NXFit is a program for obtaining optimized structural parameters from amorphous materials by simultaneously fitting X-ray and neutron pair-distribution functions. Partial correlation functions are generated in Q space, summed and Fourier transformed for comparison with the experimental data in r space. NXFit uses the Nelder–Mead method to vary a set of `best guess' parameters to achieve a fit to experimentally derived data. The output parameters from NXFit are coordination number, atomic separation and disorder parameter for each atomic correlation used in the fitting process. The use of NXFit has been demonstrated by fitting both X-ray and neutron diffraction data from two quite different amorphous materials: a melt-quenched (Na 2 O) 0.5 (P 2 O 5 ) 0.5 glass and a (TiO 2 ) 0.18 (SiO 2 ) 0.82 sol–gel.

Melt quenched silicate glasses containing calcium, phosphorus and alkali metals have the ability to promote bone regeneration and to fuse to living bone. Of these glasses 45S5 Bioglass® is the most widely used being sold in over 35 countries as a bone graft product for medical and dental applications; particulate 45S5 is also incorporated into toothpastes to help remineralize the surface of teeth. Recently it has been suggested that adding titanium dioxide can increase the bioactivity of these materials. This work investigates the structural consequences of incorporating 4 mol% TiO(2) into Bioglass® using isotopic substitution (of the Ti) applied to neutron diffraction and X-ray Absorption Near Edge Structure (XANES). We present the first isotopic substitution data applied to melt quench derived Bioglass or its derivatives. Results show that titanium is on average surrounded by 5.2(1) nearest neighbor oxygen atoms. This implies an upper limit of 40% four-fold coordinated titanium and shows that the network connectivity is reduced from 2.11 to 1.97 for small quantities of titanium. Titanium XANES micro-fluorescence confirms the titanium environment is homogenous on the micron length scale within these glasses. Solid state magic angle spinning (MAS) NMR confirms the network connectivity model proposed. Furthermore, the results show the intermediate range order containing Na-O, Ca-O, O-P-O and O-Si-O correlations are unaffected by the addition of small quantities of TiO(2) into these systems.

The structures of Ca60Mg15Cu25, Ca60Mg20Cu20 and Ca60Mg25Cu15 metallic glasses have been investigated by neutron and X-ray diffraction. The correlation functions show a peak manifold in the region 2.2 Å to 4.5 Å, arising from the various atom pairs for these glasses. The results show clearly that there are contacts between the solute atoms (Cu and Mg) in agreement with a simple estimate of the maximum solute atom fraction beyond which solute-solute contact becomes topologically necessary. The Cu-Mg and Cu-Ca distances are consistent with the sum of covalent radii, whereas all other interatomic distances are consistent with the sum of metallic radii. The neutron and X-ray diffraction correlation functions were simultaneously fitted with a series of symmetric peaks to obtain coordination numbers and interatomic distances, but only the results from the first two peaks, Cu-Cu and Cu-Mg, are of reasonable reliability. The Percus-Yevick approximation for binary hard sphere systems has been used to simulate the results. This shows that the results of fits to the Cu-Cu and CuApproved for public release; distribution unlimited. 2 Mg correlations give a reasonable description for atoms which are in close contact, but do not include an additional contribution at longer distance due to atoms which are almost in contact. The fits to the Cu-Ca peak are strongly affected by overlaps with both the longer distance peaks used in the fit, and the broad trailing edge in the distributions of interatomic distances that is not taken into account by fitting with symmetric peaks. Final results show that copper has a total of 6.5 neighbours which are in close contact, but has a total coordination number of about 12-13, when atoms which are almost in contact are included.

The structures of Ca60Mg15Cu25, Ca60Mg20Cu20 and Ca60Mg25Cu15 metallic glasses have been investigated by neutron and X-ray diffraction. The correlation functions show a peak manifold in the region 2.2-4.5 angstrom, arising from the various atom pairs for these glasses. The results show clearly that there are contacts between the solute atoms (Cu and Mg) which agree with a simple estimate of the maximum solute atom fraction beyond which solute solute contact becomes topologically necessary. The Cu-Mg and Cu-Ca distances are consistent with the sum of covalent radii, whereas all other interatomic distances are consistent with the sum of metallic radii. The neutron and X-ray diffraction correlation functions were simultaneously fitted with a series of symmetric peaks to obtain coordination numbers and interatomic distances, but only the results from the first two peaks, Cu-Cu and Cu-Mg, are of reasonable reliability. The Percus-Yevick approximation for binary hard sphere systems has been used to simulate the results. This shows that the results of fits to the Cu-Cu and Cu-Mg correlations give a reasonable description for atoms which are in close contact, but do not include an additional contribution at longer distance due to atoms which are almost in contact. The fits to the Cu-Ca peak are strongly affected by overlaps with both the longer distance peaks used in the fit, and the broad trailing edge in the distributions of interatomic distances that is not taken into account by fitting with symmetric peaks. Final results show that copper has a total of 6.5 neighbours which are in close contact, but has a total coordination number of about 12-13, when atoms which are almost in contact are included. (C) 2011 Elsevier Ltd. All rights reserved.

