Browsing by Author "Schmid, S"
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- ItemA (3 + 3)-dimensional “hypercubic” oxide-ionic conductor: type ii bi2o3–nb2o5(ACS Publications, 2013-04-09) Ling, CD; Schmid, S; Blanchard, PER; Petříček, V; McIntyre, GJ; Sharma, N; Maljuk, A; Yaremchenko, AA; Kharton, VV; Gutmann, MJ; Withers, RLThe high-temperature cubic form of bismuth oxide, δ-Bi2O3, is the best intermediate-temperature oxide-ionic conductor known. The most elegant way of stabilizing δ-Bi2O3 to room temperature, while preserving a large part of its conductivity, is by doping with higher valent transition metals to create wide solid-solutions fields with exceedingly rare and complex (3 + 3)-dimensional incommensurately modulated ?hypercubic? structures. These materials remain poorly understood because no such structure has ever been quantitatively solved and refined, due to both the complexity of the problem and a lack of adequate experimental data. We have addressed this by growing a large (centimeter scale) crystal using a novel refluxing floating-zone method, collecting high-quality single-crystal neutron diffraction data, and treating its structure together with X-ray diffraction data within the superspace symmetry formalism. The structure can be understood as an ?inflated? pyrochlore, in which corner-connected NbO6 octahedral chains move smoothly apart to accommodate the solid solution. While some oxide vacancies are ordered into these chains, the rest are distributed throughout a continuous three-dimensional network of wide δ-Bi2O3-like channels, explaining the high oxide-ionic conductivity compared to commensurately modulated phases in the same pseudobinary system. © 2013, American Chemical Society.
- ItemComposition and temperature dependent structural investigation of the perovskite-type sodium-ion solid electrolyte series Na1/2−xLa1/2−xSr2xZrO3(Elsevier, 2021-05-15) Yang, FZT; Peterson, VK; Schmid, SOwing to their vast chemical and structural flexibility, crystalline perovskite-type metal oxides (ABO3) are amongst the most promising solid electrolytes for use in all-solid-state batteries for large scale energy storage applications. The perovskite-type sodium-ion solid electrolyte series Na1/2-xLa1/2-xSr2xZrO3 have the highest reported ionic conductivities, and we re-examine their room temperature crystal structures using X-ray and high-resolution neutron powder diffraction. In contrast to a previous report, four members of the series, x = 1/16, 1/8, 1/6, and 1/4, were found to adopt orthorhombic symmetry with the space group Pbnm. Variable temperature neutron diffraction data (room temperature to 1100 °C) were used to probe temperature-dependent structural changes for the member of the series with the highest reported ionic conductivity (x = 1/6). A phase transition from orthorhombic Pbnm to tetragonal I4/mcm was identified at 800 °C. Crown Copyright © 2021 Published by Elsevier B.V
- ItemCrystallographic characterization of fluorapatite glass-ceramics synthesized from industrial waste(Cambridge University Press, 2017-09-15) Loy, CW; Matori, KA; Zainuddin, N; Whitten, AE; Rehm, C; de Campo, L; Sokolova, AV; Schmid, SA series of phase transformations of a novel fluoroaluminosilicate glass forming a range of fluorapatite glass-ceramics on sintering are reported. The sintering process induces formation of fluorapatite, mullite, and anorthite phases within the amorphous silicate matrices of the glass-ceramics. The fluoroaluminosilicate glass, SiO2–Al2O3–P2O5–CaO–CaF2, is prepared from waste materials, such as rice husk ash, pacific oyster shells, and disposable aluminium cans. The thermally induced crystallographic and microstructure evolution of the fluoroaluminosilicate glass towards the fluorapatite glass-ceramics, with applications in dental and bone restoration, are investigated by powder X-ray diffraction and small-angle neutron-scattering techniques. © Cambridge University Press.
