84 research outputs found
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O Solid-State NMR Spectroscopy of Functional Oxides for Energy Conversion
The main aim of this thesis is the development of O solid-state nuclear magnetic resonance (NMR) spectroscopic techniques to study the local structure and ion dynamics of functional oxide materials for applications in energy conversion, in particular as electrodes and electrolytes in solid oxide fuel cells (SOFCs). Broadly, the work comprises two related areas: (1) application of a combined experimental and computational methodology to enable the first O solid-state NMR studies of paramagnetic oxides, in particular a class of perovskite-derived structures used as mixed ionic-electronic conductors (MIECs) for SOFC cathodes, and (2) further uses of multinuclear variable-temperature NMR spectroscopy, with emphasis on O NMR results, to elucidate mechanistic details of oxide-ion motion and sublattice exchange in a novel family of promising SOFC electrolyte materials based on -BiO.
In the first section, O magic-angle spinning (MAS) NMR spectra of the paramagnetic MIEC, LaNiO, are presented and rationalized with the aid of periodic DFT calculations. Advanced NMR pulse programming and quadrupolar filtering techniques are coupled to extract high-resolution spectra. In particular, these data reveal local structural distortions in LaNiO that arise from incorporation of interstitial oxide defects. Moreover, variable-temperature spectra indicate the onset of oxide-ion motion involving the interstitials at 130 °C, which is linked to an orthorhombictetragonal phase transition. By analyzing the ion dynamics on the spectral timescale, specific motional mechanisms are elucidated that prove relevant to understanding the functionality and conductivity of this phase.
Next, a similar methodology is applied to the Sr-doped analogues, LaSrNiO, in an exploration of the defect chemistry and electronic structure of these phases (0 1). By following the doping-induced evolution of spectral features assigned to interstitial and equatorial oxygen environments, changes in the ionic and electronic conductivity, respectively, are rationalized. This approach has been extended to the acquisition and assignment of O NMR spectra of isostructural SmSrNiO and PrSrNiO phases, promising SOFC cathode materials that exhibit paramagnetism on the A site (A = Sm, Pr).
The final section details the characterization of oxide-ion motion in the fluorite-type phases BiVO and BiPO ( = 0.087 and 0.148) developed as SOFC electrolytes. Variable-temperature NMR experiments between room temperature and 923 K reveal two distinct mechanisms. For the V-doped phases, an oxide-ion conduction mechanism is observed that involves oxygen exchange between the Bi-O sublattice and rapidly rotating VO tetrahedral units. The more poorly conducting P-doped phase exhibits only vacancy conduction with no evidence of sublattice exchange, a result ascribed to the differing propensities of the dopants to undergo variable oxygen coordination. These initial insights suggest chemical design rules to improve the next generation of oxide-ion conducting materials
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A 17O Paramagnetic NMR Study of Sm2O3, Eu2O3, and Sm-/Eu- Substituted CeO2
Paramagnetic solid-state NMR of lanthanide (Ln) containing materials can be challenging due to the high electron spin
states possible for the Ln f electrons, which result in large paramagnetic shifts, and these difficulties are compounded
for 17O due to the low natural abundance and quadrupolar character. In this work, we present examples of 17O NMR
experiments for lanthanide oxides and strategies to overcome these difficulties. In particular, we record and assign the
17O NMR spectra of monoclinic Sm2O3 and Eu2O3 for the first time, as well as performing density functional theory
(DFT) calculations to gain further insight into the spectra. The temperature dependence of the Sm3+ and Eu3+
magnetic susceptibilities are investigated by measuring the 17O shift of the cubic sesquioxides over a wide
temperature range, which reveal non-Curie temperature dependence due to the presence of low-lying electronic
states. This behaviour is reproduced by calculating the electron spin as a function of temperature, yielding shifts which
agree well with the experimental values. Using the understanding of the magnetic behaviour gained from the
sesquioxides, we then explore the local oxygen environments in 15 at% Sm- and Eu-substituted CeO2, with the 17O
NMR spectrum exhibiting signals due to environments with zero, one and two nearest neighbour Ln ions, as well as
further splitting due to oxygen vacancies. Finally, we extract an activation energy for oxygen vacancy motion in these
systems of 0.35 ± 0.02 eV from the Arrhenius temperature dependence of the 17O T1 relaxation constants, which is
found to be independent of the Ln ion within error. The relation of this activation energy to literature values for oxygen
diffusion in Ln-substituted CeO2 is discussed to infer mechanistic information which can be applied to further develop
these materials as solid-state oxide-ion conductors.Oppenheimer Foundation.
NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0012583.
Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility
Scientific Data and Computing Center, a component of the Computational Science Initiative, at Brookhaven National Laboratory, under Contract No. DE-SC001270
Natural abundance solid-state 33S NMR study of NbS3: applications for battery conversion electrodes.
We report ultra-wideline, high-field natural abundance solid-state 33S NMR spectra of the Li-ion battery conversion electrode NbS3, the first 33S NMR study of a compound containing disulfide (S22-) units. The large quadrupolar coupling parameters (CQ ≈ 31 MHz) are consistent with values obtained from DFT calculations, and the spectra provide evidence for the linear Peierls distortion that doubles the number of 33S sites
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Evolution of lithium ordering with (de)-lithiation in β- LiVOPO4: Insights through solid state NMR and first principles DFT calculations
The lithium ion battery cathode material β-VOPO4 is capable of intercalating more than one Li ion per transition metal ion due to the accessibility of both the V5+/V4+ and V4+/V3+ redox couples at ~4.5 V and ~2.3 V vs. Li, respectively, giving a theoretical capacity greater than ~300 mAh g−1. The ability to perform full and reversible two Li-ion intercalation in this material, however, has been a matter of debate and the poor crystallinity of the fully lithiated phase has thus far precluded its complete structural characterization by conventional diffraction-based methods. In this work, 7Li and 31P NMR spectroscopy, in combination with first principles DFT calculations, indicate that chemical lithiation results in a single phase β-Li2VOPO4 exhibiting a complex Li ordering scheme with lithium ions occupying multiple disordered environments. 2D NMR 7Li correlation experiments were used to deduce the most likely Li ordering for the β-Li2VOPO4 phase from amongst several DFT optimised structures. In contrast, electrochemically lithiated β-Li2-xVOPO4 discharged to 1.6 V exhibits, in addition to β-Li2VOPO4, a β-Li1.5VOPO4 phase. The existence of β-Li1.5VOPO4 is not reflected in the flat galvanostatic charge and discharge curves nor is evident from diffraction-based methods due to the very close structural similarity between the β-Li1.5VOPO4 phase and β-Li2VOPO4 phases. We demonstrate that solid state NMR spectroscopy, in combination with DFT results provides a powerful tool for identifying intermediate states formed during charge/discharge of these complex phosphates as these phases can be distinguished from the end member phases primarily by the nature of the lithium ordering.NECCES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583
Internet‐Based Pain Self‐Management for Veterans: Feasibility and Preliminary Efficacy of the Pain EASE Program
ObjectiveTo develop and test the feasibility and preliminary efficacy of a cognitive behavioral therapy–based, internet‐delivered self‐management program for chronic low back pain (cLBP) in veterans.MethodsPhase I included program development, involving expert panel and participant feedback. Phase II was a single‐arm feasibility and preliminary efficacy study of the Pain e‐health for Activity, Skills, and Education (Pain EASE) program. Feasibility (ie, website use, treatment credibility, satisfaction) was measured using descriptive methods. Mixed models were used to assess mean within‐subject changes from baseline