Browsing by Author "Liu, J"
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- ItemCation order and magnetic behaviour in mixed metal bismuth scheelite Bi3FeMo2O12(International Union of Crystallography, 2021-08-14) Saura-Múzquiz, M; Mullens, BG; Liu, J; Vogt, T; Maynard-Casely, HE; Avdeev, M; Kennedy, BJThe scheelites are a family of compounds with chemical formula ABO4, and a characteristic crystal structure consisting of AO8 dodecahedra and BO4 tetrahedra. This structure is flexible and can accommodate a large variety of cations with a range of atomic radii and valence combinations. Scheelite-type oxides, such as CaWO4, BiVO4 and NaLa(MoO4)2 have been extensively studied due to their diverse range of physical and electronic properties [1]. In particular, Bi3+ containing molybdates have been found to be efficient photocatalysts due to the strong repulsive force of the 6s2 lone pair of Bi3+, resulting in distortion of the BO4 tetrahedra and alteration of the band gap [2, 3]. In 1974 Bi3FeMo2O12 (BFMO) was reported as the first scheelite-type compound containing trivalent cations on the tetrahedral sites [4]. Interestingly, two different polymorphs of BFMO can be isolated by varying the synthesis conditions [5]. The tetragonal scheelitetype polymorph, described by space group I41/a with a = 5.32106(13) Å and c = 11.656(4) Å, can be prepared by a sol-gel route from aqueous solution of the constituent ionic species and has a disordered arrangement of the Fe and Mo cations. When heated above 500 °C, a 2:1 ordering of the Mo and Fe cations occurs, which lowers the symmetry to monoclinic (C2/c). The corresponding superstructure has a tripling of the a axis (a = 16.9110 (3) Å, b = 11.6489(2) Å, c= 5.25630(9) Å, β = 107.1395(11)°). The two structures are illustrated in Figure 1. In the present study, both polymorphs of BFMO were synthesized and their structure and magnetic properties characterized using a combination of powder diffraction, microscopy and magnetometry techniques. In situ neutron powder diffraction (NPD) measurements of the structural evolution of disordered tetragonal BFMO with increasing temperature showed that no amorphization takes place prior to the formation of the ordered monoclinic phase. The lack of a structural break-down, despite the substantial cation movement required in such a transformation, suggests that a certain degree of local cation order exists in the “disordered” tetragonal phase, facilitating the direct conversion to the fully ordered monoclinic structure. Instead of the expected amorphization and recrystallization, the conversion takes place via a 1st order phase transition, with the tetragonal polymorph exhibiting negative thermal expansion prior to its conversion into the monoclinic structure. Zero-field-cooled/field-cooled and field-dependent magnetization curves of the monoclinic structure revealed the existence of a magnetic transition below 15 K. The long-range nature of the low temperature magnetic structure in the monoclinic polymorph was verified by high-resolution NPD data, which revealed the emergence of an incommensurate magnetic structure. There is no evidence for long-range magnetic order in the tetragonal polymorph. This is, to the best of our knowledge, the first study of the phase transition mechanism and magnetic properties of this complex system and represents a milestone in the structural understanding and targeted design of Bi3+ containing molybdates as efficient photocatalysts. © 2021 The Authors
- ItemCrafting the magnonic and spintronic response of BiFeO3 films by epitaxial strain(Nature Publishing Group, 2013-04-28) Sando, D; Agbelele, A; Rahmedov, D; Liu, J; Rovillain, P; Toulouse, C; Infante, IC; Pyatakov, AP; Fusil, S; Jacquet, E; Carrétéro, C; Deranlot, C; Lisenkov, S; Wang, D; Le Breton, JM; Cazayous, M; Sacuto, A; Juraszek, J; Zvezdin, AK; Bellaiche, L; Dkhil, B; Barthélémy, A; Bibes, MMultiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property—antiferromagnetism—has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mössbauer and Raman spectroscopies combined with Landau–Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves. © 2013, Nature Publishing Group.
- ItemElectromagnon and phonon excitations in multiferroic TbMnO3(Americal Physical Society, 2012-07-30) Rovillain, P; Liu, J; Cazayous, M; Gallais, Y; Measson, MA; Sakata, H; Sacuto, AWe have performed Raman measurements on a TbMnO3 single crystal under magnetic field along the three crystallographic directions. The flip of the spin spiral plane creates an electromagnon excitation. In addition to the electromagnons induced by the Heisenberg coupling, we have detected the electromagnon created by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified all the vibrational modes of TbMnO3. Their temperature dependencies show that only one phonon observed along the polarization axis is sensitive to the ferroelectric transition. This mode is tied to the Tb3+ ion displacements that contribute to the ferroelectric polarization. © 2012, American Physical Society.
