Solid State NMR as a probe of Inorganic Materials:Examples from Glasses and Sol-gels
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Solid State NMR as a probe of Inorganic Materials:Examples from Glasses and Sol-gels Paul Guerry1, Donna L Carroll1, Phillips N Gunawidjaja1, Prodipta Bhattacharya1, Daniela Carta2, David M Pickup2, Ifty Ahmed3, Ensanya Abouneel3, Pam A Thomas1, Jonathan C Knowles3, Robert J Newport2, and Mark E. Smith1 1 University of Warwick, Department of Physics, Coventry, CV4 7AL, United Kingdom 2 University of Kent, School of Physical Sciences, Canterbury, CT2 7NH, United Kingdom 3 Eastman Institute UCL, 256 Gray's Inn Road, London, WC1X 8LD, United Kingdom ABSTRACT To understand amorphous and structurally disordered materials requires the application of a wide-range of advanced physical probe techniques and herein a combined methodology is outlined. The relatively short-range structural sensitivity of solid state NMR means that it is a core probe technique for characterizing such materials. The aspects of the solid state NMR contribution are emphasized here with examples given from a number of systems, with especial emphasis on the information available from 17O NMR in oxygen-containing materials. 17O NMR data for crystallization of pure sol-gel prepared oxides is compared, with new data presented from In2O3 and Sc2O3. Sol-gel formed oxide mixtures containing silica have been widely studied, but again the role and effect of the other added oxide varies widely. In a ternary ZrO2-TiO2-SiO2 silicate sol-gel the level of Q4 formation is dependent not only on the composition, as expected, but also the nature of the second added oxide. Sol-gel formed phosphates have been much less widely studied than silicates and some 31P NMR data from xerogel, sonogel and melt-quench glasses of the same composition are compared. The effect of small amounts of added antibacterial copper on phosphate glass networks is also explored. INTRODUCTION Understanding the structure of amorphous solids along with the development of that structure (e.g. with heat treatment) and distinguishing subtle differences between materials with very similar chemical composition is one of the most challenging contemporary problems for structural materials science. The challenge is to collect sufficiently comprehensive, high quality experimental data sets from complementary probe techniques so as to be able to describe accurately and unambiguously the structure of such amorphous materials. A range of modern advanced characterization methods must be combined in any methodology to probe different length scales (see Figure 1 [1]). Standard bulk characterization techniques such as thermal analysis and mass loss provide background information about how a material is changing, and the supposition is that this is largely related to changes of the material’s structure. For amorphous materials, diffraction techniques provide much information via a pairwise (i.e. atom-atom) correlation function T(r) when carried out with intense, modern X-ray and neutron sources. A key here is to use sources that provide a large Q-range (where Q = (4π/λsinθ), 2θ is the scattering angl
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