Browsing by Author "Liu, S"
Now showing 1 - 20 of 22
Results Per Page
- ItemAnion Disorder in Lanthanoid Zirconates Gd2-xTbxZr2O7(American Chemical Society., 2013-08-05) Reynolds, EM; Blanchard, PER; Kennedy, BJ; Ling, CD; Liu, S; Avdeev, M; Zhang, Z; Cuello, GJ; Tadich, A; Jang, LYThe pyrochlore?defect fluorite order?disorder transition has been studied for a series of oxides of the type Gd2?xTbxZr2O7 by a combination of diffraction and spectroscopy techniques. Synchrotron X-ray diffraction data suggest an abrupt transition from the coexistence of pyrochlore and defect fluorite phases to a single defect fluorite phase with increasing Tb content. However neutron diffraction data, obtained at ? ≈ 0.497 Å for all Gd-containing samples to minimize absorption, not only provide evidence for independent ordering of the anion and cation sublattices but also suggest that the disorder transition across the pyrochlore?defect fluorite boundary of Ln2Zr2O7 is rather gradual. Such disorder was also evident in X-ray absorption measurements at the Zr L3-edge, which showed a gradual increase in the effective coordination number of the Zr from near 6-coordinate in the pyrochlore rich samples to near 7-coordinate in the Tb rich defect fluorites. These results indicate the presence of ordered domains throughout the defect fluorite region, and demonstrate the gradual nature of the order?disorder transition across the Gd2?xTbxZr2O7 series. © 2013, American Chemical Society.
- ItemDesigning new n = 2 Sillen-Aurivillius phases by lattice-matched substitutions in the halide and [Bi2O2]2+ layer(Australian Institute of Physics, 2014-02-05) Liu, S; Blanchard, PER; Kennedy, BJ; Ling, CD; Avdeev, MThe chemical and structural flexibility of the perovskite structure, which makes it so ubiquitous in nature and useful in a range of technological applications, extends to layered variants such as Ruddlesden-Popper, Dion- Jacobson and Aurivillius phases. Multi-layered variants such as the Sillen-Aurivillius phases are related to Aurivillius phases by the insertion of an additional halide layer between every second [Bi2O2]2+ layer. Sillen-Aurivillius phases exist in various combinations of n number of perovskite layers and m halide layers. We have synthesised a new n = 2, m = 1 Sillen-Aurivillius compound Bi3Sr2Nb2O11Br based on Bi3Pb2Nb2O11Cl by simultaneously replacing Pb2+ with Sr2+ and Cl- with Br-. Rietveld refinements against X-ray and neutron powder diffraction data revealed a significant relative compression in the stacking axis, in contrary to the belief of inserting a significantly larger halide layer in the new compound. We could not stabilise other combinations such as Bi3Sr2Nb2O11Cl and Bi3Pb2Nb2O11Br due to inter-layer mismatch. Sr2+ doping reduces the impact of the stereochemically active 6s2 lone pair found on Bi3+/Pb2+ site, resulting in a contraction of the stacking axis by 1.22 % and an expansion of the a-b plane by 0.25 %, improving inter-layer compatibility with Br-. XANES analysis shows that the ferroelectric distortion of the B-site cation is less apparent in Bi3Sr2Nb2O11Br compared to Bi3Pb2Nb2O11Cl. Variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion.