- ItemIn situ neutron diffraction study on layered oxides Na0.5Ni0.25Mn0.75O2(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Liu, J; Didier, C; Sale, M; Sharma, N; Guo, ZP; Peterson, VK; Ling, CDLayered oxides based on first-row transition metals dominate cathode materials for commercial batteries and remain highly interesting as well as challenging in their structural study during electrochemical reactions. Neutron diffraction is a powerful method to obtain periodic structural information complementary to that obtained by X-ray diffraction. Although inferior to X-ray diffraction in signal resolution, neutron diffraction reveals more reliable structural evolution as the whole bulk of materials are fluxed with neutron beam. Na0.5Ni0.25Mn0.75O2 is a potential sodium ion battery cathode due to its high operating voltage 3.2 V vs Na+/Na and high capacity 130 mAh/g. Its stoichiometry is designed to only utilize the redox couple Ni4+/Ni2+ to avoid the unstable redox couple Mn4+/Mn3+. The high voltage phase for this material has been under debate. The fact that sodium-containing layered oxides are highly hydroscopic, especially at low sodium content, makes it hard to study the final phase ex situ. In the work presented here, we have pushed the signal resolution of in situ neutron diffraction to the limit by loading the optimized material mass at the positive side and the corresponding amount of amorphous hard carbon at the negative side of a pouch cell. The result is the first robust proof of the reversible structural evolution from P3, O3 to O3s on charging and back to O3, P3 on discharging. © 2020 The authors.
- ItemLattice and spin excitations in multiferroic h-YbMnO3(American Physical Society, 2012-11-09) Liu, J; Toulouse, C; Rovillain, P; Cazayous, M; Gallais, Y; Measson, MA; Lee, N; Cheong, SW; Sacuto, ALattice and spin excitations have been studied by Raman scattering in hexagonal YbMnO3 single crystals. The temperature dependences of the phonon modes show that the E-2 mode at 256 cm(-1) related to the displacement of Mn and O ions in a-b plane is coupled to the spin order. The A(1) phonon mode at 678 cm(-1) presents a soft mode behavior at the Neel temperature. Connected to the motion of the apical oxygen ions along the c direction, this mode controls directly the Mn-Mn interactions between adjacent Mn planes and the superexchange path. Crystal field and magnon mode excitations have been identified. The temperature investigation of the spin excitations shows that the spin structure is strongly influenced by the Yb-Mn interaction. Under a magnetic field along the c axis, we have investigated the magnetic reordering and its impact on the spin excitations. © 2012, American Physical Society.
- ItemReversible electrochemical lithium cycling in a vanadium(IV)- andnNiobium(V)-based Wadsley–Roth phase(American Chemical Society (ACS), 2023-05-09) Lawrence, EA; Davenport, MA; Devi, R; Cai, Z; Avdeev, M; Belnap, JR; Liu, J; Alnaser, H; Ho, A; Sparks, TD; Gautam, GS; Allred, JM; Ji, HWFast charging remains one of the greatest safety challenges in Li-ion batteries due to Li-dendrite growth occurring on graphite anodes if they are lithiated too quickly. The search for high-rate anodes has highlighted materials in the Wadsley-Roth (WR) shear phase family. The relative abundance of V compared with traditional WR compositions of Nb and W makes V-based phases attractive. However, the high voltage and poor reversibility typically associated with V redox have made V-rich WR phases less studied than Nb- and W-rich phases. Here, we show that a new V-rich Wadsley-Roth phase, V7Nb6O29, achieves excellent rate capability and 80% capacity retention after 228 cycles with a relatively low average voltage of 1.76 V vs Li/Li+ compared with other V-rich WR phases. Single-crystal X-ray diffraction reveals a P4/m space group with repeating 2 × 2 × ∞ and 3 × 3 × ∞ blocks of V4+ and Nb5+ octahedra. Combined neutron pair distribution function analysis, X-ray absorption spectroscopy, and density functional theory calculations show that V redox is the primary source of capacity and that cycling stability is provided by the stable octahedral coordination adopted by V4+ in the material. © American Chemical Society
- ItemSynthesis and characterization of the crystal structure and magnetic properties of the new fluorophosphate LiNaCo[PO4]F(American Chemical Society, 2012-08-02) Ben Yahia, H; Shikano, M; Koike, S; Tatsumi, K; Kobayashi, H; Kawaji, H; Avdeev, M; Miiller, W; Ling, CD; Liu, J; Whangbo, MHThe new compound LiNaCo[PO4]F was synthesized by a solid state reaction route, and its crystal structure was determined by single-crystal X-ray diffraction measurements. The magnetic properties of LiNaCo[PO4]F were characterized by magnetic susceptibility, specific heat, and neutron powder diffraction measurements and also by density functional calculations. LiNaCo[PO4]F crystallizes with orthorhombic symmetry, space group Pnma, with a = 10.9334(6), b = 6.2934(11), c = 11.3556(10) angstrom, and Z = 8. The structure consists of edge-sharing CoO4F2 octahedra forming CoFO3 chains running along the b axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The magnetic susceptibility follows the Curie Weiss behavior above 60 K with theta = -21 K. The specific heat and magnetization measurements show that LiNaCo[PO4]F undergoes a three-dimensional magnetic ordering at T-mag = 10.2(5) K. The neutron powder diffraction measurements at 3 K show that the spins in each CoFO3 chain along the b-direction are ferromagnetically coupled, while these FM chains are antiferromagnetically coupled along the a-direction but have a noncollinear arrangement along the c-direction. The noncollinear spin arrangement implies the presence of spin conflict along the c-direction. The observed magnetic structures are well explained by the spin exchange constants determined from density functional calculations. © 2012, American Chemical Society.
