A series of glass samples were prepared from a mixtures of B2Oa, Na20 and NiO. The role of nickel oxide in a glass matrix was studied by using infrared spectra, optical absorption, magnetic susceptibility, density, and differential thermal analysis (DTA). It was shown that the addition of nickel oxide at different concentrations to the glass batches causes some deformation in the glass structure. The values of ligand field strength and Racah parameter indicated an increasing degree of covalency. The glass samples exhibited diamagnetic behaviour with NiO content up to 1 g, then paramagnetic behaviour. The densities and glass transition temperatures decreased with increase in the NiO content up to 0.2 g and then increased again. This tendency may be related to changes in the glass structure.
X-ray absorption spectroscopy has been used to investigate the environment of all four cations in a series of six samples of (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). Interatomic distances and their mean square variations, together with some coordination numbers, have been obtained from an analysis of the EXAFS using the multiple-scattering fast curved-wave theory. The environments of the Ba, Cu and Y atoms were found to be invariant with changing composition, the structural parameters being in good agreement with crystallographic data for the end-point materials. The environment of the Pr atom was found to change with composition, both the mean Pr-O distance and its mean square variation varying in a characteristic way. The variations with composition may be closely modelled by the forms and . These results have been interpreted in terms of a combination of two Pr-O distances, each invariant with composition, the proportions of these varying linearly with praseodymium content. The consequences of this variation, both for the praseodymium valence and the superconducting properties of the material, are considered.
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