A Route to Improving E lectron M obility in Oxide Materials

1. CNMS User Project Highlight A Route to Improving Electron Mobility in Oxide Materials • Scientific Achievement • The electron mobility in a semiconducting oxide is shown to be dramatically enhanced by the increase of the material’s dielectric constant via screening of defects and impurities. This observation was made in doped crystals of the model ferroelectric KTaxNb1-xO3, in which the temperature at which the dielectric constant peaks, can be continuously tuned via composition. • Significance • Room-temperature electron mobilities in functional oxides are still too low for practical applications, ranging from energy harvesting (photovoltaics, thermoelectrics) to energy storage (battery materials). The observed direct link between dielectric constant and mobility points to a general approach to improving the performance of these technologically relevant oxides. Electron mobility (orange, left axis) and carrier density (green, right axis) for KTa0.91Nb0.09O3. Dashed orange line shows the expected trend without dielectric-screening enhancement. Arrow indicates the ferroelectric transition temperature Tc. Photograph: insulating (clear) and Ca-doped semiconducting (dark) KTaxNb1-xO3. • Research Details • CNMS capability: Temperature-dependent x-ray diffraction and optical measurements of band gaps were performed at the CNMS. • Hall measurements were performed in the users’ own facilities on flux-grown, Ca-doped single crystals, confirming that the high dielectric constant at the ferroelectric transition increases the electron mobility. • Resources of the National Energy Research Scientific Computing Center were used for the DFT (band structure) calculations. W.Siemons, M.A. McGuire, V.R. Cooper, M.D. Biegalski, I.N. Ivanov, G.E. Jellison, L.A. Boatner, B.C. Sales, H.M. Christen, “Dielectric-Constant-Enhanced Hall Mobility in Complex Oxides,” Advanced Materials. DOI: 10.1002/adma.201104665.