Browsing by Author "Liu, H"
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- ItemFormation mechanism of black LiTaO3 single crystals through chemical reduction(Wiley-Blackwell, 2011-02-01) Yan, T; Zheng, FF; Yu, Y; Qin, SB; Liu, H; Wang, JY; Yu, DHLithium tantalate (LiTaO3, LT) wafers of different colors were prepared through chemical reduction of regular congruent LT wafers. Samples with different colors corresponding to different annealing temperatures were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and measurements of the Curie temperature and density. It was found that chemical reduction does not influence the basic LT structure. The Ta charge state change due to chemical reduction was found to be the main reason for the formation of black LT wafers.© 2011, Wiley-Blackwell
- ItemLow temperature neutron diffraction on congruent and near stoichiometric LiNbO3(World Scientifice Publishing Company, 2012-08-30) Yao, SH; Sang, YH; Yu, DH; Avdeev, M; Liu, H; Wang, JY; Zhang, NNNeutron powder diffraction has been carried out on a congruent LiNbO(3) sample containing (7)Li isotope (C(7)LN) and a near stoichiometric Mg doped LiNbO3 sample (Mg: NSLN) in the temperature range of 4 K and 90 K. Large anisotropic displacement parameters (ADPs) of the Li ions have shown evidence of large disorder along the c-axis for both samples. The results have shown no evidence for the existence of anomalous structural behavior for both samples at low temperatures, although abnormal structural features at 55 K and 100 K for a LiNbO3 crystal having different Li content as the samples used in the present studies have been observed by Fernandez-Ruiz et al. [Phys. Rev. B 72 (2005) 184108]. © 2012, World Scientific Publishing Co.
- ItemManganese metaphosphate Mn(PO3)2 as a high‐performance negative electrode material for lithium‐ion batteries(Wiley, 2020-06-15) Xia, Q; Naeyaert, PJP; Avdeev, M; Schmid, S; Liu, H; Johannessen, B; Ling, CDWe report a novel negative conversion electrode material, manganese (II) metaphosphate Mn(PO3)2. This compound can be synthesized by a facile solid-state method, and after carbon-coating delivers an attractively high reversible capacity of 477 mAh/g at 0.1 C and 385 mAh/g at 1 C. We investigated the reaction mechanism with a combination of ex situ X-ray absorption spectroscopy, in situ X-ray diffraction, and high-resolution transmission electron microscopy. We observed a direct conversion process by monitoring the first discharge in operando, in which Mn(PO3)2 reacts with Li to give fusiform Mn nanograins a few Ångstroms in width, embedded in a matrix of lithium conducting LiPO3 glass. Due to the fine nanostructures of the conversion products, this conversion reaction is completely reversible. © 1999-2021 John Wiley & Sons, Inc.
- ItemNeutron scattering studies on ionic diffusion behaviors of superionic α-Cu2−δ Se(AIP Publishing, 2022-10-10) Li, L; Liu, H; Avdeev, M; Yu, DH; Danilkin, SA; Wang, MWe present studies on crystal structure and ionic diffusion behaviors of superionic Cu2−δ Se (δ = 0, 0.04, and 0.2) by utilizing neutron powder diffraction and quasi-elastic neutron scattering. In the superionic phase, the structural model with Cu ions occupying the Wyckoff sites of 8c and 32f provides the best description of the structure. As the content of Cu increasing in Cu2−δ Se, the Cu occupancy increases on the 32f site but decreases on the 8c site. Fitting to the quasi-elastic neutron scattering spectra reveals two diffusion modes: the localized diffusion between the 8c and 32f sites and the long-range diffusion between the adjacent 8c sites using the 32f site as a bypass. Between 430 and 650 K, we measured that the compound with more Cu content exhibits a larger long-range diffusion coefficient. Temperature in this range does not affect the long-range diffusion process obviously. Our results suggest the two diffusion modes cooperative and, thus, provide a microscopic understanding of the ionic diffusion of the Cu ions in superionic Cu2−δ Se. © 2024 AIP Publishing LLC
- ItemNickel metaphosphate as a conversion positive electrode for lithium‐ion batteries(Wiley, 2020-06-09) Xia, Q; Avdeev, M; Schmid, S; Liu, H; Johannessen, B; Ling, CDLithium storage schemes based on conversion chemistry have been used in a large variety of negative electrodes achieving capacities 2–3 times higher than graphite. However, to date, relatively few positive electrode examples have been reported. Here, we report a new conversion positive electrode, Ni(PO3)2, and systematic studies on its working and degradation mechanisms. Crystalline Ni(PO3)2 undergoes an electrochemistry-driven amorphization process in the first discharge to form a fine microstructure, consisting of Ni domains ∼2 nm wide that form a percolating electron-conducting network, embedded in a glassy LiPO3 matrix. P does not participate electrochemically, remaining as P5+ in [PO3]− throughout. The electrode does not recrystallise in the following first charge process, remaining amorphous over all subsequent cycles. The low ionicity of the Ni−[PO3] bond and the high Li+ conductivity of the LiPO3 glass lead to high intrinsic electrochemical activity, allowing the micro-sized Ni(PO3)2 to achieve its theoretical capacity of 247 mAh/g. The performance of the Ni(PO3)2 electrode ultimately degrades due to the growth of larger and more isolated Ni grains. While the theoretical capacity of Ni(PO3)2 is itself limited, this study sheds new light on the underlying chemical mechanisms of conversion positive electrodes, an important new class of electrode for solid-state batteries. © 2020 Wiley-VCH GmbH
