Browsing by Author "Söhnel, T"

Now showing 1 - 19 of 19
  • No Thumbnail Available
    Item
    “114”-Type nitrides LnAl(Si4−xAlx)N7Oδ with unusual [AlN6] octahedral coordination
    (Wiley, 2017-02-28) Huang, S; Huang, Z; Cao, P; Zujovic, Z; Price, JR; Avdeev, M; Que, M; Suzuki, F; Kido, T; Ouyang, X; Kaji, H; Fang, M; Liu, YG; Gao, W; Söhnel, T
    Aluminum–nitrogen six-fold octahedral coordination, [AlN6], is unusual and has only been seen in the high-pressure rocksalt-type aluminum nitride or some complex compounds. Herein we report novel nitrides LnAl(Si4−xAlx)N7Oδ (Ln=La, Sm), the first inorganic compounds with [AlN6] coordination prepared via non-high-pressure synthesis. Structure refinements of neutron powder diffraction and single-crystal X-ray diffraction data show that these compounds crystallize in the hexagonal Swedenborgite structure type with P63mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagomé layers of [SiN4] tetrahedra. Solid-state NMR data of high-purity La-114 powders confirm the unusual [AlN6] coordination. These compounds are the first examples of the “33-114” sub-type in the “114” family. The additional site for over-stoichiometric oxygen in the structure of 114-type compounds was also identified. © 1999-2021 John Wiley & Sons, Inc.
  • Thumbnail Image
    Item
    Cu5SbO6 – synchrotron, neutron diffraction studies and magnetic properties
    (Australian Institute of Physics, 2011-02-04) Söhnel, T; Rey, E; Ling, CD; Avdeev, M; Johannessen, B; Wallwork, KS; Kremer, RK; Whangbo, MH
    One very interesting compound in the system Cu/Sb/O is the mixed-valent Cu5SbO6 = (Cu1+(Cu2+ 2/3Sb5+ 1/3)O2) which is crystallising in the high temperature modification as a modified Delafossite structure type. Compounds like Delafossite, CuFeO2, is one of the few groups of compounds showing the rare property of multiferroic behaviour. In Cu5SbO6 the magnetically active brucite-like CuO2 layer is diluted in an ordered fashion with nonmagnetic Sb5+. Cu5SbO6 also shows a phase transition, which exhibits a rather complicated behaviour. It depends on the temperature and the reaction conditions (reactants for preparation, pressure, open or closed system). High resolution Synchrotron and neutron powder diffraction measurements could clearly distinguish between the high temperature and the low temperature modification and reveal an ordering (HT-modification) / disordering (LT-modification) effect of the Sb5+ and Cu2+ ions in the brucite-like layers. The LT-modification can also be assigned to what had wrongly been described in the literature as Cu4.5SbO5. XANES Cu-K edge measurements and NPD measurements should clarify a potential oxidation of the Cu1+ to Cu2+ and a connected additional inclusion of oxygen in the structure. According to magnetic measurements and DFT calculations the magnetic structure in Cu5SbO6 can be described with a short range ferromagnetic-antiferromagnetic interaction model of the (Cu2+) pairs in the (Cu2+ 2/3Sb5+ 1/3)O2 layers with a super-exchange via the nonmagnetic Sb5+ atoms. The systematic replacement of the non-magnetic Sb5+ with magnetically active M5+ ions should change the magnetic properties dramatically and could lead to an long range ordering in the system. First results of Mn and Mo doping will also be presented.
  • Thumbnail Image
    Item
    Exploring the pyrophosphate series K2Cu1-xFexP2O7
    (Australian Institute of Physics, 2020-02-04) Silk, R; Avdeev, M; Sauceda Flores, JA; Ulrich, C; Söhnel, T
    Phosphate materials are of great interest to materials science. Metal phosphate compounds are known to exhibit conductive properties for battery use [1], photocatalytic abilities to decompose other compounds [2], the ability to conduct protons [3], etc. High temperature sintering techniques were used to produce the diphosphate series K2Cu1-xFexP2O7. The material forms two different modifications, a tetragonal (P-421m) and an orthorhombic modification (Pbnm) as shown in Figure 1. The crystal structure was determined through the use of powder X-ray diffraction (PXRD). PXRD patterns show a shift in peaks to lower angles with increasing iron content, which is consistent with an increase of lattice constant parameters. The presence of additional phases such as KPO3 can also be observed. UV-Vis measurements show how the transitions change which increasing amounts of iron and different modifications. Tauc plots revealed that the material has a direct band gap of approximately 3 eV. IR measurements revealed that water had been absorbed by the material and there a slight shift in peak position with increasing iron content. First magnetic measurements did not show any long-range ordering down to 2 K, the compounds remained paramagnetic. The K2CuP2O7 and K2Cu0.75Fe0.25P2O7 samples show short-range antiferromagnetic contribution across both modifications.