to 10 weeks post‐baseline in pain interference (primary outcome, West Haven‐Yale Multidimensional Pain Inventory, scale of 0 to 6), pain intensity, mood, fatigue, sleep, and depression.ResultsPhase I participants (n = 15) suggested modifications including style changes, content reduction, additional “Test Your Knowledge” quizzes, and cognitive behavioral therapy skill practice monitoring form revisions for enhanced usability. In Phase II, participants (n = 58) were mostly male (93%) and White (60%), and had an average age of 55 years (standard deviation [SD] = 12) and moderate pain (mean score 5.9/10); 41 (71%) completed the post‐baseline assessment. Participants (N = 58) logged on 6.1 (SD = 8.6) times over 10 weeks, and 85% reported being very or moderately satisfied with Pain EASE. Pain interference improved from a mean of 3.8 at baseline to 3.3 at 10 weeks (difference 0.5 [95% confidence interval 0.1 to 0.9], P = 0.008). Within‐subject improvement also occurred for some secondary outcomes, including mood and depression symptoms.DiscussionVeterans with cLBP may benefit from technology‐delivered interventions, which may also reduce pain interference. Overall, veterans found that Pain EASE, an internet‐based self‐management program, is feasible and satisfactory for cLBP.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154929/1/papr12861.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154929/2/papr12861_am.pd
Revealing the Structure and Oxygen Transport at Interfaces in Complex Oxide Heterostructures via 17O NMR Spectroscopy
Vertically aligned nanocomposite (VAN) films, comprising nanopillars of one phase embedded in a matrix of another, have shown great promise for a range of applications due to their high interfacial areas oriented perpendicular to the substrate. In particular, oxide VANs show enhanced oxide-ion conductivity in directions that are orthogonal to those found in more conventional thin-film heterostructures, however the structure of the interfaces and its influence on conductivity remain unclear. In this work 17O NMR spectroscopy is used to study CeO2–SrTiO3 VAN thin films: selective isotopic enrichment is combined with a lift-off technique to remove the substrate, facilitating detection of the 17O NMR signal from single atomic layer interfaces. By performing the isotopic enrichment at variable temperatures, the superior oxide-ion conductivity of the VAN films compared to the bulk materials is shown to arise from enhanced oxygen mobility at this interface; oxygen motion at the interface is further identified from 17O relaxometry experiments. The structure of this interface is solved by calculating the NMR parameters using density functional theory combined with random structure searching, allowing the chemistry underpinning the enhanced oxide-ion transport to be proposed. Finally, a comparison is made with 1% Gd-doped CeO2–SrTiO3 VAN films, for which greater NMR signal can be obtained due to paramagnetic relaxation enhancement, while the relative oxide-ion conductivities of the phases remain similar. These results highlight the information that can be obtained on interfacial structure and dynamics with solid-state NMR spectroscopy, in this and other nanostructured systems, our methodology being generally applicable to overcome sensitivity limitations in thin-film studie
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Interactions of Oxide Surfaces with Water Revealed with Solid-State NMR Spectroscopy.
