Peter Khalifah, Associate Professor
Joint with Brookhaven National Laboratory
B.S. Duke University, 1996
Ph.D. Princeton University, 2001
Post Doctoral Research Fellow, Oak Ridge National Laboratory, 2001 - 2004
Lecturer, University of Massachusetts, 2004 - 2007
Phone: (631) 632-7796 | BNL 344-7689
Materials Chemistry, Solid State Chemistry
Periodic solids provide the backbone of the high-tech industry due to their amplification of the interactions between individual atomic and molecular building blocks assembled within their crystalline lattices. This group focuses on designing functionality into crystalline solids using elemental substitution and structural control to fine-tune the energy levels of bulk materials. Our expertise in materials synthesis, structural characterization, and physical properties measurements allows us to tackle all aspects of this "internal design" process.
Renewable energy: Semiconductors of certain metal oxides have the capability of harnessing solar energy to split water, producing hydrogen gas. This process has the potential to solve the two looming energy crises (limited supply of hydrocarbon fuels and global warming from steeply rising CO2 levels), provided that the overall efficiency of this process can be raised. We are pursuing strategies to drastically raise the efficiency of photoelectrolysis by tuning the energy levels of oxide semiconductors to optimal positions.
Metal-metal bonding in solids: While most metal oxides are best understood by thinking about the electronic interactions between atomic orbitals (s,p,d,f), there is a small subset of compounds where this approach fails. When there are direct interactions between metals (instead of the more typical interactions mediated by bridging oxygens), the electronic states within the solid can resemble those of molecular orbitals (σ,π,δ) and not atomic orbitals. We seek to understand the potentially unique behavior of this class of compounds through a mixture of synthesis, physical properties measurements, electronic structure calculations, and scattering (neutron and x-ray) experiments.
Functional materials: A major component of our research is materials discovery and materials design. We continuously search for materials with novel or enhanced properties, such as multiferroics for computing applications, thermoelectrics for solid state energy generation and refrigeration, dielectrics for microwave communications, and superconductors for power transmission and magnetic field generation. We are also interested in producing materials that provide insights into the physical laws which govern the behavior of electronic and magnetic materials.
Crystal growth and crystallography: The processes of biomineralization are used by living organisms to grow a sophisticated range of microstructured and oriented crystals. We would like to adapt some of these methodologies to the preparation of oriented arrays of technologically-relevant inorganic materials. Also, we are interested in taking advantage of improvements in laboratory x-ray diffraction technology and molecular modeling software to broaden the range of molecular structures whose atomic positions can be solved and refined from powder diffraction data, and to better understand the forces driving molecular packing. While our primary expertise is with metal oxides, we are interested in trying to adapt some solid state techniques to the growth of molecular crystals. This group also spends some time dealing with complex crystallographic challenges, such as highly absorbing, twinned, and incommensurate structures.
D. J. Singh, R. C. Rai, J. L. Musfeldt, S. Auluck, N. Singh, P. Khalifah, S. McClure, D. G. Mandrus, “Optical properties and electronic structure of spinel ZnRh2O4”, Chem. Materials, 18, 2696-2700 (2005)
P. Khalifah, R. Osborn, Q. Huang, H. W. Zandbergen, R. Jin, Y. Liu, D. Mandrus, and R. J. Cava. “Orbital ordering transition in La4Ru2O10”, Science, 297, 2237-40 (2002).
P. Khalifah and R. J. Cava. “Metal-metal bonding in the KSbO3-type oxides La4Ru6O19 and La3Ru3O11: A mechanism for band gap formation in t2g states”, Physical Review B, 64, 085111 (2001).
P. Khalifah, K. D. Nelson, R. Jin, Z. Q. Mao, Y. Liu, Q. Huang, X. P. A. Gao, A. P. Ramirez, and R. J. Cava. “Non-Fermi-liquid behavior in La4Ru6O19”, Nature, 411, 669-71 (2001).
P. Khalifah, Q. Huang, D. M. Ho, H. W. Zandbergen, and R. J. Cava. “La7Ru3O18 and La4.87Ru2O12: Geometric frustration in two closely related structures with isolated RuO6 octahedra”, Journal of Solid State Chemistry, 155, 189-97 (2000).