Browsing by Author "Xu, D"

Now showing 1 - 8 of 8
  • No Thumbnail Available
    Item
    Antiferromagnetism and metamagnetism in ErFeCuGe4O12
    (Elsevier, 2018-09-15) Xu, D; Avdeev, M; Battle, PD
    Polycrystalline ErFeCuGe4O12 has been prepared in a solid-state reaction. It adopts a tetragonal crystal structure; space group P4/nbm with a = 9.6416(1), c = 4.7532(1) at room temperature. The Er3+ cations are in square-antiprismatic coordination and the Fe3+ and Cu2+ cations are disordered over one six-coordinate site. The magnetic moments of the three cations adopt an antiferromagnetic arrangement on cooling below 20 K in H = 0 kOe. The magnetic structure consists of ferromagnetic (001) sheets with the spin direction in neighbouring sheets alternating between [001] and [00 ̅At 5 K the ordered moment of Er3+ was determined by neutron diffraction to be 7.90(3) µB and the mean moment of Fe3+ and Cu2+ was 2.43(2) µB. The magnetic structure is unchanged in an applied field of 10 kOe but in fields ≥ 20 kOe the compound begins a metamagnetic transition to a ferromagnetic structure with all atomic moments aligned along [001]. © 2018 Elsevier Inc.
  • No Thumbnail Available
    Item
    Experimental and computational study of the magnetic properties of ZrMn2−xCoxGe4O12
    (Royal Society of Chemistry, 2017-05-15) Xu, D; Sale, M; Avdeev, M; Ling, CD; Battle, PD
    Polycrystalline samples in the solid solution ZrMn2−xCoxGe4O12 (x = 0.0, 0.5, 1.0, 1.5 and 2.0) have been prepared using the ceramic method and characterised by a combination of magnetometry, X-ray diffraction and neutron diffraction. They all adopt the space group P4/nbm with a ∼ 9.60, c ∼ 4.82 Å and show long-range magnetic order with transition temperatures, TC, in the range 2 ≤ TC/K ≤ 10. The underlying magnetic structure is the same in each case but the ordered spins lie along [001] when x = 0.0 and in the (001) plane for all other compositions. In all cases the magnetically-ordered phase is a weak ferromagnet although the magnitude of the spontaneous magnetisation and the strength of the coercive field are composition-dependent. The magnetic structure can be rationalized by considering the strengths of the interactions along the distinct M–O–Ge–O–M superexchange pathways in the crystal and the observed magnetic structure is entirely consistent with the predictions of ab initio calculations. © The Royal Society of Chemistry 2017
  • No Thumbnail Available
    Item
    A high-temperature performing and near-zero energy loss lead-free ceramic capacitor
    (Royal Society of Chemistry, 2023-08-21) Li, D; Xu, D; Zhao, W; Avdeev, M; Jing, H; Guo, Y; Zhou, T; Liu, W; Wang, D; Zhou, D
    A pivotal obstacle of obtaining dielectric ceramics with large recoverable energy density (Wrec) and ultrahigh energy efficiency (η) desperately needs to be overcome for the development of advanced energy storage devices for high pulsed power systems, especially via an environment-friendly lead-free method. Here we report a series of lead-free dielectric bulk ceramics for high-temperature energy storage capacitors with near-zero energy loss. Confirmed by aberration-corrected scanning transmission electron microscopy and phase-field simulation, a judiciously designed heterostructure in which rhombohedral and tetragonal polar nanoregions are embedded in a cubic paraelectric matrix was constructed. The combination of the increased breakdown strength and the minimized polarization hysteresis, respectively, based on the heterostructure design and repeated rolling process, contributes to a large Wrec of 10.28 J cm−3 and a record-high η of 97.11%, superior to the reported lead-free bulk ceramics. Based on such structure-induced advantages, the wide-temperature stability (25–200 °C) and high performance (Wrec ∼ 6.35 ± 9.1% J cm−3, η ∼ 94.82% ± 3.4%) of the dielectric ceramics broaden their application in high temperature energy storage systems. This work conspicuously contributes to the development of the next generation high-temperature capacitors and suggests a new paradigm that may stimulate the development of higher-performance energy storage dielectrics. Facebook Twitter LinkedIn YouTube© Royal Society of Chemistry 2024
  • No Thumbnail Available
    Item
    Magnetic properties of CeM1.5M’0.5Ge4O12 (M = Mn, Co; M’ = Ni, Cu)
    (Elsevier, 2018-09-01) Xu, D; Avdeev, M; Battle, PD
    A study of the solid solutions CeM2-xM’xGe4O12 (M = Mn, Co; M’ = Ni, Cu) by X-ray diffraction and magnetometry is described. For M = Co the introduction of Ni and Cu was possible for x ≤ 0.5; for M = Mn attempts to introduce Cu were unsuccessful but CeMn1.5Ni0.5GeO4 was obtained as a single phase. These compositions crystallise in the space group P4/nbm with a ~9.76, c ~4.85 Å. They all order antiferromagnetically with TN< 10 K. The magnetic structures adopted by CeMn1.5Ni1.5Ge4O12 and CeCo1.5Cu0.5Ge4O12 were shown by neutron diffraction to be the same as those adopted by CeMn2Ge4O12 and CeCo2Ge4O12, respectively. The in-field metamagnetic transition of the latter to a weakly ferromagnetic phase was shown to persist in the Cu-doped composition. The available data suggest that the anisotropy associated with the Co2+ cation plays a dominant role in determining the magnetic behaviour of these compounds.© 2018 Elsevier Inc.
