1. Metals and the Metallic State : Turning Insulators into Metals
A sample of sodium tungsten bronze; an example of a metallic oxide (see also 5).
There are numerous systems and materials for which small changes in temperature, pressure or composition can transform an insulating, non-metallic, material into a highly conducting metallic state. Professor C.N.R. Rao of Bangalore has drawn a graphic analogy, noting this process is akin to "Turning Wood into Copper". A detailed understanding of this remarkable electronic and thermodynamic phase transition is one of our major continuing interests, and covers a wide range of systems and materials.
In addition, materials close to the Metal-Insulator Transition are excellent candidates for new, high temperature superconductors.
“The Metal-Insulator Transition: A Perspective”
P. P. Edwards, R. L. Johnston, C. N. R. Rao, D. P. Tunstall & F. Hensel, Phil. Trans. Roy. Soc. Lond. A., 356, 5 (1998).
“What, Why and When is a Metal?”
P.P. Edwards in ‘The New Chemistry’, ed; N. Hall, Cambridge University Press, pp 85 (2000).
P. P. Edwards & F. Hensel, ChemPhysChem., 3, 53 (2002).
“The Insulator-Superconductor Transformation in Cuprates”
P. P. Edwards, N. F. Mott & A. S. Alexandrov, J. Supercond., 11, 151 (1998).
“Vibronic Coupling in Molecules and in Solids”
W. Grochala, R. Hoffmann & P. P. Edwards, Chem.-Eur. J., 9(2), 575 (2003).
2. The Continuing Challenge of High-Temperature Superconductivity
The higest Tc material : HgBa2Ca2Cu3O8+d.
The observation in 1987 of high-temperature superconductivity (High Tc) by J.G. Bednorz and K.A. Müller represents one of the greatest experimental discoveries of the last century. The remarkable phenomenon of High Tc still is not yet understood and one of the greatest scientific challenges for this century is to try and synthesise yet - higher - transition temperature superconductors. Our ultimate goal is a deep understanding of this fascinating natural phenomenon. We try to synthesise materials which we believe might be new superconductors. One recent example is a collaboration with Wojciech Grochala (University Warsaw) centres on fluoroargenates, some of the most oxidising systems known. At the other extreme of the Periodic Table we look for superconductivity in metal-ammonia solutions – the most reducing chemical system. The project also involves thin - film synthesis of superconductors by the laser ablation technique (see 5 and 6)
“Synthesis and Superconducting Properties of the Strontium Copper Oxyfluoride Sr2CuO2F2+d”
M. Al-Mamouri, P.P. Edwards, C. Greaves & M. Slaski, Nature, 369, 382 (1994).
“Mercurocuprates: The Highest Transition-Temperature Superconductors”
P. P. Edwards, G. B. Peacock, J. P. Hodges, A. Asab & I. Gameson, in High-Tc Superconductivity 1996: Ten Years after the Discovery, E. Kaldis, E. Liarokapis & K. A. Müller (editors), Kluwer Academic Publishers, Vol. 343, 135 (1997).
“Bulk Synthesis of the 135K Superconductor HgBa2Ca2Cu3O8+d”
G. B. Peacock, I. Gameson & P. P. Edwards, Adv. Mater., 9, 248 (1997).
“The Metal-Insulator-Transition and High Temperature Superconductivity”
P. P. Edwards, Advances in Superconductivity XII, Proceedings of the 12th International Symposium on Superconductivity (ISS ‘99), T. Yamashita and K. Tanabe, eds., Springer Verlag, Tokyo, 85 (2000).
“Meissner-Ochsenfeld superconducting anomalies in the Be-Ag-F system”
W. Grochala, A. Porch & P. P. Edwards, Solid State Commun., 130(1-2), 137 (2004).
“Possibility of a Liquid Superconductor”
P. P. Edwards. C. N. R. Rao, N. Kumar & A. S. Alexandrov, ChemPhysChem., 7, 2015 (2006).
3. Divided Metals : The Size-Induced Metal-Insulator Transition
From the front cover of “Size-Dependent Chemistry: Properties of Nanocrystals” see selected publications.