- ItemDefect perovskites in the SrO-ZrO2-Nb2O5 system(Australian Institute of Physics, 2006-02-07) Schmid, S; Elcombe, MM; Rhode, MCompounds that can reversibly intercalate lithium have the potential to be used as cathodes in rechargeable lithium ion batteries. Two characteristics, the availability of interstitial or defect sites for the incorporation of lithium and the presence of reducible cations are found in some defect perovskites. The aim of this study is to synthesise a number of defect perovskites, which might be useful as host materials for Li intercalation, and investigate their structures using X-ray and neutron powder diffraction. The SrxNbO3, 0.7 ≤ x ≤ 1, solid solution having niobium in both oxidation states +IV and +V whenever x < 1, has been reported to adopt the ideal cubic perovskite structure across the whole solid solution field. Despite intensive searching when data were collected on good quality single crystals no additional reflections were detected . This indicates random ordering between strontium and vacancies on the perovskite A sites. Given the vacancies in the structure (particularly at the low strontium end of the solid solution) and the accompanying presence of niobium +V, which can be easily reduced by lithium metal, this solid solution appeared to be an interesting candidate to investigate Liintercalation properties. Given that niobium +IV is not stable at high temperatures in air but rather gets oxidised, previous syntheses of the solid solution were conducted in high vacuum. Substitution of all niobium +IV by zirconium +IV allows syntheses to be carried out in air. Since previous studies have shown that niobium and zirconium are able to occupy positions in a structure at random [2-4], it was expected that a similar solid solution might be formed. Therefore an investigation was undertaken in the SrO-ZrO2-Nb2O5 system to see whether an analogous solid solution is indeed formed, what the extent of the solid solution range is and whether this material has the potential to intercalate Li ions reversibly.
- ItemFeMn3Ge2Sn7O16 : a spin-liquid candidate with a perfectly isotropic 2-D kagomé lattice(Australian Institute of Physics, 2020-02-05) Allison, MC; Wurmehl, S; Büchner, B; Valla, J; Söhnel, T; Avdeev, M; Schmid, S; Ling, CDThe compound Fe4Si2Sn7O16 has a hitherto unique crystal structure, consisting of ionic oxide layers based on edge-sharing FeO6 and Sn4+O6 octahedra alternating with layers of intermetallic character based on FeSn2+6 octahedra, separated by covalent SiO4 tetrahedra. [1,2] The ionic layers contain kagomé lattices of magnetic Fe2+ cations (octahedral crystal field, high-spin [HS] d6, S = 2) with perfect trigonal symmetry; while the intermetallic layers are non-magnetic because the Fe2+ is in the low-spin (S = 0) state. The formula is more correctly written as Fe4Si2Sn7O16 to differentiate the one LS-Fe2+ per formula unit in the intermetallic layer from the three HS-Fe2+ per formula unit in the kagomé oxide layer. Fe4Si2Sn7O16 also has a unique magnetic ground state below a Néel ordering temperature TN = 3.5 K, in which the spins on 2/3 of the Fe2+ sites in the kagomé oxide layers order antiferromagnetically, while 1/3 remain disordered and fluctuating down to at least 0.1 K.  The nature and origin of this unique “striped” partial spin-liquid state is unclear. The fact that it breaks trigonal symmetry, which the more conventional q = 0 or √3×√3 kagomé states would not, raises the possibility that the anisotropic distribution of the 6 unpaired spins on HS-Fe2+ (t2g4eg2) plays a role. To test this possibility, we have now synthesised an isotropic analogue with a kagomé lattice of HS Mn2+ (t2g3eg2), by co-substituting Ge4+ for Si4+ in the bridging/stannite layers to match the lattice dimensions between layers. We found that FeMn3Ge2Sn7O16 has the same “striped” magnetic ground state as Fe4Si2Sn7O16, in the same temperature range, ruling out this explanation. However, the zero-field striped structure is collinear for FeMn3Ge2Sn7O16 vs. non-collinear for Fe4Si2Sn7O16, which may indeed be a consequence of the change in anisotropy on the magnetic kagomé site, and suggests that FeMn3Ge2Sn7O16 is an even more ideal spin-liquid candidate than Fe4Si2Sn7O16. We also found that an external applied magnetic field lifts the degeneracy on the disordered site, giving rise to another ordered magnetic structure never before observed nor predicted on a kagomé lattice.
