Surface Space‐Charge Potential and Oxygen Surface Exchange Coefficient of SrTiO3: The Effect of Surface Orientation

Abstract

Abstract 18O2/16O2 exchange experiments on terminated (100), (110), and (111) oriented samples of single‐crystal SrTiO3 are used to study the effect of surface orientation on the oxygen surface exchange coefficient kO∗ and the surface space‐charge potential Φ0. Isotope exchanges are carried out at temperatures 922 kO∗(100). All kO∗ data are consistent with a change in the activation enthalpy of surface exchange from 3.0 eV at high temperatures to 1.8 eV at lower temperatures. The transition is attributed to a change from a charge‐transfer mechanism at high temperatures to a mechanism involving surface OH species. The transition temperature depends on the surface orientation, Ttr(111) ≈ Ttr(110) > Ttr(100). Values of Φ0 obtained varied between 0.50 V and 0.37 V, with isothermal values obeying Φ0(111) ≈ Φ0(110) < Φ0(100). Φ0 data is analysed to obtain the OH− surface coverage for the low‐temperature regime. Similarities between the behavior of Φ0 and that of kO∗ are highlighted.

Keywords

• space‐charge layer
• strontium titanate
• surface exchange