Mahmoud Abd El Hafez M. Adam

The crystallization kinetics of glassy alloy SeGe20, to which small concentrations of foreign elements such as In, Tl, As, Sb and Bi are added, were investigated at temperatures of 75, 85, 95 and 105°C. It is found that the crystallization process of the annealed doped and undoped glassy alloy SeGe20 is one-dimensional. The rate of crystallization depends on the doping element and its concentration. The effect of introducing elements on the crystallization process is discussed. © 1988.

The d.c. conductivity, a.c. conductivity and thermoelectric power of the compounds H3N+(CH2)+ NH3FeCl4, where n=2, 3, 7 and 10, have been studied over a temperature range of 150-500 K. The conductivity results confirm the presence of more than one structural phase transition for each compound investigated. The thermoelectric power measurements showed that electrons are the main charge carriers in all crystal phases. The conductivity results were explained on the basis of an electron hopping mechanism over the whole temperature range. © 1988 Chapman and Hall Ltd.

The electrical conductivity of γ-irradiated and unirradiated finely-divided spinels of composition (Znx2+Fe1-x2+Fe23+)O42-was studied in a nitrogen atmosphere as a function of temperature. The results of both γ-irradiated and unirradiated ferrites with compositions x ≤ 0.79 showed that the electrical conduction occurred by fast electron exchange amongst Fe2+ and Fe3+ ions situated on octahedral sites in the spinel lattice, by a hopping mechanism. For composition x > 0.79 it was found that the transition of the charge carriers through cation vacancies is the predominant mechanism. Some breaks in the conductivity-temperature curves were found near the Curie points. Seebeck voltage measurements showed that γ-irradiated and unirradiated spinels behave as n-type semiconductors. The effect of γ-irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed. © 1988 Chapman and Hall Ltd.

The dielectric constant ε and the pyroelectric current Ip for the compounds (CH2)8(NH3)2FeCl4-xBrx(x=0, 1 and 2) have been measured in the range from the liquid nitrogen temperature up to near the melting points. Measurements of the dielectric constant have been carried out at various frequencies. A calculation of the electric dipole moments at the background and transition points is given. Calorimetric measurements have also been carried out and the values of the enthalpy change ΔH and entropy change ΔS are also reported.