Browsing by Author "Li, R"

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    Ionic and electronic properties of the topological insulator Bi2Te2Se investigated via β-detected nuclear magnetic relaxation and resonance of Li8
    (American Physical Society, 2019-03-08) McFadden, RML; Chatzichristos, A; Chow, KH; Cortie, DL; Dehn, MH; Fujimoto, D; Hossain, MD; Ji, H; Karner, VL; Kiefl, RF; Levy, CDP; Li, R; McKenzie, I; Morris, GD; Ofer, O; Pearson, MR; Stachura, M; Stachura, RJ; MacFarlane, WA
    We report measurements on the high-temperature ionic and low-temperature electronic properties of the three-dimensional topological insulator Bi2Te2Se using ion-implanted Li8β-detected nuclear magnetic relaxation and resonance. With implantation energies in the range 5-28keV, the probes penetrate beyond the expected range of the topological surface state, but are still within 250nm of the surface. At temperatures above ∼150K, spin-lattice relaxation measurements reveal isolated Li+8 diffusion with an activation energy EA=0.185(8)eV and attempt frequency τ0-1=8±3×1011s-1 for atomic site-to-site hopping. At lower temperature, we find a linear Korringa-type relaxation mechanism with a field-dependent slope and intercept, which is accompanied by an anomalous field dependence to the resonance shift. We suggest that these may be related to a strong contribution from orbital currents or the magnetic freeze-out of charge carriers in this heavily compensated semiconductor, but that conventional theories are unable to account for the extent of the field dependence. Conventional NMR of the stable host nuclei may help elucidate their origin. ©2019 American Physical Society.
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    Local metallic and structural properties of the strongly correlated metal LaNiO3 using 8Li β–NMR
    (American Physical Society, 2019-10-07) Karner, VL; Chatzichristos, A; Cortie, DL; Dehn, MH; Foyevtsov, O; Foyevtsova, K; Fujimoto, D; Kiefl, RF; Levy, CDP; Li, R; McFadden, RML; Morris, GD; Pearson, MR; Stachura, M; Ticknor, JO; Cristiani, G; Logvenov, G; Wrobel, F; Keimer, B; Zhang, J; Mitchell, JF; MacFarlane, WA
    We report β-detected NMR of ion-implanted Li8 in a single crystal and thin film of the strongly correlated metal LaNiO3. Spin-lattice relaxation measurements reveal two distinct local environments, both metallic as evident from T-linear Korringa 1/T1 below 200K with slopes comparable to other metals. A small approximately temperature-independent Knight shift of ∼74ppm is observed, yielding a normalized Korringa product characteristic of substantial antiferromagnetic correlations. We find no evidence for a magnetic transition from 4 to 310K. The similarity of these features in the two very different samples indicates that they are intrinsic and unrelated to dilute oxygen vacancies. We attribute the two environments to two distinct but similar crystallographic Li8 sites and not to any form of phase inhomogeneity, but this is inconsistent with the conventional rhombohedral structure of LaNiO3, and also cannot be simply explained by the common alternative orthorhombic or monoclinic distortions. ©2024 American Physical Society.
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    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