Browsing by Author "Xu, Z"

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    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
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    In-situ neutron diffraction study of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals under uniaxial mechanical stress
    (American Institute of Physics, 2012-04-26) Li, Q; Liu, Y; Luzin, V; Studer, AJ; Wan, YH; Li, ZR; Norén, L; Withers, RL; Xu, Z
    In this paper, we report the phase transition behavior of ternary relaxor ferroelectric single crystals of 0.25Pb(In1/2Nb1/2)O-3-0.44Pb(Mg1/3Nb2/3)O-3-0.31PbTiO(3) subject to a uniaxial mechanical stress up to 400 MPa. The resultant in situ neutron diffraction data are interpreted in terms of the polarization rotation theory and provide direct structural evidence for the stress-induced polarization rotation pathway deduced from studies of macroscopic physical properties under stress. It is suggested that an intermediate, metastable orthorhombic phase is induced above a critical pressure of similar to 75 MPa. This critical stress level appears to be unaffected by sample poling although the ground states (at zero stress) for the poled and unpoled crystals are different. The critical stress level, however, does decrease with increasing temperature. The elastic behavior of the intermediate phases is also studied based on a calculation of the associated lattice strains. (C) 2012 American Institute of Physics.
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    Structural transitions in [001]/[111]-oriented 0.26Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 single crystals probed via neutron diffraction and electrical characterization
    (AIP Publishing LLC, 2013-04-19) Li, Q; Liu, Y; Wang, J; Studer, AJ; Withers, RL; Li, ZR; Xu, Z
    We report changes in the metric symmetry of unpoled and electrically poled single crystals of 0.26Pb(In1/2 Nb 1/2)O3-0.46Pb(Mg1/3 Nb 2/3)O3-0.28PbTiO3, as revealed by neutron diffraction in conjunction with electrical measurements. The unpoled crystals show relaxor characteristics and an average rhombohedral symmetry that persists from ambient temperature up to the Curie temperature of ∼165 °C. Poling along a [111] direction enhances the rhombohedral distortion away from cubic metric symmetry but appears not to induce any monoclinic phases. By contrast, the poled [001]-oriented crystal has orthorhombic (or monoclinic MC ) metric symmetry at 25 °C. An intermediate transition to a metrically tetragonal phase around 120 °C is confirmed for both poled crystals. © 2013, AIP Publishing LLC.
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    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
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    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
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    Temperature dependence of electrical properties and crystal structure of 0.29Pb(In1/2Nb1/2)O-3-0.44Pb(Mg1/3Nb2/3)O-3-0.27PbTiO(3) single crystals
    (Hindawi Publishing Corporation, 2013-10-07) Li, Q; Liu, Y; Studer, AJ; Li, ZR; Withers, RL; Xu, Z
    We characterized the temperature dependent ( ∼ 25–200°C) electromechanical properties and crystal structure of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals using in situ electrical measurement and neutron diffraction techniques. The results show that the poled crystal experiences an addition phase transition around 120°C whereas such a transition is absent in the unpoled crystal. It is also found that the polar order persists above the maximum dielectric permittivity temperature at which the crystal shows a well-defined antiferroelectric behavior. The changes in the electrical properties and underlying crystal structure are discussed in the paper. © 2013, Qian Li et al. This is an open access article distributed under the Creative Commons Attribution Licence