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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Free-spin dominated magnetocaloric effect in dense Gd3+double perovskites Eliseanne C. Koskelo , Cheng Liu , Paromita Mukherjee , Nicola D. Kelly , Sian E. Dutton Chemistry Of Materials DOI: 10.1021/acs.chemmater.2c00261 Diamond Proposal Number(s): [28349] Show Abstract ▼ Abstract: Frustrated lanthanide oxides with dense magnetic lattices are of fundamental interest for their potential in cryogenic refrigeration due to a large ground state entropy and suppressed ordering temperatures but can often be limited by short-range correlations. Here, we present examples of frustrated fcc oxides, Ba2GdSbO6 and Sr2GdSbO6, and the new site-disordered analogue Ca2GdSbO6 ([CaGd]A[CaSb]BO6), in which the magnetocaloric effect is influenced by minimal superexchange (J1 ∼ 10 mK). We report on the crystal structures using powder X-ray diffraction and the bulk magnetic properties through low-field susceptibility and isothermal magnetization measurements. The Gd compounds exhibit a magnetic entropy change of up to −15.8 J/K/molGd in a field of 7 T at 2 K, a 20% excess compared to the value of −13.0 J/K/molGd for a standard in magnetic refrigeration, Gd3Ga5O12. Heat capacity measurements indicate a lack of magnetic ordering down to 0.4 K for Ba2GdSbO6 and Sr2GdSbO6, suggesting cooling down through the liquid 4-He regime. A mean-field model is used to elucidate the role of primarily free-spin behavior in the magnetocaloric performance of these compounds in comparison to other top-performing Gd-based oxides. The chemical flexibility of the double perovskites raises the possibility of further enhancement of the magnetocaloric effect in the Gd3+fcc lattices.	Mar 2022
B18-Core EXAFS	Insights into the electric double-layer capacitance of two-dimensional electrically conductive metal–organic frameworks Jamie W. Gittins , Chloe J. Balhatchet , Yuan Chen , Cheng Liu , David G. Madden , Sylvia Britto , Matthias J. Golomb , Aron Walsh , David Fairen-Jimenez , Sian E. Dutton , Alexander C. Forse Journal Of Materials Chemistry A 6 DOI: 10.1039/D1TA04026J Diamond Proposal Number(s): [14239] Open Access Show Abstract ▼ Abstract: Two-dimensional electrically conductive metal–organic frameworks (MOFs) have emerged as promising model electrodes for use in electric double-layer capacitors (EDLCs). However, a number of fundamental questions about the behaviour of this class of materials in EDLCs remain unanswered, including the effect of the identity of the metal node and organic linker molecule on capacitive performance, and the limitations of current conductive MOFs in these devices relative to traditional activated carbon electrode materials. Herein, we address both these questions via a detailed study of the capacitive performance of the framework Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with an acetonitrile-based electrolyte, finding a specific capacitance of 110–114 F g−1 at current densities of 0.04–0.05 A g−1 and a modest rate capability. By directly comparing its performance with the previously reported analogue, Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), we illustrate that capacitive performance is largely independent of the identity of the metal node and organic linker molecule in these nearly isostructural MOFs. Importantly, this result suggests that EDLC performance in general is uniquely defined by the 3D structure of the electrodes and the electrolyte, a significant finding not demonstrated using traditional electrode materials. Finally, we probe the limitations of Cu3(HHTP)2 in EDLCs, finding a limited stable double-layer voltage window of 1 V and only a modest capacitance retention of 81% over 30 000 cycles, both significantly lower than state-of-the-art porous carbons. These important insights will aid the design of future conductive MOFs with greater EDLC performances.	Jun 2021
I15-Extreme Conditions	Tuning dimensionality in van-der-Waals antiferromagnetic Mott insulators TM PS3 Matthew John Coak , David M. Jarvis , Hayrullo Hamidov , Charles Haines , Patricia Lebre Alireza , Cheng Liu , Suhan Son , Inho Hwang , Giulio I. Lampronti , Dominik Daisenberger , Paul Nahai-Williamson , Andrew Wildes , Siddharth S. Saxena , J.-G. Park Journal Of Physics: Condensed Matter DOI: 10.1088/1361-648X/ab5be8 Diamond Proposal Number(s): [21368] Show Abstract ▼ Abstract: We present an overview of our recent work in tuning and controlling the structural, magnetic and electronic dimensionality of 2D van-der-Waals antiferromagnetic compounds (Transition-Metal)PS3. Low-dimensional magnetic systems such as these provide rich opportunities for studying new physics and the evolution of established behaviours with changing dimensionality. These materials can be exfoliated to monolayer thickness and easily stacked and combined into functional heterostructures. Alternatively, the application of hydrostatic pressure can be used to controllably close the van-der-Waals interplanar gap and tune the crystal structure and electron exchange paths towards a 3D nature. We collect and discuss trends and contrasts in our data from electrical transport, Raman scattering and synchrotron x-ray measurements, as well as insight from theoretical calculations and other results from the literature. We discuss structural transitions with pressure common to all materials measured, and link these to Mott insulator-transitions in these compounds at high pressures. Key new results include magnetotransport and resistivity data in the high-pressure metallic states, which show potentially interesting qualities for a new direction of future work focused on low temperature transport and quantum critical physics.	Nov 2019

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