We are interested in how the fundamental properties of a material change as we vary the characteristic physical size of individual particles of the metallic elements of the periodic table. The picture (right) shows colloidal (nanoscale) gold... Finely divided bulk gold (left) through to tiny particles (right) of diameter around 50Å. We probe the phenomenon of The Size - Induced Metal - Insulator Transition using a microwave absorption technique, developed by Dr. Adrian Porch at Cardiff University, which requires no physical attachment of electrodes to the sample. Remarkably, nanoscale particles of gold exibit conductivities of a factor of at least 10 million below that of the bulk metal - gold is now no longer a metallic conductor. This size regime also coincides with extremely high catalytic activity from the particles - gold is no longer a noble metal.
“On the Size-Induced Metal-Nonmetal Transition in Particles and Clusters”
P. P. Edwards, R. L. Johnston & C. N. R. Rao, in Metal Clusters in Chemistry, eds. P. R. Raithby & P. Braunstein, Wiley-V.C.H., 1454, (1999).
“Metal Nanoparticles and Their Assemblies”
C. N. R. Rao, G.U. Kulkarni, P. J. Thomas & P. P. Edwards, Chem. Soc. Rev., 29, 27 (2000).
“The Size-Induced Metal-Insulator Transition in Colloidal Gold”
P. P. Edwards, S. R. Johnson, M. O. Jones, A. Porch & R. L. Johnston, Studies in Surface Science and Catalysis, 132, 719 (2001).
“Size-Dependent Chemistry: Properties of Nanocrystals”
P. P. Edwards, C. N. R. Rao, G. U. Kulkarni & P. J. Thomas, Chem. Eur. J., 8, 29 (2002).
From the front cover of “Synthersis and Crystal Structure of Li4BH4(NH2)3” see selected publications.
Hydrogen is widely regarded as a most promising alternative to carbon-based fuels since it will help alleviate the inevitable environmental and energy supply concerns when fossil fuels become scarce and/or unsustainable because of ecological and energy/security reasons. Hydrogen has many advantages as an energy carrier; it is light weight, highly abundant and when used in fuel cells it generates no emissions other than normally benign water molecules.
We are particularly interested in the storage of hydrogen in solids for use in vehicular transportation and stationary applications, where, typically, a fuel cell provides the power source.
This research theme encompasses carbon, light-metal hydrides and new materials for hydrogen storage. At the heart of the activity is an attempt to understand -and hence control- the micro-, meso-, and nano-structure of low atomic number hydrogen storage materials. To achieve a breakthrough requires a suitable storage material of 6-7 weight percent hydrogen.
5. Transparent Conducting Oxides : Metals to See Through
A pellet of Indium Tin Oxide sample (left) and this same material in thin film form (see 6).
Transparent conductors (TC) are extremely important functional materials, with numerous applications. The most important TC is indium tin oxide (ITO), as it possesses the ideal combination of optical transparency and high electrical conductivity. We are interested in understanding the basic materials science of these intriguing materials to allow us to develop new, more efficient – and cheaper – TCOs; this project involves close colaboration with Merck and Dr. Adrian Porch at Cardiff University.
“Basic Materials Physics of Transparent Conducting Oxides”
P. P. Edwards, A. Porch, M. O. Jones, V. Morgan and R. Perks, Dalton Transactions, 19, 2995 (2004).
“Transparent Current Spreading Layers for Optoelectronic Devices”
A. Porch, D. V. Morgan and R. M. Perks, M. O. Jones and P. P. Edwards, J. Appl. Phys., 96(8), 4211 (2004).
“Electromagnetic Absorption in Transparent Conducting Films”
A. Porch, D. V. Morgan, R. M. Perks, M. O. Jones and P. P. Edwards, J. Appl. Phys., 95(9), 4734 (2004).
Many advanced materials show enhanced and attractive properties in thin film form; it is also possible to synthesise materials as thin films which are not thermodynamically stable under normal (conventional) synthetic conditions. We produce functional thin film materials using the technique of pulsed laser and vapour deposition. Some of our areas of research are:
Use of pulsed laser deposition as a chemical synthesis tool.