An array of different structural probes has been used to define the effect of adding Zn and Ti to a sodium–calcium phosphate glass. X-ray absorption spectroscopy at the Zn K-edge suggests that the Zn atoms occupy mixed (4- and 6-fold) sites within the glass matrix. X-ray diffraction reveals a feature at 2.03 Å that develops with the addition of Zn and Ti and is consistent with Zn–O and Ti–O near-neighbour distances. Neutron diffraction is used to resolve two distinct P–O distances and highlights the decrease in P···P coordination number from 2.0 to 1.7 as the Ti metal concentration rises, which is attributed to the O/P fraction moving away from the metaphosphate value of 3.0 to 3.1 with the addition of Ti. Other correlations, such as those associated with CaOx and NaOx polyhedra, remain largely unaffected. These results suggest that the network forming P···P correlation is most disrupted, with the disorder parameter rising from 0.07 to 0.10 Å with the additional modifiers. Zn appears to be introduced into the network as a direct replacement for Ca and causes no structural variation over the composition range studied.

Degradable iron-phosphate glasses with the composition of (CaO)(0.30)-(Na(2)O)(0.20-x)-(Fe(2)O(3))(x)-(P(2)O(5))(0.50), x = 0.01-0.05, were studied by Fe K-edge X-ray absorption spectroscopy (both near-edge, XANES, and extended, EXAFS). The addition of up to 5 mol% iron oxide is known to enhance the durability of the phosphate glass while maintaining biocompatibility. The results from the two techniques used here both show that iron is in the Fe(III) oxidation state and has octahedral coordination. This suggests that Fe is cross-linking the phosphate chains and therefore strengthening the network structure, resulting improved chemical durability of the glasses. (C) 2008 Elsevier B.V. All rights reserved.

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO2–CaO–Na2O–P2O5 glasses. Both conventional melt-quenched glasses of composition (TiO2) x (CaO)0.30(Na2O)(0.20−x)(P2O5)0.50, where x = 0.01, 0.03 and 0.05, and sol–gel derived (TiO2)0.25(CaO)0.25(P2O5)0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO6 site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO5. The spectra from the (TiO2)0.25(CaO)0.25(P2O5)0.50 sol–gel samples reveal greater distortion in the TiO6 site in the dried gel compared to the heat-treated sol–gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.

Neutron diffraction with isotopic substitution has been used to probe the local environment of silver in a melt‐quench derived bioresorbable phosphate glass. Samples enriched with 107Ag and 109Ag were prepared and neutron diffraction data collected. A first‐order difference was taken between the data sets to give detailed information about the silver environment in the glass matrix. The measured Ag‐O correlation has three components in the first coordination shell at 2.28 Å, 2.51 Å, and 2.58 Å with coordination numbers of 2.1, 2.7, and 1.1, respectively, consistent with silver occupying a distorted octahedral environment. These results have been correlated with those from Ag K‐edge X‐ray absorption near‐edge spectroscopy measurements. The results suggest that the addition of silver to the (CaO)0.3(Na2O)0.2(P2O5)0.5 system has a significant effect on the host phosphate network, with shorter and more branched chains replacing the long chains and rings normally associated with the metaphosphate composition.

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO2-CaO-Na2O-P2O5 glasses. Both conventional melt-quenched glasses of composition (TiO2)x(CaO)0.30(Na2O)0.20-x(P2O5)0.50, where x = 0.01, 0.03 and 0.05, and sol-gel derived (TiO2)0.25(CaO)0.25(P2O5)0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO6 site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO5. The spectra from the (TiO2)0.25(CaO)0.25(P2O5)0.50 sol-gel samples reveal greater distortion in the TiO6 site in the dried gel compared to the heat-treated sol-gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.

An improved sol-gel synthesis of (CaO)(0.3)(Na2O)(0.2)(P2O5)(0.5) bioresorbable glass has been developed. The structures of both the dried gel and the stabilised sol-gel glass have been characterised using high-energy XRD, P-31 MAS NMR and FT-IR spectroscopy. The structure of the analogous melt-quench prepared glass has also been studied for comparison. The results show that the dried gel has a structure consisting of mainly Q(0) and Q(1) phosphate units, whereas that of the stabilised sol-gel glass comprises predominantly Q(1) and Q(2) units. Furthermore, it is demonstrated that the structure of the sol-gel glass is similar to that of its melt-quenched counterpart except for the presence of hydroxyl groups which terminate the phosphate chains, reducing the connectivity of the network.