- ItemDesigning new n=2 Sillen-Aurivillius phases by lattice-matched substitutions in the halide and [Bi 2Oc2] 2+ layer(Australian Institute of Nuclear Science and Engineering (AINSE), 2013-12-02) Liu, S; Blanchard, PER; Avdeev, M; Kennedy, BJ; Ling, CDThe chemical and structural flexibility of the perovskite structure, which makes is so ubiquitous in nature and useful in a range of technological applications, extends to layered variants such as Ruddleston-Popper, Dion-Jacobsen and Aurivillius phases. Multi-layered variants such as the Sillen-Aurivillius phases are related to Aurivillius phases by the insertion of an additional halide layer between every second [Bi2 02 2+ layer. Sillen-Aurivillius phases exist in various AnXm combinations, where n is the number of perovskite layers A and m the number of halide layers X. We have synthesised a new n=2 Sillen-Aurivillius compound Bi3 Sr2 Nb2 O11 Br based on Bi3 Pb2 Nb2 O11 Cl by simultaneously replacing Pb2+ with Sr2+ and Cl - with Br -. Rietveld refinements against X-ray and neutron powder diffraction data revealed a significant relative compression in the stacking axis (c axis) in contrary to the belief of inserting a significantly larger halide layer in the new compound. We could not stabilise other combinations such as Bi3 Sr2 Nb2 O11 Cl and Bi3 Pb2 Nb2 O11 Br due to inter-layer mismatch. Sr2+ doping reduces the impact of the stereochemically active 6s2 lone pair found on Pb2+and Bi3+, resulting in a contraction of the c axis by 1.22 % and an expansion of the a-b plane by 0.25 %, improving inter-layer compatibility with Br-. XANES analysis shows that the ferroelectric distortion of the B-site cation is less apparent in Bi3 Sr2 Nb2 O11 Br compared to Bi3 Pb2 Nb2 O11 Cl. Variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion.
- ItemDesigning new n=2 sillen-aurivillius phases by lattice-matched substitutions in the halide and [Bi2O2](2+) layers(Academic Press Inc Elsevier Science, 2013-09-01) Liu, S; Blanchard, PER; Avdeev, M; Kennedy, BJ; Ling, CDAbstract A new n=2 Sillen–Aurivillius compound Bi3Sr2Nb2O11Br has been synthesised based on Bi3Pb2Nb2O11Cl by simultaneously replacing Pb2+ with Sr2+ and Cl− with Br−. Rietveld refinements against X-ray and neutron powder diffraction data revealed a significant relative compression in the stacking axis (c-axis) of the new compound. Sr2+ doping reduces the impact of the stereochemically active 6s2 lone pair found on Pb2+ and Bi3+, resulting in a contraction of the c-axis by 1.22% and an expansion of the ab plane by 0.25%. This improves the inter-layer compatibility with the larger halide Br−. Analysis of X-ray absorption near-edge spectroscopy data show that the ferroelectric distortion of the B-site cation is less apparent in Bi3Sr2Nb2O11Br compared to Bi3Pb2Nb2O11Cl, and variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion.© 2013, Elsevier Inc
- ItemDiffraction and spectroscopic study of pyrochlores Bi2−xFe1+xSbO7(Elsevier, 2014-03-15) Zhou, Q; Blanchard, PER; Kennedy, BJ; Ling, CD; Liu, S; Avdeev, M; Aitken, JB; Tadich, A; Brand, HEAThe structural and electronic properties of the series Bi2−xFe1+xSbO7 (0 ⩽ x ⩽ 0.6) were investigated using a combination of diffraction and spectroscopy. Synchrotron and neutron diffraction analysis show that Fe3+ cations substitute for Bi3+ onto the A site with increasing x, which was further confirmed by analysis of the Fe K/L-edge X-ray absorption near-edge spectra. The diffraction analysis indicated the presence of displacive disorder along the A2O chains, likely the result of the Bi3+ 6s2 lone pair, as well as non-Vegard-like behaviour of the lattice parameters in the Fe-poor region. Fe K-edge extended X-ray absorption fine-structure analysis of Bi2FeSbO7 confirmed the displacive disorder of the Bi3+ cations as well as Sb5+ and Fe3+ disorder on the B site. © 2013 Elsevier B.V.