Deposition of so-called 'precursor films' for treatment external (ex-situ) to the laser chamber to induce interesting electronic and magnetic behaviour, e.g. the formation of high temperature mecurocuprate superconductors (see 2).
Production of transparent conducting oxides (see 5).
“Synthesis, Structure and Magnetic Characterisation of Pulsed Laser-Ablated Superconducting La2CuO4Fx Thin Films”
S. T.Lees, I. Gameson, M. O. Jones, P. P. Edwards & M. Slaski, Chem. Mater, Special Issue: ‘Frontiers in Inorganic Materials Chemistry’, 10, 3146 (1998).
“Improvement of Critical Current Density in Sb-doped HgBa2Ca2Cu3O8+d Superconductor Prepared by Hg Vapour Diffusion Process”
J. Q. Li, C. C. Lam, J. S. Abell, G. B. Peacock, P. P. Edwards & L. J. Shen, Physica C, 325, 109 (1999).
“(Hg,Sb)Ba2Ca2Cu3O8+d Thick Films on YSZ Substrates”
J. Q. Li, C. C. Lam, G. B. Peacock, N. C. Hyatt, I. Gameson, P. P. Edwards, T. C. Shields & J. S. Abell, Supercond. Sci. Technology, 13, 169 (2000).
“TI(Hg,Sb)Ba2Ca2Cu3O8+d Thick Films on YSZ Substrates”
J. Q. Li, C. C. Lam, G. B. Peacock, N. C. Hyatt, I. Gameson, P. P. Edwards, T. C. Shields & J. S. Abell, J. Superconductor Science & Technology, 13(2), 169 (2000).
“Microsctructure of Laser-Ablated Superconducting La2CuO4Fx Thin Films on SrTiO3”
P. P. Edwards, G. Kong, M. O. Jones & J. S. Abell, J. Mater. Res., 16, 3309 (2001).
“Microstructure of superconducting Hg0.5Cr0.5Sr2CuO4+d thin films on SrTiO3”
G. Kong, I. P. Jones, J. S. Abell, M. O. Jones & P. P. Edwards, Physica C, 372, 700 (2002).
7. Microwave Synthesis, Processing and Characterization
A microwave induced gas plasma reacting with a solid state sample in an alumina boat.
Microwave frequency radiation may be used as an efficient alternative to traditional energy sources for solid state synthesis. Furthermore, microwave radiation can be used as a processing tool for functional materials and a method also for determining their electronic properties. We investigate:
Quick and energy efficient synthesis routes for important functional materials.
New synthesis techniques involving either microwave-only initiated reactions or hybrid methods combining existing techniques with microwave radiation.
Developmental synthesis techniques whereby the reaction products are controlled by the precise chemical and physical nature of the reactants.
Microwave plasma processing of materials to induce desired functional properties.
Development of new microwave frequency sensors to investigate electronic properties.
“Rapid Synthesis of Colossal Magnetoresistance Manganites by Microwave Dielectric Heating”
K. E. Gibbons, M.O. Jones, S. J. Blundell, A. I. Mihut, I. Gameson, P. P. Edwards, Y. Miyazaki, N.C. Hyatt and A. Porch, J. Chem. Soc. Chem. Comm, 159 (2000).
“Microwave Enhanced Reaction of Carbohydrates with Amino-Derivatised Labels and Glass Surfaces”
E. A. Yates, M. O. Jones, C. E. Clarke, A. K. Powell, S. R. Johnson, A. Porch, P. P. Edwards and J. E.Turnbull, J. Mater. Chem., 13(9), 2061 (2003).
