Date of Award


Degree Type


Degree Name

Doctor of Philosophy


To investigate the controversial {dollar}\beta\sb1\leftrightarrow\beta\sb2{dollar} phase transformation in the {dollar}\beta{dollar}-{dollar}\rm (Bi\sb2O\sb3)\sb{lcub}1-x{rcub}(SrO)\sb{lcub}x{rcub}{dollar} phase, a series of compositions across the phase were prepared by conventional grinding, pressing and firing ceramic techniques. Electrical conductivity measurements demonstrated that the samples were comparable to those used in other laboratories. X-ray diffraction analysis confirmed that the cations are located on a hexagonal sublattice, but details of the anion sublattice could not be resolved, because of the low X-ray scattering factor of {dollar}\rm O\sp{lcub}2-{rcub}.{dollar};The compositional dependence of the lattice parameters of the hexagonal crystal structure of the {dollar}\beta{dollar}-{dollar}\rm (Bi\sb2O\sb3)\sb{lcub}1-x{rcub}(SrO)\sb{lcub}x{rcub}{dollar} phase, which was determined at {dollar}27\sp\circ\rm C{dollar} using X-ray diffraction, revealed two distinct trends. The a and c parameters were both approximately constant for compositions below x = 0.28, whereas for compositions greater than x = 0.28, the c parameter increased progressively with the amount of substituted strontium, while the a parameter showed no significant changes.;An investigation into the temperature dependence of the lattice parameters revealed reversible discontinuities in the a and c lattice parameters at high temperatures, although the basic hexagonal crystal structure was unchanged. The c parameter discontinuity was greatest at low values of x, whereas the a parameter discontinuity was greatest in the middle of the phase and both effects decreased to the detection limit at x {dollar}<{dollar} 0.40. These discontinuities are not caused by changes in the cation sublattice, as the X-ray diffraction peak intensities were not modified on cycling through the transformation. Instead, the discontinuities are attributed to modifications in the {dollar}\rm O\sp{lcub}2-{rcub}{dollar} occupancy of the anion sublattice, or, more precisely, in the distribution of {dollar}\rm O\sp{lcub}2-{rcub}{dollar} vacancies among these sites. The {dollar}\beta\sb1\leftrightarrow\beta\sb2{dollar} phase boundary, omitted from the most recent published phase diagram for the {dollar}\rm Bi\sb2O\sb3{dollar}-SrO system, was found to be asymmetric with respect to composition, in contrast to earlier reports. A revised phase diagram is presented incorporating these results.



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