I15-1-X-ray Pair Distribution Function (XPDF)
I15-Extreme Conditions
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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
Diamond Proposal Number(s):
[21714, 27500]
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.
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Feb 2023
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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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I15-Extreme Conditions
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Diamond Proposal Number(s):
[21714]
Open Access
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.
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May 2021
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I15-Extreme Conditions
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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
Diamond Proposal Number(s):
[21714]
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.
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Jan 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[17691]
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.
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Jan 2021
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I15-Extreme Conditions
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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
Diamond Proposal Number(s):
[21714]
Open Access
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.
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Sep 2020
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I15-Extreme Conditions
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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
Diamond Proposal Number(s):
[19590]
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.
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Aug 2019
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[10355]
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.
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Jul 2019
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I11-High Resolution Powder Diffraction
I15-Extreme Conditions
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Diamond Proposal Number(s):
[14322]
Abstract: Distinctive structure-property relationships are revealed in the relaxor ferroelectric ceramic solid solution, (1-x)K0.5Bi0.5TiO3 - xBiMg0.5Ti0.5O3: 0.02 < x < 0.08. The constructed phase diagram and results of in-situ synchrotron X-ray diffraction provide explanations for temperature and electric field dependent anomalies in dielectric, ferroelectric and electromechanical properties. At room temperature a mixed phase tetragonal and pseudocubic phase field occurs for compositions 0 > x ≤ 0.07. As temperature rises to ≥ 150 °C, the ferroelectric tetragonal relaxor phase changes to a pseudocubic ergodic relaxor phase; this change in length scale of polar order is responsible for an inflection in relative permittivity - temperature plots. The transition is reversed by a sufficient electric field, thereby explaining the constricted form of polarisation-electric field loops measured at >150°C. It is also responsible for a change in slope of the strain-electric field (S-E) plots which are relatively linear in the ferroelectric regime i.e. at temperatures up to 150 °C, giving unipolar strains of 0.11 % at 20 °C and 0.14% at 150 °C (50 kV cm-1 field). The additional contribution from the effect of the field-induced pseudocubic to tetragonal transition, generates strains of ∼ 0.2 % at 185 °C. Unusual for a piezoelectric solid solution, the maximum strains and charge coefficients (d33 =150 pC N-1, 20 °C) do not coincide with a morphotropic or polymorphic phase boundary.
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Feb 2019
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[10355]
Abstract: The structures and functional properties of Na0.5Bi0.5TiO3–xKNbO3 (NBT-xKN)
solid solutions, with x in the range from 0.01 to 0.09, were investigated using a
combination of high-resolution synchrotron X-ray powder diffraction (SXPD) and
ferroelectric property measurements. For low KN contents, an irreversible transformation from cubic to rhombohedral phases was observed after the application
of a high electric field, indicating that the polar nanoregions (PNRs) in the
unpoled state can be transformed into metastable long-range ordered ferroelectric
domains in the poled state. In contrast, the near-cubic phase of the unpoled ceramics was found to be remarkably stable and was retained on cooling to a temperature of 175°C. Upon heating, the field-induced metastable ferroelectric rhombohedral phase transformed back to the nanopolar cubic state at the structural transformation temperature, TST, which was determined as approximately 225°C and 125°C for KN contents of 3% and 5% respectively. For the field-induced rhombohedral phase in the poled specimens, the pseudo-cubic lattice
parameter, ap, exhibited an anomalous reduction while the inter-axial angle
increased towards a value of 90° on heating, resulting in an overall increase in volume. The observed structural changes were correlated with the results of temperature-
dependent dielectric, ferroelectric and depolarization measurements, enabling the construction of a phase diagram to define the stable regions of the different ferroelectric phases as a function of composition and temperature.
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Apr 2017
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