Electron mobility (orange, left axis) and carrier density (green, right axis) for KTa0.91Nb0.09O3. The dashed orange line shows the expected trend in the absence of dielectric-screening enhancement. Arrow indicates the ferroelectric transition temperature Tc. Photograph shows insulating (clear) and Ca-doped semiconducting (dark) KTaxNb1-xO3 crystals.
The electron mobility in a semiconducting oxide is shown to be dramatically enhanced by the increase of the material’s dielectric constant near its ferroelectric transition temperature. Understanding how the charge carrier mobility can be increased in complex oxides is one of the most significant challenges in utilizing these functional materials in numerous applications, ranging from energy harvesting (photovoltaics, thermoelectrics) to energy storage (battery materials): the currently achieved room-temperature mobilities are too low to be practical. This study now combines results from measurements of electronic transport and optical properties with band structure calculations for semiconducting (Ca-doped) single crystals of the model ferroelectric KTaxNb1-xO3. This material’s ferroelectric transition temperature, and thus the temperature at which the dielectric permittivity peaks, can be compositionally tuned over a broad temperature range. Analyzing the temperature dependencies of dielectric permittivity, carrier concentration, band structure, and electronic mobility shows that charge carrier scattering at defects and impurities is greatly reduced by dielectric screening. The observation will aid in designing oxides in which the mobility is optimized for a specific operating temperature.
For more information, please contact Michael McGuire, mcguirema@ornl.gov.
Wolter Siemons, Michael A. McGuire, Valentino R. Cooper, Michael D. Biegalski, Ilia N. Ivanov, Gerald E. Jellison, Lynn A. Boatner, Brian C. Sales, and Hans M. Christen, "Dielectric-Constant-Enhanced Hall Mobility in Complex Oxides," Advanced Materials. DOI: 10.1002/adma.201104665.