Phase distribution, composition and disorder in Y2(Hf,Sn)2O7 ceramics : insights from solid-state NMR spectroscopy and first-principles calculations

The authors would like to thank the ERC (EU FP7 Consolidator Grant 614290 “‘EXONMR’”), and EPSRC for support for SS and ASG (EP/L005581/1). SEA would like to thank the Royal Society and Wolfson Foundation for a merit award. We acknowledge support from the Collaborative Computational Project on NMR Crystallography CCP-NC funded by EPSRC (EP/M022501/1).A NMR crystallographic approach, combining 89Y, 119Sn and 17O NMR spectroscopy with X-ray diffraction and first-principles calculations has been used investigate the number and type of phases present, and the local structure and disorder in Y2Hf2–xSnxO7 ceramics. Although a phase change is predicted with increasing Hf content, NMR spectra clearly show the presence of a significant two-phase region, with a Sn-rich pyrochlore and relatively Hf-rich defect fluorite phase co-existing for much of the compositional series. A single-phase pyrochlore is found only for the Sn end member, and a single defect fluorite phase only for x = 0 to 0.2. A solid-solution limit of ~10% is seen for the substitution of Hf into Y2Sn2O7, although no evidence is seen for any cation ordering or antisite disorder in this phase. In the defect fluorite phase there is preferential ordering of oxygen vacancies around Sn, which is only ever seen in a six-coordinate environment. The remaining vacancies are more likely to be associated with Hf than with Y, although this distinction is less apparent at higher Sn concentrations. To acquire 17O NMR spectra samples were post-synthetically exchanged with 17O2(g), although high temperatures (> 900 ºC) were required to ensure uniform enrichment of different chemical species. although these 17O NMR spectra confirm the formation of mixed-metal materials and the presence of two phases, more quantitative analysis is hindered by the overlap of signals from pyrochlore and defect fluorite phases. In all cases, DFT calculations play a vital role in the interpretation and assignment of the NMR spectra, and in understanding the local structure and disorder in these complex multi-phase materials.PostprintPostprintPeer reviewe

Iron phosphate glasses: Bulk properties and atomic scale structure

© 2017 The Authors Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137 Cs to 137 Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137 Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10 −6 K −1 to 13.4 × 10 −6 K −1 , when 25 wt. % of Cs 2 O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The Fe II content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The Fe II content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data

Remote physiological monitoring: Clinical, financial, and behavioral outcomes in a heart failure population

This article reports on the outcomes associated with remote physiological monitoring (RPM) conducted as part of a heart failure disease management program. Claims data, medical records, data transmission records, and survey results for 91 individuals ages 50–92 (mean 74 years) successfully completing a heart failure RPM program were analyzed for time periods before, during, and after the monitoring intervention. The program was associated with significant reductions in per member per month costs and emergency room and hospital utilization. More detailed analyses were performed for specific gender and age subgroups. Participant surveys indicated high levels of satisfaction, and improvements in self-perceived health status, self-efficacy, and self-management behaviors. This study is the first to assess the impact of a RPM program following removal of the monitoring equipment. The results indicate that RPM, as a component of a traditional disease management program, has a sustained, beneficial effect on participants’ lifestyles after the monitoring period has ended

Transformation of Cs-IONSIV® into a ceramic wasteform by hot isostatic pressing

A simple method to directly convert Cs-exchanged IONSIV® IE-911 into a ceramic wasteform by hot isostatic pressing (1100 °C/190 MPa/2 hr) is presented. Two major Cs-containing phases, Cs2TiNb6O18 and Cs2ZrSi6O15, and a series of mixed oxides form. The microstructure and phase assemblage of the samples as a function of Cs content were examined using XRD, XRF, SEM and TEM/EDX. The chemical aqueous durability of the materials was investigated using the MCC-1 and PCT-B standard test methods. For HIPed Cs-IONSIV® samples, the MCC-1 normalised release rates of Cs were <1.57 × 10−1 g m−2 d−1 at 0–28 days, and <3.78 × 10−2 g m−2 d−1 for PCT-B at 7 days. The low rates are indicative of a safe long-term immobilisation matrix for Cs formed directly from spent IONSIV®. It was also demonstrated that the phase formation can be altered by adding Ti metal due to a controlled redox environment

Resistance to amorphisation in Ca1-xLa2x/3TiO3 perovskites – a bulk ion-irradiation study

The changes induced from 1 MeV Kr+ and 5 MeV Au+ ion irradiation at room temperature have been utilised to determine the impact of cation vacancies on the radiation damage response of bulk Ca1-xLa2x/3TiO3 perovskite structured ceramics. Perovskite systems have long been considered as candidate waste forms for the disposition of actinide wastes, and doping with multi-valent elements such as Pu may lead to cation deficiency. Based on GAXRD and TEM analysis, two regions of resistance/susceptibility to amorphisation have been confirmed with reference to CaTiO3. Increased resistance to amorphisation has been observed for 0.1 ≤ x ≤ 0.4, with an increased susceptibility to amorphisation for x ≥ 0.5. It is proposed that these processes are induced by enhanced recovery from radiation damage for 0.1 ≤ x ≤ 0.4, and reduced tolerance for disorder/the increasingly covalent nature of the A-O bond for x ≥ 0.5. Lattice parameter analysis of the x = 0 and 0.5 samples showed a saturation in radiation damage induced volume swelling at 4.7 ± 0.1% and 1.8 ± 0.1%, respectively, while the saturation limit for the b parameter was lower than the respective a and c orthorhombic parameters. In the x = 0.2 and 0.4 samples, amorphisation was not observed, however the b parameter was found to swell to a lesser extent than the a and c parameters. Swelling was not observed for the ion irradiated x ≥ 0.6 samples

A Transmission Electron Microscopy study of the Interaction between Defects in Amorphous Silicon and a Moving Crystalline/Amorphous Interface

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Simulation of alpha decay of actinides in iron phosphate glasses by ion irradiation

A surrogate approach of ion beam irradiation is employed to simulate alpha decay of actinides in iron phosphate nuclear waste glasses. Bismuth and helium ions of different energies have been selected for simulating glass matrix modification owing to radiolysis and ballistic damage due to recoil atoms. Structural modification and change in coordination number of network former were probed by employing Reflectance Fourier-Transform Infrared (FT-IR), and Raman spectroscopies as a consequence of ion irradiation. Depolymerisation is observed in glass sample irradiated at intermediate energy of 2 MeV. Helium blisters of micron size are seen in glass sample irradiated at low helium ion energy of 30 keV