8. Ultrafine Materials in Zeolites Hosts : Metal Nanowires and Oxide Particles
From the front cover of “Electron Beam Induced Growth of Bare Silver Nanowires from Zeolite Crystallites” see selected publications.
Incorporation or dispersion of microscopic alkali and transition metal clusters within highly porous zeolitic host materials.
The production of complex metal oxides by salt occlusion and the decomposition of ion-exchanged and salt-occluded zeolite precursors.
The production of metal and metal alloy nano-sized particles within zeolite host materials, and ultafine wires outside zeolites.
“Electron Beam Induced Growth of Bare Silver Nanowires from Zeolite Crystallites”
P. P. Edwards, M. J. Edmondson, W. Zhou & S. A. Sieber, Advanced Materials, 13, 1608 (2001).
“TEM Studies of the In-situ Growth of Silver Metal Nanowires from Zeolites”
W. Zhou, M. J. Edmondson, P. A. Anderson & P. P. Edwards, Electron Microscopy and Analysis, 168, 397 (2001).
“Silver Nanowires: Inclusion in and Extrusion from a Mesoporous Template”
L. M. Worboys, P. P. Edwards & P. A. Anderson, Chem. Comm., 23, 2894 (2002).
“Production of Ultrafine Single-Crystal Copper Wires through Electron Beam Irradiation of Cu-Containing Zeolite X”
P. A. Anderson, M. J. Edmondson, P. P. Edwards, et al., Zeitschrift fur Anorganische und Allgemenie Chemie, 631(2-3): 443 (2005)
“Synthesis of Micro-Crystals of Transparent Cobalt Aluminate, Shrouded in Siliceous Material, from Co(II)-Exchanged Zeolite X”
M. T. J. Lodge, P. P. Edwards, P. A. Anderson, M. O. Jones & I. Gameson, Polyhedron, 25 (2), 568 (2006).
9. Metals in Liquid Ammonia : Electronic Solutions
A bead of Sodium Potassium alloy in anhydrous liquid ammonia. The blue colouration is due to the presence of solvated electrons.
Here we study the science and applications of solutions of alkali (and other) metals in non aqueous solvents. These fascinating systems, containing solvated electrons, metal anions and a variety of other species, have long been utilised in sythetic chemistry, part of our activities link with Professor Neil Skipper and his group at UCL. We interrogate their intrinsic properties (e.g. probing the structure and dynamics of the various species) and the composition - induced electrolyte - to - metal transition. We are also interested in their applications as highly-reducing (and selective) systems in the synthesis of new materials and the functionalisation of existing systems.
“Metallization of Alkali Anions in Condensed Phases”
N. C. Pyper and P. P. Edwards, J. Am. Chem. Soc., 122, 5092 (2000).
“Polarons, Bipolarons and Possible High-Tc Superconductivity In Metal-Ammonia Solutions”
P. P. Edwards, Plenary Lecture at MTSC 2000 Conference on “Major Trends in Superconductivity in the New Millennium”, Journal of Superconductivity, 13(6), 933 (2000).
“The Transition to the Metallic State in Alkali and Low-Z Fluids”
W. J. Nellis, R. Chau, P. P. Edwards & R. Winter, Z. Phys. Chemie-Int. J. Res. Phys. Chem. Chem. Phys., 217(7), 795 (2003).
“Possibility of a Liquid Superconductor”
P. P. Edwards. C. N. R. Rao, N. Kumar & A. S. Alexandrov, ChemPhysChem., 7, 2015 (2006).
Elemental carbon in all of its now – recognised form, is a fascinating material. The area has suffered after many disappointments with the promises from what has been termed “the waves of fashion”. Nevertheless, carbon will play a major role in the materials science of the future; the arrival of this new project, linking our activities with those of M. L. H. Green (Oxford Chemistry), A. H. Windle (Cambridge Materials) and A. Porch (Cardiff Electrical Engineering) is to explore methods of utilising the materials chemistry and physics of carbon in broad areas of technology, from energy storage materials, through super-efficient conductors of electricity and heat, to superior radar absorbing systems.