- ItemPhase transition enhanced thermoelectric performance in Cu2Se(Australian Institute of Physics, 2014-02-06) Liu, H; Shi, X; Zhang, W; Chen, L; Danilkin, SAWorldwide efforts to searching for good thermoelectric materials are frequently focusing on normal phases in crystalline semiconductors. The material’s thermoelectric performance is described the parameter of figure of merit, zT, which is around unity around room temperature and above 1.5 at high temperatures. In the Cu2Se with anti-fluorite structure above 400K, Se atoms form a rigid face-centred cubic lattice, while the copper ions are highly disordered or moving around the tetrahedral voids with liquid-like mobility, resulting in an extraordinarily low lattice thermal conductivity, which enables zT up to 1.5 at 1,000K. Here, we report significantly enhanced thermoelectric performance during the phase transitions in Cu2Se and iodine doped Cu2Se. It is showed that the critical electron and phonon scattering greatly improve the thermopower and strongly reduce the thermal coductivity, leading to the improvement in the figure of merit more than 3-7 times compared to the normal phases, and achieving zT value of 2.3 at 400K. This mechanism pave a new way to increase the figure of merit of thermoelectric materials, and expend the utility of thermoelectrics in electronic cooling industry.z
- ItemResults of an international comparison of activity measurements of 68Ge(Elsevier B. V., 2018-04) Cessna, JT; Fitzgerald, R; Zimmerman, BE; Laureano-Pérez, L; Bergeron, DE; van Wyngaardt, WM; Smith, ML; Jackson, TW; Howe, B; da Silva, CJ; Iwahara, A; da Cruz, PAL; Zhang, M; Liu, H; Liang, JC; Fréchou, C; Bobin, C; Cassette, P; Kossert, K; Nähle, O; Marganiec-Gałązka, J; Joseph, L; Ravindra, A; Kulkarni, DN; Yunoki, A; Sato, Y; Lee, KB; Lee, JM; Agusbudiman, A; Dziel, T; Listkowska, A; Tymiński, Z; Sahagia, M; Antohe, A; Ioan, MR; Luca, A; Krivosek, M; Ometakova, J; Javornik, A; Zalesakova, M; García-Toraño Martinez, E; Roteta, M; Mejuto, M; Nedjadi, Y; Juget, F; Yuan, MC; Yeh, CY; Yeltepe, E; Dirican, A; Keightley, JD; Pearce, AKAn international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a 68Ge/68Ga solution. Results for the activity concentration, CA, of 68Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)β-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11) kBq g−1, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6 mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence. An international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a 68Ge/68Ga solution. Results for the activity concentration, CA, of 68Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)β-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11) kBq g−1, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6 mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence. An international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a 68Ge/68Ga solution. Results for the activity concentration, CA, of 68Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)β-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11) kBq g−1, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6 mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence. © 2021 Elsevier Ltd.
- ItemTemperature effects in lattice dynamics of SnSe(International Conference on Neutron Scattering, 2017-07-12) Danilkin, SA; Yu, DH; Deng, GC; Avdeev, M; Kutten, R; Pomjakushina, E; Shi, X; Liu, HTinselenide demonstrates a record high thermoelectric figure of merit [1]. The distinctive feature of this material is very low thermal conductivity directly related to peculiarities of SnSe lattice dynamics. We studied the temperature dependence of the crystal structure, phonon dispersion curves and vibrational density of states (VDOS) of SnSe in the temperature range from 300 to 750 K using neutron scattering instruments at ANSTO. We found that frequencies of longitudinal and transverse phonons in SnSe have remarkably low frequencies, in particular the acoustic phonons propagating along a - axis perpendicular to the b-c layers. The low-energy TOc [100] optic mode polarized along c-axis is highly anharmonic and shows the soft-mode behavior. Measurements of VDOS during heating reveal rather complex modifications of the spectrum showing a significant softening of SnSe phonon frequencies as a function of temperature. The DFT-MD simulation describes softening of phonons at frequencies around 7.5 and 16 meV in agreement with the experiment. By analyzing the displacements of a Sn atom from DFT-MD, the strong anisotropy of thermal parameters was found near the phase transition temperature.
