ANSTO :: Browsing by Author "Lu, T"

Browsing by Author "Lu, T"

Now showing 1 - 14 of 14

Collective nonlinear electric polarization via defect-driven local symmetry breaking
(Royal Society of Chemistry, 2019-05-17) Dong, W; Cortie, DL; Lu, T; Sun, QB; Narayanan, N; Hu, WB; Jacob, L; Li, Q; Yu, DH; Chen, H; Chen, AP; Wei, XY; Wang, G; Humphrey, MG; Frankcombe, TJ; Liu, Y
In this work, we report the defect-mediated, abnormal non-linear polarization behavior observed in centrosymmetric rutile TiO2 where less than 1 at% of sterically mismatched Mg2+ ions are introduced to create ferroelectric-like polarization hysteresis loops. It is found that the Image ID:c9mh00516a-t2.gif defect cluster produces a dipole moment exceeding 6 Debye, with a rotatable component. Such a polarization is further enhanced by the displacement of neighboring Ti4+ ions. The coupling between such defect-driven symmetry-breaking regions generates a collective nonlinear electrical polarization state that persists to high temperatures. More importantly, an observation of abnormal bias shift of polarization hysteresis suggests an antiparallel alignment of certain dipoles frozen relative to the external poling electric field, which is associated with oxygen vacancy hopping. This result challenges the long-standing notion of parallel alignment of dipoles with the external electric field in ferroelectrics. This work also reveals an unexpected new form of non-linear dielectric polarization (non-ferroelectricity) in solid-state materials. © Royal Society of Chemistry 2024
Critical role of the coupling between the octahedral rotation and a-site ionic displacements in PbZrO3-based antiferroelectric materials investigated by in situ neutron diffraction
(American Physical Society, 2017-12-21) Lu, T; Studer, AJ; Yu, DH; Withers, RL; Feng, Y; Chen, H; Islam, SS; Xu, Z; Liu, Y
This in situ neutron-diffraction study on antiferroelectric (AFE) Pb0.99(Nb0.02Zr0.65Sn0.28Ti0.05)O3 polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated with octahedral rotation and A-site ionic displacements. The temperature-induced phase transition indicates that the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and decoupled in the high-temperature FE phase. However, both temperature and E-field-induced phase transitions between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral rotation and A-site ionic displacements in stabilizing the AFE structure, which provides not only experimental evidence to support previous theoretical calculations, but also an insight into the design and development of AFE materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the samples’ FE and AFE properties. ©2017 American Physical Society - Open access
Defect structure and property consequence when small Li+ ions meet BaTiO3
(American Physical Society, 2020-08-31) Narayanan, N; Lou, Q; Rawal, A; Lu, T; Liu, Z; Chen, J; Langley, J; Chen, H; Hester, JR; Cox, N; Fuess, H; McIntyre, GJ; Li, G; Yu, DH; Liu, Y
In the present work the longstanding issue of the structure and dynamics of smaller ions in oxides and its impact on the properties was investigated on 7% Li-doped BaTiO3. The investigation combined several techniques, notably neutron powder diffraction (NPD), nuclear magnetic resonance (7Li-NMR), electron paramagnetic resonance (EPR), electron microprobe, electric polarization (EP) measurement, and electronic structure calculations based on density-functional theory (DFT). Electron microprobe confirmed multiple phases, one containing incorporated Li in the BaTiO3 host lattice and another glassy phase which breaks the host lattice due to excessive Li accumulation. While the average structure of Li in BaTiO3 could not be determined by NPD, 7Li-NMR revealed one broad “disordered” and multiple “ordered” peaks. Local structure models with different defect types involving Li+ were modeled and the corresponding chemical shifts (δ) were compared with experimental values. It is found that the closest defect model describing the ordered peaks, is with Ti4+ being replaced by four Li+ ions. The biexponential behavior of the spin-lattice relaxation of the ordered peaks each with a short and a long relaxation discloses the existence of paramagnetic ions. Finally, EPR revealed the existence of the paramagnetic ion Ti3+ as a charge-transfer defect. DFT calculations disclosed local antipolar displacements of Ti ions around both types of defect sites upon insertion of Li+. This is in accordance with the experimental observation of pinching effects of the EP in Li-doped BaTiO3. These studies demonstrate the huge impact of the local structure of the doped smaller/lighter ions on the functional properties of oxides. ©2020 American Physical Society
Defect structure-property correlations in Li doped BaTiO3
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Narayanan, N; Lou, Q; Rawal, A; Lu, T; Liu, Z; Chen, J; Langley, J; Chen, H; Hester, JR; Cox, N; Fuess, H; McIntyre, GJ; Li, G; Yu, DH; Liu, Y; Li, G
