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A light scattering study of the borates Zn4B6O13 and Ni3B7O13I

This work describes a light scattering study of two crystilline borates, a system for automated Brillouin spectroscopy, and a theoretical investigation of incommensurate-commensurate transitions. Firstly, the Raman spectrum of zinc metaborate (Zn4B6013) is reported and discussed, and a tentative assignment is made of vibrations of tha B-O framework. An interference feature in the spectrum is analysed in terms of models involving anharmonic phonon-phonon and phonon-continuum coupling. The inelastic and elastic light scattering spectrum of nickel-iodine buracite (N13B7013I) is presented for the first time, at temperatures between 6 K and 295 K. Anomalies in the phonon lifetimes and frequencies at 130 K are correlated with concomitant abnormalities in the structural, elastic and magnetoelectric properties, but a structural transition at this temperature is not indicated. The dynamics of the improper paraelectric-ferroelectric transition at 68 K are discussed, and possible symmetries considered. Furthermore, the data reveals a new transition at 7 K, which is thought to be both structural and magnetic. Critical modes are studied, and a strongly temperature dependent mode is identified, whose behaviour cannot be fully explained. A proven modular approach to computer control of experiments is presented, and a system for control of Brillouin scattering experiments is described. Examples of the resultant spectra are presented, along with some speculation as to future developments. Finally, the theory of incommensurate-commensurate lock-in transitions has been studied, and the method and conclusions are detailed. Two distinct types of lock-in transition are identified, and the corresponding distortion profiles are derived within a simple Landau theory.
Date January 1978
CreatorsMurray, Alan Fraser
PublisherUniversity of Edinburgh
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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