Anthony Kevin Cheetham
Email Address
akc@nus.edu.sg
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COLLEGE OF DESIGN & ENG
faculty
ENGINEERING
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Publication Stacking Faults Assist Lithium-Ion Conduction in a Halide-Based Superionic Conductor(American Chemical Society (ACS), 2022-03-24) Sebti, Elias; Evans, Hayden A; Chen, Hengning; Richardson, Peter M; White, Kelly M; Giovine, Raynald; Koirala, Krishna Prasad; Xu, Yaobin; Gonzalez-Correa, Eliovardo; Wang, Chongmin; Brown, Craig M; Cheetham, Anthony K; Canepa, Pieremanuele; Clément, Raphaële J; Dr Canepa Pieremanuele; MATERIALS SCIENCE AND ENGINEERINGPublication Role of hydrogen-bonding and its interplay with octahedral tilting in CH3NH3PbI3(Royal Society of Chemistry, 2015) Lee, J.-H; Bristowe, N.C; Bristowe, P.D; Cheetham, A.K; MATERIALS SCIENCE AND ENGINEERINGFirst principles calculations on the hybrid perovskite CH3NH3PbI3 predict strong hydrogen-bonding which influences the structure and dynamics of the methylammonium cation and reveal its interaction with the tilting of the PbI6 octahedra. The calculated atomic coordinates are in excellent agreement with neutron diffraction results. © The Royal Society of Chemistry 2015.Publication Topochemical conversion of a dense metal-organic framework from a crystalline insulator to an amorphous semiconductor(Royal Society of Chemistry, 2015) Tominaka, S; Hamoudi, H; Suga, T; Bennett, T.D; Cairns, A.B; Cheetham, A.K; MATERIALS SCIENCE AND ENGINEERINGThe topochemical conversion of a dense, insulating metal-organic framework (MOF) into a semiconducting amorphous MOF is described. Treatment of single crystals of copper(i) chloride trithiocyanurate, CuICl(ttcH3) (ttcH3 = trithiocyanuric acid), 1, in aqueous ammonia solution yields monoliths of amorphous CuI1.8(ttc)0.6(ttcH3)0.4, 3. The treatment changes the transparent orange crystals of 1 into shiny black monoliths of 3 with retention of morphology, and moreover increases the electrical conductivity from insulating to semiconducting (conductivity of 3 ranges from 4.2 × 10-11 S cm-1 at 20 °C to 7.6 × 10-9 S cm-1 at 140°C; activation energy = 0.59 eV; optical band gap = 0.6 eV). The structure and properties of the amorphous conductor are fully characterized by AC impedance spectroscopy, X-ray photoelectron spectroscopy, X-ray pair distribution function analysis, infrared spectroscopy, diffuse reflectance spectroscopy, electron spin resonance spectroscopy, elemental analysis, thermogravimetric analysis, and theoretical calculations. © The Royal Society of Chemistry 2015.Publication Research Update: Mechanical properties of metal-organic frameworks - Influence of structure and chemical bonding(2014) Li, W; Henke, S; Cheetham, A.K; MATERIALS SCIENCE AND ENGINEERINGMetal-organic frameworks (MOFs), a young family of functional materials, have been attracting considerable attention from the chemistry, materials science, and physics communities. In the light of their potential applications in industry and technology, the fundamental mechanical properties of MOFs, which are of critical importance for manufacturing, processing, and performance, need to be addressed and understood. It has been widely accepted that the framework topology, which describes the overall connectivity pattern of the MOF building units, is of vital importance for the mechanical properties. However, recent advances in the area of MOF mechanics reveal that chemistry plays a major role as well. From the viewpoint of materials science, a deep understanding of the influence of chemical effects on MOF mechanics is not only highly desirable for the development of novel functional materials with targeted mechanical response, but also for a better understanding of important properties such as structural flexibility and