In the present work we investigate the important issue of the structure and dynamics of smaller ions in oxides and the resulting impact on its functional properties. For this purpose, we selected a 7% Li-doped BaTiO3. Li is a vital ingredient in novel energy storage technologies such as Li-ion batteries. The smaller Li-ion can influence the structural stability, homogeneity, local environment, and dynamic behavior of the host lattice, affecting and optimizing the dielectric and multiferroic properties of novel polar functional materials [1-2]. However, the Li-ion positions and dynamics in functional materials are not completely understood, controversially discussed and are the subject of extensive ongoing research [3]. Furthermore, sample inhomogeneity due to Li migration to the grain boundary and/or development of multiple phases complicates the elucidation of the structure-property correlations that may lead to incorrect interpretations [4]. The selection of BaTiO3 as the host lattice is due to materials based on this being considered as the alternative to the piezoelectric lead zirconate titanate, citing environmental issues [5]. BaTiO3 also crystallizes in a simple perovskite structure and Li ions can be effectively doped into it at lower doping levels. Very recently, field-dependent electric polarization measurements on BaTiO3 exhibited a polarization–electric field double hysteresis loop upon Li doping [4]. These drastic changes to the electric polarization, related to the doping poses a good test case for the investigation of the Li induced defect structure model and its influence on the functional properties. To elucidate the above structure-property correlations, we combined several techniques, such as neutron powder diffraction electron microprobe associated with the wavelength-dispersive spectroscopy, 7Li nuclear magnetic resonance spectroscopy (NMR), electron paramagnetic resonance (EPR), electric polarization measurement, and theoretical calculations based on density functional theory [6].
Lead-free (Ag,K)NbO3 materials forhigh-performance explosive energy conversion
(Science Advances, 2020-05-20) Liu, Z; Lu, T; Xue, F; Nie, HC; Withers, RL; Studer, AJ; Kremer, F; Narayanan, N; Dong, XL; Yu, DH; Chen, LQ; Liu, Y; Wang, GS
Explosive energy conversion materials with extremely rapid response times have broad and growing applications in energy, medical, defense, and mining areas. Research into the underlying mechanisms and the search for new candidate materials in this field are so limited that environment-unfriendly Pb(Zr,Ti)O3 still dominates after half a century. Here, we report the discovery of a previously undiscovered, lead-free (Ag0.935K0.065)NbO3 material, which possesses a record-high energy storage density of 5.401 J/g, enabling a pulse current ~ 22 A within 1.8 microseconds. It also exhibits excellent temperature stability up to 150°C. Various in situ experimental and theoretical investiga-tions reveal the mechanism underlying this explosive energy conversion can be attributed to a pressure-induced octahedral tilt change from a−a−c+ to a−a−c−/a−a−c+, in accordance with an irreversible pressure-driven ferroelectric-antiferroelectric phase transition. This work provides a high performance alternative to Pb(Zr,Ti)O3 and also guidance for the further development of new materials and devices for explosive energy conversion. Copyright © 2020 The Authors. CC-By 4.0 licence
Lead-free (Ag,K)NbO3materials for high-performance explosive energy conversion
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Liu, Z; Lu, T; Xue, F; Withers, RL; Studer, AJ; Narayanan, N; Dong, XL; Yu, D; Chen, L; Wang, G; Liu, Y
Explosive energy conversion materials with extremely rapid response times have a diverse and growing range of applications in energy, medical, and mining areas. Research into the underlying mechanisms and the search for new candidate materials is so limited that Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 is still the dominant material after half a century. In this work, we report the discovery of a new, lead-free ferroelectric material, (Ag0.935K0.065)NbO3 for explosive energy conversion applications. This material not only possesses a record-high energy storage density of 5.401 J/g, but also exhibits excellent temperature stability (up to a disruptive ferroelectric to ferroelectric phase transition at 150oC) by comparison with Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (which exhibits the ferroelectric to ferroelectric phase transition but at the much lower temperature of 41~70oC). (Ag0.935K0.065)NbO3 enables extremely high power, energy conversion within 1.8 microseconds, generating a pulse with e.g. a current ~ 22 A. Furthermore, pressure-dependent physical characterization, together with transmission electron microscopy, in-situ neutron diffraction analysis and theoretical modelling, reveals the mechanism underlying the observed explosive energy conversion behavior. It is found that the fast release of the stored energy can be attributed to a pressure-induced octahedral tilt change from a-a-c+ to AgNbO3-type a-a-c-/a-a-c+, in accordance with an irreversible pressure driven FE-AFE phase transition. This work provides not only an alternative (with significantly better performance) to the current commercially-employed lead-containing materials, but also provides guidance for the further development of new materials and devices for explosive energy conversion applications. Copyright © 2020 The Authors.
