. et al. (5 more authors) (2014) A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3. Nature Materials, 13 (1). 31 -35. ISSN 147631 -35. ISSN -1122 https://doi.org/10.1038/NMAT3782 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Introductory paragraphOxide ion conductors find important technical applications in electrochemical devices such as solid oxide fuel cells (SOFCs), oxygen separation membranes and sensors 1-9 . Na 1/2 Bi 1/2 TiO 3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity which is problematic for its piezoand ferroelectric applications 10-15 . Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~ 0.01 S cm -1 at 600 o C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives [10][11][12][13][14][15] . NBT exhibits maximum relative permittivity,  r ~ 3000 at ~ 320 o C (T max ) and possesses a distorted perovskite structure with extensive chemical, cationdisplacement and octahedral tilt disorder. 14 The resulting complex nanodomain structure is well known to facilitate high and temperature stable permittivity behaviour which is suitable for the fabrication of high temperature ceramic capacitors in addition to easy phase switching under the application of a large electric field which creates large strains suitable for actuator applications [10][11][12][13][14][15] . One drawback of NBT for piezoelectric and capacitor applications, however, is its high leakage conductivity 10,11 . The piezoelectric properties and room temperature dc conductivity depend on the nominal starting composition 10,11 , the origin of which has not been resolved. Here we report on the surprising and dramatic sensitivity of the ionic and electronic transport properties of NBT on low levels of A-site nonstoichiometry in the nominal starting composition. We demonstr...

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Pure phase CeO2 nanorods (about 40–50 nm in diameter and 0.3–2 µm in length) were synthesized through a solvothermal synthesis method. The addition of ethylenediamine is critical to obtain CeO2 nanorods. Other experimental conditions, such as the solvent composition, surfactant and the cerium source precursor were of importance in the final product morphology. The reaction temperature and reaction time also had significant influence on the yield of CeO2 nanorods. A possible formation mechanism of CeO2 nanorods was discussed mainly based on the dependences of controlling parameters on the final morphologies. In addition, the optical properties of CeO2 nanorods were investigated. The UV–visible adsorption spectrum and photoluminescence spectrum of the CeO2 nanorods showed unusual red-shift and enhanced light emission, respectively.

Nearly monodisperse flowerlike CeO2 microspheres were synthesized via a simultaneous polymerization-precipitate reaction, metamorphic reconstruction, and mineralization under hydrothermal condition as well as subsequent calcination. The obtained CeO2 microsphere consists of 20-30 nm thick nanosheets as petals. It has an open three-dimensional (3D) porous and hollow structure and possesses high surface area, large pore volume, and marked hydrothermal stability. It can be doped easily after synthesis, and the initial 3D texture is maintained. The controlling factors and a possible formation mechanism are discussed in detail. This novel material can be used as a support for catalysts with various purposes. With CuO loaded on flowerlike CeO2, the catalytic activities and hydrothermal stability of Cu/CeO2 for ethanol stream reforming were examined. At 300 degrees C, the H2 selectivity reached a maximum value of 74.9 mol %, while CO was not detected within the precision of the gas chromatogram. It produced a hydrogen-rich gas mixture in the wide temperature range (300-500 degrees C) and showed excellent hydrothermal stability at high temperature (550 degrees C), which is a good choice for ethanol processors for hydrogen fuel cell applications.

Recently, there has been considerable interest in the perovskite phase Na 0.5 Bi 0.5 TiO 3 (NBT) as a promising lead-free piezoelectric material. Here we report low levels of Na nonstoichiometry (±2 atom % on the A-site) in the nominal starting composition of NBT ceramics can lead to dramatic changes in the magnitude of the bulk (grain) conductivity ( b ) and the conduction mechanism(s). Nominal starting compositions with Na-excess exhibit high levels of oxide-ion conduction with  b ~ 2.2 mScm -1 (at 600 °C) and an activation energy (E a ) < 1 eV whereas those with Na-deficiency are dielectrics based on intrinsic electronic conduction across the band gap with  b ~ 1.6 Scm -1 (at 600 °C) and E a ~ 1.7 eV.Drying of reagents especially Na 2 CO 3 changes the starting stoichiometry slightly due to small amount of adsorbed moisture in the raw materials but influences significantly the electrical properties. This demonstrates the bulk electrical properties of NBT to be highly sensitive to low levels of A-site nonstoichiometry and reveals how to fine-tune the nominal starting composition of NBT ceramics to suppress leakage conductivity for piezoelectric and high temperature capacitor applications.

Active learning—the field of machine learning (ML) dedicated to optimal experiment design—has played a part in science as far back as the 18th century when Laplace used it to guide his discovery of celestial mechanics. In this work, we focus a closed-loop, active learning-driven autonomous system on another major challenge, the discovery of advanced materials against the exceedingly complex synthesis-processes-structure-property landscape. We demonstrate an autonomous materials discovery methodology for functional inorganic compounds which allow scientists to fail smarter, learn faster, and spend less resources in their studies, while simultaneously improving trust in scientific results and machine learning tools. This robot science enables science-over-the-network, reducing the economic impact of scientists being physically separated from their labs. The real-time closed-loop, autonomous system for materials exploration and optimization (CAMEO) is implemented at the synchrotron beamline to accelerate the interconnected tasks of phase mapping and property optimization, with each cycle taking seconds to minutes. We also demonstrate an embodiment of human-machine interaction, where human-in-the-loop is called to play a contributing role within each cycle. This work has resulted in the discovery of a novel epitaxial nanocomposite phase-change memory material.

The structure and thermoelectric (TE) properties of La-doped, A-site-deficient SrTiO 3 (Sr 1−3x/2 La x TiO 3 ) ceramics sintered in air and N 2 /5% H 2 have been investigated. Airsintered ceramics with 0.10 ≤ x < 0.30 appear cubic by X-ray diffraction (XRD) but exhibit superstructure consistent with a tetragonal cell (a 0 a 0 c − ), according to electron diffraction (ED) studies. 0.30 ≤ x < 0.50 have additional short-range A-site vacancy (V A ) ordering, and x ≥ 0.50 are orthorhombic with an a − a − c + tilt system and long-range V A ordering. 0.10 ≤ x ≤ 0.50 reduced in N 2 /5% H 2 are oxygen-deficient and appear cubic in XRD patterns but exhibit superstructure compliant with an a 0 a 0 c − tilt system by ED. For x = 0.50, additional short-range V A order is observed, and x > 0.50 are orthorhombic with an a − a − c + tilt system and long-range V A ordering. x = 0.15 sintered in N 2 /5% H 2 shows the largest dimensionless TE figure-of-merit ZT = 0.41 at 973 K reported for n-type SrTiO 3 -based ceramics, suggesting that the accommodation of La through formation of (V Sr ) coupled with reduction in N 2 /5% H 2 represents a new protocol for the development of oxide-based thermoelectrics.

Structural features of pentagonal Ag nanorods have been investigated by means of transmission electron microscopy (TEM). Cross-section observations directly reveal the remarkable fivefold twinning structure and related defects in this kind of nanomaterial. High-resolution TEM observations in combination with fast-Fourier processing indicate that the well-defined twinning relationship appears on at least two of the five twinning boundaries. Electron-energy-loss spectroscopy analysis on the center regions of the nanorods demonstrates that the Ag-M4,5 peaks shift to lower energy in comparison with results from the Ag crystal.