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Instruments / Technical Area	Publication Details	Published
I15-1-X-ray Pair Distribution Function (XPDF) I15-Extreme Conditions	Multiple local symmetries result in a common average polar axis in high-strain BiFeO3-based ceramics Ge Wang , Tengfei Hu , Wenxuan Zhu , Zhilun Lu , Annette Kleppe , Maria Diaz Lopez , Antonio Feteira , Derek C. Sinclair , Zhengqian Fu , Houbing Huang , Dawei Wang , Ian M. Reaney Physical Review Letters 130 DOI: 10.1103/PhysRevLett.130.076801 Diamond Proposal Number(s): [21714, 27500] Show Abstract ▼ Abstract: For the first time, the origin of large electrostrain in pseudocubic BiFeO 3 -based ceramics is verified with direct structural evidence backed by appropriate simulations. We employ advanced structural and microstructural characterizations of BiFeO 3 -based ceramics that exhibit large electrostrain ( > 0.4 % ) to reveal the existence of multiple, nanoscale local symmetries, dominantly tetragonal or orthorhombic, which have a common, averaged direction of polarization over larger, meso- or microscale regions. Phase-field simulations confirm the existence of local nanoscale symmetries, thereby providing a new vision for designing high-performance lead-free ceramics for high-strain actuators.	Feb 2023
I15-Extreme Conditions	In situ poling X-ray diffraction studies of lead-free BiFeO3-SrTiO3 ceramics Zhilun Lu , Ge Wang , Linhao Li , Yuhe Huang , Antonio Feteira , Weichao Bao , Annette K. Kleppe , Fangfang Xu , Dawei Wang , Ian M. Reaney Materials Today Physics 71 DOI: 10.1016/j.mtphys.2021.100426 Diamond Proposal Number(s): [21714] Open Access Show Abstract ▼ Abstract: The origin of the large electrostrain in BiFeO3-BaTiO3 (BF-BT) ceramics is controversial and has been attributed to either a field-induced transition to a long-range ferroelectric (FE) state or to multi-symmetry, polar nanoregions within a pseudocubic matrix whose vectors approximately align with the direction of the applied field. The (1-x)BiFeO3-xSrTiO3 (BF-xST) solid solution is structurally and microstructurally similar to BF-BT and provides a further case study to assess the origin of electrostrain. In BF-xST, electrostrain is optimised at x = 0.4 (0.15%) which zero field, room temperature full-pattern X-ray diffraction (XRD) Rietveld refinement and scanning/transmission electron microscopy suggest is composed of 15% rhombohedral (R) cores, surrounded by 85% pseudocubic (PC) shells. In-situ poling synchrotron XRD revealed that all peaks remained singlet and exhibited no change in full width half maximum up to 100 kV cm-1, confirming the absence of long-range FE order and the retention of short-range polar order, despite the large applied field. Strain anisotropy (calculated from individual peaks) of ε220 > ε111 > ε200 and the associated strain orientation distribution however, indicate the existence of local orthorhombic (O), rhombohedral (R) and tetragonal (T) symmetries. The data therefore imply the existence under poling of multi-symmetry polar nanoregions in BF-0.4ST rather than a long FE phase, supporting the model described by Wang and co-workers (2019) for BF-BT compositions.	May 2021
I15-Extreme Conditions	Ultrahigh energy density in short-range tilted NBT-based lead-free multilayer ceramic capacitors by nanodomain percolation Hongfen Ji , Dawei Wang , Weichao Bao , Zhilun Lu , Ge Wang , Huijing Yang , Ali Mostaed , Linhao Li , Antonio Feteira , Shikuan Sun , Fangfang Xu , Dejun Li , Chao-Jie Ma , Shi-Yu Liu , Ian M. Reaney Energy Storage Materials 12 DOI: 10.1016/j.ensm.2021.01.023 Diamond Proposal Number(s): [21714] Show Abstract ▼ Abstract: Dense pseudocubic 0.62Na0.5Bi0.5TiO3-0.3Sr0.7Bi0.2TiO3-0.08BiMg2/3Nb1/3O3 (NBT-SBT-0.08BMN) ceramics with excellent recoverable energy density, Wrec = 7.5 J/cm3, and conversion efficiency, η = 92%, were synthesized. Large electric breakdown strength was facilitated by electrical homogeneity, high resistivity and large activation energy (1.86 eV). Transmission electron microscopy identified the presence of polar nano-regions (PNRs) in a matrix of short coherence in-phase and antiphase octahedral tilting. Combining polar and tilt order restricted the crystal classes of PNRs to tetragonal, orthorhombic and monoclinic. Using these symmetries, the enhancement of polarization was explained using Landau-Devonshire phenomenology and percolation theory. Octahedral tilting and introduction of larger B-site ions (Mg2+, Nb5+) inhibited long range polar coupling, minimizing strain and maximizing η. Wrec was further improved to 18 J/cm3 (>1000 kV/cm) in multilayers whose properties were stable from 0.01–100 Hz, from 20°C–160°C and up to 106 cycles, attractive for pulsed power applications and power electronics.	Jan 2021
