Hybrid Framework Materials
A large part of our effort is devoted to exploring the exciting field of metal-organic framework materials, which are crystalline phases containing both inorganic and organic structural elements. Much of our work focuses on dense MOFs, where we are studying phase transitions, conductivity and ferrolelectric properties Typically, they are made by hydrothermal or solvothermal synthesis with conventional heating or microwaves. We are interested in a variety of broad questions relating to these materials, including the synthetic and other factors that control the dimensionalities of the reaction products.
Since metal-organic framework materials can exhibit the functionality of both inorganic and organic materials, they have a diverse range of properties and show potential for applications in a number of areas. Nanoporous hybrids are of interest for hydrogen storage and CO2 sequestration, as well as for shape-selective catalysis. One of the unique aspects of hybrid frameworks is the facility with which homochiral materials can be created by using single enantiomer organic ligands. We are just beginning to explore the properties of this interesting class of compounds.
Light Conversion Materials
The second main theme of our research concerns new light conversion materials for applications in solid state lighting, displays, photovoltaic devices and photocatalysis. The development of solid state lighting has the potential to make an enormous impact on energy consumption throughout the world, as well as bringing lighting to off-grid villages in developing countries. One of the challenges is to develop novel down-conversion phosphors that will harvest the blue of near UV light from LEDs and convert it efficiently into the other colors that are required for high quality white light. We are developing a range of inorganic phosphors that will achieve this objective, many of them based upon tunable Ce3+ systems. We are also developing methods of preparing nanoparticles of our phosphors, which may give enhanced device performance.
Materials Chemistry of Technetium Oxides
The group has a long-standing tradition of research on transition metal oxides, and the technetium oxides are certainly the least well understood of these materials. However, they are of great significance because of the widespread occurrence of 99Tc in fission products from nuclear reactors. Our previous experience with oxides of manganese and rhenium (above and below technetium, respectively, in the periodic table) puts us in a strong position to have an impact in this area. We have started by exploring the binary oxides of Tc, probing the detailed structure of TcO2 for the first time and attempting to synthesize the technetium analogue of the classical metallic oxide, ReO3. Our first principles (DFT) calculations on TcO3 indicate that it should be stable with respect to disproportionation into TcO2 and Tc2O7. The focus of our current work in this area is on the ternary oxides of technetium, a field that is almost entirely unexplored.
Some representative publications
- Structural Diversity and Chemical Trends in Hybrid Inorganic-Organic Framework Materials. A.K. Cheetham, C.N.R. Rao and R.K. Feller, JCS Chem. Comm. 2006, 4780-4795.
- Adsorption of Molecular Hydrogen on Coordinatively Unsaturated Ni(II) Sites in a Nanoporous Hybrid Material. P.M. Forster, J. Eckert, B.D. Heiken, J.B. Parise, J.W. Yoon, S.H. Jhung, J.-S. Chang, and A.K. Cheetham, J. Amer. Chem. Soc. 2006, 128, 16846-16850.
- There's room in the middle. A.K. Cheetham and C.N.R. Rao, Science 2007, 318, 58-59.
- Structure-property correlations in Ce-doped garnet phosphors for use in solid state lighting. G. Gundiah, J.L. Wu and A.K. Cheetham, Chem. Phys. Lett. 2007, 441, 250-254.
- Structural Studies of TcO2 by Neutron Powder Diffraction and First-Principles Calculations. E.E. Rodriguez, A. Llobet, A. Sattelberger, F. Poineau, T. Hartmann, J. Bhattacharjee, U.V. Waghmare, and A.K. Cheetham, J. Amer. Chem. Soc. 2007, 129, 10244-10248.