  • Thumbnail Image
    Item
    FeMn3Ge2Sn7O16 : 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, CD
    The 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. [3] 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.
  • Thumbnail Image
    Item
    Increase of the stability range of the skyrmion phase in doped Cu2OSeO3
    (Australian Institute of Physics, 2020-02-04) Sauceda Flores, JA; Rov, R; Camacho, L; Spasovski, M; Vella, J; Yick, S; Gilbert, EP; Han, MG; Zhu, Y; Seidel, J; Kharkov, Y; Sushkov, OP; Söhnel, T; Ulrich, C
    A skyrmion is a topological stable particle-like object comparable to a spin vortex at the nanometre scale. It consists of an about 50 nm large spin rotation and its spin winding number is quantized. Once formed, the skyrmions order in a two dimensional, typically hexagonal superstructure perpendicular to an applied external magnetic field (see Fig. 1). Its dynamics has links to flux line vortices as in high temperature superconductors. Cu2OSeO3 is a unique case of a multiferroic materials where the skyrmion dynamics could be controlled through the application of an external electric field. The direct control of the skyrmion dynamics through a non-dissipative method would offer technological benefits and unique possibilities for testing fundamental theories also related to the Higgs Boson whose theoretical description has similarities to skyrmions. Important for technological applications is a stability range of the skyrmion phase up to room temperature. While room temperature skyrmion materials exist, Cu2OSeO3 orders magnetically below 58 K. Our combined small angle neutron scattering (see Fig. 2), SQUID magnetization measurements and electron microscopy investigations did provide direct evidence that the stability range of the skyrmion phase can be extended in Te-doped Cu2OSeO3. The understanding of this effect will help to obtain deeper insights in the magnetic correlations in charge of the skyrmion formation and will thus help to systematically search for skyrmion materials with phase transition temperatures towards room temperature.
  • Thumbnail Image
    Item
    It has it all: Cu5Sb2SiO12 - seven crystallographic independent positions for Cu2+ in one compound
    (Australian Institute of Physics, 2017-02-01) Olney, T; Wilson, D; Avdeev, M; Söhnel, T
    Cu5Sb2SiO12 is the only copper – antimony silicate know so far. We were also able to grow single crystals of Cu5Sb2SiO12 using chemical transport reactions and to solve the crystal structure completely. The crystal structure of the compound is truly remarkable as it contains seven structurally independent Cu2+-positions, all of them showing different coordination spheres (typical distorted CuO6 octahedra, [2+2+2] coordination, 5-fold coordination and CuO8 with 4 medium and 4 long bonds [4+4]). This is a very unique and very promising situation, which could be used for partial oxidation and reduction of Cu analogous to Cu containing high temperature superconductors, as well as replacing Cu with other M2+ transition metals. An anti-ferromagnetic long range ordering of Cu2+ could be shown for Cu5Sb2SiO12 below 27 K. First NPD measurements without magnetic field at temperatures below the ordering temperature do not show any magnetic peaks, which should be observed for a long range antiferromagnetic ordering. Our own field-dependent measurements confirm the magnetic ordering, but the magnetic ordering is only clearly visible in susceptibility data with external fields of about 3 T and higher. Manganese and Cobalt doped versions of the copper-antimony silicate have been synthesised. Since there are seven crystallographic independent positions for Cu2+ with very different coordination spheres, there should be preferential sites for the Mn and Co to be incorporated into the structure. Lab X-ray and neutron powder diffraction data show that doping appears to work well up until Cu2Mn3Sb2SiO12. All materials have been synthesised at 900°C in air, a temperature where the stable ion should be Mn3+ rather than Mn2+, which can be seen in studies of the Cu5-xMnxSbO6 system. Mn doping leads to much stronger magnetic ordering in the compounds and the antiferromagnetic ordering could finally observed in neutron powder data.
