Browsing by Author "Wang, X"
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- ItemAlumina template-assisted electrodeposition of Bi2Te2.7Se0.3 nanowire arrays(Elsevier, 2010-06-01) Li, XL; Cai, KF; Li, H; Yu, DH; Wang, X; Wang, HFBi2Te2.7Se0.3 nanowire arrays have been fabricated by electrodeposition into the pores of an anodic aluminum oxide (AAO) template followed by annealing at 300°C under Ar atmosphere. The as-prepared nanowires were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The nanowires are uniform single crystalline with diameter of ~14 nm. © 2010, Elsevier Ltd.
- ItemCrystallographic and magnetic structure study in SrCoO3-x by high resolution x-ray and neutron powder diffraction(Australian Institute of Physics, 2016-02-04) Chang, FF; Reehuis, M; Hester, JR; Avdeev, M; Xiang, F; Wang, X; Seidel, J; Ulrich, CTransition metal oxides (TMOs) represent a wide set of materials with a broad range of functionalities, including superconductivity, magnetism, and ferroelectricity, which can be tuned by careful choice of parameters such as strain, oxygen content, and applied electric and magnetic fields. This tunability makes TMO’s ideal candidate materials for use in developing novel information and energy technologies and SrCoO3 provides a particularly interesting system for investigation due to its propensity to form oxygen-vacancy-ordered structures as the oxygen content is decreased. The ties between structural and functional properties of this material are obvious as it undergoes simultaneously structural and magnetic phase transitions between two topotactic phases: from a ferromagnetic perovskite phase at SrCoO3.0 to the antiferromagnetic brownmillerite SrCoO2.5. In this study we have determined their crystallographic and magnetic structures of SrCoO2.50, SrCoO2.875, and cubic SrCoO3.00 using high resolution X-ray and neutron powder diffraction from 4 K to 600 K. The correct structure of oxygen-deficient end-member SrCoO2.5 was determined in space group of Imma, instead of Pnma or Ima2 proposed previously, with G-type antiferromagnetic order up to TN = 570 K. In SrCoO2.875, clear peak splitting was observed from (200) in cubic phase to (004) and (440) in tetragonal phase, indicating that the precise structure is I4/mmm with a = b = 10.829(9) Å and c = 7.684(2) Å at 95 K, and the corresponding magnetic structure is ferromagnetic with 1.86(4) μB per formula, in accordance to a spin configuration of cobalt ions with an intermediate spin state of both on Co3+ and on Co4+. The end member SrCoO3.00 possesses a simple cubic crystal structure with a = 3.817(2) Å at 95 K, and ferromagnetic order up to 280 K. The magnetic moment of 1.96(8) μB /Co4+ corresponds to an intermediate spin state of Co4+.
- ItemEvolution of crystallization and magnetic phase transition in Cu1-xZnxFe2O4 studied by neutron powder diffraction(American Physical Society, 2017-03-13) Chang, FF; Avdeev, M; Deng, G; Hester, JR; Wang, X; Ulrich, CHigh resolution and high intensity neutron powder diffraction were applied to study the crystallographic and magnetic phase transition in Cu1-xZnxFe2O4 from 4 K to 750 K. Structural phase transition from cubic to tetragonal phase was observed in CuFe2O4. Ferrimagnetic order was observed in CuFe2O4 and short-range antiferromagnetic scattering was observed below 10 K in cubic ZnFe2O4 which is strongly restrained by addition of slightly amount of Cu2+ ions. Upon doping, ferromagnetic order temperature was gradually reduced from 789 K. Collinear spin setting was observed and no indication of frustration was found even up to doping rate of x = 0.6. Highly frustrated Cu0.04Zn0.96Fe2O4 and ZnFe2O4 behave short-range antiferromagnetic order, induced by the competing between ferromagnetic interaction from first-nearest neighbor and antiferromagnetic interaction from the third-nearest neighbor in tetrahedron formed by Fe ions on B sites. © 2021 American Physical Society
- ItemMagnetic interplay of Mn and Yb sites in YbMn2Si2 – crystal field and electronic structure studies(Australian Institute of Physics, 2018-01-30) Mole, RA; Cortie, DL; Hofmann, M; Wang, JL; Yu, DH; Wang, X; Campbell, SJThe layered RT2X2 series of compounds (R = rare-earth, T = 3d, 4d transition metal, X = Si, Ge) of bct ThCr2Si2–type structure (I4/mmm) is one of the most widely studied systems in condensed matter and materials science [e.g. 1]. Yb-based compounds are of particular interest with their intermediate valence character leading to a wide range of unusual physical and magnetic properties. Following investigation of the magnetic dynamics of YbT2Si2 for non-magnetic T = Ni, Co and Fe [2], we investigated YbMn2Si2 to explore the interaction between the crystal field excitations of Yb atoms and the magnetic ordering of Mn atoms by thermal inelastic neutron scattering [3]. Here we extend these studies of crystal field splittingof YbMn2Si2 to high resolution (800 μeV and a dynamic range of ~14 meV; PELICAN, OPAL) over the temperature range 5-65 K. The results have been analysed in terms of a crystal field model above and below TN2, the temperature at which the collinear antiferromagnetic structure AFil (TN1 = 526(4) K > T > TN2 = 32(2) K) transforms to the low temperature structure below TN2 in which the magnetic cell is doubled along the c-axis [e.g. 3]. Density functional theory with a Hubbard correction (DFT+U method) was used to model YbMn2Si2. A key finding is that the 4f electron Ueffparameter in this compound needs to be negative to stabilise the trivalent state of YbMn2Si2 with the strength of these interactions reflected in contraction of the lattice parameter.