- ItemSynthesis of vertically aligned carbon nanotube arrays on polyhedral Fe/Al2O3 catalysts(Royal Society of Chemistry, 2011-06-14) Liu, J; Yuan, LX; Yang, XS; Elbert, A; Harris, ATPolyhedral Fe/Al(2)O(3) catalysts prepared by an impregnation method were used for the synthesis of vertically aligned carbon nanotube (CNT) arrays from the pyrolysis of ethylene at 800 degrees C. © 2011 Royal Society of Chemistry
- ItemThermal expansion and steam oxidation of uranium mononitride analysed via in situ neutron diffraction(Elsevier B. V., 2023-03) Liu, J; Gasparrini, C; White, JT; Johnson, KD; Lopes, DA; Peterson, VK; Studer, AJ; Griffiths, GJ; Lumpkin, GR; Wenman, MR; Burr, PA; Sooby, ES; Obbard, EGIn situ neutron powder diffraction experiments are applied to physical, kinetic, and microstructural characterization of uranium mononitride as a promising light water reactor fuel material. The temperature-variable coefficient of thermal expansion and isotropic Debye Waller factors are obtained by sequential Rietveld refinement over 499–1873 K. Oxidation of a UN pellet (95.2% density) under flow of 11 mg/min D2O is observed to initiate above 623 K and the rate increases by a factor of approximately 10 from 673 to 773 K, with activation energy 50.6 ± 1.3 kJ/mol; uranium oxide is the only solid corrosion product. Crown Copyright © 2022 Published by Elsevier B.V.
- ItemUnlocking fast and reversible sodium intercalation in NASICON Na4MnV(PO4)3 by fluorine substitution(Elsevier, 2021-11) Hou, J; Hadouchi, M; Sui, L; Liu, J; Tang, M; Kan, WH; Avdeev, M; Zhong, G; Liao, YK; Lai, YH; Chu, YH; Lin, HJ; Chen, CT; Hu, ZW; Huang, YH; Ma, JThe exploitation of high energy and high power densities cathode materials for sodium ion batteries is a challenge. Na-super-ionic-conductor (NASICON) Na4MnV(PO4)3 is one of promising high-performance and low-cost cathode materials, however, still suffers from not reaching the theoretical capacity, low rate capability, and poor cycling stability. In this work, we deploy a novel sodium-deficient NASICON fluorinated phosphate cathode material for sodium ion batteries which demonstrates, notably, high energy and high power densities concomitant with high sodium diffusion kinetics. The enhanced performance of this novel Na3.85⬜0.15MnV(PO3.95F0.05)3 cathode was evidenced by demonstrating a relatively high energy density of ∼380 Wh kg−1 at low rate with much improved rate capability compared to non-doped Na4MnV(PO4)3, and long cycling life over 2000 cycles at high current rates. The structural investigation during battery operation using in situ x-ray diffraction (XRD) reveals bi-phase mechanism with high structural reversibility. The combined XRD and 23Na nuclear magnetic resonance (NMR) analyses demonstrate that the sodium extraction/insertion from Na2 is faster than Na1 site. These findings open promising prospects for unlocking of high energy and high power densities of NASICON phosphate materials by fluorine substitution towards high-performance sodium ion batteries. © 2021 Elsevier B.V.