framework breathing. The present work discusses the intrinsic connection between chemical effects and the mechanical behavior of MOFs through a number of prototypical examples. © 2014 Author(s).Publication Synthesis and Characterization of the Rare-Earth Hybrid Double Perovskites: (CH3NH3)2KGdCl6 and (CH3NH3)2KYCl6(American Chemical Society, 2017) Deng, Z; Wei, F; Brivio, F; Wu, Y; Sun, S; Bristowe, P.D; Cheetham, A.K; MATERIALS SCIENCE AND ENGINEERINGTwo hybrid rare-earth double perovskites, (CH3NH3)2KGdCl6 and (CH3NH3)2KYCl6, have been synthesized by a solution evaporation method and their structures determined by variable temperature single-crystal X-ray diffraction. The diffraction results show that at room temperature both perovskites adopt a rhombohedral structure with R3m symmetry, as found previously for (MA)2KBiCl6, and lattice parameters of a = 7.7704(5) Å and c = 20.945(2) Å for (MA)2KGdCl6 and a = 7.6212(12) Å and c = 20.742(4) Å for (MA)2KYCl6. Both phases exhibit a rhombohedral-to-cubic phase transition on heating to ?435 K for (MA)2KYCl6 and ?375 K for (MA)2KGdCl6. Density functional calculations on the rhombohedral phase indicate that both materials have large direct band gaps, are mechanically stable, and, in the case of (MA)2KGdCl6, could exhibit magnetic ordering at low temperatures. © 2017 American Chemical Society.Publication Preface to Special Topic: Metal-organic framework materials(2014) Li, W; Gao, S; Cheetham, A.K; MATERIALS SCIENCE AND ENGINEERING[No abstract available]Publication Tuneable mechanical and dynamical properties in the ferroelectric perovskite solid solution [NH3NH2]1-x[NH3OH]xZn(HCOO)3(Royal Society of Chemistry, 2016) Kieslich, G; Kumagai, S; Forse, A.C; Sun, S; Henke, S; Yamashita, M; Grey, C.P; Cheetham, A.K; MATERIALS SCIENCE AND ENGINEERINGWe report how mechanical and dynamical properties in formate-based perovskites can be manipulated by the preparation of an A-site solid-solution. In the series [NH3NH2]1-x[NH3OH]xZn(HCOO)3 with xmax = 0.48, the substitution of [NH3NH2]+ by [NH3OH]+ is accompanied by a series of complex changes in crystal chemistry which are analysed using PXRD, SCXRD, 1H solid state NMR, DSC and nanoindentation. NMR shows increased motion of [NH3NH2]+ in [NH3NH2]0.52[NH3OH]0.48Zn(HCOO)3, which results in a shift of the ferroelectric-to-paraelectric phase transition temperature from Tc = 352 K (x = 0) to Tc = 324 K (x = 0.48). Additionally, the loss of hydrogen bonds directly influences the mechanical response of the framework; the elastic moduli and hardnesses decrease by around 25% from E110 = 24.6 GPa and H110 = 1.25 GPa for x = 0, to E110 = 19.0 GPa and H110 = 0.97 GPa for x = 0.48. Our results give an in-depth insight into the crystal chemistry of ABX3 formate perovskites and highlight the important role of hydrogen bonding and dynamics. © 2016 The Royal Society of Chemistry.Publication Understanding the Structural and Electronic Properties of Bismuth Trihalides and Related Compounds(AMER CHEMICAL SOC, 2020-03-16) Deng, Zeyu; Wei, Fengxia; Wu, Yue; Seshadri, Ram; Cheetham, Anthony K; Canepa, Pieremanuele; Dr Canepa Pieremanuele; MEDICINE; MATERIALS SCIENCE AND ENGINEERING; COLLEGE OF DESIGN AND ENGINEERINGBismuth trihalides, BiX3 (X = F, Cl, Br, and I), have been thrust into prominence recently because of their close chemical relationship to the halide perovskites of lead, which exhibit remarkable performance as active layers in photovoltaic cells and other optoelectronic devices. In the present work, we have used calculations based on density functional theory to explore the energetics and electronic properties of BiX3 in a variety of known and hypothetical structure types. The results for BiX3 are compared with those obtained for the halides of the later rare earths, represented by YX3 and LuX3. The