Low-Temperature Resistance Anomaly atSrTiO3Grain Boundaries: Evidence for an Interface-Induced Phase Transition

Abstract

Variable temperature transport between 1.4 and 300 K, structural imaging, and theoretical calculations were used to characterize the properties of electrically active 24° and 36.8° $[001]$ tilt ${\mathrm{SrTiO}}_3$ grain boundaries with 0.1 at. % niobium doping. An anomaly in boundary resistance and capacitance characteristics typical of a positive temperature coefficient effect is observed. This behavior is indicative of interface-induced dipole ordering. The detailed atomic structures of these grain boundaries were determined from a comparison of ab initio calculations and $Z$-contrast TEM images. The number of excess electrons at the boundaries determined experimentally and theoretically agrees and is associated with the boundary structural units.