  • Thumbnail Image
    Item
    Low pressure synchrotron x-ray powder diffraction of Cu5-xMxSbO6 (M=Cr, Mn, W)
    (Australian Institute of Physics, 2016-02-04) Wilson, DJ; Söhnel, T; Smith, KL; Brand, HEA; Ulrich, C; Graham, PJ; Chang, FF; Allison, MC; Vyborna, NH
    The large crystallographic and chemical diversity of copper-based metal oxides is one of their highlighting features and cause for pursuit into copper based material research. An interesting feature seen in copper based metal oxides is the coexistence of different copper oxidation states, in different crystallographic positions, within the same compound. This can lead to a mixture of magnetically active Cu2+ and magnetically inactive Cu1+ within the same compound, with different structural motifs. One interesting compound that demonstrates this coexistence of mixed copper oxidation states is Cu5SbO6, which crystallises in a modified delafossite structure type (CuFeO2). Here, the magnetically active brucite-like CuO2 layer was diluted in an ordered fashion with non-magnetic Sb5+. These layers were separated by linearly coordinated, magnetically inactive Cu1+. Rietveld refinements on a range of preparation temperatures revealed a low-temperature (LT) and high-temperature modification (HT) phase transition. This is related to an ordering (HT)/disordering (LT) effect of the Sb5+/Cu2+ brucite-like layers between the Cu1+ ions. Substituting the Cu2+ or Sb5+ in the layers with other transition metals (Cr, Mn, W) could present interesting changes to the properties of the material, and potentially influence the ordered/disordered stacking of the layers. By using solid-state Raman spectroscopy, we could show that this structure displayed a pressure-induced phase transition at room temperature for the ordered modification, which was not observed for the disordered modification. Lowering the pressure from ambient down to 20 mbar showed phonon modes at about 700 cm-1 and 550 cm-1 disappeared almost completely. Neutron powder diffraction experiments were conducted at atmospheric and low pressure on both ordered and disordered modifications. On analysis of the neutron diffraction patterns, we could show a very small shift in the reflections, and thus changes in the unit cell parameters, for the ordered modification, while these shifts were not observed for the disordered modification. These shifts should also be observed in synchrotron powder diffraction patterns. Therefore, we investigated the nature of this phase transition with variable pressure synchrotron X-ray powder diffraction.
  • Thumbnail Image
    Item
    Magnetic ordering in superconducting sandwiches
    (Australian Institute of Physics, 2020-02-04) Chan, A; van der Heijden, NJ; Söhnel, T; Simpson, MC; Rule, KC; Causer, GL; Lee, WT; Bernard, C; Mallett, BPP
    Our cuprate-manganite ‘superconducting sandwich’ multilayers exhibit a highly unusual magnetic-field induced insulating-to-superconducting transition, contrary to the commonly held understanding that magnetic fields are detrimental to superconductivity. This new behaviour is a result of the specific magnetic and electronic properties of the manganite coupling with the cuprate (YBa2Cu3O7-δ, YBCO). Due to the specific manganite composition, Nd0.65(Ca0.7Sr0.3)0.35MnO3 (NCSMO), we hypothesize the behaviour to originate from CE-type antiferromagnetic ordering as well as charge and orbital ordering. Zero-field cooled polarized neutron reflectometry (PNR) data in Fig 1(A) shows a sizable spin-flip (R+-) signal which may result from disordered ferromagnetic domains which sum to give a vanishing macroscopic magnetization. Initial elastic neutron scattering measurements performed on 100 nm thin film NCSMO display signatures of magnetic ordering (Fig 1(B)). Future neutron scattering measurements will look at the modification of magnetic order in a superlattice to better understand the relationship between NCSMO magnetization and our newly discovered insulating-to-superconducting transition.
