electrical conductivity of solid-state devices, the deepest insight into the process might be gained by studying the energy levels and wavefunctions (or, alternatively for bulk materials, the bandstructure). 

D. L. Chapman, for potassium tri-iodide. 0. Gropp measured the effect of temp, on the conductivity of solid and frozen soln. of sodium iodide. For the effect of press, on the electrical properties, vide alkali chlorides. A. Reis found the free energy for the separation of the ions of K1 to be 144 lrilogrm. cals, per mol. for iN al, 158 Lil, 153 and for HI, 305. S. W. Serkofi 35 measured the conductivity of lithium iodide in methyl alcohol P. Walden, of sodium iodide in acetonitrile P. Dutoit in acetone, benzonitrite, pyridine, acetophenone. J. C. Philip and H. R. Courtman, B. B. Turner, J. Fischler, and P. Walden of potassium iodide in methyl or ethyl alcohol J. C. Philip and H. P. Courtman in nitromethane P. Dutoit in acetone. H. C. Jones, of rubidium iodide in formamide. S. von Lasczynsky and S. von Gorsky, of potassium and sodium iodides in pyridine. A. Heydweiller found the dielectric constants of powdered and compact potassium iodide to be respectively 3 00 and 5 58. 

The mechanism of the thermal decompn of unirradiated and of briefly preirradiated Ba azide was postulated by Mott (Ref 13) and studied by Thomas, Tompkins (Ref 20). However, on detailed examination of the photo and ionic conductivity of this salt, the latter authors found that their results did not agree with the mechanism postulated previously (Ref 21). Jacobs and Tompkins (Ref 23) in their study of the ionic conductance of solid metallic azides found that all salt obeyed the equation log k " log A... 

Na and K azides were detd in solns of varying concns by Petrikalns Ogrins (Ref 12).They also detd the density and refractive index for crystn Na and K azides. The ionic conductance of solid Li azide, as detd by Jacobs Tomkins (Ref 18), obeyed the general equation log k = log A - (E/2.303RT) where k is the specific conductivity in ohm-1 cm"1 A is a constant and E is activation energy in kcal/ mol. For Li azide log A 0.840, E is 19.1 and T, the temp range 300 370°K. The Raman Effect of crystn Li azide was detd by Kahovec Kohlrausch (Ref 14/, the observed frequency, 1368.7 cm-1, corresponded to the oscillation in a linear triatomic molecule. 

Figure 15-8. Electrical conductivity of solid electrolytes (and concentrated H2S04 (aq)) as a function of temperature.

The thermal conductivity of solid rubbers is of the order of 1-2 x l10 W/mk which is in the region of fairly low conductivity where experimental errors due to heat loss will be greatest. A heated disc procedure or unguarded hot plate is satisfactory for some purposes, particularly if thin test pieces can be used. However, for the lowest conductivity materials a guarded hot plate is really necessary to give precise results. 

Olson. J R.. Topp. K.A, and R O Pohl "Specific Heal and Thermal Conductivity of Solid Fullerenes," Science. 1145 (February (9. 1993). 

The thermal conductivity of solid iodine between 24.4 and 42.9°C has been found to remain practically constant at 0.004581 J/(crnsK) (33). Using the heat capacity data, the standard entropy of solid iodine at 25°C has been evaluated as 116.81 J/ (mol-K), and that of the gaseous iodine at 25°C as 62.25 J/(mol-K), which compares satisfactorily with the 61.81 value calculated by statistical mechanics (34,35). 

However, conductive elastomers have only ca <10-3 of the conductivity of solid metals. Also, the contact resistance of elastomers changes with time when they are compressed. Therefore, elastomers are not used where significant currents must be carried or when low or stable resistance is required. Typical applications, which require a high density of contacts and easy disassembly for servicing, include connection between liquid crystal display panels (see Liquid CRYSTALS) and between printed circuit boards in watches. Another type of elastomeric contact has a nonconducting silicone rubber core around which is wrapped metalized contacts that are separated from each other by insulating areas (25). A newer material has closely spaced strings of small spherical metal particles in contact, or fine solid wires, which are oriented in the elastomer so that electrical conduction occurs only in the Z direction (26). 

According to M. Faraday,16 liquid and solid yellow phosphorus are nonconductors of electricity G. L. Knox said that the electrical conductivity of fused phosphorus is small A. Matthiessen observed that if the conductivity of silver be 100 at 0°, then that of red and yellow phosphorus is 0 0gl23 at 20° and G. Foussereau gave 0-957 XlO-11 mho for the conductivity of solid phosphorus at 11°, and 0-641 Xl0 10 mho at 42°, while for liquid phosphorus, he obtained 0-435 X10-6 mho at 25°, and 0-289 X 10 5 mho at 100°. P. W. Bridgman found the electrical resistances, R, of black phosphorus at different temp, and press., p, in kgrms. per sq. cm., were ... 

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