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158. Phase Transition Behavior of the Layered Perovskite CsBi0.6La0.4Nb2O7: A Hybrid Improper Ferroelectric.

Author

Dixon, Charlotte A. L., McNulty, Jason A., Knight, Kevin S., Gibbs, Alexandra S., and Lightfoot, Philip

Subjects
PHASE transitions, PEROVSKITE, FERROELECTRIC materials
Abstract

The phase behavior of the layered perovskite CsBi0.6La0.4Nb2O7, of the Dion-Jacobson family, has been studied by high-resolution powder neutron diffraction between the temperatures of 25 < T < 850 °C. At ambient temperature, this material adopts the polar space group P21am; this represents an example of hybrid improper ferroelectricity caused by the interaction of two distinct octahedral tilt modes. Within the limits of our data resolution, the thermal evolution of the crystal structure is consistent with a first-order transition between 700 and 750 °C, with both tilt modes vanishing simultaneously, leading to the aristotype space group P4/mmm. This apparent "avalanche transition" behavior resembles that seen in the related Aurivillius phase SrBi2Nb2O9. [ABSTRACT FROM AUTHOR]

Published
2017
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160. A Novel Copper Oxalate, Na2Cu(C2O4)2.

Author

Yao, Wenjiao, Armstrong, A. Robert, and Lightfoot, Philip

Subjects
COPPERWORK, HYDROTHERMAL synthesis, SINGLE crystals, X-ray powder diffraction, COORDINATION polymers synthesis
Abstract

A novel copper oxalate Na2Cu(C2O4)2 was synthesized through a hydrothermal method and characterized by single-crystal X-ray diffraction. It crystallizes in monoclinic system, P21/ n space group with a = 72578(3) Å, b = 5.7711(4) Å, c = 8.6604(8) Å, β = 106.948(9)°. The structure displays a novel stacking pattern of [Cu(C2O4)2]2- units connected through electrostatic attraction by Na+ cations. Structural comparisons are made to related compounds. [ABSTRACT FROM AUTHOR]

Published
2016
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167. Formation of [ (super)15 N] (sub)3 N-(4-phenyl-furazan-3-yl)-benzamide by a furoxan to furazan rearrangement during the attempted synthesis of [(super)15 N] (sub)3 2-oxy-4-phenylfurazan-3-carbonitrile

Author

Butler, Anthony R., Lightfoot, Philip, and Short, Douglas M.

Subjects
Chemistry, Organic -- Research, Nitriles -- Research, Amino acids -- Research, Biological sciences, Chemistry
Abstract

A study of the Capdevielle reaction for the one-pot conversion of aldehydes to nitriles is presented. Experiments demonstrate that under mild conditions 3-substituted furoxans are susceptible to rearrangement when substituted with amine nucleophiles.

Published
1999

168. Nb-93 NMR and DFT investigation of the polymorphs of NaNbO3

Author

Johnston, Karen E., Griffin, John M., Walton, Richard I., Dawson, Daniel M., Lightfoot, Philip, Ashbrook, Sharon E., Johnston, Karen E., Griffin, John M., Walton, Richard I., Dawson, Daniel M., Lightfoot, Philip, and Ashbrook, Sharon E.

Abstract

Sodium niobate (NaNbO3) has a particularly complex phase diagram, with a series of phase transitions as a function of temperature and pressure, and even at room temperature a number of different structural variations have been suggested. Recent work has demonstrated that bulk powders of NaNbO3, prepared using a variety of synthetic approaches, contain a mixture of perovskite phases; the commonly reported Pbcm phase and a second, polar phase tentatively identified as belonging to space group P2(1)ma. The two phases exhibit very similar Na-23 MAS NMR spectra, although high-resolution MQMAS spectra were able to distinguish between them. Here, we investigate whether different perovskite polymorphs can be distinguished and/or identified using a variety of Nb-93 NMR methods, including MAS, MQMAS and wideline experiments. We compare the experimental results obtained for these more common perovskite materials to those for the metastable ilmenite polymorph of NaNbO3. Our experimental results are supported by first-principles calculations of NMR parameters using a planewave pseudopotential approach. The calculated NMR parameters appear very different for each of the phases investigated, but high forces on the atoms indicate many of the structural models derived from diffraction require optimisation of the atomic coordinates. After geometry optimisation, most of these perovskite phases exhibit very similar NMR parameters, in contrast to recent work where it was suggested that Nb-93 provides a useful tool for distinguishing NaNbO3 polymorphs. Finally, we consider the origin of the quadrupolar coupling in these materials, and its dependence on the deviation from ideality of the NbO6 octahedra.