  • No Thumbnail Available
    Item
    Magnetic ordering in superconducting sandwiches
    (Australian Nuclear Science and Technology Organisation, 2021-11-24) Chan, A; van der Heijden, NJ; Causer, GL; Söhnel, T; Simpson, MC; Rule, KC; Lee, WTH; Bernhard, C; Mallett, BPP
    Our cuprate-manganite ‘superconducting sandwich’ multilayers exhibit a highly unusual magnetic-field induced insulating-to-superconducting transition (IST), contrary to the commonly held understanding that magnetic fields are detrimental to superconductivity [1, 2]. This new behaviour is a result of the specific magnetic and electronic properties of the manganite coupling with the high-Tc cuprate (YBa2Cu3O7-δ, YBCO). Due to the specific manganite composition, Nd0.65(Ca0.7Sr0.3)0.35MnO3 (NCSMO), we hypothesize the behaviour to originate from CE-type antiferromagnetic ordering as well as charge and orbital ordering [3]. The magnetic data presented here will focus on polarized neutron reflectometry (PNR) and elastic neutron scattering on a YBCO-NCSMO trilayer and superlattice. The model that best described the PNR data for the trilayer had antiparallel moments at the YBCO-NCSMO interfaces. In the superlattice, the direction of moments at NCSMO interfaces were found to alternate with film depth whose long-ranged ordering was broken below 35 K in a 1 T applied field. The stability of the AFM order in the superlattice was further supported by a robustness of magnetic in-plane half-order elastic scattering peaks at 9 T. This evidences the interplay of magnetism and superconductivity that play a role in realizing the IST effect in our superconducting sandwiches. © The Authors
  • Thumbnail Image
    Item
    Molecular structure analysis of the chlorhexidine salts
    (Elsevier. B. V, 2023-10-15) Rashidnejad, H; Ramezanitaghartapeh, M; Mokarizadeh, M; Price, JR; Söhnel, T; Mahon, PJ
    Novel organic salts comprising of chlorhexidine di-cation (CHX) with perchlorate H2CHX(ClO4)2·2H2O (CHXPC) and hydrogen citrate H2CHX(C6H6O7).H2O (CHXHC) were prepared, and their crystal structures studied. Despite extensive applications of chlorhexidine as an antimicrobial agent, CHXPC and CHXHC are amongst just a few reported crystal structures containing CHX that have been characterized so far. Exhibiting different structural patterns in their crystal packing, the CHXPC and CHXHC was distinguishable from one another with U- and S- shaped conformations, respectively. Their wide variety of hydrogen bonds were investigated from different point of views, among which were the overall structure of the salts, di-cations and oxyanions, and also their capability of forming 2D- and 3D-frameworks of hydrogen bonding. In addition, multifurcated multi-centered hydrogen bonding, such as bifurcated three-centered and trifurcated four-centered hydrogen bonds were observed in the structures of CHXPC and CHXHC as well. In comparison with normal single hydrogen bonding, the multifurcated hydrogen bonding indicated more flexibility with arrangements in their geometry. The hydrogen bonds containing oxygen-oxygen as donor and acceptor (O ̶ H···O) were employed to estimate their acidity (pKa) and strength (EHB) with different directionality. Hirshfeld surface analysis (HSA) was also used to confirm the intermolecular interactions in the structures of CHXPC and CHXHC. © 2023 Elsevier B.V.
  • Thumbnail Image
    Item
    Preparation and structural characterisation of pure and Te-doped Cu2OSeO3
    (Australian Institute of Physics, 2020-02-04) Rov, R; Sauceda Flores, JA; Gilbert, EP; Yick, S; Ulrich, C; Söhnel, T
    Cu2OSeO3 is a multiferroic materials that shows the formation of skyrmions at low temperatures. A skyrmion is a topologically protected particle-like magnetic spin structures on the order of 10-100 nm. Recent studies have also shown that the skyrmions can be manipulated through applications such as an external electric fields and heat. This offers the potential for development for a much more stable, energy efficient and faster storage in memory devices. The magnetic skyrmions pack into a hexagonal lattice with the skyrmion lattice only stable in a narrow magnetic field-temperature range [1,2]. Here we present the preparation of pure and Te-doped Cu2OSeO3 single crystals with chemical vapour transport, the structural characterisation with X-ray and neutron single crystal diffraction, small angle neutron scattering and magnetisation measurements. Mapping of the magnetic field-temperature phase diagram showed that tellurium doping resulted in an enlarged stability range for the skyrmion phase had been achieved [3].