  • No Thumbnail Available
    Item
    Magnetic properties of CeMn2–xCoxGe4O12 (0 ≤ x ≤ 2) as a function of temperature and magnetic field
    (American Chemical Society, 2017-02-15) Xu, D; Avdeev, M; Battle, PD; Liu, XQ
    Polycrystalline samples, prepared by a solid-state route, of compositions in the solid solution CeMn2–xCoxGe4O12 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were characterized by X-ray diffraction, neutron diffraction, and magnetometry. They adopt space group P4/nbm with a ≈ 9.78 and c ≈ 4.85 Å and become anti-ferromagnetic (x = 0.0, 1.5, 2.0) or weakly ferromagnetic (x = 0.5, 1.0) at 4.2 ≤ T ≤ 7.6 K. The ordered moments lie along [001] when x = 0.0 and in the (001) plane otherwise. The unit cell doubles along [001] when x = 1.5 and 2.0 order anti-ferromagnetically, but the doubling is lost when a first-order metamagnetic transition to weak ferromagnetism occurs on the application of a 10 kOe magnetic field. The ordered moments at 1.6 K for x = 0.0 and 2.0 are 4.61(2) and 2.58(2) μB, respectively; the corresponding effective moments in the paramagnetic phase are 5.91 and 5.36 μB. © 2017 American Chemical Society
  • No Thumbnail Available
    Item
    Magnetic properties of Ln2CoGe4O12 and LnBCoGe4O12 (Ln = Gd, Tb, Dy, Ho, Er; B = Sc, Lu)
    (Royal Society of Chemistry, 2017-11-03) Xu, D; Avdeev, M; Battle, PD; Ryan, DH
    Polycrystalline samples of Ln2CoGe4O12 (Ln = Gd, Tb, Dy, Ho or Er) and LnBCoGe4O12 (B = Sc or Lu) have been prepared and characterised by a combination of magnetometry, 155Gd Mössbauer spectroscopy and, in the case of Tb2CoGe4O12 and TbScCoGe4O12, neutron diffraction. The holmium- and erbium-containing compositions remain paramagnetic down to 2 K, those containing dysprosium behave as spin glasses and the terbium and gadolinium-containing compounds show long-range magnetic order with transition temperatures below 4 K in all cases. The data can be rationalized qualitatively in terms of the interplay between magnetic anisotropy and crystal field effects. © Royal Society of Chemistry 2021
  • No Thumbnail Available
    Item
    Structural chemistry and magnetic properties of LnMnFeGe4O12 (Ln = Y, Eu, Lu)
    (Elsevier, 2017-10-01) Xu, D; Avdeev, M; Battle, PD; Cadogan, JM; Lamont, H
    Polycrystalline samples of LnMnFeGe4O12 (Ln = Y, Eu, Lu) have been prepared using the ceramic method and characterised by a combination of magnetometry, Mössbauer spectroscopy, X-ray diffraction and neutron diffraction. They all adopt the space group P4/nbm with a ~ 9.670, c ~ 4.81 Å and show long-range antiferromagnetic order with transition temperatures 15 ≤ TN/K ≤ 17. The magnetic structure is the same in each case and consists of an A-type ordering of (001) planes; the ordered spins lie in the (001) plane. Comparison with isostructural compounds leads to the conclusion that subtle structural changes play a greater role than the electronic configuration of the cation in determining the magnetic structure. © 2017 Elsevier Inc.
  • No Thumbnail Available
    Item
    Ultralow loss and high tunability in a non‐perovskite relaxor ferroelectric
    (Wiley, 2022-11-10) Li, R; Xu, D; Avdeev, M; Zhang, L; Chen, XF; Gou, GY; Wang, D; Liu, WF; Zhou, D
    Dielectric ceramics are fundamental for electronic systems, including energy storages, microwave applications, ultrasonics, and sensors. Relaxor ferroelectrics show superb performance among dielectrics due to their high efficiency and energy density by the nature of nanodomains. Here, a novel non‐perovskite relaxor ferroelectric, Bi6Ti5WO22, with ultralow loss, ≈10−3, highly tunable permittivity, ≈2200 at room temperature with 40% tunability and the superparaelectric region at room temperature is presented. The actual crystal structure and the nanodomains of Bi6Ti5WO22 are demonstrat Various‐temperature neutron powder diffraction and in situ high‐resolution transmission‐electron‐microscopy illustrate the twinning effect, subtle structure change and micro‐strain in the material influenced by temperature, manifesting the actual crystal structure of Bi6Ti5WO22. Compared with dielectric loss of BaTiO3‐based dielectric tunable materials, the loss of Bi6Ti5WO22 is more than an order of magnitude lower, which makes it exhibit a figure of merit (≈240), much higher than that of conventional dielectric tunable materials (< 100), endorse the material great potential for direct applications. The present research offers a strategy for discovering novel relaxor ferroelectrics and a highly desirable material for fabricating energy storage capacitors, microwave dielectrics, and ultrasonics. © 1999-2024 John Wiley & Sons, Inc