Magnetic structure and spin correlations in magnetoelectric honeycomb Mn4Ta2O9
(American Physical Society, 2018-10-22) Narayanan, N; Senyshyn, A; Mikhailova, D; Faske, T; Lu, T; Liu, Z; Weise, B; Ehrenberg, H; Mole, RA; Hutchison, WD; Fuess, H; McIntyre, GJ; Liu, Y; Yu, DH
We elucidate the magnetic interactions and the role of spin (electron) correlation in determining the ground state of the honeycomb compound Mn4Ta2O9, by neutron powder diffraction, inelastic neutron scattering (INS), specific-heat (CP) measurements, and electronic-structure calculations. The antiferromagnetic long-range order with moments along c occurs at 102 K with strong exchange striction and small anisotropy. It is escribed by the three-dimensional Ising model. Diffuse magnetic scattering has been observed above TN, which is attributed to the two-dimensional spin correlations within the Mn2+ honeycombs. This is confirmed by the calculated exchange constants. INS experiments and spin-wave simulations together with CP measurements reveal two gapped modes on the ab plane, originating from the rotation of the spins away from the easy axis c. The magnetic anisotropy is mainly determined by an electron-correlation-assisted dipole-dipole interaction. This work provides insight into the competing origins of the magnetic anisotropy, which leads to different magnetic ground states in the family of honeycomb compounds. ©2018 American Physical Society
Role of a-site molecular ions dynamics in the polar functionality of perovskite metal-organic framework
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Lu, T; Cortie, DL; Li, Z; Narayanan, N; Liu, Z; Sun, QB; Frankcombe, TJ; McIntyre, GJ; Yu, DH; Liu, Y
Recent studies on organic-inorganic hybrid perovskites (OIHPs) and ferroelectric metal-organic framework perovskites (MOFPs) reveal their superb performance as highly efficient photovoltaics and promising ferroelectrics. This has enabled a new generation of optic electronic-mechanical devices based on green chemistry. However, the ultimate strategies to optimize these polarization-related functionalities are not yet clear, leading to confused reports in the literature. In this work, we investigate a rationally selected series of molecular ions within Mg(HCOO)3– frameworks to form [CH3NH3]Mg(HCOO)3 (MAMOF),[(CH3)2NH2]Mg(HCOO)3 (DMAMOF), and [C(NH2)3]Mg(HCOO)3 (GUAMOF). Single-crystal X-ray diffraction, inelastic neutron spectroscopy and ab initio molecular dynamics are used to achieve detailed structural pictures of three MOFPs. Intriguingly, our study reveals that the alignments of protonated amines are highly dependent on the directional hydrogen bonds that link N-H units to the surrounding MgO6 octahedra. The alignments of different amines and their dynamics are therefore determined by the acceptor O provided by the distortive frameworks. We successfully assigned the alignments of the A-site ions associated with different polar behavior to the dielectric properties for three MOFPs and propose that the configuration of the A-site molecular ions and potential hydrogen bonds are critical to enable the design of polarization-related functionalities in both MOFPs and OIHPs.
