Browsing by Author "Williams, J. O."

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    Dislocations in Orthorhombic Minerals: Part 1.—Naturally-occurring Barytes
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (10), 1972) Williams, J. O.; Tennakoon, D. T. B.; Thomas, J. M.
    The emergence points of dislocations at cleavage faces of natural barytes crystals have been identified using the etchpit technique. The alignments of these etchpits and the observation of slip traces both in as-grown and deliberately deformed crystals yield the active slip planes in this material. The results compare favourably with a recent independent study of natural barytes crystals employing the X-ray topographical technique. Comparisons are made between barytes and the isomorphous ammonium perchlorate. It is found that, with one notable exception, the dislocation structures of these two materials are identical and probably characteristic of the space group, Pmna. The slip systems are {201}[101]; {401}[010]; {110}; {001}[010J; {010} [001]; {101} or {101} [010], {110} [001] and {201} [001], the last-named being active in barytes only. The important criterion when considering the y-irradiation behaviour of these two materials is the thermal stability of the respective lattices.
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    Electrical Conduction in Ammonium Perchlorate
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (12), 1972) Owen, G. P.; Thomas, J. M.; Williams, J. O.
    D.c. along with a few a.c. electrical measurements are reported for ammonium perchlorate (AP) in compressed disc and single crystal form. The near-identity of the electrical conductivity of AP to that of certain other alkali perchlorates (also measured) makes conduction by protons according to schemes previously suggested unlikely though not impossible. The non-ohmic behaviour of ammonium perchlorate single crystals shows that the “ classical ” theory of ionic conduction based on the migration and creation of point defects is not adequate to describe fully the conduction process. The possibility of various electronic mechanisms, including Schottky emission of electrons from the metallic electrodes with associated carrier injection into the crystal is discussed. As none of these mechanisms is entirely satisfactory, the electrical conductivity of AP is thus considered to be complex and, in particular, to be controlled by a number of processes operative under different conditions of temperature, applied field and gas pressure.