  • No Thumbnail Available
    Item
    Striped 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, T
    We 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
  • Thumbnail Image
    Item
    Structure and magnetic properties of the AB3Si2Sn7O16 layered oxides
    (Australian Institute of Physics, 2017-02-03) Allison, MC; Ling, CD; Schmid, S; Avdeev, M; Stuart, G; Söhnel, T
    Layered transition metal compounds with geometrically frustrated architectures are widely studied due to the novel effects that arise in a material where lattice geometry prevents the formation of a stable low temperature magnetic ground state in which all interactions between electron spins are satisfied. The parent compound for this study, Fe4Si2Sn7O16, provides a novel situation in oxide compounds. It can be described as a layered composite of oxygen linked (FeSn6) octahedra (the stannide layer) and (FeO6)/(SnO6) octahedra with a kagomé topology (the oxide layer). These layers are separated by SiO4 tetrahedra and the divalent iron in both layers appear to highly substitutionally liable, this combination of features therefore provides a rare opportunity to study a new series of materials with two discrete magnetically frustrated lattices (triangular and kagomé). To date, we have studied the changes in structure as iron is systematically replaced in the structure with iridium, ruthenium, cobalt and/or manganese. Refinements of the X-ray and neutron powder diffraction data show that each transition metal has strong preferences for either the stannide or oxide layer positions dependent upon ionic size and electronic configuration. In this presentation we will show the current results of our studies on the structure, electronic configuration and magnetic properties.
  • No Thumbnail Available
    Item
    Structure of BiRe2O6 re-investigated using single-crystal neutron Laue diffraction
    (Insitute of Physics, 2010-12-16) Sharma, N; Söhnel, T; McIntyre, GJ; Piltz, RO; Ling, CD
    Single crystals of BiRe 2 O 6 of typical volume 0.03 mm 3 were grown by chemical vapor transport and characterized using room-temperature single-crystal neutron diffraction in monoclinic C 2/ c symmetry with cell parameters a = 16.1178(11), b = 4.9235(3), c = 5.5278(3) Ã… and β = 92.475(5) ° ( R all = 11.39 wR all = 7.97). The structure contains ordered layers of corner sharing units of Re 2 O 10 with Re-Re distances of 2.519(1) Ã…. The unit cell is doubled along c in comparison to previous studies based on X-ray diffraction data where the layer stacking was described as disorderd. © 2010, Insitute of Physics.
  • Thumbnail Image
    Item
    Substitutional doping of trirutiline transition metal antimonates, MSb2O6
    (International Union of Crystallography, 2021-08-14) Patel, S; Kang, HB; Maynard-Casely, HE; Söhnel, T
    In the Cu-Sb-O ternary system, CuSb2O6 is the most intensively studied compound, owing to its unusual structural and magnetic behaviour. Jahn-Teller distortions from the Cu2+ cause an axial elongation of the Cu-O octahedra to give rise to a monoclinic structure (s.g. P21/n)[1,2]. At high temperatures, this material undergoes a second-order phase transition to the tetragonal phase (s.g. P42/mnm), isostructural to room temperature structures of CoSb2O6 and NiSb2O6[3]. This modification may only be possible through an intermediate orthorhombic modification in Pnmm as defined through systematic symmetry reduction [4]. Through the doping of CuSb2O6 with Co and Ni, this structural transition can be investigated. Neutron, lab X-ray and synchrotron single crystal and powder diffraction have been used to study phase transitions in both solid state solutions. In the Cu1-xCoxSb2O6 system, it was found that two phases exist between compositions x = 0.2 and 0.5, with a Cu-rich monoclinic phase and a Co-rich tetragonal phase [4]. By contrast, the Cu1-xNixSb2O6 system exhibits a single-phase region from x = 0.4, where only the tetragonal phase remains. A phase transition can be observed in the solid solution where the monoclinic phase becomes tetragonal at high temperature. The orthorhombic intermediate structure can only be observed through Synchrotron powder diffraction. X-ray absorption spectroscopy indicates that there has been a partial reduction of Cu2+ to Cu1+ in the higher doping concentrations of Cu1-xNixSb2O6; neutron powder diffraction on these materials confirm a net oxygen deficiency in the materials. Compounds with similar structures have also been investigated, including NiSb2-xSnxO6 and ZnSb2-xSnxO6, which also show a net oxygen deficiency in the structure. At higher temperatures, these materials also indicate a mixed occupation of Ni and Sb on the 2a and 4f sites, that suggests the material is undergoing a high temperature phase transition to the rutile phase. © The Authors
  • No Thumbnail Available
    Item
    Synthesis and structural determination of the disordered bixbyite Cu3-xSb1+xO5.5+3x/2 with spin-glass behaviour
    (Wiley, 2019-01-28) Spasovski, M; Avdeev, M; Söhnel, T
    The ternary copper antimony oxide Cu3-xSb1+xO5.5+3x/2 (x=0.23) has been synthesized under 0.8–1.3 MPa pO2 at 1022–1082 °C. Rietveld refinements of X-ray and neutron powder diffraction patterns concluded that the oxide adopts a bixbyite type structure, crystallising in the cubic space group Ia-3 with the unit cell parameter a=9.61164(4) Å at room temperature from powder neutron diffraction data. The cationic 8b and 24d sites were found to be occupationally disordered where both Cu and Sb could be found on both sites. This is supported by X-ray absorption spectroscopy experiments showing more than one possible Cu environment. There was a significant net deficiency of oxygen in the compound which was first inferred from observations of a thermochromic-like phenomena and also seen from in situ high temperature neutron diffraction experiments. Magnetic susceptibility and magnetization measurements show paramagnetic behaviour with spin-glass like transition below 6 K. © 1999-2021 John Wiley & Sons, Inc.
