Atomic scale characterization of point and extended defects in niobate thin films

Metallic line defect in wide-bandgap transparent perovskite BaSnO3

A line defect with metallic characteristics has been found in optically transparent BaSnO₃ perovskite thin films. The distinct atomic structure of the defect core, composed of Sn and O atoms, was visualized by atomic-resolution scanning transmission electron microscopy (STEM). When doped with La, dopants that replace Ba atoms preferentially segregate to specific crystallographic sites adjacent to the line defect. The electronic structure of the line defect probed in STEM with electron energy-loss spectroscopy was supported by ab initio theory, which indicates the presence of Fermi level-crossing electronic bands that originate from defect core atoms. These metallic line defects also act as electron sinks attracting additional negative charges in these wide-bandgap BaSnO₃ films.

Sputtered SrxNbO3 as a UV-Transparent Conducting Film

Expanding the application space of transparent electrodes toward the ultraviolet range has been found challenging when utilizing the conventional approach to degenerately dope semiconductors with band gaps larger than ZnO or In₂O₃. Here, it is shown that the correlated metal Sr_xNbO₃ with x < 1 is ideally suited as a UV-transparent electrode material, enabling UV light-emitting diodes for a wide range of applications from water disinfection to polymer curing. It is demonstrated that Sr_xNbO₃ thin films can be grown by radio frequency (RF) sputtering and that they remain in the perovskite phase despite a sizeable Sr deficiency. The electrical and optical properties are characterized and compared to those of commonly used indium tin oxide (ITO) and Sn-doped Ga₂O₃ transparent conductor standards. Sr_xNbO₃ films were found to have sheet resistances as low as 30 Ω sq^-1 with optical transmission at a wavelength of 280 nm up to 86%, marking a two-order-of-magnitude increase over the performance of traditional UV-transparent conductors. The compatibility of Sr_xNbO₃ with a physical vapor deposition technique that is widely employed in the transparent conductor coating industry along with the robustness of the highly electrically conducting and optically transparent perovskite phase makes it an ideal transparent electrode for applications in the UV spectrum.

Electronic and plasmonic phenomena at nonstoichiometric grain boundaries in metallic SrNbO3

Grain boundaries could exhibit exceptional electronic structure and exotic properties, which are determined by a local atomic configuration and stoichiometry that differs from the bulk. However, optical and plasmonic properties at the grain boundaries in metallic oxides have rarely been discussed before. Here, we show that non-stoichiometric grain boundaries in the newly discovered metallic SrNbO₃ photocatalyst show exotic electronic, optical and plasmonic phenomena in comparison to bulk. Aberration-corrected scanning transmission electron microscopy and first-principles calculations reveal that a Nb-rich grain boundary exhibits an increased carrier concentration with quasi-1D metallic conductivity, and newly induced electronic states contributing to the broad energy range of optical absorption. More importantly, dielectric function calculations reveal extended and enhanced plasmonic excitations compared with bulk SrNbO₃. Our results show that non-stoichiometric grain boundaries might be utilized to control the electronic and plasmonic properties in oxide photocatalysis.