I15-1-X-ray Pair Distribution Function (XPDF)	Thermally-induced local structural transformations in Na0.5Bi0.5TiO3-KNbO3 ceramics Ge Wang , Anton Goetzee-Barral , Zhilun Lu , Dean S. Keeble , David A. Hall Journal Of The European Ceramic Society 35 DOI: 10.1016/j.jeurceramsoc.2021.01.040 Diamond Proposal Number(s): [17691] Show Abstract ▼ Abstract: The local symmetry of (1-x)Na0.5Bi0.5TiO3-xKNbO3 (NBT-xKN, x = 0.01-0.07) ceramics was thoroughly examined using high-energy synchrotron x-ray scattering and analysed using the Pair-Distribution Function (PDF) method. At room temperature, the structure of NBT-xKN (x = 0.01-0.07) ceramics was best refined using monoclinic C1c1 structures within the local-range (r<22 Å) and rhombohedral R3c within medium-range (22 Å 420 °C (above the temperature of the maximum dielectric peak, Tm), as confirmed by in-situ temperature-dependent PDF analysis.	Jan 2021
I15-Extreme Conditions	Mechanism of enhanced energy storage in AgNbO3-based lead-free antiferroelectrics Zhilun Lu , Weichao Bao , Ge Wang , Shikuan Sun , Linhao Li , Jinglei Li , Huijing Yang , Hongfen Ji , Antonio Feteira , Dejun Li , Fangfang Xu , Annette K. Kleppe , Dawei Wang , Shi-Yu Liu , Ian M. Reaney Nano Energy DOI: 10.1016/j.nanoen.2020.105423 Diamond Proposal Number(s): [21714] Open Access Show Abstract ▼ Abstract: The mechanisms underpinning high energy storage in lead-free Ag1-3xNdxTayNb1-yO3 antiferroelectric (AFE) ceramics have been investigated. Rietveld refinements of in-situ synchrotron X-ray data reveal that the structure remains quadrupled and orthorhombic under electric field (E) but adopts a non-centrosymmetric space group, Pmc21, in which the cations exhibit a ferrielectric configuration. Nd and Ta doping both stabilise the AFE structure, thereby increasing the AFE-ferrielectric switching field from 150 to 350 kV cm-1. Domain size and correlation length of AFE/ferrielectric coupling reduce with Nd doping, leading to slimmer hysteresis loops. Pmax is optimised through A-site aliovalent doping which also decreases electrical conductivity, permitting the application of a larger E. These effects combine to enhance energy storage density to give Wrec = 6.5 J cm-3 for Ag0.97Nd0.01Ta0.20Nb0.80O3.	Sep 2020
I15-Extreme Conditions	Origin of the large electrostrain in BiFeO3-BaTiO 3 based lead-free ceramics Ge Wang , Zhongming Fan , Shunsuke Murakami , Zhilun Lu , David A. Hall , Derek C. Sinclair , Antonio Feteira , Xiaoli Tan , Jacob L. Jones , Annette K. Kleppe , Dawei Wang , Ian M. Reaney Journal Of Materials Chemistry A 21 DOI: 10.1039/C9TA07904A Diamond Proposal Number(s): [19590] Show Abstract ▼ Abstract: High electrostrain and breakdown strength (1 − x)BiFeO3-0.3BaTiO3-xNd(Li0.5Nb0.5)O3 (BF-BT-xNLN) ceramics were studied by in situ synchrotron X-ray diffraction (XRD) in combination with Rietveld refinement and conventional transmission electron microscopy. At zero field, compositions transformed from majority ferroelectric rhombohedral to pseudocubic as the NLN concentration increased, with 0.27% strain achieved at 60 kV cm−1 for x = 0.01. The large measured macroscopic strain was commensurate with peak shifting in XRD peak profiles, yielding 0.6% total strain at 150 kV cm−1. Strain anisotropy of ε200 > ε220 > ε111 was observed but despite the large applied field, no peak splitting was detected. We therefore concluded that the large electrostrain is not achieved through a conventional relaxor to field induced long-range ferroelectric transition. Instead, the data supports a model where local polar regions distort in the direction of the applied field within multiple local symmetries (pseudosymmetry) without long range correlation. We proposed that pseudosymmetry is maintained in BF-BT-xNLN even at high field (150 kV cm−1) due to the large ion radii mismatch and competing ionic/covalent bonding between Ba2+ and Bi3+ ions.	Aug 2019
I11-High Resolution Powder Diffraction	Electric field‐induced irreversible relaxor to ferroelectric phase transformations in Na0.5Bi0.5TiO3‐NaNbO3 ceramics Ge Wang , Zhilun Lu , Zhenbo Zhang , Antonio. Feteira , Chiu C. Tang , David Hall Journal Of The American Ceramic Society DOI: 10.1111/jace.16676 Diamond Proposal Number(s): [10355] Show Abstract ▼ Abstract: (1-x)Na0.5Bi0.5TiO3-xNaNbO3 (x=0.02, 0.04, 0.06 and 0.08) ceramics were fabricated by solid state reaction. High-resolution synchrotron x-ray powder diffraction (SXPD) data, coupled with macroscopic electromechanical measurements, reveal the occurrence of an electric field-induced irreversible crystallographic transformation for x=0.02 and 0.04, from a pseudo-cubic non-ergodic relaxor to a rhombohedral or coexisting rhombohedral-tetragonal long range-ordered ferroelectric phase respectively. The highest unipolar electrostrain, corresponding to an effective longitudinal piezoelectric strain coefficient of approximately 340 pm V-1, was obtained for x=0.04; this effect is attributed to enhanced domain switching as a result of the co-existing rhombohedral and tetragonal phases for this composition, which is critical for piezoelectric actuator applications.	Jul 2019

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