  • Thumbnail Image
    Item
    Synthesis, structure and geometrically frustrated magnetism of the layered oxide-stannide compounds Fe(Fe3−xMnx)Si2Sn7O16
    (Royal Society of Chemistry, 2016-05-23) Allison, MC; Avdeev, M; Schmid, S; Liu, S; Söhnel, T; Ling, CD
    Fe4Si2Sn7O16 has a unique crystal structure that contains alternating layers of Fe2+ ions octahedrally coordinated by O (oxide layer) and Sn (stannide layer), bridged by SiO4 tetrahedra. The formula can be written as FeFe3Si2Sn7O16 to emphasise the distinction between the layers. Here, we report the changes in structure and properties as iron is selectively replaced by manganese in the oxide layer. Solid-state synthesis was used to produce polycrystalline samples of Fe(Fe3−xMnx)Si2Sn7O16 for x ≤ 2.55, the structures of which were characterised using high-resolution synchrotron X-ray and neutron powder diffraction. Single-crystal samples were also grown at x = 0.35, 0.95, 2.60 and characterised by single crystal X-ray diffraction. We show that manganese is doped exclusively into the oxide layer, and that this layer contains exclusively magnetically active high-spin M2+ transition metal cations; while the stannide layer only accommodates non-magnetic low-spin Fe2+. All samples show clear evidence of geometrically frustrated magnetism, which we associate with the fact that the topology of the high-spin M2+ ions in the oxide layer describes a perfect kagomé lattice. Despite this frustration, the x = 0 and x = 2.55 samples undergo long-range antiferromagnetic ordering transitions at 3.0 K and 2.5 K, respectively. © The Royal Society of Chemistry 2016 - CC BY 3.0
  • Thumbnail Image
    Item
    Tuning magnetic frustration in bixbyites
    (Australian Institute of Physics, 2020-02-05) Spasovski, M; Avdeev, M; Söhnel, T
    The cubic bixbyite structure (α-Mn2O3) has a deep history in solid-state chemistry, the first structural solution was completed by Zachariasen and later corrected by Pauling.[1] Related to the fluorite structure with ¼ of the anions removed, these vacancies force the displacement of the remaining anions changing the coordination from cubic to strongly distorted octahedra. Today bixbyites are commonplace in every household found in everything from batteries, TV monitors and touch screens to industry catalysts. The ternary oxide Cu3TeO6 is an ordered bixbyite that has been the focus of intense study due to its interesting magnetic spin-web structure.[2-5] We have synthesized powders and single crystals from the solid solution Cu2.25+3x/4Sb1-xTexO4.75+5x/4, Ga and Mn doped variants. Through single crystal, powder X-ray diffraction (XRD) and neutron diffraction (ND) we have seen that the bixbyite lattice can accommodate for a large variation of dopant pressure through site disorder and defects.[6] K and L-edge X-ray absorption spectroscopy has shown the bixbyite structure will also accommodate a large variation of charged species which when coupled with defects and site disorder manifests itself into interesting frustrated magnetic structures varying from canonical spin-glasses to complex anti-ferromagnetic order.
  • Thumbnail Image
    Item
    Using neutron diffraction to explore lithium displacement within cubic phase stabilised Ga-doped Li6.75La3Zr1.75Ta0.25O12 lithium garnet oxides
    (Elsevier, 2023-12-15) Christopher, TD; Zhang, T; Huang, S; Zujovic, Z; Avdeev, M; Cao, P; Söhnel, T
    Typical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75–3xGaxLa3Zr1.75Ta0.25O12 x ≥ 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change. © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY licence.