Research:
My active areas of research are variations on a common thread; the hydrothermal synthesis of novel transition metal oxide compounds with desirable physical properties. All of our syntheses are conducted under hydrothermal conditions, which involve subjecting reactants to temperatures above 100 ºC in the presence of water. An autogenous pressure is generated, requiring the use of a sealed pressure vessel. The role of hydrothermal chemistry in preparative inorganic chemistry is well established. The autoclaves used in low temperature hydrothermal syntheses contain removable inert liners, which sequester all reactants. Standard commercially available autoclave volumes range between 23 and 125 mL. The working limits of this autoclave design preclude work above 250 ºC and 120 bar.
Hydrothermal reactions contain many interrelated variables, including temperature, pressure, reaction time, pH, aging time, template, reagent concentrations and solvent level. The autogenous pressure generated in each reaction necessitates the use of a pressure vessel, most often a fluoro(ethylene-propylene) “Teflon” cup in a stainless steel screw top jar. This apparatus makes direct in-situ observation of reactions difficult, and the role of many reaction components remains poorly understood. My research is focused upon three aspects of hydrothermal chemistry. First, I am interested in how the point symmetry of organic amines templates affects the three-dimensional symmetry of the resulting solid. We are made significant progress in constraint of centrosymmetry in our compounds, in an effort to force noncentrosymmetry and nonlinear optical activity. Second, most hydrothermal reactions employ a mineralizer, an aggressive agent that promotes dissolution of poorly soluble reactants. I am interested in the use of combinations of mineralizers, namely sulfuric and hydrofluoric acids. Third, a systematic study of the effects reagent concentration variations is ongoing through the construction of composition space diagrams and prisms.
Our primary method of characterizing these compounds is diffraction, both powder and single crystal. A GBC-Difftech MMA powder X-ray diffractometer is located in the laboratory, while we need to go off site for single crystal diffraction. Students learn to solve and refine single crystal data using programs such as Crystals and Wingx.