Facet-Dependent and Adjacent Facet-Related Electrical Conductivity Properties of SrTiO3 Crystals

Electrical conductivity measurements show that the {100} faces of a perfect SrTiO3 cube are insulating, but the {110} faces of a SrTiO3 truncated rhombic dodecahedron are considerably more conductive. Interestingly, compared to electrodes touching the proximal {110} faces, adjacent {110} face contacts give notably higher current. Unexpectedly, while the {110} faces of a truncated rhombic dodecahedron remain much more conductive than its {100} faces, the adjacent conductive {110} facets may cause the poorly conductive {100} facets to become more conductive through slight current leakage to the adjacent conductive faces. Consistent with previous insulating behavior observed for a {110}-bound Cu2O rhombic dodecahedron, the {110} faces of a Cu2O rhombicuboctahedral microcrystal remain insulating. Thus, the influence of adjacent conductive facet may be avoided using sharper electrodes. Still, the adjacent facet effect may always be present even with the use of sharp electrodes. Current-rectifying asymmetric I-V curves were recorded with electrodes contacting the {100} and {110} faces of a SrTiO3 truncated rhombic dodecahedron. The electrical facet effects can be understood with different degrees of band bending at these crystal surfaces and thus different barrier heights to charge carrier transport across these surfaces. Finally, high-resolution transmission electron microscopy (HR-TEM) images over the surfaces of SrTiO3 truncated rhombic dodecahedra and cubes were taken, showing notable shifts in atomic positions within the few layers of surface lattice planes relative to the atomic positions of the interior lattice, suggesting that the lattice deviations within the thin surface layer as predicted by density functional theory (DFT) calculations may be visually observable.