- ItemExpanding the applications of the ilmenite mineral to the preparation of nanostructures: TiO2 nanorods and their photocatalytic properties in the degradation of oxalic acid(Wiley-Blackwell, 2013-01-14) Tao, T; Chen, Y; Zhou, D; Zhang, HZ; Liu, S; Amal, R; Sharma, N; Glushenkov, AMThe mineral ilmenite is one of the most abundant ores in the Earth's crust and it is the main source for the industrial production of bulk titanium oxide. At the same time, methods to convert ilmenite into nanostructures of TiO2 (which are required for new advanced applications, such as solar cells, batteries, and photocatalysts) have not been explored to any significant extent. Herein, we describe a simple and effective method for the preparation of rutile TiO2 nanorods from ball-milled ilmenite. These nanorods have small dimensions (width: 520 nm, length: 50100 nm, thickness: 25 nm) and possess large specific surface areas (up to 97 m2?g-1). Dissolution/hydrolysis/precipitation is proposed as a growth mechanism. The nanorods were found to have attractive photocatalytic properties in the degradation of oxalic acid. Their photocatalytic activity is close to that of the benchmark Degussa P25 material and better than that of a commercial high-surface-area rutile powder. © 2013, Wiley-Blackwell
- ItemImpact of Cu doping on the structure and electronic properties of LaCr1–yCuyO3(ACS Publications, 2014-01-31) Qasim, I; Blanchard, PER; Liu, S; Kennedy, BJ; Avdeev, MOxides of the type LaCr1–yCuyO3 have been prepared using solid-state methods and their crystal structures refined using synchrotron X-ray powder diffraction. The solubility limit of Cu was found to be around y = 0.2, and such oxides are orthorhombic in space group Pbnm. X-ray absorption spectroscopy measurements at the Cr and Cu L-edges demonstrated that the Cr remains trivalent upon Cu doping, with the Cu being present as Cu(III). The oxides are found to be antiferromagnets, and the Néel temperature, TN, decreases as the Cu content is increased. The crystal and magnetic structures of one example La(Cr0.85Cu0.15)O3 have been investigated between 3 and 350 K by neutron powder diffraction. The samples are semiconductors. © 2014, American Chemical Society.
- ItemInvestigating the local structure of lanthanoid hafnates Ln2Hf2O7 via diffraction and spectroscopy(American Chemical Society, 2013-02-07) Blanchard, PER; Liu, S; Kennedy, BJ; Ling, CD; Avdeev, M; Aitken, JB; Cowie, BCC; Tadich, AThe lanthanoid hafnates Ln2Hf2O7 (Ln = La, Pr, Nd, Sm?Tm) were studied using a combination of synchrotron X-ray and neutron powder diffraction together with X-ray absorption and Raman spectroscopy. Spectroscopic methods revealed a gradual increase in disorder from the ideal pyrochlore structure to the defect fluorite structure as the size of the Ln cation increases. The line shape of the Hf L3-edge X-ray absorption near edge spectra which is sensitive to the local coordination environment changed with increasing disorder. The general line shape of the O K-edge XANES and Raman spectra also indicated an increase in disorder across the Ln2Hf2O7 series. Differences in the diffraction and spectroscopy analysis reflect the greater sensitivity of the spectroscopy techniques to local ordering. © 2013, American Chemical Society
- ItemInvestigating the order-disorder phase transition in Nd2-xYxZr2O7via diffraction and spectroscopy(Royal Society of Chemistry, 2013-01-01) Blanchard, PER; Liu, S; Kennedy, BJ; Ling, CD; Zhang, Z; Avdeev, M; Cowie, BCC; Thomsen, L; Jang, LYThe pyrochlore-defect fluorite phase transition in the mixed-metal zirconate Nd2-xYxZr2O7 (0 <= x <= 2) solid solution was investigated using synchrotron X-ray and neutron diffraction, as well as X-ray absorption spectroscopy. Diffraction analysis revealed a two-phase region between 1.0 <= x <= 1.2. In the pyrochlore phase, Zr L-3-edge XANES analysis demonstrated a gradual change in the local coordination environment of the B site with increasing Y content that was consistent with an increase in disorder. Although Y L-3-edge XANES analysis suggested that the Y cations remained in an ordered coordination environment in the pyrochlore phase, disorder did gradually increase once the fluorite phase formed. It was found that Y cations prefer an ordered coordination environment near the phase boundary whereas Zr cations prefer a disordered coordination environment. © 2013, Royal Society of Chemistry
- ItemKey role of Bismuth in the magnetoelastic transitions of Ba3BiIr2O9 and Ba3BiRu2O9 as revealed by chemical doping(America Chemical Society, 2013-12-24) Blanchard, PER; Huang, Z; Kennedy, BJ; Liu, S; Miiller, W; Reynolds, EM; Zhou, Q; Avdeev, M; Zhang, Z; Aitken, JB; Cowie, BCC; Jang, LY; Tan, TT; Li, S; Ling, CDThe key role played by bismuth in an average intermediate oxidation state in the magnetoelastic spin-gap compounds Ba3BiRu2O9 and Ba3BiIr2O9 has been confirmed by systematically replacing bismuth with La3+ and Ce4+. Through a combination of powder diffraction (neutron and synchrotron), X-ray absorption spectroscopy, and magnetic properties measurements, we show that Ru/Ir cations in Ba3BiRu2O9 and Ba3BiIr2O9 have oxidation states between +4 and +4.5, suggesting that Bi cations exist in an unusual average oxidation state intermediate between the conventional +3 and +5 states (which is confirmed by the Bi L3-edge spectrum of Ba3BiRu2O9). Precise measurements of lattice parameters from synchrotron diffraction are consistent with the presence of intermediate oxidation state bismuth cations throughout the doping ranges. We find that relatively small amounts of doping (∼10 at%) on the bismuth site suppress and then completely eliminate the sharp structural and magnetic transitions observed in pure Ba3BiRu2O9 and Ba3BiIr2O9, strongly suggesting that the unstable electronic state of bismuth plays a critical role in the behavior of these materials. © 2013, American Chemical Society.
