Tailoring of unipolar strain in lead-free piezoelectrics using the ceramic/ceramic composite approach

The electric-field-induced strain response mechanism in a polycrystalline ceramic/ceramic composite of relaxor and ferroelectric materials has been studied using in situ high-energy x-ray diffraction. The addition of ferroelectric phase material in the relaxor matrix has produced a system where a small volume fraction behaves independently of the bulk under an applied electric field. Inter- and intra-grain models of the strain mechanism in the composite material consistent with the diffraction data have been proposed. The results show that such ceramic/ceramic composite microstructure has the potential for tailoring properties of future piezoelectric materials over a wider range than is possible in uniform compositions.open1

Thermal Expansion Behavior in TcO2. Towards breaking the Tc-Tc bond.

The structure of TcO2 between 25 and 1000 °C has been determined in-situ using powder diffraction methods and is found to remain monoclinic in space group P21/c. The thermal expansion in TcO2 is highly anisotropic with negative thermal ex-pansion of the b-axis observed above 700 °C. This is the result of an anomalous expansion along the a-axis that is a consequence of weakening of the Tc-Tc bonds.Australian Synchrotron Australian Research Counci

Structure and Magnetism in Sr1-xAxTcO3 Perovskites. The importance of the A-site cation.

The Sr1-xBaxTcO3 (x = 0, 0.1, 0.2) oxides were prepared and their solid-state and magnetic structure studied as a function of the temperature by x-ray and neutron powder diffraction. The refined Tc moments at room temperature and Nèel temperatures for Ba0.1Sr0.9TcO3 and Ba0.2Sr0.8TcO3 were 2.32(14) μβ and 2.11(13) μβ and 714 °C and 702 °C respectively. In contrast to expectations, the Nèel temperature in the series Sr1-xAxTcO3 decreases with increasing Ba content. This observation is consistent with previous experimental measurements for the two series AMO3 (M = Ru, Mn; A = Ca, Sr, Ba) where the maximum magnetic ordering temperature was observed for A = Sr. Taken with these previous results the current work demonstrates the critical role of the A-site cation in the broadening of the π* bandwidth and ultimately the magnetic ordering temperature.Australian Synchrotron Australian Research Counci

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Conductivity and microstructural characterisation of doped Zirconia-Ceria and Lanthanum Gallate electrolytes for the intermediate-temperature, solid oxide fuel cell

