I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[18215]
Abstract: The addition of nano-fillers has been widely proposed as a method to enhance the dielectric properties of high voltage polymeric insulation, though there are mixed reports in the literature. Here the potential of silica nano-particles to extend the time to failure specifically through resistance to electrical tree growth in epoxy resin is determined. The benefit of silane treating the nano-particles before compounding is clearly established with regard to slowing tree growth and subsequent time to failure. The growth of trees in needle-plane samples is measured in the laboratory with loadings of 1, 3 and 5 wt% nano-filler. In all cases the average times to failure are extended, but silane treatment of the nano-particles prior to compounding yields much superior results. The emergence of a pronounced inception time before tree growth is also noted for the higher-filled, silane-treated cases. The average time to failure of silane-treated 5 wt% filled material was 28 times that of the unfilled resin. The improvement in performance between the nanocomposites with untreated and treated fillers is attributed to fewer agglomerations and improved dispersion of the filler in the treated cases. Measurements of Partial Discharge (PD) indicated significant differences in PD patterns during the growth of trees in the treated and untreated cases. This distinction may provide a quality control method for monitoring materials. In particular, long periods in which PDs were not measured were observed in the silane-treated cases. Visual imaging of tree growth in the unfilled material allowed the changing nature of the tree from fine to tree to dark tree to be observed as it grew. Corresponding PD measurements suggest the dark tree is gradually becoming conductive, and that growth of maximum PD measured is dependent on the relative rates of the growth of the tree and its carbonization. X-ray computer tomography identified significant differences in average tree channel diameters (a reduction from 2.8 µm to 2.0 µm for 1 wt% and 3 wt% cases). This implies that in addition to tree length changes, evaporated tree volumes also change and may explain the change in partial discharge characteristics observed.
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Jul 2021
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John
Irvine
,
Jennifer
Rupp
,
Gang
Liu
,
Xiaoxiang
Xu
,
Sossina M
Haile
,
Xin
Qian
,
Alem
Snyder
,
Robert
Freer
,
Dursun
Ekren
,
Stephen
Skinner
,
Ozden
Celikbilek
,
Shigang
Chen
,
Shanwen
Tao
,
Tae Ho
Shin
,
Ryan
O'Hayre
,
Jake
Huang
,
Chuancheng
Duan
,
Meagan
Papac
,
Shuangbin
Li
,
Andrea
Russell
,
Veronica
Celorrio
,
Brian
Hayden
,
Hugo
Nolan
,
Xiubing
Huang
,
Ge
Wang
,
Ian
Metcalfe
,
Dragos
Neagu
,
Susana Garcia
Martin
Open Access
Abstract: Inorganic perovskites exhibit many important physical properties such as ferroelectricity, magnetoresistance and superconductivity as well their importance as Energy Materials. Many of the most important energy materials are inorganic perovskites and find application in batteries, fuel cells, photocatalysts, catalysis, thermoelectrics and solar thermal. In all these applications, perovskite oxides, or their derivatives offer highly competitive performance, often state of the art and so tend to dominate research into energy material. In the following sections, we review these functionalities in turn seeking to facilitate the interchange of ideas between domains. The potential for improvement is explored and we highlight the importance of both detailed modelling and in situ and operando studies in taking these materials forward.
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May 2021
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Abstract: Despite their ubiquitous usage and increasing societal dependence on Li-ion batteries, there remains a lack of detailed empirical evidence of Li intercalation/deintercalation into graphite even though this process dictates the performance, longevity, and safety of the system. Here, we report direct detection and dissociation of specific crystallographic phases in the lithiated graphite, which form through a stepwise staging process. Using operando measurements, LiC18, LiC12, and LiC6 phases are observed via distinct low-frequency Raman features, which are the result of displacement of the graphite lattice by induced local strain. Density functional theory calculations confirm the nature of the Raman-active vibrational modes, to the layer breathing modes (LBMs) of the lithiated graphite. The new findings indicate graphene-like characteristics in the lithiated graphite under the deep charged condition due to the imposed strain by the inserted Li. Moreover, our approach also provides a simple experimental tool to measure induced strain in the graphite structure under full intercalation conditions.
