Hiu Chan

Using transmission electron microscopy, in-situ changes in ferroelastic domains in 0.7PbO 3 -0.3PbTiO 3 single crystals were observed at 60 to -163°C. At -163°C, the microscopic tweed morphology of the ferroelastic domains rotated by 90°, and certain orientation changes in the mesoscopic sawtooth domains took place. At this temperature, the ferroelastic domains became coarsened and certain S-shaped mesoscopic domains were reshaped. The disappearance and/or changes in the orientations of both the sawtooth and the ferroelastic domains were reversible upon return to room temperature. On heating to 60°C, both the mesoscopic sawtooth and the microscopic tweed domains were stable below 53°C. Above 53°C, the mesoscopic walls disappeared and the contrast of the tweed domains became blurred. Upon return to room temperature from 60°C, the mesoscopic domain patterns could not be retrieved, indicating that the transformation was irreversible. The morphology of the tweeds at this temperature indicated a structural transition from a two-variant domain state to a multivariant state, eliminating mesoscopic boundaries

This thesis studies whether there is a tenable distinction between a priori justification and a posteriori justification. My research considers three possible conceptions of a priori: Justification Independent of Experience, Mere Meaning Based Justification and Justification by Rational Insight, and examines whether they can provide a sound and significant distinction between a priori and a posteriori. This thesis contains five chapters. Chapter 1 introduces the background knowledge of the a priori/a posteriori distinction. Chapter 2 analyzes the traditional conception of a priori, i.e. justification independent of experience, and considers whether the distinction based on it is tenable. Five approaches for defining “experience” are examined, but none of them succeed in providing a distinction between a priori and a posteriori. Chapter 3 focuses on the empiricist conception of the a priori, i.e. a priori as mere meaning based justification, and argues that the distinction based on it has a problem of classification. Chapter 4 concerns the rationalist conception of the a priori, i.e. a priori as justification by rational insight, and argues that neither the idea of justification by rational insight itself nor the distinctive features of rational insight could provide a distinction between a priori and a posteriori. Given that none of the current major accounts seem to work, we should not be optimistic about the potential for success in accounting for the distinction between a priori and a posteriori. In the last chapter, I will conclude the thesis and point out the implication of abandoning the a priori/a posteriori distinction: a need to reform our understanding of the nature of different sources of justification and knowledge.