- ItemLong- and short-range structure studies of KBT-KBZ solid-solutions using synchrotron radiation(Royal Society of Chemistry, 2015-01-14) Liu, S; Blanchard, PER; Zhang, Z; Kennedy, BJ; Ling, CDThe relaxor ferroelectric K0.5Bi0.5TiO3 has been synthesised in a solid-solution series with K0.5Bi0.5ZrO3, as K0.5Bi0.5Ti1−xZrxO3. High-resolution synchrotron X-ray powder diffraction and X-ray absorption near edge structure spectroscopy were used to characterise the long-range average and local structural behaviour. Rietveld refinements against diffraction data show that a pseudocubic tetragonal region exists across the whole solid-solution series, with truly cubic symmetry only observed at x = 1 (pure KBZ). Variable-temperature diffraction data for x = 0 (pure KBT) showed a broad ferroelectric transition from tetragonal to cubic symmetry at approximately 683 K with a coexistence of both phases close to that temperature, accompanied by a marked volume contraction. Ti K-edge data showed that Zr doping has a minimal effect on Ti off-centering, and revealed no evidence for local clustering. Metal L-edges showed that Ti4+ cations remain off-centered with increasing Zr content, while Zr4+ cations approach a higher-symmetry coordination environment, most likely due to the increased size of the Zr atoms. Although there is a minimal effect on actual Ti-offsets, an effective dilution of these environments by Zr doping leads to a reduction in polar domains and a diminished ferroelectric response. © 2015 Royal Society of Chemistry
- ItemA new n = 4 layered Ruddlesden–Popper phase K2.5Bi2.5Ti4O13 showing stoichiometric hydration(American Chemical Society, 2016-01-22) Liu, S; Avdeev, M; Liu, Y; Johnson, MR; Ling, CDA new bismuth-containing layered perovskite of the Ruddlesden–Popper type, K2.5Bi2.5Ti4O13, has been prepared by solid-state synthesis. It has been shown to hydrate to form stoichiometric K2.5Bi2.5Ti4O13·H2O. Diffraction data show that the structure consists of a quadruple-stacked (n = 4) perovskite layer, with potassium ions occupying the rock salt layer and its next-nearest A site. The hydrated sample was shown to remove the offset between stacked perovskite layers relative to the dehydrated sample. Computational methods show that the hydrated phase consists of intact H2O molecules in a vertical “pillared” arrangement bridging across the interlayer space. Rotations of H2O molecules about the c axis were evident in molecular dynamic calculations, which increased in rotation angle with increasing temperature. In situ diffraction data for the dehydrated phase point to a broad structural phase transition from orthorhombic to tetragonal at ∼600 °C. The relative bismuth-rich composition in the perovskite block results in a higher transition temperature compared to related perovskite structures. Water makes a significant contribution to the dielectric constant, which disappears after dehydration. © 2016 American Chemical Society
- ItemOrdered vs. disordered perovskites; structural studies of Fe-doped SrIrO3 and SrRuO3(Academic Press Inc Elsevier Science, 2013-10-01) Qasim, I; Blanchard, PER; Liu, S; Tang, CG; Kennedy, BJ; Avdeev, M; Kimpton, JAThe structures of the two Fe containing perovskites Sr2IrFeO6 and SrRu0.5Fe0.5O3 have been established using a combination of synchrotron and neutron diffraction methods. Sr2IrFeO6 and SrRu0.5Fe0.5O3 are shown to be monoclinic I2/m and tetragonal I4/mcm respectively The former exhibits a rock-salt like ordering of the Fe and Ir cations and displays a sequence of phase transitions associated with the loss of the octahedral tilts upon heating; 12 / m → I 4 / m → F m 3 ¯ m . The Fe and Ru cations are disordered in SrRu0.5Fe0.5O3 and this shows a single structural phase transition upon heating due to the loss of the in-phase tilts, viz. I 4 / m c m → P m 3 ¯ m . In both cases XANES measurements show partial oxidation of the Fe3+ to Fe4+. The difference in the structures between the two is remarkable given the similar size of Ir5+ and Ru5+, and this is reflected in their magnetic properties. © 2013, Elsevier Ltd.