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Apr 2021
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[22198]
Abstract: Solid state batteries have attracted extensive attention, but the lithium penetration through the solid electrolyte remains a critical barrier to commercialisation and is not yet fully understood. In this study, the 3D morphological evolution of cracks with deposited lithium were tracked as they penetrated through the solid electrolyte during repetitive plating. This is achieved by utilising in-situ synchrotron X-ray computed tomography with high spatial and temporal resolutions. Thin-sheet cracks were observed to penetrate the solid electrolyte without immediate short-circuiting of the cell. Changes in their width and volume were quantified. By calculating the volume of deposited lithium, it was found that the lithium was only partially filled in cracks, and its filling ratio quickly dropped from 94.95% after the 1st plating to ca. 20% after the 4th plating. The filling process was revealed through tracking the line profile of grayscale along cracks. It was found that lithium grew much more slowly than cracks, so that the cracks near the cathode side were largely hollow and the cell could continue to operate. The deposited lithium after short circuit was segmented and its distribution was visualised. DVC analysis was applied to map local high stress and strain, which aggregated along cracks and significantly increased at areas where new cracks formed.
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Apr 2021
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[17825]
Open Access
Abstract: Half-Heusler alloys are an important class of thermoelectric materials that combine promising performance with good engineering properties. This manuscript reports a variable temperature synchrotron X-ray diffraction study of several TiNiSn- and VFeSb-based half-Heuslers. A Debye model was found to capture the main trends in thermal expansion and atomic displacement parameters. The linear thermal expansion coefficient α(T) of the TiNiSn based samples was found to be independent of alloying or presence of Cu interstitials with αav = 10.1 × 10-6 K-1 between 400-850 K. The α(T) of VFeSb and TiNiSn are well-matched, but NbFeSb has a much reduced αav = 8.9 × 10-6 K-1, caused by a stiffer lattice structure. This is confirmed by analysis of the Debye temperatures, which indicate significantly larger bond force constants for all atomic sites in NbFeSb. This work also reveals substantial amounts of Fe interstitials in VFeSb, whilst these are absent for NbFeSb. The Fe interstitials are linked to low thermal conductivities, but also reduce the bandgap and lower the onset of thermal bipolar transport.
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Mar 2021
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Open Access
Abstract: CdTe is currently the largest thin-film photovoltaic technology. Non-radiative electron–hole recombination reduces the solar conversion efficiency from an ideal value of 32% to a current champion performance of 22%. The cadmium vacancy (VCd) is a prominent acceptor species in p-type CdTe; however, debate continues regarding its structural and electronic behavior. Using ab initio defect techniques, we calculate a negative-U double-acceptor level for VCd, while reproducing the VCd1– hole–polaron, reconciling theoretical predictions with experimental observations. We find the cadmium vacancy facilitates rapid charge-carrier recombination, reducing maximum power-conversion efficiency by over 5% for untreated CdTe—a consequence of tellurium dimerization, metastable structural arrangements, and anharmonic potential energy surfaces for carrier capture.
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Mar 2021
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[24685]
Open Access
Abstract: This paper presents a diamond gammavoltaic cell – a solid state device which converts gamma radiation into electricity - with a novel design and promising capabilities. Gammavoltaics pose a unique challenge among radiovoltaics due to the highly penetrating nature of gamma rays. Adapting existing radiovoltaic and dosimeter designs by increasing their thickness risks throttling the flowing current, due to an attendant increase in series resistance. The presented design partially decouples this relationship, by creating a low-coverage hydrogen-terminated collection volume around the device, exploiting the transfer doping effect. This paper proves that hydrogen termination is necessary for the gammavoltaism exhibited. Data are then presented from current-voltage curves taken using synchrotron radiation, over the range 50 – 150 keV. A drop in series resistance over the range is discovered, and linked to the transition from the photoelectric effect to Compton scattering. The cell produces an open-circuit voltage VOC = 0.8 V. Its short-circuit current ISC and maximum power Pmax are found to also depend on photon energy, reaching maxima at ∼ 150 keV, where ISC > 10 μA and Pmax > 3 μW, normalised in flux to 2 × 1011 γ.s-1. Groundwork is hence laid for developing this type of cell for micropower applications.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Ashok S.
