Robert A. Welch Chair of Science
Director of the Texas Center for Superconductivity at UH
The synthesis and properties of transition metal oxide systems with layered or framework structures are one focus of my research. We study the synthesis of new compounds with asymmetric layer structures, open framework structures that can absorb molecules, and new synthetic techniques including hydrothermal electro-crystallization and reactions in ionic liquids. Asymmetric layer structures that we have investigated include the compounds A2(MO3)3XO3 where A = alkali metal, M = Mo, W and X = Se or CH3P-. All are inherently non-centrosymmetric and show nonlinear optical properties. We also use hydrothermal synthesis and coordination chemistry to construct new open framework structures. Recent examples include assembly of cluster anions such as [V2P2BO10]6 18- into framework structures, the synthesis of Ni(CN)4(Ph3Sn)2.xS, a coordination system with a very low-density framework, and single crystal growth and structure refinement of the titano-silicate ETS-10.
The synthesis and properties of oxides that have applications in high temperature ionic devices, such as fuel cells, oxygen transport membranes and sensors is a second research area. The major part of our work centers on mixed metal oxides withthe ABO3 perovskite structure. Because the database of perovskite oxide ionic properties is limited, we investigate new compositions to establish structure-property relationships. We use a variety of techniques to characterize the surface reactivity and bulk transport properties of materials. We use oxygen permeation through membranes, electrical conductivity relaxation, dc conductivity, ac impedance spectroscopy and other techniques to establish transport properties at high temperature in a variety of gas atmospheres. Isotope exchange together with secondary ion mass spectroscopy depth profiling, gives important and complementary information about ionic transport across interfaces.
US Editor, Solid State Ionics
Associate Editor, Materials Research Bulletin
Editorial Advisory Board, Progress in Solid State Chemistry, Journal of Solid State Chemistry, Solid State Sciences