Role of a-site molecular ions in the polar functionality of metal–organic framework perovskites
(American Chemical Society (ACS), 2021-12-28) Lu, T; Cortie, DL; Li, ZX; Narayanan, N; Liu, Z; Sun, QB; Frankcombe, TJ; McIntyre, GJ; Yu, D; Liu, Y
Recent studies on organic–inorganic hybrid perovskites (OIHPs) and ferroelectric metal–organic framework perovskites (MOFPs) reveal their superb performance as highly efficient materials for photovoltaics and ferroelectrics. This has enabled the development of a new generation of optic-electronic-mechanical devices based on green chemistry. However, the fundamental understanding of these polarization-related functionalities is not yet clear, which has hindered the progress in further designing and developing materials with expected properties. In this work, we investigate three MOFPs that have the same Mg(HCOO)3– frameworks with different molecular ions: [CH3NH3][Mg(HCOO)3] (MA-MOF), [(CH3)2NH2][Mg(HCOO)3] (DMA-MOF), and [C(NH2)3][Mg(HCOO)3] (GUA-MOF). Single-crystal and powder X-ray diffraction, inelastic neutron spectroscopy, and ab initio molecular dynamics simulations are combined to achieve a detailed description of the three MOFPs’ static and dynamic structures as a function of temperature. Intriguingly, our study reveals that the alignments and motions of the guest molecular ions are highly dependent on the directional hydrogen bonds that link N–H units to the surrounding MgO6 octahedra through the O acceptor from the frameworks. At the same time, the size, dynamic behavior, and alignments of the A-site molecular ions influence the distortive framework structures and their temperature-dependent deformation. Therefore, the mutual interaction between the guest and the framework determines the overall functionalities of the MOFPs. This study indicates that the configuration of the A-site molecular ions and the potential hydrogen bonds are critical to design the polar functionalities in both MOFPs and OIHPs. © 2021 American Chemical Society
Susceptible ferroelectric/antiferroelectric phase transition near the surface of Nb-doped lead zirconate stannate titanate from surface processing
(American Chemical Society, 2016-05-23) Lu, T; Studer, AJ; Cortie, DL; Lau, K; Yu, DH; Feng, Y; Chen, H; Xu, Z; Withers, RL; McIntyre, GJ; Liu, Y
This work systematically investigated the structure and property of the near-surface and bulk regions of Pb0.99(Nb0.02Zr0.73Sn0.21Ti0.04)O3 ceramics using a combination of X-ray and neutron diffraction, piezoresponse force microscopy, and conventional ferroelectric/piezoelectric characterization. It is found that mechanical force can induce an antiferroelectric/ferroelectric phase transition within micrometers of the surface. Such a phase transition is strongly dependent on the processing scenario, leading to differences from the bulk region. This work provides crucial insights into the sensitivity of this class of AFE materials. Clearly, surface processing conditions must be taken into account for both accurate structural determination and practical applications. © 2016 American Chemical Society
Symmetry analysis of the ferroic transitions in the coupled honeycomb system (Fe, Co, Mn)4Ta2O9
(Australian Institute of Physics, 2020-02-04) Narayanan, N; Faske, T; Lu, T; Liu, Z; Brennan, M; Hester, JR; Avdeev, M; Senyshyn, A; Mikhailova, D; Ehrenberg, H; Hutchison, WD; Mole, RA; Fuess, H; McIntyre, GJ; Liu, Y; Yu, DH
Exotic phenomena such as spin liquid, spin-orbital entities, magnetic order induced multiferroicity (type ii) or quantum criticality have recently triggered extensive research on the ground state properties of frustrated magnetic systems. The ground states of these compounds are determined by the coupling of the spin to the orbital, charge and lattice degrees of freedom. One of the extensively investigated lattices is the honeycomb lattice due to the development of the Kitaev model for quantum spin liquids [1-2]. In this work, we are interested in the coupled honeycomb system M4A2O9 (M=Fe, Co and Mn and A=Nb, Ta). All members have two crystallographically distinct M sites, which are in the distorted octahedral oxygen cages. These cages form edge-shared coplanar and corner-shared buckled honeycombs respectively which are interconnected in the perpendicular direction leading to competing exchange paths. The M=Co and Mn members were magnetoelectrics, whereas Fe2Ta2O9 was reported to exhibit both magnetoelectric and (type ii) multiferroic phases depending on the temperature [3-4]. Magnetoelectrics and multiferroics are technically highly relevant with a variety of applications such as MRAMs and field sensors. However, the coupling mechanism is very complicated [5]. Furthermore, due to the group properties of the symmetry analysis methods such as representation analysis and magnetic space groups, the magnetic structure of the Nb counterpart Co4Nb2O9 is controversially discussed. It is therefore apparent that the above discussed diversities of the properties are determined by the magnetic structure and the closely related electronic structure. These can be elucidated by investigating the structure and dynamics of these compounds, which will help to understand the emergence of different ground states and the diverse phase transitions in this family of materials In this work, we systematically investigate the magnetic and electronic structure of the (Fe, Co, Mn)4Ta2O9 system. We combined several different techniques of neutron powder diffraction, inelastic neutron scattering, heat capacity, electronic band structure calculations and spin wave modeling based on linear spin wave theory.