- ItemMolten FLiNaK salt infiltration into degassed nuclear graphite under inert gas pressure(Elsevier B.V., 2015-04-01) He, ZT; Gao, L; Qi, W; Zhang, BL; Wang, X; Song, JL; He, XJ; Zhang, C; Tang, H; Holmes, R; Xia, HH; Zhou, XTInfiltration of molten FLiNaK salt into degassed nuclear graphite samples under inert gas pressure was studied. The weight gain of different grades (2020, 2114, IG-110, NBG-8, G1 and G2) of nuclear graphite during infiltration with different pressures was measured. Molten salt infiltration was compared with mercury intrusion porosimetry where it was found that mercury infiltration was a useful predictor of the threshold pressure and infiltration volume per gram graphite for molten salt infiltration. The distribution and morphology of salt in the graphite were observed by scanning electron microscopy, with very little difference between the molten salt content at the center and edge of samples for samples infiltrated at pressure higher than the threshold pressure. Increased molten salt infiltration with increased pressure resulted from the occupation of smaller pores and full occupation of the larger irregular pores. The similarity of weight gain between molten salt infiltration equilibrated at 20 and 100 h showed 20 h was adequate to obtain equilibrium. © 2014 Elsevier Ltd.
- ItemPolarized neutron reflectometry of epitaxial Fe[0.25 + x] Pt[0.75 – x] layers.(Institute of Electrical and Electronics Engineers (IEEE), 2018-04-27) Mankey, GJ; Causer, GL; Cortie, DL; Wang, X; Zhu, H; Lonescu, M; Klose, FEpitaxial Fe[0.25 + x]Pt[0.75 - x] layers can be either antiferromagnetic (AF) or ferromagnetic (FM) depending on the degree of chemical ordering controlled by the deposition temperature. Our neutron diffraction studies were the first to study AF phase transitions in these thin films [1] and we have also shown using PNR that a mixed AF-FM film is exchange biased with itself [2]. In AF-FM exchange-biased superlattices with a modulated chemical order parameter, PNR shows the magnetization can be modulated through the film thickness with no composition modulations [3]. Our recent results reveal that He+ ion bombardment and annealing can be applied toward controlling magnetic phases in epitaxial Fe [0.25] Pt [0.75] layers [4]. © Copyright 2024 IEEE - All rights reserved, including rights for text and data mining and training of artificial intelligence and similar technologies.
- ItemSignificant reduction in thermal conductivity and improved thermopower of electron‐doped Ba1–xLaxTiO3 with nanostructured rectangular pores(Wiley, 2021-04) Ahmed, AlJ; Cortie, DL; Yun, FF; Rahman, Y; Islam, KN; Bake, A; Konstantinov, K; Hossain, SA; Alowasheeir, A; Yamauchi, Y; Wang, XElectron‐doped BaTiO3 is a less studied n‐type metal oxide thermoelectric material. In this work, the electrical conductivity of BaTiO3 samples has been improved by introducing La to yield an n‐type Ba1–xLaxTiO3 semiconducting material. Density functional theory calculations show that the optimal electron‐doping occurs at x = 0.2, and this is also confirmed experimentally. To improve the thermoelectric properties further, nanostructured cuboidal pores are introduced into the bulk Ba1–xLaxTiO3 using F127 surfactant micelles for a chemical templating process, followed by spark plasma sintering. Interestingly, transmission electron microscopy images and X‐ray powder diffraction analysis confirms that our fabricated samples are cubic BaTiO3 perovskite phase with the nanostructured rectangular‐prism pores of >4 nm. Scanning electron microscopy images show that all the samples have similar grain boundaries and uniform La doping, which suggests that the large reduction in the lattice thermal conductivity in the F127‐treated samples arises primarily from the pore distribution, which introduces anisotropic phonon scattering within the unique nanoarchitecture. The sample with 20 at% La doping and nanopores also shows a thermopower that is doubled compared to the related sample without porosity. Together with the lattice thermal conductivity, enables a significant improvement in figure of merit, zT compared to the other samples. © 2021 Wiley-VCH GmbH.
- ItemTemperature and magnetic field dependent magnetization of nanoparticulate ZnFe2O4 produced by mechanochemical synthesis(Australian Institute of Nuclear Science and Engineering, 2016-02-02) Nesa, F; Wang, X; Wang, JL; Kennedy, SJ; Campbell, SJ; Hoffman, MZnFe2O4 is basically a non-inverted ferrite which is enormously used as ferrofluids, magnetoelectric refrigeration and contrast agent for magnetic resonance imaging. A series of nanoparticulate ZnFe2O4 of average sizes F ~ 9 nm to 90 nm with a range of inversion 0.008 to 0.35 has been produced by mechanochemical synthesis. The blocking temperature of the investigated samples has increased with increasing crystallite size and accordingly behaved as Curie-Weiss paramagnetic materials. The temperature dependent magnetic behavior of these nanoparticulates has been investigated over the temperature range from 5 K to 300 K at a magnetic field of 100 oe. DC magnetization over a magnetic field range of 0 oe to 10000 oe at 5 K, 150 K and 200 K has been observed which interpreted that the samples are superparamagnetic materials. All the samples showed the normal magnetic hysteresis below blocking temperature which also shows that the coercively increases with decreasing inversion 1. The frequency dependent magnetic behaviour of nanoparticulate ZnFe2O4 of 90 nm crystallite size has also been studied over a frequency range of 10 Hz to 10000 Hz which interpreted that with the increase of frequency the magnetization of this sample increased to saturation magnetization for all samples are approximately at 100 K temperature.