- ItemGiant magnetoelastic effect at the opening of a spin-gap in Ba3BiIr2O9(American Chemical Society, 2012-01-26) Miiller, W; Avdeev, M; Zhou, Q; Kennedy, BJ; Sharma, N; Kutteh, R; Kearley, GJ; Schmid, S; Knight, KS; Blanchard, PER; Ling, CDAs compared to 3d (first-row) transition metals, the 4d and 5d transition metals have much more diffuse valence orbitals. Quantum cooperative phenomena that arise due to changes in the way these orbitals overlap and interact, such as magnetoelasticity, are correspondingly rare in 4d and 5d compounds. Here, we show that the 6H-perovskite Ba3BiIr2O9, which contains 5d Ir4+ (S = 1/2) dimerized into isolated face-sharing Ir2O9 bioctahedra, exhibits a giant magnetoelastic effect, the largest of any known 5d compound, associated with the opening of a spin-gap at T* = 74 K. The resulting first-order transition is characterized by a remarkable 4% increase in Ir–Ir distance and 1% negative thermal volume expansion. The transition is driven by a dramatic change in the interactions among Ir 5d orbitals, and represents a crossover between two very different, competing, ground states: one that optimizes direct Ir–Ir bonding (at high temperature), and one that optimizes Ir–O–Ir magnetic superexchange (at low temperature). © 2012 American Chemical Society
- ItemIn situ neutron powder diffraction using custom-made lithium-ion batteries(Jove, 2014-011-10) Brant, WR; Schmid, S; Du, GD; Brand, G; Pang, HEA; Peterson, VK; Guo, ZP; Sharma, NLi-ion batteries are widely used in portable electronic devices and are considered as promising candidates for higher-energy applications such as electric vehicles.1,2 However, many challenges, such as energy density and battery lifetimes, need to be overcome before this particular battery technology can be widely implemented in such applications.3 This research is challenging, and we outline a method to address these challenges using in situ NPD to probe the crystal structure of electrodes undergoing electrochemical cycling (charge/discharge) in a battery. NPD data help determine the underlying structural mechanism responsible for a range of electrode properties, and this information can direct the development of better electrodes and batteries. We briefly review six types of battery designs custom-made for NPD experiments and detail the method to construct the ‘roll-over’ cell that we have successfully used on the high-intensity NPD instrument, WOMBAT, at the Australian Nuclear Science and Technology Organisation (ANSTO). The design considerations and materials used for cell construction are discussed in conjunction with aspects of the actual in situ NPD experiment and initial directions are presented on how to analyze such complex in situ data.
- ItemIncommensurate Modulated Structures in the Ta2O5-Al2O3 System(CSIRO Publishing, 2012-01-01) Schmid, S; Fung, VMembers of the (1 - x)Ta2O5 center dot xAl(2)O(3) series were synthesized, and the structures investigated using synchrotron X-ray powder diffraction and neutron powder diffraction data for the first time. Structural models were developed and refined using the Rietveld method and a [3 + 1] dimensional incommensurately modulated composite structure approach with a composition dependent modulation vector q, and superspace group Xmmm(0 beta 0)s00. Displacive atomic modulation functions across the (1 - x)Ta(2)O(5 center dot)xAl(2)O(3) series were found to be very similar, and strongly resemble those for the Ta2O5-WO3 system, in line with the notion that there are structure types in higher dimensional space just as there are in 3D space. Bond valence sum calculations and bond distance plots showed that the introduction of the modulation to the structural model generally led to more favourable bond valence sum values and bond distances. Fourier difference plots were examined, and the occupational modulation of aluminium refined to determine that the aluminium atoms preferentially occupy the octahedral sites. © 2012, CSIRO Publishing.
- 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.
- ItemMicrostructural evolution of dental glass-ionomer cements during setting reaction followed using SANS and USANS(International Conference on Neutron Scattering, 2017-07-12) Loy, CW; Matori, KA; Zainuddin, N; Whitten, AE; Rehm, C; de Campo, L; Schmid, SGlass-ionomer cement (GIC) is a biocompatible material which is clinically used for dental filling. The main challenges for further developing GIC in dental applications are improving the mechanical strength and controlling the setting reaction. During the setting reaction, poly (acrylic acid) attacks the fluoroaluminosilicate glass particles to form a siliceous hydrogel layer, glass core and polyalkenoate matrix in paste form. The siliceous hydrogel layer undergoes dehydration to yield a strong cross-linkage to bind both polymer and glass particles into a cement structure. This study presents the application of small angle neutron scattering (SANS) and ultra small angle neutron scattering (USANS) with contrast variation techniques to study the microstructure evolution of a complex GIC paste during 48 hours of the setting reaction. A few GIC pastes are prepared from medical grade poly (acrylic acid), SiO2–Al2O3–P2O5–Na2O–CaO–CaF2-based fluoroaluminosilicate glasses and a mixture of H2O:D2O solvent following the ISO9917-1:2007 cement preparation method. The combination of SANS (Bilby@ACNS) and USANS (Kookaburra@ACNS) provides microstructure information of GIC paste over the length scale of 1 nm to 10 µm. The microstructure change of each phase in GIC pastes is investigated at different contrast conditions by varying the H2O:D2O ratio for both neutron scattering experiments. The macro- and nano-scale features of the polymer-glass-hydrogel phases in GIC paste during the setting reaction as well as their impact on mechanical strengths are presented in this study.