Hydrous materials are ubiquitous in the natural environment and efforts have previously been made to investigate the structures and dynamics of hydrated surfaces for their key roles in various chemical and physical applications, with the help of theoretical modeling and microscopy techniques. However, an overall atomic-scale understanding of the water-solid interface, including the effect of water on surface ions, is still lacking. Herein, we employ ceria nanorods with different amounts of water as an example and demonstrate a new approach to explore the water-surface interactions by using solid-state NMR in combination with density functional theory. NMR shifts and relaxation time analysis provide detailed information on the local structure of oxygen ions and the nature of water motion on the surface: the amount of molecularly adsorbed water decreases rapidly with increasing temperature (from room temperature to 150 °C), whereas hydroxyl groups are stable up to 150 °C, and dynamic water molecules are found to instantaneously coordinate to the surface oxygen ions. The applicability of dynamic nuclear polarization for selective detection of surface oxygen species is also compared to conventional NMR with surface selective isotopic-labeling: the optimal method depends on the feasibility of enrichment and the concentration of protons in the sample. These results provide new insight into the interfacial structure of hydrated oxide nanostructures, which is important to improve performance for various applications
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Surface Chemistry Dependence on Aluminum Doping in Ni-rich LiNi 0.8 Co 0.2− y Al y O 2 Cathodes
Abstract: Aluminum is a common dopant across oxide cathodes for improving the bulk and cathode-electrolyte interface (CEI) stability. Aluminum in the bulk is known to enhance structural and thermal stability, yet the exact influence of aluminum at the CEI remains unclear. To address this, we utilized a combination of X-ray photoelectron and absorption spectroscopy to identify aluminum surface environments and extent of transition metal reduction for Ni-rich LiNi0.8Co0.2−yAlyO2 (0%, 5%, or 20% Al) layered oxide cathodes tested at 4.75 V under thermal stress (60 °C). For these tests, we compared the conventional LiPF6 salt with the more thermally stable LiBF4 salt. The CEI layers are inherently different between these two electrolyte salts, particularly for the highest level of Al-doping (20%) where a thicker (thinner) CEI layer is found for LiPF6 (LiBF4). Focusing on the aluminum environment, we reveal the type of surface aluminum species are dependent on the electrolyte salt, as Al-O-F- and Al-F-like species form when using LiPF6 and LiBF4, respectively. In both cases, we find cathode-electrolyte reactions drive the formation of a protective Al-F-like barrier at the CEI in Al-doped oxide cathodes
Polar surface structure of oxide nanocrystals revealed with solid-state NMR spectroscopy
Abstract: Compared to nanomaterials exposing nonpolar facets, polar-faceted nanocrystals often exhibit unexpected and interesting properties. The electrostatic instability arising from the intrinsic dipole moments of polar facets, however, leads to different surface configurations in many cases, making it challenging to extract detailed structural information and develop structure-property relations. The widely used electron microscopy techniques are limited because the volumes sampled may not be representative, and they provide little chemical bonding information with low contrast of light elements. With ceria nanocubes exposing (100) facets as an example, here we show that the polar surface structure of oxide nanocrystals can be investigated by applying 17O and 1H solid-state NMR spectroscopy and dynamic nuclear polarization, combined with DFT calculations. Both CeO4-termination reconstructions and hydroxyls are present for surface polarity compensation and their concentrations can be quantified. These results open up new possibilities for investigating the structure and properties of oxide nanostructures with polar facets
Global survival trends for brain tumors, by histology: analysis of individual records for 556,237 adults diagnosed in 59 countries during 2000–2014 (CONCORD-3)
Background:
Survival is a key metric of the effectiveness of a health system in managing cancer. We set out to provide a comprehensive examination of worldwide variation and trends in survival from brain tumors in adults, by histology.
Methods:
We analyzed individual data for adults (15–99 years) diagnosed with a brain tumor (ICD-O-3 topography code C71) during 2000–2014, regardless of tumor behavior. Data underwent a 3-phase quality control as part of CONCORD-3. We estimated net survival for 11 histology groups, using the unbiased nonparametric Pohar Perme estimator.
Results:
The study included 556,237 adults. In 2010–2014, the global range in age-standardized 5-year net survival for the most common sub-types was broad: in the range 20%–38% for diffuse and anaplastic astrocytoma, from 4% to 17% for glioblastoma, and between 32% and 69% for oligodendroglioma. For patients with glioblastoma, the largest gains in survival occurred between 2000–2004 and 2005–2009. These improvements were more noticeable among adults diagnosed aged 40–70 years than among younger adults.
Conclusions:
To the best of our knowledge, this study provides the largest account to date of global trends in population-based survival for brain tumors by histology in adults. We have highlighted remarkable gains in 5-year survival from glioblastoma since 2005, providing large-scale empirical evidence on the uptake of chemoradiation at population level. Worldwide, survival improvements have been extensive, but some countries still lag behind. Our findings may help clinicians involved in national and international tumor pathway boards to promote initiatives aimed at more extensive implementation of clinical guidelines
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