Low-Temperature Resistance Anomaly at SrTiO3 Grain Boundaries: Evidence for an Interface-Induced Phase Transition

Variable temperature transport between 1.4 and 300 K, structural imaging, and theoretical calculations were used to characterize the properties of electrically active 24º and 36.8º [001] tilt SrTiO3 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.