- ItemMultiple competing magnetic interactions in Na4Ni7(PO4)6(American Chemical Society, 2019-07-22) Xia, Q; Wang, CH; Schmid, S; Avdeev, M; Ling, CDThe low-temperature magnetic behavior and ground state of the candidate sodium-ion battery cathode compound Na4Ni7(PO4)6 have been investigated by physical property measurements and neutron powder diffraction. On cooling, Na4Ni7(PO4)6 undergoes three successive long-range spin ordering transitions to Phase I (below TN = 17 K), Phase II (below TN′ = 9.1 K), and Phase III (below TN″ = 4.6 K) with ordering vectors [0, 1, 1/2], [0, 2/3, 1/2], and [∼0.076, 2/3, 1/2], respectively. All three magnetic phases can be described in terms of ferromagnetic Ni2+ stripes with antiferromagnetic interactions between them. The moment amplitude of all stripes is the same in Phase I but varies in Phase II, while Phase III is an incommensurate variation on Phase II. Phases I and II both feature a crystallographically unique Ni site with no ordered magnetic moment due to geometric frustration; the resolution of which may be the driving force behind the final transition to Phase III. Even among transition-metal phosphates, which typically show complex spin ordering due to competition between superexchange and super-superexchange (through PO4 linkers), Na4Ni7(PO4)6 has one of the richest magnetic phase diagrams explored so far. © 2019 American Chemical Society
- 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 evolution and intermittent disorder in electrochemically lithiated graphite determined using in operando neutron diffraction(American Chemical Society, 2020-03-24) Didier, C; Pang, WK; Guo, ZP; Schmid, S; Peterson, VKSince their commercialization in 1991, lithium-ion batteries (LIBs) have revolutionized our way of life, with LIB pioneers being awarded the 2019 Nobel Prize in Chemistry. Despite the widespread use of LIBs, many LIB applications are not realized due to performance limitations, determined largely by the ability of electrode materials to reversibly host lithium ions. Overcoming such limitations requires knowledge of the fundamental mechanism for reversible ion intercalation in electrode materials. In this work, the still-debated structure of the most common commercial electrode material, graphite, during electrochemical lithiation is revisited using in operando neutron powder diffraction of a commercial 18650 lithium-ion battery. We extract new structural information and present a comprehensive overview of the phase evolution for lithiated graphite. Charge–discharge asymmetry and structural disorder in the lithiation process are observed, particularly surrounding phase transitions, and the phase evolution is found to be kinetically influenced. Notably, we observe pronounced asymmetry over the composition range 0.5 > x > 0.2, in which the stage 2L phase forms on discharge (delithiation) but not charge (lithiation), likely as a result of the slow formation of the stage 2L phase and the closeness of the stage 2L and stage 2 phase potentials. We reconcile our measurements of this transition with a stage 2L stacking disorder model containing an intergrown stage 2 and 2L phase. We resolve debate surrounding the intercalation mechanism in the stage 3L and stage 4L phase region, observing stage-specific reflections that support a first-order phase transition over the 0.2 > x > 0.04 range, in agreement with minor changes in the slope of the stacking axis length, despite relatively unchanging 00l reflection broadening. Our data support the previously proposed /ABA/ACA/ stacking for the stage 3L phase and an /ABAB/BABA/ stacking sequence of the stage 4L phase alongside experimentally derived atomic parameters. Finally, at low lithium content 0 < x < 0.04, we find an apparently homogeneous modification of the structure during both charge and discharge. Understanding the phase evolution and mechanism of structural response of graphite to lithiation under battery working conditions through in operando measurements may provide the information needed for the development of alternative higher performance electrode materials. © 2020 American Chemical Society
- ItemRapid lithium insertion and location of mobile lithium in the defect perovskite Li0.18Sr0.66Ti0.5Nb0.5O3(Wiley-V C H Verlag GMBH, 2012-06-18) Brant, WR; Schmid, S; Kuhn, A; Hester, JR; Avdeev, M; Sale, M; Gu, QFFast and fancy: Lithium that was originally disordered within the structure of the perovskite Li0.18Sr0.66Ti0.5Nb0.5O3 can be induced into ordering within the yellow region of the unit cell by low temperatures and treatment with n-butyl-lithium. The fast kinetics of lithium insertion, in connection with a color change, make this nontoxic, air-stable material a suitable candidate for use in electrochromic systems or lithium-storage batteries. © 2012, Wiley-VCH Verlag GmbH & Co. KGaA