Symmetry-mode analysis for intuitive observation of structure–property relationships in the lead-free antiferroelectric (1− x) AgNbO3–xLiTaO3
(International Union of Crystallography, 2019-06-21) Lu, T; Tian, Y; Studer, AJ; Narayanan, N; Li, Q; Withers, RL; Jin, L; Mendez-Gonzalez, Y; Pelaiz-Barranco, A; Yu, DH; McIntyre, GJ; Xu, Z; Wei, X; Yan, H; Liu, Y
Functional materials are of critical importance to electronic and smart devices. A deep understanding of the structure–property relationship is essential for designing new materials. In this work, instead of utilizing conventional atomic coordinates, a symmetry-mode approach is successfully used to conduct structure refinement of the neutron powder diffraction data of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics. This provides rich structural information that not only clarifies the controversial symmetry assigned to pure AgNbO3 but also explains well the detailed structural evolution of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics, and builds a comprehensive and straightforward relationship between structural distortion and electrical properties. It is concluded that there are four relatively large-amplitude major modes that dominate the distorted Pmc21 structure of pure AgNbO3, namely a Λ3 antiferroelectric mode, a T4+ a−a−c0 octahedral tilting mode, an H2 a0a0c+/a0a0c− octahedral tilting mode and a Γ4− ferroelectric mode. The H2 and Λ3 modes become progressively inactive with increasing x and their destabilization is the driving force behind the composition-driven phase transition between the Pmc21 and R3c phases. This structural variation is consistent with the trend observed in the measured temperature-dependent dielectric properties and polarization–electric field (P-E) hysteresis loops. The mode crystallography applied in this study provides a strategy for optimizing related properties by tuning the amplitudes of the corresponding modes in these novel AgNbO3-based (anti)ferroelectric materials. © International Union of Crystallography - Open Access
The symmetry-mode decomposition for better understanding of the structural evolution presented in polar functional materials
(Society of Crystallographers in Australia and New Zealand, 2017-12-03) Lu, T; Tian, Y; Studer, AJ; Withers, RL; Wei, X; Yu, DH; Liu, Y
The phase and structure evolution of the (1-x)AgNbO3-xLiTaO3 solid solution is investigated by the neutron diffraction, dielectric and ferroelectric measurements. The symmetry-mode decomposition of the distorted AgNbO3 structure defined on the experimental space group, Pmc21 has been conducted. The four main modes, T4+, H2, Λ3 and Γ4-, exhibit large distorted amplitude to stabilise the Pmc21 structure. The mode refinement with referring to the Pmc21 was adopted to (1-x)AgNbO3-xLiTaO3 material system. It is found that with the increasing LiTaO3 concentration, the orthorhombic phase partially transfers to the rhombohedral R3c phase and the fraction of the R3c phase gradually increases. Correspondingly, the mode amplitudes of the H2 and Λ3 drop abruptly. The hidden structural correlation between H2 and Λ3 modes facilitates the understanding of the antiferroelectric nature observed in the AgNbO3. The variation of the main modes rationally bridges the Pmc21 and R3c phases, revealing the underlying phase transition mechanism of these two phases. Additionally, the evolution of the R3c phase fraction and corresponded mode amplitude in both Pmc21 and R3c phases provides a clear picture to explain the additional peak observed in the temperature-dependent dielectric spectra and composition-dependent polarisation-electric field hysteresis loops.
Understanding the unusual response to high pressure in KBe2BO3F2
(Springer Nature, 2017-06-22) Yu, DH; Avdeev, M; Sun, DH; Huston, LQ; Shiell, TB; Sun, QB; Lu, T; Gu, QF; Liu, H; Bradby, JE; Yie, N; Liu, Y; Wang, JY; McIntyre, GJ
Strong anisotropic compression with pressure on the remarkable non-linear optical material KBe2BO3F2 has been observed with the linear compression coefficient along the c axis found to be about 40 times larger than that along the a axis. An unusual non-monotonic pressure response was observed for the a lattice parameter. The derived bulk modulus of 31 ± 1 GPa indicates that KBe2BO3F2 is a very soft oxide material yet with stable structure up to 45 GPa. A combination of high-pressure synchrotron powder X-ray diffraction, high-pressure Raman spectroscopy, and Density Functional Theory calculations points to the mechanism for the unusual pressure response being due to the competition between the K-F bond length and K-F-K bond angle and the coupling between the stretching and twisting vibration modes. This article is licensed under a Creative Commons Attribution 4.0 International License.

Browsing by Author "Lu, T"

Results Per Page

Sort Options