The electrical conductivity of pure KI and CdI₂-doped KI has been studied in the temperature range 200 to 23°C. Two regions A and B (corresponding to different activation energy of conductivity) are identified. The region A can be given a conventional interpretation in terms of migration of cation vacancies in the bulk, their concentration being determined by impurities. U (the energy for migration of cation vacancies) amounts to 0.96 ± 0.02 eV. Observed activation energies higher than this value are accounted for by association and precipitation effects. Association energy of cation vacancies with impurities (0.48 eV. for Cd⁺₂) and heat of solution (0.25 eV. for CdI₂) obtained here are comparable with known values for other alkali halides. Region B found in this work represents unusual behaviour and has not previously been observed in any alkali halides. The activation energy of conductivity is considerably less than the energy needed for the migration of cation vacancies in the bulk. The activation energy E(formula omitted) (for region B) is about 0.57 eV. in a single crystal and 0.38 eV. in a pure KI pellet. Such low activation energies cannot be given a similar interpretation as for region A. It is suggested that the cation vacancies are in regions of unusually high mobility such as dislocations and grain boundaries. This effect may arise partly from a lower activation energy for motion of vacancies in these regions and partly from a vacancy concentration in these regions which increases with decreasing temperature, under the control of "space- charge" effects. The value 0.57 eV. appears to refer to isolated dislocations or low angle boundaries, while the value of 0.38 eV. refers to large angle intercrystalline boundaries in a pellet. A strong piece of evidence for this suggestion comes from the conductivity runs on single crystals. In an untreated single crystal, just as in pure pellets, two regions A and B are identified but region B disappears in crystals annealed overnight and reappears in a mechanically strained crystal. Moreover, region A remains almost undisturbed in each case. This means that the conduction process in region B is governed by dislocations and grain boundaries whereas region A is governed by motion of cation vacancies in the bulk. / Science, Faculty of / Chemistry, Department of / Graduate

In lightly doped semiconductors (LDSs), electrons can exist in localized states around impurities and dc electronic conduction can occur by electrons hopping between localized states. Such hopping is the dominant mechanism for conduction if the temperature is so low that the contribution from band electrons is negligible. According to theories of hopping conduction, at low enough temperature T, the conductivity σ will be o=σ₀e⁻(T₀/T)¼ where T₀ is a temperature which depends on the material. Experimental work on doped semiconductors which exhibits this form of σ is scarce. Recently, however, conductivities which were clearly of this form were reported for lightly doped n-GaAs and lightly doped n-InP. The experimental results were surprising in that the temperature ranges were well above, and the T₀ values well below, the limits set by the theories. To understand these experimental results, hopping in LDSs is modelled in this dissertation using a resistor network. This dissertation is unique in that the conductivity of the unabridged resistor network is examined in a temperature range (called "the high temperature regime") where kT is comparable to the spread ∆ε in the energies of localized electrons. A numerical simulation is performed and an analytic theory based on percolation methods is presented. In this dissertation, an analytic approach is developed for the first time for studying how, in the high temperature regime, the conductivity of the unabridged resistor network depends on the density of localized states. It is found that, in either two or three dimensions, if the density of states is flat, σ is of the activated form o=σ₀e ⁻εa/kt. The activation energies are found to be εa=0.28∆ε in two dimensions and εa =0.20∆ε in three dimensions. These values are considerable improvements over the estimates of previous workers, who used the low temperature asymptotic form of the resistance in the high temperature regime. It is also revealed that σ can be o=µσ₀e ⁻(T₀/T)¼ in the high temperature regime if the density of states decreases with |ε⁻µ₀| for energy e far enough away from the zero temperature chemical potential µ₀, These results are in accord with the experimental results described above. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Note:

No description available.

No description available.

Monomers, polymers, charge-transfer complexes of 2-benzylidene-1,3-dithioles (Dithiafulvenes), and 1,3-dithiolium (Dithiafulvenium) salts of dithioesters and poly(dithioesters) were synthesized. The infrared, nuclear magnetic resonance (NMR) and ultra violet spectra of these materials were also reported. Condensation polymerization of piperidinium tetrathio terephthalate with α-halocarbonyl compounds using phase-transfer techniques yielded poly(dithioesters) that upon dehydrative cyclization with sulfuric acid gave poly(1,3-dithiafulvenium) salts. Polymerization of substituted dithiafulvenes with diacid chlorides, p-phenylene diisocyanate or terephthalaldehyde yielded polymers with inherent viscosities of 0.10 dL/g to 0.21 dL/g. The electric resistivity of the charge-transfer complexes of several dithiafulvenes and the electron donors TCNQ and TNF measured by the two-probe method was found to be >10⁶ Ω.cm at room temperature, hence behaving like insulators. Polyesters and polyesterimides of 4,4'-sulfonyl diphenol were synthesized. The low molecular weight polymers had viscosities of 0.12 to 0.20 dL/g. The polymers formed brittle films and their IR and NMR spectra were reported.

Digitized by Kansas Correctional Industries

The development of the conductivity coefficients is reviewed for both highly degenerate metals, having an energy dependent relaxation time, and semiconductors, obeying Boltzmann statistics and having a relaxation time varying as the energy to the λ power.

The electrical conductivity of the pyromagmas from the Northeast Crater of Mount Etna, Sicily was measured over the temperature range 1032°C to 1071°C and over the frequency range 1 kHz to 400 kHz. Measurements were made using a four-terminal Wenner array in conjunction with a Wavetek Model 110B portable signal generator and Hewlett Packard Model 731 portable electronic voltmeters. The electrical conductivity is of the order of 0.4 mhos/m with less than 20% dispersion over the frequency range. Over the 40 degree temperature interval the temperature coefficient of resistance corresponds to an activation energy of 1.5 ± 0.5 eV. The value for the electrical conductivity of the gas-charged pyromagma is related to values determined in the laboratory for gas-free melts of lava and for glasses and slags of similar chemical composition. An original design of semi-expendable graphite-molybdenum electrode contributed greatly to the reliability of the measurements. A chromatographic analysis of the vent gases, and a silicate analysis, a modal analysis and a normal analysis of the lavas are included for completeness. Finally, as an aid to future electromagnetic probing activity, an analysis and estimate are made of the variation of electrical conductivity of pyromagma with depth in a volcanic conduit. / Graduation date: 1970

No description available.