- ItemA simple electrochemical cell for in-situ fundamental structural analysis using synchrotron X-ray powder diffraction(Elsevier Science BV, 2013-12-15) Brant, WR; Schmid, S; Du, GD; Gu, QF; Sharma, NA simple in-situ cell design is formulated based on the various in-situ electrochemical cells developed over the last three decades. The cell is targeted at those researchers who are not necessarily in the field of lithium ion battery research but are interested in synthesising and performing fundamental structural analyses of compounds that cannot be made via any other route. Therefore, this design uses only components that are routinely available and can be machined in-house. The effectiveness of the initial cell design is demonstrated through kinetic analysis of the lithium insertion reaction for the Li0.18Sr0.66Ti0.5Nb0.5O3 defect perovskite using data obtained from hundreds of diffraction patterns. Within the first discharge it has been possible to identify three regions with different rates of crystal lattice expansion. These regions extend from 1.01 to 1.47 V, 1.47-1.58 V and 1.58-2.07 V with rates of crystal lattice expansion determined to be 1.765(6) x 10(-5) angstrom min(-1), 1.44(5) x 10(-5) angstrom min(-1) and 2.47(1) x 10(-5) angstrom min(-1), respectively. These three regions correlate with three distinct regions in the electrochemical profile, between 1.00 and 1.36 V, 1.36-1.55 V and 1.55-1.80 V. © 2013, Elsevier Ltd.
- ItemSmall angle neutron scattering study of a gehlenite-based ceramic fabricated from industrial waste(Trans Tech Publications, 2017-11-13) Loy, CW; Matori, K.A; Zainuddin, N; Whitten, AE; de Campo, L; Nasir, NIM; Pallan, NFB; Zaid, MHM; Alassan, ZN; Schmid, SThis paper presents a small angle neutron scattering (SANS)study of a novel porous gehlenite-based ceramic, synthesised from a homogeneous powder mixture of soda-lime-silicate (SLS)glass,α-alumina, calcite and calcium fluoride via solid-state sintering at 1200 °C. The products of sintering at single temperatures from 600 to 1200 °C are examined by X-ray diffraction (XRD). Sintering of the mixture below1200 °C forms two intermediate phases (Na2CaSi3O8and Ca4Si2O7F2). Nepheline and α-alumina are minor phases in the gehlenite-based ceramic fabricated through sintering at 1200 °C. The microstructure of the gehlenite-based ceramic is investigated using field-emission scanning electron microscopy (FESEM) and SANS at the Australian Centre for Neutron Scattering. This study also evaluated the specific surface area of the gehlenite-based ceramic (~3.0 m2cm–3) from quantitative analysis of SANS data. ©2019 Trans Tech Publications, Switzerland
- ItemSodium uptake in cell construction and subsequent in operando electrode behaviour of Prussian blue analogues, Fe[Fe(CN)6]1−x·yH2O and FeCo(CN)6(Royal Society of Chemistry, 2014-07-23) Pramudita, JC; Schmid, S; Godfrey, T; Whittle, T; Alam, AKMM; Hanley, TL; Brand, HEA; Sharma, NThe development of electrodes for ambient temperature sodium-ion batteries requires the study of new materials and the understanding of how crystal structure influences properties. In this study, we investigate where sodium locates in two Prussian blue analogues, Fe[Fe(CN)6]1-x·yH2O and FeCo(CN)6. The evolution of the sodium site occupancies, lattice and volume is shown during charge-discharge using in situ synchrotron X-ray powder diffraction data. Sodium insertion is found to occur in these electrodes during cell construction and therefore Fe[Fe(CN)6]1-x·yH2O and FeCo(CN)6 can be used as positive electrodes. NazFeFe(CN)6 electrodes feature higher reversible capacities relative to NazFeCo(CN)6 electrodes which can be associated with a combination of structural factors, for example, a major sodium-containing phase, ∼Na0.5FeFe(CN)6 with sodium locating either at the x = y = z = 0.25 or x = y = 0.25 and z = 0.227(11) sites and an electrochemically inactive sodium-free Fe[Fe(CN)6]1-x·yH2O phase. This study demonstrates that key questions about electrode performance and attributes in sodium-ion batteries can be addressed using time-resolved in situ synchrotron X-ray diffraction studies. © 2014 Royal Society of Chemistry Open Access CC Licence
