Browsing by Author "Xing, XR"

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    Domain wall and interphase boundary motion in a two-phase morphotropic phase boundary ferroelectric: Frequency dispersion and contribution to piezoelectric and dielectric properties
    (American Physical Society, 2012-07-12) Jones, JL; Aksel, E; Tutuncu, G; Usher, TM; Chen, J; Xing, XR; Studer, AJ
    In ferroelectric materials, enhanced dielectric and piezoelectric property coefficients are found in compositions near morphotropic phase boundaries (MPBs). The material response in these compositions may be contributed by enhanced intrinsic piezoelectric distortions or increased interface motion, e.g., contributions from domain wall and interphase boundary motion, though the relative effect of these mechanisms in different materials is not yet well understood. One of the major challenges to developing this understanding is the availability and sensitivity of in situ characterization techniques, particularly during the application of cyclic electric fields of subcoercive or weak amplitude, conditions at which the property coefficients are measured. Here, we use time-resolved neutron diffraction to resolve the subtle electric-field-induced crystallographic strain mechanisms in a prototypical MPB composition, 36%BiScO(3)-64%PbTiO(3), that contains coexisting monoclinic and tetragonal phases. We observe multiple cooperative electromechanical effects including domain wall motion in both the monoclinic and tetragonal phases, interphase boundary motion between the two phases, and electric-field-induced lattice strains. The measured effects span four orders of magnitude in frequency, facilitating the discrimination of intrinsic and extrinsic contributions to properties. Domain wall motion in the monoclinic phase dominates the response, leading to shifts of diffraction peaks as high as 2300 pm/V; these shifts reflect the field-induced changes in average pseudocubic (00h) lattice spacing of the monoclinic phase parallel to the electric field. Domain wall motion in the tetragonal phase is also readily apparent and exhibits a degree of frequency dispersion similar to that measured in both the relative permittivity and piezoelectric coefficients at similar conditions. © 2012, American Physical Society.
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    Neutron diffraction study of unusual magnetic behaviors in the Ho2Fe11Al6 intermetallic compound
    (American Chemical Society, 2019-09-30) Cao, Y; Lin, K; Liu, ZN; Hu, JY; Wang, CW; Avdeev, M; Li, Q; Deng, JX; Chen, J; Zhang, HJ; Xing, XR
    Knowledge of structure–property relationships is fundamental but significant in the exploitation of magnetic materials. Here we report that the high Al substitution for Fe transformed the crystal structure from a hexagonal Ho2Fe17 compound to a rhombohedral Ho2Fe11Al6 compound. Intriguingly, the latter shows unusual evolution of magnetization around 86 and 220 K compared with the former. Integrated investigations of the detailed structure analysis and magnetic performance on the Ho2Fe11Al6 compound demonstrate that the Ho2Fe11Al6 compound possesses a stable rhombohedral structure (R3̅m) from 5 to 430 K with preferred occupation of Al atoms and ferrimagnetic structure in which the magnetic moments of Ho and Fe lie antiparallel in the basal plane below the Curie temperature. The results of the temperature dependence of moments reveal that the disparate rates of change of the moments for Ho and Fe sublattices give rise to unusual evolution of magnetization around 86 and 220 K and then turn to paramagnetic above 280 K. This work provides clear structure and magnetization information on the Ho2Fe11Al6 compound, which may be beneficial to guiding the future development of magnetic materials. © 2019 American Chemical Society
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    Quantified zero thermal expansion in magnetic R2Fe17-based intermetallic compounds (R = rare earth)
    (American Chemical Society, 2023-06-13) Cao, YL; Matsukawa, T; Gibbs, A; Avdeev, M; Wang, CW; Wu, H; Huang, QZ; Ohoyama, K; Ishigaki, T; Zhou, H; Li, Q; Miao, J; Lin, K; Xing, XR
    Zero thermal expansion (ZTE) has been a fascinating task for the past few decades due to its great scientific and practical merits. To realize ZTE, negative thermal expansion is typically employed by chemical substitutions on tuning structure features, which often relies on trial and error. Here, we report on exploring quantification of thermal expansion with magnetic ordering in an intermetallic class of R2Fe17 (R = rare earth), which can accurately determine the ZTE composition using a documented database. It demonstrates that the magnetic ordering of the Fe-sublattice contributes to the thermal expansion anomaly through simultaneous examinations of magnetization and neutron powder diffraction. Alternative elements can be manipulated on a Fe-sublattice to control both the total ordered magnetic moments of the Fe-sublattice and Curie temperature, which tailors the temperature variation of the magnetic contributions on thermal expansion. The current work might point to a future for ZTE high throughput searches, anticipated to benefit applications. © 2023 American Chemical Society
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    Structural distortion and dielectric permittivities of KCoO2-type layered nitrides Ca1–xSrxTiN2
    (American Chemical Society, 2020-07-03) Lu, SL; Wang, YH; Lu, FQ; Feng, J; Lin, K; Xu, DM; Avdeev, M; Liu, LJ; Kuang, XJ; Xing, XR
    Among the KCoO2-type phases, the orthorhombic layered nitride CaTiN2 is a newly reported high dielectric permittivity material (εr ∼ 1300–2500 within 104–106 Hz from 80 to 450 K) while the tetragonal SrTiN2 is reported to display an unintentional metallic conduction property. In this work, a Ca1–xSrxTiN2 solid solution was synthesized, in which the insulating SrTiN2 end member and some Sr-doped CaTiN2 samples were successfully obtained, and therefore, the dielectric properties of the Ca1–xSrxTiN2 solid solution were investigated. The Sr substitution for Ca drove an orthorhombic-to-tetragonal phase transformation in Ca1–xSrxTiN2, which reduced the dielectric permittivity significantly. The tetragonal SrTiN2 displays a much lower dielectric permittivity (εr ∼ 20–70 in 105–106 Hz and 10–300 K) than that of CaTiN2. The comparison on the dielectric permittivities and structures of CaTiN2 and SrTiN2 indicates that the structural distortion arising from the splitting of N planes between Ti layers within the TiN2 pyramidal layers could be a plausible structural origin of the high bulk dielectric permittivity of CaTiN2. © 2020 American Chemical Society
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    Ultrawide temperature range super-invar behavior of R2(Fe, Co)17 materials (R = rare earth)
    (American Physical Society, 2021-07-30) Cao, YL; Lin, KM; Khmelevskyi, S; Avdeev, M; Taddei, KM; Zhang, Q; Huang, QZ; Li, Q; Kato, K; Tang, CC; Gibbs, A; Wang, CW; Deng, JX; Chen, J; Zhang, HJ; Xing, XR
    Super Invar (SIV), i.e., zero thermal expansion of metallic materials underpinned by magnetic ordering, is of great practical merit for a wide range of high precision engineering. However, the relatively narrow temperature window of SIV in most materials restricts its potential applications in many critical fields. Here, we demonstrate the controlled design of thermal expansion in a family of R2(Fe,Co)17 materials (R=rare Earth). We find that adjusting the Fe-Co content tunes the thermal expansion behavior and its optimization leads to a record-wide SIV with good cyclic stability from 3–461 K, almost twice the range of currently known SIV. In situ neutron diffraction, Mössbauer spectra and first-principles calculations reveal the 3d bonding state transition of the Fe-sublattice favors extra lattice stress upon magnetic ordering. On the other hand, Co content induces a dramatic enhancement of the internal molecular field, which can be manipulated to achieve “ultrawide” SIV over broad temperature, composition and magnetic field windows. These findings pave the way for exploiting thermal-expansion-control engineering and related functional materials. © 2021 American Physical Society