Published
2011

174. NdBaScO4: aristotype of a new family of geometric ferroelectrics?

Author

Cochrane, Amber K., Telfer, Michael, Dixon, Charlotte A. L., Zhang, Weiguo, Halasyamani, P. Shiv, Bousquet, Eric, and Lightfoot, Philip

Subjects
PEROVSKITE, ARISTOTYPE, OXIDE minerals, FERROELECTRIC crystals, FERROELECTRIC materials, OCTAHEDRAL molecules
Abstract

NdBaScO4 represents the aristotype structure of a new series of 〈110〉-cut layered perovskites; it is suggested that compositional fine-tuning is likely to produce a family of new geometric ferroelectrics, driven primarily by octahedral tilting. [ABSTRACT FROM AUTHOR]

Published
2016
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176. V2O2F4(H2O)2·H2O: a new V4+ layer structure related to VOF3.

Author

Black, Cameron and Lightfoot, Philip

Subjects
*OXYFLUORIDES, *CRYSTAL structure, *IONIC liquids
Abstract

VIV oxyfluorides are of interest as frustrated magnets. The successful synthesis of two-dimensionally connected vanadium(IV) oxyfluoride structures generally requires the use of ionic liquids as solvents. During solvothermal synthesis experiments aimed at producing two- and three-dimensional vanadium(IV) selenites with triangular lattices, the title compound, diaquatetra-μ-fluorido-dioxidodivanadium(IV) monohydrate, V2O2F4(H2O)2·H2O, was discovered and features a new infinite V4+-containing two-dimensional layer comprised of fluorine-bridged corner- and edge-sharing VOF4(H2O) octahedral building units. The synthesis was carried out under solvothermal conditions. The V4+ centre exhibits a typical off-centring, with a short V=O bond and an elongated trans-V-F bond. Hydrogen-bonded water molecules occur between the layers. The structure is related to previously reported vanadium oxyfluoride structures, in particular, the same layer topology is seen in VOF3. [ABSTRACT FROM AUTHOR]

Published
2016
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177. V2O2F4(H2O)2·H2O: a new V4+ layer structure related to VOF3.

Author

Black, Cameron and Lightfoot, Philip

Subjects
OXYFLUORIDES, CRYSTAL structure, IONIC liquids
Abstract

VIV oxyfluorides are of interest as frustrated magnets. The successful synthesis of two-dimensionally connected vanadium(IV) oxyfluoride structures generally requires the use of ionic liquids as solvents. During solvothermal synthesis experiments aimed at producing two- and three-dimensional vanadium(IV) selenites with triangular lattices, the title compound, diaquatetra-μ-fluorido-dioxidodivanadium(IV) monohydrate, V2O2F4(H2O)2·H2O, was discovered and features a new infinite V4+-containing two-dimensional layer comprised of fluorine-bridged corner- and edge-sharing VOF4(H2O) octahedral building units. The synthesis was carried out under solvothermal conditions. The V4+ centre exhibits a typical off-centring, with a short V=O bond and an elongated trans-V-F bond. Hydrogen-bonded water molecules occur between the layers. The structure is related to previously reported vanadium oxyfluoride structures, in particular, the same layer topology is seen in VOF3. [ABSTRACT FROM AUTHOR]

Published
2016
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178. Extending the Family of V4+ S=½ Kagome Antiferromagnets.

Author

Clark, Lucy, Aidoudi, Farida H., Black, Cameron, Arachchige, Kasun S. A., Slawin, Alexandra M. Z., Morris, Russell E., and Lightfoot, Philip

Subjects
VANADIUM compounds, ANTIFERROMAGNETISM, CRYSTAL structure, THERMAL analysis, MAGNETIC susceptibility, IMIDAZOLES
Abstract

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Published
2015
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