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Instruments / Technical Area	Publication Details	Published	Actions
I11-High Resolution Powder Diffraction	High- versus low-spin Ni2+ in elongated octahedral environments: Sr2NiO2Cu2Se2, Sr2NiO2Cu2S2, and Sr2NiO2Cu2(Se1–xSx)2 Robert D. Smyth , Jack N. Blandy , Ziyu Yu , Shuai Liu , Craig V. Topping , Simon J. Cassidy , Catherine F. Smura , Daniel N. Woodruff , Pascal Manuel , Craig L. Bull , Nicholas P. Funnell , Christopher J. Ridley , John E. Mcgrady , Simon J. Clarke Chemistry Of Materials 6 DOI: 10.1021/acs.chemmater.2c02002 Diamond Proposal Number(s): [13284, 18786, 25166] Open Access Show Abstract ▼ Abstract: Sr2NiO2Cu2Se2, comprising alternating [Sr2NiO2]2+ and [Cu2Se2]2– layers, is reported. Powder neutron diffraction shows that the Ni2+ ions, which are in a highly elongated NiO4Se2 environment with D4h symmetry, adopt a high-spin configuration and carry localized magnetic moments which order antiferromagnetically below ∼160 K in a √2a × √2a × 2c expansion of the nuclear cell with an ordered moment of 1.31(2) μB per Ni2+ ion. The adoption of the high-spin configuration for this d8 cation in a pseudo-square-planar ligand field is supported by consideration of the experimental bond lengths and the results of density functional theory (DFT) calculations. This is in contrast to the sulfide analogue Sr2NiO2Cu2S2, which, according to both experiment and DFT calculations, has a much more elongated ligand field, more consistent with the low-spin configuration commonly found for square-planar Ni2+, and accordingly, there is no evidence for magnetic moment on the Ni2+ ions. Examination of the solid solution Sr2NiO2Cu2(Se1–xSx)2 shows direct evidence from the evolution of the crystal structure and the magnetic ordering for the transition from high-spin selenide-rich compounds to low-spin sulfide-rich compounds as a function of composition. Compression of Sr2NiO2Cu2Se2 up to 7.2 GPa does not show any structural signature of a change in the spin state. Consideration of the experimental and computed Ni2+ coordination environments and their subtle changes as a function of temperature, in addition to transitions evident in the transport properties and magnetic susceptibilities in the end members, Sr2NiO2Cu2Se2 and Sr2NiO2Cu2S2, suggest that simple high-spin and low-spin models for Ni2+ may not be entirely appropriate and point to further complexities in these compounds.	Oct 2022
I11-High Resolution Powder Diffraction	Synthesis, structure, magnetism and cation ordering in Ba3-Sr Fe2O5Cu2Ch2 (x = 0, 1, 2; Ch = S, Se) and BaCa2Fe2O5Cu2S2 Robert D. Smyth , John A. D. Wilson , Pascal Manuel , Simon J. Clarke Journal Of Solid State Chemistry 15 DOI: 10.1016/j.jssc.2021.122841 Diamond Proposal Number(s): [18786, 25166] Show Abstract ▼ Abstract: The layered oxide chalcogenides Ba3-xSrxFe2O5Cu2Ch2 (x = 0, 1, 2; Ch = S, Se) and BaCa2Fe2O5Cu2S2 are reported here for the first time. They are isostructural with the previously reported Sr3Fe2O5Cu2Ch2, crystallising in the I4/mmm space group. This structure is related to the n = 2 Ruddlesden-Popper type structure which is common for oxides and contains Sr3Fe2O5 perovskite-related slabs intergrown with Cu2Ch2 layers which resemble fragments of the antifluorite structure. In the oxide slabs, a double layer of FeO5 pyramids is formed by the sharing of apical oxide ions. Structural analysis shows a clear partial ordering of the alkaline earth cations of different sizes over the available 12 and 8-coordinate sites which correlates with the size variation of the alkaline earth cations. Long range magnetic ordering on a √2a × √2a × c expansion of the nuclear cell reveals nearest neighbour Fe3+ moments coupling antiferromagnetically via all the Fe–O–Fe linkages. In Ba3Fe2O5Cu2Se2, the moments are oriented in the ab-plane, whereas in Ba3-xSrxFe2O5Cu2Ch2 (x = 2; Ch = S, Se), the Fe3+ moments are tilted towards the c-axis, reflecting that high spin d5 ions with no orbital angular momentum have only a weak preference for a particular spin direction.	Dec 2021

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