Thomas O Mason

Structure-Property Relationships in Electroceramics          

Our group investigates fundamental structure-property relationships in technologically important electroceramics, including transparent conducting oxides (TCOs), transparent oxide semiconductors (TOSs), ionic ceramics, and mixed ionic/electronic ceramics (MIECs).  Our work addresses the development of electroceramics for energy-conversion systems, such as photovoltaics and fuel cells.

The rare combination of optical transparency and high electronic mobility is found in oxides of a select group of metals (e.g., Zn, In, Sn).  TCOs serve as transparent electrodes in a wide range of applications, from flat panel displays to solar cells.  More recently, their semiconducting analogues (TOSs) are being employed as active elements in flexible and transparent thin film transistors.  In both cases, we investigate their underlying defect chemistry and how this governs transparent semiconductivity and conductivity.  An exciting new area of research involves amorphous forms of TCO and TOS materials.

High ionic conductivity is required for advanced electrochemical systems, e.g., batteries and fuel cells. We are investigating the role of nanocrystallinity in the transport properties of “nano-ionics” as electrolytes for such applications. In particular, owing to enhanced grain boundary transport, nano-ionics may enable lower operating temperatures than currently available with state-of-the-art solid oxide fuel cells (SOFCs). MIECs combine both ionic and electronic conductivity, and see application as SOFC electrodes.Our research addresses the role of grain boundaries in the transport properties of both nano-MIEC and nano-ionic materials.

Our group is developing models and methods for characterizing the grain core vs. grain boundary properties of nanoceramics.  We employ AC-impedance spectroscopy (AC-IS) and our newly developed “nano-Grain Composite Model” to separate local electrical/dielectric properties of technologically important electroceramics.

The Mason group is supported by the National Science Foundation and the Department of Energy. We are also active in the Materials Research Science & Engineering Center (MRSEC) and in two Energy Frontier Research Centers—ANSER (Argonne-Northwestern Solar Energy Research) Center, dealing with organic photovoltaics (employing oxide transparent electrodes), and the Center for Inverse Design, dealing with all-inorganic thin film photovoltaics.