Menon
,
Seda
Ulusoy
,
Dickson O.
Ojwang
,
Lars
Riekehr
,
Christophe
Didier
,
Vanessa K.
Peterson
,
German
Salazar-Alvarez
,
Peter
Svedlindh
,
Kristina
Edström
,
Cesar Pay
Gomez
,
William R.
Brant
Diamond Proposal Number(s):
[21804]
Open Access
Abstract: Li- and Mn-rich layered oxides show significant promise as electrode materials for future Li-ion batteries. However, an accurate description of its crystallography remains elusive, with both single-phase solid solution and multiphase structures being proposed for high performing materials such as Li1.2Mn0.54Ni0.13Co0.13O2. Herein, we report the synthesis of single- and multiphase variants of this material through sol–gel and solid-state methods, respectively, and demonstrate that its crystallography is a direct consequence of the synthetic route and not necessarily an inherent property of the composition, as previously argued. This was accomplished via complementary techniques that probe the bulk and local structure followed by in situ methods to map the synthetic progression. As the electrochemical performance and anionic redox behavior are often rationalized on the basis of the presumed crystal structure, clarifying the structural ambiguities is an important step toward harnessing its potential as an electrode material.
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Feb 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[23152]
Open Access
Abstract: Tantalum‐doped lithium lanthanum zirconate garnet (Li7‐xLa3Zr2‐xTaxO12, LLZTO) has received interest as a solid electrolyte for solid‐state lithium batteries due to its good electrochemical properties and ionic conductivity. However, the source of discrepancies for reported values of ionic conductivity in nominally or nearly equivalent compositions of LLZTO is not completely clear. Herein, synthesis‐related factors that may contribute to the differences in performance of garnet electrolytes are systematically characterized. The conductivity of samples with composition Li6.4La3Zr1.4Ta0.6O12 prepared by various methods including solid‐state reaction, combustion, and molten salt synthesis are compared. Varying levels of elemental inhomogeneity, comprising a variation in Ta and Zr‐content on the level of individual LLZTO particles, are identified. The elemental inhomogeneity is found to be largely preserved even after high temperature sintering and correlated with reduced ionic conductivity. We show that the various synthesis and processing‐related variables in each of the preparation methods play a role in these compositional variations, and that even LLZTO synthesized via conventional, high‐temperature solid‐state reaction can exhibit substantial variability in local composition. However, by improving reagent mixing and employing LLZTO powder with low agglomeration and small particle size distribution, the compositional uniformity, and hence ionic conductivity, of sintered garnet electrolytes can be improved.
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Feb 2021
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[20757]
Open Access
Abstract: Understanding the kinetics of the crystallization process for organometal halide perovskite formation is critical in determining the crystalline, nanoscale morphology and therefore the electronic properties of the films produced during thin film formation from solution. In this work, in situ grazing incidence small-angle X-ray scattering (GISAXS) and optical microscopy measurements are used to investigate the processes of nucleation and growth of pristine mixed halide perovskite (MAPbI3–xClx) crystalline films deposited by bar coating at 60 °C, with and without additives in the solution. A small amount of 1,8-diiodooctane (DIO) and hydriodic acid (HI) added to MAPbI3–xClx is shown to increase the numbers of nucleation centers promoting heterogeneous nucleation and accelerate and modify the size of nuclei during nucleation and growth. A generalized formation mechanism is derived from the overlapping parameters obtained from real-time GISAXS and optical microscopy, which revealed that during nucleation, perovskite precursors cluster before becoming the nuclei that function as elemental units for subsequent formation of perovskite crystals. Additive-free MAPbI3–xClx follows reaction-controlled growth, in contrast with when DIO and HI are present, and it is highly possible that the growth then follows a hindered diffusion-controlled mechanism. These results provide important details of the crystallization mechanisms occurring and will help to develop greater control over perovskite films produced.
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Feb 2021
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