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The family of phases Li3M2XO6 (M = Mg, Co, Ni; X = Nb, Ta, Sb) has a novel rock salt superstructure in which the X cations occupy one set of octahedral sites with the Li and M cations distributed over three octahedral sites in a non-random manner. The non-random site occupancies vary depending on M and X and appear to be an equilibrium feature of the structure. Li3Ni2NbO6 undergoes a continuous order-disorder transition and can be doped with Cr3+ by a number of mechanisms to give either ordered or disordered rock salt structures. The phase diagram of the solid solutions of general formula Li3-xNi2-xCr xNbO6 has been determined and shows solid solutions for both ordered and disordered polymorphs with a transition zone that is 200-300A°C wide. Li3Ni2TaO6 and Cr-doped Li3Ni 2NbO6 compositions are modest semiconductors. The alpha and beta structures of polymorphic Li2CuZrO 4 have been determined. Both structures are ordered rock salt with unique sites for Zr and one set of Li atoms; in the alpha polymorph, Cu and the other set of Li atoms are partially ordered over two sites, but in beta-Li 2CuZrO4 all cations are uniquely ordered. In the phase transition from alpha-Li2CuZrO4 to the low temperature beta polymorph, the CuO6 octahedra, which predominantly corner-share in alpha, become edge-sharing. Magnetic susceptibility data indicate that, in both polymorphs, there are both ferromagnetic and antiferromagnetic interactions. The predominant interactions in the alpha phase are antiferromagnetic whereas in the beta polymorph, they are ferromagnetic. Conductivity measurements show that beta-Li2CuZrO4 is a modest semiconductor.

Call number: LD2668 .T4 1950 J69 / Master of Science

by Chan Che Ping. / Chinese title: / Bibliography : leaf 132 / Thesis (M.Phil.)--Chinese University of Hong Kong, 1982

Electron microscopes offer scientists an invaluable tool in probing matter at a very small scale. Rapid advancements over the past several decades has allowed electron microscopes to routinely image samples at the atomic scale. These advancements have been in all aspects of electron microscope design – such as more stable control voltages and currents, brighter and more coherent sources, beam aberration correction, and direct electron detectors, to name a few. One very recent advancement is in shaping the electron beam to provide an almost arbitrary set of possible beam profiles. Following the demonstration of electron vortex beams in 2010, there has been a surge of interest in the potential shaping electron beams. Utilizing holographic electron diffraction gratings, an almost arbitrary set of electron beams can be generated. These diffraction gratings are challenging to create due their tiny size and the precision with which they must be fabricated. We present a comprehensive study on the fabrication and design of electron diffraction gratings with the aim of being able to produce optimal gratings that result in bright, well separated beams which closely match a desired beam profile. We have developed and optimized fabrication of these gratings with focused ion beam milling, and have been able to use the fabricated gratings in a number of important experiments. These electron diffraction gratings have allowed us to perform various experiments such as aberration correction, electron helical dichroism, advanced phase-contrast imaging, and multi-beam interferometric techniques. Holographic beam shaping will continue to be an important tool for electron microscopists.