X-ray and neutron scattering

Abstract:

The interplay between superconductivity, magnetism and crystal structure in iron-based superconductors is a topic of great interest amongst the condensed matter physics community as it is thought to be the key to understanding the mechanisms responsible for high temperature superconductivity. Alkali metal doped iron chalcogenide superconductors exhibit several unique characteristics which are not found in other iron-based superconducting materials such as antiferromagnetic ordering at room temperature, the presence of ordered iron vacancies and high resistivity normal state properties. Detailed microstructural analysis is essential in order to understand the origin of these unusual properties. Here we have used a range of complementary scanning electron microscope based techniques, including high-resolution electron backscatter diffraction mapping, to assess local variations in composition and lattice parameter with high precision and sub-micron spatial resolution. Phase separation is observed in the Cs xFe 2ySe 2crystals, with the minor phase distributed in a plate-like morphology throughout the crystal. Our results are consistent with superconductivity occurring only in the minority phase. © 2012 IOP Publishing Ltd.

Abstract:

The growth of single crystals of solid solutions of LiNbO 3 and LiTaO 3 has been studied by using a number of different techniques: Czochralski pulling, Top-Seeded Solution Growth, flux growth from LiBO 2 and LiVO 3, and by optical floating zone. Crystals with homogenous Li, Ta and Nb compositions were obtained by several techniques. Analysis of local and average compositions of Ta, Nb and Li by Raman spectroscopy, birefringence imaging and X-ray diffraction, in addition to EDAX, is described. The effects of replacing Nb by Ta and of Li non-stoichiometry on the lattice parameters and the compositional disorder over the whole composition range 0 ≤ x ≤ 1 are discussed. © 2012 Elsevier B.V. All rights reserved.