Lowering the operating temperature of the high-temperature, solid oxide fuel cell (SOFC) improves both the thermodynamic efficiency and the lifetime of this energy efficient technology. Unfortunately the rate of oxygen-ion transport through the solid electrolyte is temperature dependent, and materials previously employed as electrolytes in the high-temperature SOFC perform poorly at intermediate temperatures. Therefore new oxygen-ion conductors with enhanced ionic conductivity at intermediate temperatures are required. The bulk of the existing literature on high-temperature SOFCs has focussed on zirconia-based binary systems as electrolytes, due to their high ionic conductivity and negligible electronic conductivity. Only select compositions within the zirconia-scandia system have demonstrated acceptable ionic conductivity levels at intermediate temperatures; however unstable phase assemblage and the high economic cost of scandia are clear disadvantages. Ceria-based binary systems have demonstrated improved oxygen-ion conductivity at intermediate temperature compared to many zirconia systems, however significant levels of n-type electronic conductivity are observed at low oxygen partial pressures. Consequently it was thought unlikely that significant increases in ionic conductivity would be found in existing zirconia- and ceria-based binary systems, therefore another approach was required in an attempt to improve the performance of these established fluorite systems. The fluorite systems Zr0.75Ce0.08M0.17O1.92 (M = Nd, Sm, Gd, Dy, Ho, Y, Er, Yb, Sc) were prepared and investigated as possible, intermediate-temperature SOFC electrolytes in an attempt to combine the higher conductivity found in the ceria systems with the low electronic conductivity observed in the zirconia systems. Also it was anticipated that systems containing dopants not previously observed to confer high ionic conductivity in either zirconia- and ceria-based binary systems, might exhibit enhanced ionic conductivity with expansion of the zirconia lattice resulting from the addition of ceria. All the as-fired Zr0.75Ce0.08M0.17O1.92 compositions possessed the face-centred cubic structure and lattice parameter measurements revealed the anticipated unit cell enlargement as the size of the dopant cation increased. No unusual microstructural parameters were identified that could be expected to interfere with the ionic transport properties in the as-fired compositions. The electrical conductivity was found to be influenced by the dopant-ion radius, the presence of ceria, low oxygen partial pressures and, in some compositions, the formation of poorly conducting, ordered-pyrochlore microdomains dispersed amongst the cubic defect-fluorite matrix. In a second approach to the formulation of new oxygen-ion conductors suitable for the intermediate-temperature SOFC, compounds possessing structures other than the fluorite structure were considered. An examination of the literature for oxides having the pyrochlore, scheelite and perovskite structures showed that the Sr+2- and Mg+2-doped LaGaO3 perovskites (LSGM) possessed ionic conductivity equal to the highest conducting, zirconia and ceria binary compounds. Therefore the perovskite systems La0.9Sr0.1Ga(0.8-x)InxMg0.2O2.85 (X = 0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8) (I-LSGM) were prepared and examined, the objective being to favourably influence structural parameters believed responsible for optimal ionic conductivity, namely the unit cell symmetry and volume. It was found that In+3 systematically substituted for Ga+3 on to the B-site of LSGM at least up to the X = 0.4 composition. While In+3 was found to replace the Ga+3 as expected, Mg+2, which occupies the same crystallographic site, was also replaced by In+3. Up to the X = 0.2 composition, at least two trace level secondary phases were observed to form along with the bulk I-LSGM phase. For I-LSGM compositions with X > 0.2, significantly larger concentrations of the secondary phases were identified. Evidence of a strontium-rich, high-temperature liquid phase was observed also near the grain boundaries on as-sintered and thermally etched surfaces in LSGM and I-LSGM compositions. It is believed that the observed, high sintered density in the complex, doped-LaGaO3 systems is due to the formation of this high-temperature liquid phase. Increasing levels of diffuse scatter and superstructure formation were observed in electron diffraction patterns in the I-LSGM bulk phase (up to X = 0.2), indicating a possible decrease in vacancy concentration and reduced, localised unit cell symmetry. The electrical conductivity in the I-LSGM compositions was believed to be influenced by the distortion of the oxygen-ion conduction path, a reduction in vacancy concentration, formation of stronger dopant-vacancy associates at low temperature and the presence of ordered structures. In addition, phase instability, in the form of subtle ordering in specific crystalline planes, was observed to influence the electrical conductivity as a function of time at intermediate temperatures

Potassium-ion intercalation in graphite within a potassium-ion battery examined using in situ X-ray diffraction

Graphite has been widely used as a negative electrode material in lithium-ion batteries, and recently it has attracted attention for its use in potassium-ion batteries. In this study, the first in situ X-ray diffraction characterisation of a K/graphite electrochemical cell is performed. Various graphite intercalation compounds are found, including the stage three KC36 and stage one KC8 compounds, along with the disappearance of the graphite during the potassiation process. These results show new insights on the non-equilibrium states of potassium-ion intercalation into graphite in K/graphite electrochemical cells

Solving Key Challenges in Battery Research Using In Situ Synchrotron and Neutron Techniques

Understanding the electrochemical reaction mechanisms and kinetics in batteries is the key challenge for developing breakthroughs with new or existing electrode materials. X-rays and neutrons are excellent probes for studying atomic structure changes and phase evolution in battery materials during charge and discharge. Synchrotron X-ray powder diffraction (SXPD), with its high angular resolution and beam intensity, allows fast scattering and diffraction data collection to record crystalline structure changes that occur on short time-scales. Neutron powder diffraction (NPD) provides complementary information that is sensitive to different structural details during charge/discharge. More recently X-ray absorption spectroscopy (XAS) has been used to identify the oxidation states of transition metal ions present in new cathode compositions at different stages of battery cycling. Using in-house designed battery cells, electrodes or other cell components can be subjected to conditions designed to mimic their real operating conditions. It is preferable to investigate battery materials in operation to identify any critical intermediate stages during charge/discharge rather than using ex situ methods to analyse dismantled batteries. Examples and combinations of SXPD, XAS, and NPD measurements, which have been used to investigate lithium ion batteries and sodium ion batteries, are described and reviewed in this contribution