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Title: Mixed ionic and electronic conductivity in alkali-phosphate based glasses
Author: Mallace, Malcolm R.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1994
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A systematic investigation of three transition metal oxide (Mo, W, V) alkali phosphate-based glasses was undertaken with a view to studying the ability of these to sustain mixed ionic and electronic conductivity. The glasses were characterised by a.c. analysis and uv/vis spectroscopy. In the molybdate and tungstate glass systems large and contrary trends in ionic and electronic conductivity were highlighted. The changes were identified as being predominantly related to the alkali oxide content, for glasses containing about 50 mol% transition metal oxide. As alkali oxide was added to binary phosphate glasses a deep minimum in the isothermal conductivity plots, reminiscent of the mixed alkali effect observed in mixed ionically conducting glasses, was noted. This effect was most dramatic in the tungstate glasses, but slightly less so for the molybdate glasses. In concert with these conductivity variations the nature of the charge carrier was simultaneously determined from the shapes of impedance and spectroscopic modulus plots. This highlighted that on the low alkali side of the minimum an electronic conduction (polaronic hopping) mechanism predominated, whereas on the high alkali side of the minimum an ionic conductivity mechanism prevailed. All glasses were characterised by uv/vis spectroscopy, using either transmission or diffuse reflection techniques. Most spectra, particularly those of high transition metal content, exhibit classical "bronze-type" spectra. Spectroscopically it was found that, concurrent with the variations in electrical conductivity, dramatic changes in the relative intensities of absorption peaks in the uv/vis region of the spectrum were occurring.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available