- ItemPerovskites in low dimensional multi-layer structure types(International Union of Crystallography, 2014-08) Liu, S; Miiller, W; Liu, Y; Blanchard, PER; Avdeev, M; Kennedy, BJ; Ling, CDThis study introduces examples of structure property relationships within the multi-layered Sillen-Aurivillius family (shown in Figure) and aims to investigate the effect of chemical doping and lattice matching effects. The first example involves doping 1/3 of the n = 3 ferroelectric perovskite layers with magnetic transition metal cations in Bi 5 PbTi 3 O 1 4 Cl  with charge balancing by removing Pb 2 + for Bi 3 + . A statistical 1:2 distribution of M 3 + and Ti 4 + across all three perovskite layers was found in Bi 6 Ti 2 MO 1 4 Cl, M = Cr 3 + , Mn 3 + , Fe 3 + , resulting in highly strained structures (enhancing the ferroelectricity compared to Bi 5 PbTi 3 O 1 4 Cl) and pronounced spin-glass behavior below T i r r (0) = 4.46 K. Ferroelectric transitions were observed at high temperature for each of the new compounds. Ferroelectric properties were also measured on Bi 6 Ti 2 FeO 1 4 Cl using piezoresponse force microscopy showing hysteretic phase behavior. A new n = 2 Sillen-Aurivillius compound Bi 3 Sr 2 Nb 2 O 1 1 Br, based on Bi 3 Pb 2 Nb 2 O 1 1 Cl , was synthesized by simultaneously replacing Pb 2 + with Sr 2 + and Cl - with Br - . Inter-layer mismatch prevented the formation of Bi 3 Sr 2 Nb 2 O 1 1 Cl and Bi 3 Pb 2 Nb 2 O 1 1 Br. Sr 2 + doping reduces the impact of the stereochemically active 6s 2 lone pair found on Pb 2 + and Bi 3 + , resulting in a stacking contraction in the lattice parameters by 1.22 % and an expansion of the a-b plane by 0.25 %, improving inter-layer compatibility with Br - . X-ray Absorption Near Edge Structure spectra analysis shows that the ferroelectric distortion of the B-site cation is less apparent in Bi 3 Sr 2 Nb 2 O 1 1 Br compared to Bi 3 Pb 2 Nb 2 O 1 1 Cl. Variable-temperature neutron diffraction data show no evidence for a ferroelectric distortion. © International Union of Crystallography
- ItemProbing long- and short-range disorder in Y2Ti2–xHfxO7 by diffraction and spectroscopy techniques(American Chemical Society, 2016-11-01) Zhang, ZM; Avdeev, M; de los Reyes, M; Lumpkin, GR; Kennedy, BJ; Blanchard, PER; Liu, S; Tadich, A; Cowie, BCCWe studied the long-range average and short-range local structures in Y2Ti2–xHfxO7 (x = 0–2.0) using diffraction and spectroscopy techniques, respectively. Both neutron and synchrotron X-ray powder diffraction data show a clear phase transition of the average structure from ordered pyrochlore to disordered defect-fluorite at x ≈ 1.6; the long-range anion disorder appears to develop gradually throughout the entire pyrochlore region in contrast to the rapid loss of cation ordering from x = 1.4 to 1.6. The commonly observed two-phase region around the pyrochlore/defect-fluorite phase boundary is absent in this system, demonstrating high sample quality. X-ray absorption near-edge structure (XANES) results at the Y L2-, Ti K- and L3,2-, Hf L3-, and O K-edges indicate a gradual local structural evolution across the whole compositional range; the Y coordination number (CN) decreases and the CN around