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Date of Award

1980

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Supervisor

Dr. J.E. Greedan

Abstract

Members of the RETi0₃ series, RE = La, Ce, Pr, Nd, Gd, Y and LaᵪY₁₋ᵪ, have been prepared and characterized. Single crystals (or crystals with a small volume of twinned component) of many of these phases have been obtained from the melt for the first time using Czochralski and Stockbarger techniques.

Crystal structures of selected members of this series have been solved using single crystal X-ray diffraction data. The solutions were complicated in some cases by twinning, but all phases were found to be isostructural with GdFe0₃, space group Pbnm. While most aspects of the structures varied smoothly across the series, the environment of the Ti⁺³ ion becomes distorted in a tetragonal-like fashion for RE = Gd and Y.

The electronic behaviour of the d-electron associated with Ti⁺³ has been investigated. In transport studies, metallic behaviour is observed at high temperatures for RE = La and Ce, accompanied by a transition to semiconducting behaviour at lower temperature. The other RETi0₃ show semiconducting behaviour over the temperature range investigated, the activation energies increasing with decreasing RE⁺³ radius. In the magnetic properties, all phases show critical temperatures well above 4.2 K, except for RE = Nd.

An attempt is made to account for the observed properties of the RETi0₃ phases in terms of a model proposed by J.B. Goodenough in which the d-electron behaviour depends upon the effectiveness of relevant orbital overlaps.

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