Browsing by Author "Chen, YH"

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    Insight of a phase compatible surface coating for long-durable Li-rich layered oxide cathode
    (John Wiley & Sons, Inc, 2019-07-28) Hu, SJ; Li, Y; Chen, YH; Peng, JM; Zhou, TF; Pang, WK; Didier, C; Peterson, VK; Wang, HQ; Li, QY; Guo, ZP
    Li-rich layered oxides (LLOs) can deliver almost double the capacity of conventional electrode materials such as LiCoO2 and LiMn2O4; however, voltage fade and capacity degradation are major obstacles to the practical implementation of LLOs in high-energy lithium-ion batteries. Herein, hexagonal La0.8Sr0.2MnO3−y (LSM) is used as a protective and phase-compatible surface layer to stabilize the Li-rich layered Li1.2Ni0.13Co0.13Mn0.54O2 (LM) cathode material. The LSM is Mn O M bonded at the LSM/LM interface and functions by preventing the migration of metal ions in the LM associated with capacity degradation as well as enhancing the electrical transfer and ionic conductivity at the interface. The LSM-coated LM delivers an enhanced reversible capacity of 202 mAh g−1 at 1 C (260 mA g−1) with excellent cycling stability and rate capability (94% capacity retention after 200 cycles and 144 mAh g−1 at 5 C). This work demonstrates that interfacial bonding between coating and bulk material is a successful strategy for the modification of LLO electrodes for the next-generation of high-energy Li-ion batteries. © 2019 Wiley-VCH Verlag GmbH & Co.
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    Neutron spectroscopy of α-Fe2O3 nanorods: direct detection of long-range spin wave excitations
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-18) Cortie, DL; Casillas-Garcia, G; Squires, A; Mole, RA; Wang, XL; Liu, Y; Chen, YH; Yu, DH
    We present time-of-flight neutron spectroscopy data from PELICAN on α-Fe2O3 nanorods with an average length of 300 ± 100 nm and diameter of 60 ± 10 nm. A strong quasi-elastic neutron signal is associated with absorbed water on the nanoparticle powder, which can be removed through heat treatment. After suppressing the QENS signal, it is possible to observe weak spin wave excitations originating from the antiferromagnetic structure of the α-Fe2O3 nanocrystals. The excitations are directly compared with measurements conducted on larger microscale α-Fe2O3 particles at various temperatures to highlight differences in mode intensity and width. The interchanged spectral in tensities in the nanorod are a consequence of a suppressed spin orientation, and this is also evident in the neutron diffraction which demonstates that the weak ferromagnetic phase survives to 1.5 K. The main magnon features are similar in bulk and nanoforms and can be explained using a model Hamiltonian considering interactions up to fourth nearest-neighbors. Complementary scanning transmission electron microscopy data is presented in order to clarify the atomic-scale structure and morphology of the rods. Finally, the implications are discussed for technological devices based on magnonic transmission at surfaces and through nanowires [2]. ©The Authors.
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    Spin-wave propagation in α-Fe2O3 nanorods: the effect of confinement and disorder
    (IOP Publishing, 2019-03-07) Cortie, DL; Casillas-Garcia, G; Squires, A; Mole, RA; Wang, XL; Liu, Y; Chen, YH; Yu, DH
    Spin-wave excitations in α-Fe 2 O 3 nanorods were directly detected using time-of-flight inelastic neutron spectroscopy. The dispersive magnon features are compared with those in bulk α-Fe 2 O 3 particles at various temperatures to highlight differences in mode intensity and width. The interchanged spectral intensities in the nanorod are a consequence of a suppressed spin orientation, and this is also evident in the neutron diffraction which demonstates that the weak ferromagnetic phase survives to 1.5 K. Transmission electron microscopy shows that the ellipsoidal particles are single-crystalline with a typical length of 300 ± 100 nm and diameter of 60 ± 10 nm. The main magnon features are similar in bulk and nanoforms and can be explained using a model Hamiltonian based on Samuelson and Shirane's classical theory with exchange constants of J 1 = -1.03 meV, J 2 = -0.28 meV, J 3 = 5.12 meV and J 4 = 4.00 meV. Numerical simulations show that two distinct mechanisms may contribute to the magnon line broadening in the nanorods: a distribution of exchange interactions caused by disorder, and a shortened quasiparticle lifetime caused by the scattering of spin waves at surfaces. © 2019 IOP Publishing Ltd