Ti and Hf increases with increasing Hf content (x). The spectroscopic results suggest that the local disorder occurs long before the pyrochlore to defect-fluorite phase boundary as determined by diffraction, and this disorder evolves continuously from short- to medium- and eventually to long-range detectable by diffraction. This study highlights the complex disordering process in pyrochlore oxides and the importance of a multitechnique approach to tackle disorder over different length scales and in the anion and cation sublattices, respectively. The results are important in the context of potential applications of these oxides such as ionic conductors and radiation-resistant nuclear waste forms. © 2016 American Chemical Society
- ItemSillen-aurivillius intergrowth phases as templates for naturally layered multiferroics(American Chemical society, 2012-9-21) Liu, S; Miiller, W; Liu, Y; Avdeev, M; Ling, CDThe ferroelectric Sillen-Aurivillius phase Bi5PbTi3O14Cl, a layered structure containing three-layer perovskite-type blocks, has been modified by substituting magnetic transition metal cations M3+ = Cr3+, Mn3+, or Fe3+ for 1/3 of the Ti4+ cations, accompanied by co-doping of Bi3+ for Pb2+. The aim of the modification was to produce naturally layered ferroelectromagnetic compounds. Rietveld refinements against high-temperature synchrotron X-ray powder diffraction data show that the resulting new compounds Bi6Ti2MO14Cl undergo non-centrosymmetric (P2an) to centrosymmetric (P4/mmm) ferroelectric phase transitions for Bi6Ti2CrO14Cl at 974.6(2) K, Bi6Ti2MnO14Cl at 913.5(6) K, and Bi6Ti2FeO14Cl at 1044.8(1) K. Ferroelectric properties were measured on Bi6Ti2FeO14Cl using piezoresponse force microscopy which showed typical ferroelectric hysteresis behavior in the polarization with varying field strength as well as a piezoelectric strain. Combined Rietveld refinements against X-ray and neutron powder diffraction data indicate a statistical 1:2 distribution of M3+ and Ti4+ across all three perovskite layers, resulting in highly strained structures (enhancing the ferroelectricity compared to Bi5PbTi3O14Cl) and pronounced spin-glass (cluster glass-type) behavior below T-irr(0) = 4.46 K that we have characterized by detailed magnetic susceptibility and heat capacity measurements. © 2012, American Chemical Society.
- ItemStructural and magnetic studies of the electron doped manganites Sr 0.65 Pr 0.35− x Ce x MnO 3 (0.00 ≤ x ≤ 0.35)(IOP Publishing, 2013-07-13) Heyraud, S; Blanchard, PER; Liu, S; Zhou, Q; Kennedy, BJ; Brand, HEA; Tadich, A; Hester, JRThe nuclear and magnetic structures and properties of Sr0.65Pr0.35−xCexMnO3 (0.00 ≤ x ≤ 0.35) were investigated using a combination of synchrotron x-ray and neutron powder diffraction, along with magnetic and x-ray absorption near edge structure measurements. At room temperature, doping with Ce results in a transition from a tetragonal structure in I4/mcm to an orthorhombic one in Imma associated with the loss of long range orbital ordering. At low temperatures, we observe the formation of an orthorhombic Fmmm phase. XANES measurements demonstrate that the Ce exists as a mixture of Ce3+ and Ce4+. © 2013, IOP Publishing Ltd.