- ItemStriped magnetic ground state of the ideal kagomé lattice compound Fe4Si2Sn7O16(Society of Crystallographers in Australia and New Zealand, 2017-12-03) Ling, CD; Allison, MC; Schmid, S; Avdeev, M; Gardner, JS; Ryan, DH; Soehnel, TWe have used representational symmetry analysis of neutron powder diffraction data to determine the magnetic ground state of Fe4Si2Sn7O16. We recently reported a long-range antiferromagnetic (AFM) Néel ordering transition in this compound at TN = 3.0 K, based on magnetisation measurements . The only magnetic ions present are layers of high-spin Fe2+ (d6, S = 2) arranged on a perfect kagomé lattice (trigonal space group P-3m1). Below TN = 3.0 K, the spins on 2/3 of these magnetic ions order into canted antiferromagnetic chains, separated by the remaining 1/3 which are geometrically frustrated and show no long-range order down to at least T = 0.1 K . Moessbauer spectroscopy shows that there is no static order on the latter 1/3 of the magnetic ions — i.e., they are in a liquid-like rather than a frozen state – down to at least 1.65 K. A heavily Mn-doped sample Fe1.45Mn2.55Si2Sn7O16 has the same ground state. Although the magnetic propagation vector k = (0, ½, ½) breaks hexagonal symmetry, we see no evidence for magnetostriction in the form of a lattice distortion within the resolution of our data. To the best of our knowledge, this type of magnetic order on a kagomé lattice has no precedent experimentally and has not been explicitly predicted theoretically. We will discuss the relationship between our experimental result and a number of theoretical models that predict symmetry-breaking ground states for perfect kagomé lattices.
- ItemStriped magnetic ground state of the kagome lattice in Fe4Si2Sn7O16(American Physical Society, 2017-11-15) Ling, CD; Allison, MC; Schmid, S; Avdeev, M; Gardner, JS; Wang, CW; Ryan, DH; Zbiri, M; Söhnel, TWe have experimentally identified a different magnetic ground state for the kagome lattice, in the perfectly hexagonal Fe2+ (3d6,S=2) compound Fe4Si2Sn7O16. A representational symmetry analysis of neutron diffraction data shows that below TN=3.5 K, the spins on 23 of the magnetic ions order into canted antiferromagnetic chains, separated by the remaining 13 which are geometrically frustrated and show no long-range order down to at least T=0.1 K. Mössbauer spectroscopy confirms that there is no static order on the latter 13 of the magnetic ions—i.e., they are in a liquidlike rather than a frozen state—down to at least 1.65 K. A heavily Mn-doped sample Fe1.45Mn2.55Si2Sn7O16 has the same magnetic structure. Although the propagation vector q=(0,12,12) breaks hexagonal symmetry, we see no evidence for magnetostriction in the form of a lattice distortion within the resolution of our data. We discuss the relationship to partially frustrated magnetic order on the pyrochlore lattice of Gd2Ti2O7, and to theoretical models that predict symmetry breaking ground states for perfect kagome lattices. ©2017 American Physical Society
- ItemStriped magnetic ground state on an ideal S = 2 Kagomé lattice(International Union of Crystallography, 2017) Ling, CD; Allison, MC; Schmid, S; Avdeev, M; Ryan, DH; Soehnel, TWe have used representational symmetry analysis of neutron powder diffraction data to determine the magnetic ground state of Fe4Si2Sn7O16. We recently reported a long-range antiferromagnetic (AFM) Néel ordering transition in this compound at TN = 3.0 K, based on magnetization measurements.  The only magnetic ions present are layers of high-spin Fe2+ (d6, S = 2) arranged on a perfect kagomé lattice (trigonal space group P-3m1).  Below TN = 3.0 K, the spins on 2/3 of these magnetic ions order into canted antiferromagnetic chains, separated by the remaining 1/3 which are geometrically frustrated and show no long-range ordered down to at least T = 0.1 K. Moessbauer spectroscopy shows that there is no static order on the latter 1/3 of the magnetic ions – i.e., they are in a liquid-like rather than a frozen state – down to at least 1.65 K. A heavily Mn-doped sample Fe1.45Mn2.55Si2Sn7O16 has the same ground state. Although the magnetic propagation vector k = (0, 1/2, 1/2) breaks hexagonal symmetry, we see no evidence for magnetostriction in the form of a lattice distortion within the resolution of our data. To the best of our knowledge, this type of magnetic order on a kagomé lattice has no precedent experimentally and has not been explicitly predicted theoretically. We will discuss the relationship between our experimental result and a number of theoretical models that predict symmetry breaking ground states for perfect kagomé lattices. © International Union of Crystallography