- ItemTemperature effects in lattice dynamics of SnSe(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Danilkin, SA; Yu, DH; Deng, GC; Pomjakushina, E; Liu, H; Kearley, GJTin selenide demonstrates a record high thermoelectric figure of merit. The distinctive feature of this material is very low thermal conductivity directly related to peculiarities of SnSe lattice dynamics. We studied the temperature dependence of the crystal structure, phonon dispersion curves and vibrational density of states (VDOS) of SnSe in temperature range from 300 to 750 K using neutron scattering instruments at ANSTO. We found that frequencies of longitudinal and transverse acoustic phonons in SnSe have remarkably low frequencies, in particular the TA [100] phonon branch. Another feature of SnSe is the presence of low-frequency optic phonons in close proximity to acoustic branches and softening of TOb [100] mode. Measurements of VDOS during heating reveal rather complex modifications of the spectrum showing a significant softening of phonon groups centred at ~ 7.5 and 16 meV related to displacive Pnma – Cmcm phase transition at 830 K. The high density of low-energy modes along with observed strong phonon damping is probably responsible for the low values of lattice component of thermal conductivity in this material.
- ItemUnderstanding the unusual response to high pressure in KBe2BO3F2(Springer Nature, 2017-06-22) Yu, DH; Avdeev, M; Sun, DH; Huston, LQ; Shiell, TB; Sun, QB; Lu, T; Gu, QF; Liu, H; Bradby, JE; Yie, N; Liu, Y; Wang, JY; McIntyre, GJStrong anisotropic compression with pressure on the remarkable non-linear optical material KBe2BO3F2 has been observed with the linear compression coefficient along the c axis found to be about 40 times larger than that along the a axis. An unusual non-monotonic pressure response was observed for the a lattice parameter. The derived bulk modulus of 31 ± 1 GPa indicates that KBe2BO3F2 is a very soft oxide material yet with stable structure up to 45 GPa. A combination of high-pressure synchrotron powder X-ray diffraction, high-pressure Raman spectroscopy, and Density Functional Theory calculations points to the mechanism for the unusual pressure response being due to the competition between the K-F bond length and K-F-K bond angle and the coupling between the stretching and twisting vibration modes. This article is licensed under a Creative Commons Attribution 4.0 International License.
- ItemX-ray and neutron diffraction studies of flux and hydrothermally grown nonlinear optical material KBe2BO3F2(Royal Society of Chemistry, 2012-01-01) Sang, YH; Yu, DH; Avdeev, M; Piltz, RO; Sharma, N; Ye, N; Liu, H; Wang, JYDeep-UV nonlinear optical material KBe2BO3F2 (KBBF), fabricated by flux and hydrothermal methods, are studied by single crystal and powder X-ray diffraction (XRD) and neutron diffraction (NPD). Based on the single crystal diffraction data, the standard R32 structure is confirmed for flux grown KBBF, while the R $(3) over bar $c structure is identified for the hydrothermally grown KBBF. No clear evidence of hydrogen bonding is found in the crystals by single crystal neutron diffraction. From powder XRD and neutron diffraction, the hydrothermally grown KBBF under investigation is found to be a mixture of two components consisting of 19.8 wt% of the R32 structure and 80.2 wt% of the R $(3) over bar $c structure. No phase changes as a function of temperature up to 775 degrees C are observed for both samples from temperature dependent powder XRD data. However, a large anisotropic thermal expansion of the lattice is shown in the temperature dependent data. © 2012, Royal Society of Chemistry.
- ItemYttrium aluminum garnet nanoparticles with low antisite defects studied with neutron and x-ray diffraction(Academic Press Inc Elsevier Science, 2012-08-01) Sang, YH; Yu, DH; Avdeev, M; Qin, HM; Wang, JY; Liu, H; Lv, YHThe presence of cation antisite defects is considered to be one of the most important factors determining the fluorescence, laser, and scintillation properties of rare earth-doped yttrium aluminum garnet(YAG) materials. However, no direct evidence or systematic investigation of antisite defect evolution as a function of cation composition variation in YAG has been reported in the previous literature. In this paper, we report a combined neutron and X-ray diffraction investigation on cation antisite defects performed on specially synthesized nonstoichiometric yttrium aluminum garnet nanoparticles to try to understand the defect chemistry in the YAG system. No evidence was found for Y(Al,16a), Y(Al.24d) and Al(Y.24C) antisite defects in these specially fabricated samples within the limit of diffraction techniques. The results suggest that YAG materials containing low level or no antisite defects can be achieved through low temperature synthesis process. © 2012, Elsevier Ltd.