- ItemStructural relationships among LiNaMg[PO4]F and Na2M[PO4]F (M = Mn-Ni, and Mg), and the magnetic structure of LiNaNi[PO4]F(Royal Chemistry of Society, 2013-11) Ben Yahia, H; Shikano, H; Kobayashi, M; Avdeev, M; Liu, S; Ling, CDThe new compound LiNaMg[PO4]F has been synthesized by a wet chemical reaction route. Its crystal structure was determined from single-crystal X-ray diffraction data. LiNaMg[PO4]F crystallizes with the monoclinic pseudomerohedrally twinned LiNaNi[PO4]F structure, space group P21/c, a = 6.772(4), b = 11.154(6), c = 5.021(3) Å, β = 90.00(1)° and Z = 4. The structure contains [MgO3F]n chains made up of zigzag edge-sharing MgO4F2 octahedra. These chains are interlinked by PO4 tetrahedra forming 2D-Mg[PO4]F layers. The alkali metal atoms are well ordered in between these layers over two atomic positions. The use of group–subgroup transformation schemes in the Bärnighausen formalism enabled us to determine precise phase transition mechanisms from LiNaNi[PO4]F- to Na2M[PO4]F-type structures (M = Mn–Ni, and Mg) (see video clip 1 and 2). The crystal and magnetic structure and properties of the parent LiNaNi[PO4]F phase were also studied by magnetometry and neutron powder diffraction. Despite the rather long interlayer distance, dmin(Ni+2–Ni+2) ∼ 6.8 Å, the material develops a long-range magnetic order below 5 K. The magnetic structure can be viewed as antiferromagnetically coupled ferromagnetic layers with moments parallel to the b-axis.
- ItemStudying the effects of Zr-doping in (Bi0.5Na0.5)TiO3 via diffraction and spectroscopy(Royal Society of Chemistry, 2014-10-13) Blanchard, PER; Liu, S; Kennedy, BJ; Ling, CD; Zhang, Z; Avdeev, M; Jang, LY; Lee, JF; Pao, CW; Chen, JLThe structural properties of (Bi0.5Na0.5)Ti1−xZrxO3 (where 0 ≤ x ≤ 0.7) have been investigated using powder diffraction and X-ray absorption spectroscopy. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Doping small amounts of Zr into the B site of (Bi0.5Na0.5)TiO3 initially stabilizes the rhombohedral phase before the orthorhombic Pnma phase begins to form at x = 0.5. Analysis of the Ti K-edge and Zr L3-edge XANES spectra show that the crystallographic phase change has very little effect on the local structure of Ti4+/Zr4+ cations, suggesting that there is little change in the cation off-center displacement within the BO6 octahedra with each successive phase change. © The Royal Society of Chemistry 2014
- ItemSynthesis and characterization of the crystal and magnetic structures and properties of the hydroxyfluorides Fe(OH)F and Co(OH)F(Americal Chemical Society, 2013-12-16) Ben Yahia, H; Shikano, M; Tabuchi, M; Kobayashi, H; Avdeev, M; Tan, TT; Liu, S; Ling, CDThe title compounds were synthesized by a hydrothermal route from a 1:1 molar ratio of lithium fluoride and transition-metal acetate in an excess of water. The crystal structures were determined using a combination of powder and/or single-crystal X-ray and neutron powder diffraction (NPD) measurements. The magnetic structure and properties of Co(OH)F were characterized by magnetic susceptibility and low-temperature NPD measurements. M(OH)F (M = Fe and Co) crystallizes with structures related to diaspore-type α-AlOOH, with the Pnma space group, Z = 4, a = 10.471(3) Å, b = 3.2059(10) Å, and c = 4.6977(14) Å and a = 10.2753(3) Å, b = 3.11813(7) Å, and c = 4.68437(14) Å for the iron and cobalt phases, respectively. The structures consist of double chains of edge-sharing M(F,O)6 octahedra running along the b axis. These infinite chains share corners and give rise to channels. The protons are located in the channels and form O–H···F bent hydrogen bonds. The magnetic susceptibility indicates an antiferromagnetic ordering at ∼40 K, and the NPD measurements at 3 K show that the ferromagnetic rutile-type chains with spins parallel to the short b axis are antiferromagnetically coupled to each other, similarly to the magnetic structure of goethite α-FeOOH. © 2014, American Chemical Society