Browsing by Author "Liu, JN"

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    Electrochemically activated solid synthesis: an alternative solid-state synthetic method
    (Royal Society of Chemistry, 2018-09-29) Liu, JN; Andersen, HL; Al Bahri, OK; Bhattacharyya, S; Rawal, A; Brand, HEA; Sharma, N
    Solid-state synthesis is one of the most common synthetic methods in chemistry and is extensively used in lab-scale syntheses of advanced functional materials to ton-scale production of chemical compounds. It generally requires at least one or several high temperature and/or high-pressure steps, which makes production of compounds via solid-state methods very energy and time intensive. Consequently, there is a persistent economic and environmental incentive to identify less energy and time consuming synthetic pathways. Here, we present an alternative solid-state synthetic method, which utilizes structural changes, induced by an electrochemical "activation" step followed by a thermal treatment step. The method has been used to synthesize a Sc0.67WO4-type phase where Sc0.67WO4 has previously only been obtained at 1400 °C and 4 GPa for 1 h. Through our method the Sc0.67WO4-type phase has been prepared at only 600 °C and ambient pressure. Experimental factors that influence phase formation from the electrochemical perspective are detailed. Overall, the method presented in this work appears to be able to generate the conditions for unusual and new phases to form and thus becomes another tool for synthetic solid-state chemists. This in turn permits the exploration of a larger synthetic parameter space. © 2018 The Royal Society of Chemistry.
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    Sc1.5Al0.5W3O12 exhibits zero thermal expansion between 4 and 1400 K
    (American Chemical Society, 2021-05-06) Liu, JN; Maynard-Casely, HE; Brand, HEA; Sharma, N
    Zero thermal expansion (ZTE) is a rare physical property; however, if accessible, these ZTE or near ZTE materials can be widely applied in electronic devices and aerospace engineering in addition to being of significant fundamental interest. ZTE materials illustrate this property over a certain temperature range. Here, orthorhombic (Pnca space group) Sc1.5Al0.5W3O12 is demonstrated to deliver ZTE over the widest temperature reported to date, from 4 to 1400 K, with a coefficient of thermal expansion of αv = −6(14) × 10–8 K–1. Sc1.5Al0.5W3O12 maybe is one of the most thermally stable materials known based on the temperature range of stability and the consistent thermal expansion coefficients observed along the crystallographic axes and volumetrically. Furthermore, this work demonstrates the atomic perturbations that lead to ZTE and how varying the Sc:Al ratio can alter the coefficient of thermal expansion. © 2021 American Chemical Society
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    The Sc2WxMo3−xO12 series as electrodes in alkali-ion batteries
    (Royal Society of Chemistry, 2021-04-29) Liu, JN; Johannessen, B; Brand, HEA; Andersen, HL; Sharma, N
    Herein, the series Sc2WxMo3−xO12 (0 ≤ x ≤ 3) is synthesised and the structure and electrochemical performance in alkali-ion batteries is characterised. The structures remain in the orthorhombic Pnca space group for the whole series with the lattice parameters increasing approximately linearly from {a = 9.6336(2) Å, b = 13.2406(3) Å, c = 9.5413(2) Å} in Sc2Mo3O12 to {a = 9.6735(2) Å, b = 13.3218(3) Å, c = 9.5811(2) Å} in Sc2W3O12. Discharge against Li delivers a high initial discharge capacity of 1200 mA h g−1 for Sc2Mo3O12 with a reversible capacity of about 150 mA h g−1 after 100 cycles. Meanwhile the increase of W content reduces both the initial and overall capacities for all lithium, sodium and potassium half cells. The initial discharge capacity for Sc2W3O12 against lithium is only about 700 mA h g−1 with a reversible capacity of about 100 mA h g−1 after 100 cycles. For all sodium and potassium half cells across the series, the capacities drop dramatically after a few cycles and the reversible capacities are low, below 50 mA h g−1. Structurally, the fully potassium discharged Sc2Mo3O12 partially transforms into a new P[4 with combining macron] space group KMo4O6 phase, while the crystallinity decreases in both fully lithium and sodium discharged Sc2Mo3O12. For Sc2W3O12, only fully potassium discharged Sc2W3O12 shows a decrease in crystallinity, while the fully lithium and sodium discharged Sc2W3O12 appears to become amorphous (or particles are too small to be examined with X-ray diffraction). X-ray absorption spectroscopy demonstrates that the Mo oxidation state changes with different type and amount of alkali-ion discharge. This work illustrates the influence of composition on the electrochemical performance in this family of compounds. © 2021 The Royal Society of Chemistry
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    Structural evolution and stability of Sc2(WO4)3 after discharge in a sodium-based electrochemical cell
    (Royal Society of Chemistry, 2017-12-13) Andersen, HL; Al Bahri, OK; Tsarev, S; Johannessen, B; Schulz, B; Liu, JN; Brand, HEA; Christensen, M; Sharma, N
    Sc2(WO4)3, prepared by solid state synthesis and constructed as an electrode, is discharged to different states in half-cell batteries, versus a Na negative electrode. The structural evolution of the Na-containing electrodes is studied with synchrotron powder X-ray diffraction (PXRD) revealing an increase in microstrain and a gradual amorphization taking place with increasing Na content in the electrode. This indicates that a conversion reaction takes place in the electrochemical cell. X-ray absorption spectroscopy (XAS) at the tungsten L3 absorption edge shows a reduction in the tungsten oxidation state. Variable temperature (VT) PXRD shows that the Sc2(WO4)3 electrode remains relatively stable at higher temperatures, while the Na-containing samples undergo a number of phase transitions and/or turn amorphous above ∼400 °C. Although, Sc2(WO4)3 is a negative thermal expansion (NTE) material only a subtle change of the thermal expansion is found below 400 °C for the Na-containing electrodes. This work shows the complexity in employing an electrochemical cell to produce Na-containing Sc2(WO4)3 and the subsequent phase transitions. © 2018 The Royal Society of Chemistry.