relative thermodynamic stabilities of the known and hypothetical structures are calculated, along with their band gaps. For the BiX3 systems, we have explored the role of lone-pair effects associated with bismuth(III), and for BiI3, we have compared the predicted structural behavior as a function of pressure with the available experimental data. We have also attempted to synthesize LuF3 in the perovskite-related ReO3-type structure, which is predicted to be only ∼7.7 kJ mol-1 above the convex hull. This attempt was unsuccessful but led to the discovery of a new hydrated phase, (H3O)Lu3F10H2O, which is isomorphous with the known ytterbium analogue.Publication A chemical map of NaSICON electrode materials for sodium-ion batteries(Royal Society of Chemistry, 2020-11-21) GILL BALTEJ SINGH; Ziliang Wang; Sunkyu Park; Gopalakrishnan Sai Gautam; Jean-Noel Chotard; Laurence Croguennec; Dany Carlier; CHEETHAM, ANTHONY KEVIN; Christian Masquelier; PIEREMANUELE CANEPA; MATERIALS SCIENCE AND ENGINEERINGNa-ion batteries are promising devices for smart grids and electric vehicles due to the cost effectiveness arising from the overall abundance of sodium (Na) and its even geographical distribution. Among other factors, the energy density of Na-ion batteries is limited by the cathode electrode chemistry. NaSICONbased electrode materials are known for their wide range of electrochemical potentials, high ionic conductivity, and most importantly their structural and thermal stabilities. Using first-principles calculations, we chart the chemical space of 3d transition metal-based NaSICON phosphates with the formula NaxMM0 (PO4)3 (with M and M0 ¼ Ti, V, Cr, Mn, Fe, Co and Ni) to analyze their thermodynamic stabilities and the intercalation voltages for Na+ ions. Specifically, we compute the Na insertion voltages and related properties of 28 distinct NaSICON compositions. We investigate the thermodynamic stability of Na-intercalation in previously unreported NaxMn2(PO4)3 and NaxVCo(PO4)3. The calculated quaternary phase diagrams of the Na–P–O–Co and Na–P–O–Ni chemical systems explain the origin of the suspected instability of Ni and Co-based NaSICON compositions. From our analysis, we are also able to rationalize anomalies in previously reported experimental data in this diverse and important chemical space.Publication Rational approach to guest confinement inside MOF cavities for low-temperature catalysis(Nature Publishing Group, 2019) Wang, T.; Gao, L.; Hou, J.; Herou, S.J.A.; Griffiths, J.T.; Li, W.; Dong, J.; Gao, S.; Titirici, M.-M.; Kumar, R.V.; Cheetham, A.K.; Bao, X.; Fu, Q.; Smoukov, S.K.; MATERIALS SCIENCE AND ENGINEERINGGeometric or electronic confinement of guests inside nanoporous hosts promises to deliver unusual catalytic or opto-electronic functionality from existing materials but is challenging to obtain particularly using metastable hosts, such as metal–organic frameworks (MOFs). Reagents (e.g. precursor) may be too large for impregnation and synthesis conditions may also destroy the hosts. Here we use thermodynamic Pourbaix diagrams (favorable redox and pH conditions) to describe a general method for metal-compound guest synthesis by rationally selecting reaction agents and conditions. Specifically we demonstrate a MOF-confined RuO 2 catalyst (RuO 2 @MOF-808-P) with exceptionally high catalytic CO oxidation below 150 °C as compared to the conventionally made SiO 2 -supported RuO 2 (RuO 2 /SiO 2 ). This can be caused by weaker interactions between CO/O and the MOF-encapsulated RuO 2 surface thus avoiding adsorption-induced catalytic surface passivation. We further describe applications of the Pourbaix-enabled guest synthesis (PEGS) strategy with tutorial examples for the general synthesis of arbitrary guests (e.g. metals, oxides, hydroxides, sulfides). © 2019, The Author(s).