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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Novel S = 1/2 kagome lattice materials: Cs2TiCu3F12 and Rb2TiCu3F12 Lewis Downie , Elena Ardashnikova , Chiu Tang , Alexandre Vasiliev , Peter Berdonosov , Valery Dolgikh , Mark De Vries , P Lightfoot Crystals 5 (2), 226 - 243 DOI: 10.3390/cryst5020226 Diamond Proposal Number(s): [7980] Open Access Show Abstract ▼ Abstract: Two new members of the A2B′Cu3F12 family of kagome-related materials have been prepared, in order to further understand the crystal-chemical relationships, phase transitions and magnetic behaviour within this family of potentially frustrated S = ½ two-dimensional quantum magnets. Cs2TiCu3F12 adopts a crystal structure with the ideal kagome lattice topology (space group R3¯ 3 ¯ m) at ambient temperature. Diffraction studies reveal different symmetry-lowering structural phase transitions in single crystal and polycrystalline forms at sub-ambient temperatures, with the single crystal form retaining rhombohedral symmetry and the powder form being monoclinic. In both cases, long-range antiferromagnetic order occurs in the region 16–20 K. Rb2TiCu3F12 adopts a distorted triclinic structure even at ambient temperatures.	May 2015
I11-High Resolution Powder Diffraction	Structural phase transitions in the kagome lattice based materials Cs2−xRbxSnCu3F12 (x = 0, 0.5, 1.0, 1.5) L. J. Downie , C. Black , E. I. Ardashnikova , C. C. Tang , A. N. Vasiliev , A. N. Golovanov , P. S. Berdonosov , V. A. Dolgikh , P. Lightfoot Crystengcomm 16 (32), 6084-6089 DOI: 10.1039/C4CE00788C Diamond Proposal Number(s): [7980] Show Abstract ▼ Abstract: The solid solution Cs2−xRbxSnCu3F12 (x = 0, 0.5, 1.0, 1.5) has been investigated crystallographically between 100 and 300 K using synchrotron X-ray powder diffraction and, in the case of x = 0, neutron powder diffraction. For Cs2SnCu3F12 (x = 0), there is a structural transition from the previously reported room temperature rhombohedral symmetry (R[3 with combining macron]m) to monoclinic (P21/n) symmetry at 170 K. This transformation is repeated for the x = 0.5 composition, but with an increased transition temperature of 250 K. For x = 1.0 the monoclinic phase is found at 300 K, suggesting that the transition temperature is increased even further. For x = 1.5 a different behaviour, more akin to that previously reported for Rb2SnCu3F12, is found: a single phase transition between rhombohedral symmetry (R[3 with combining macron]) and triclinic symmetry (P[1 with combining macron]) is found at 280 K. In agreement with previous single crystal studies, Cs2SnCu3F12 powder exhibits strong antiferromagnetic interactions (Θ ~ −268 K) and long-range magnetic order at TN ~ 19.3 K. The finite magnetic moment observed for T < TN might be explained by a Dzyaloshinskii–Moriya interaction, due to the lowering of symmetry from rhombohedral to monoclinic, which was not suggested in the earlier single crystal study.	Jun 2014
I11-High Resolution Powder Diffraction	Re-entrant structural phase transition in a frustrated kagome magnet, Rb2SnCu3F12 Lewis J. Downie , Stephen P. Thompson , Chiu Tang , Simon Parsons , Philip Lightfoot Crystengcomm DOI: 10.1039/c3ce41422a Open Access Show Abstract ▼ Abstract: Rb2SnCu3F12 has been studied using synchrotron powder X-ray diffraction, powder neutron diffraction and single crystal X-ray diffraction at a range of temperatures (100–500 K). A broad but clear phase transition, possibly of re-entrant character, is found to occur in the powder form, whereas the corresponding transition is not seen in the single crystal.	Aug 2013
I11-High Resolution Powder Diffraction	Structural, magnetic and electrical properties of the hexagonal ferrites MFeO3 (M=Y, Yb, In) Lewis J. Downie , Richard J. Goff , Winfred Kockelmann , Sue D. Forder , Julia E. Parker , Finlay D. Morrison , Philip Lightfoot Journal Of Solid State Chemistry 190, 52-60 DOI: 10.1016/j.jssc.2012.02.004 Show Abstract ▼ Abstract: The hexagonal ferrites MFeO3 (M=Y, Yb, In) have been studied using a combination of neutron and X-ray powder diffraction, magnetic susceptibility, dielectric measurements and Fe-57 Mossbauer spectroscopy. This study confirms the previously reported crystal structure of InFeO3 (YAlO3 structure type, space group P6(3)/mmc), but YFeO3 and VbFeO(3) both show a lowering of symmetry to at most P6(3)cm (ferrielectric YMnO3 structure type). However, Mossbauer spectroscopy shows at least two distinct Fe sites for both YFeO3 and YbFeO3 and we suggest that the best model to rationalise this involves phase separation into more than one similar hexagonal YMnO3-like phase. Rietveld analysis of the neutron diffraction data was carried out using two hexagonal phases as a simplest case scenario. In both YFeO3 and YbFeO3, distinct dielectric anomalies are observed near 130 K and 150 K. respectively. These are tentatively correlated with weak anomalies in magnetic susceptibility and lattice parameters, for YFeO3 and YbFeO3, respectively, which may suggest a weak magnetoelectric effect. Comparison of neutron and X-ray powder diffraction shows evidence of long-range magnetic order in both YFeO3 and YbFeO3 at low temperatures. Due to poor sample crystallinity, the compositional and structural effects underlying the phase separation and possible magnetoelectric phenomena cannot be ascertained.	Jun 2012

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