Defect association in acceptor-doped SrTiO3: case study for Fe ′TiV ˙˙O and Mn ″TiV ˙˙O

Abstract

The association of acceptor cations (Fe^′_Ti and Mn^″_Ti) with oxygen vacancies in Fe- and Mn-doped SrTiO₃ single crystals is investigated using in-situ EPR spectroscopy. Effective association enthalpies Δ_assH⁰_eff and entropies Δ_assS⁰_eff are determined, and Δ_assH⁰_eff is found to depend strongly on the dopant concentration. This dependence can be roughly described by a correction term in the chemical potential that is proportional to the cube root of the defect concentration. Extrapolation to infinite dilution yields an association enthalpy of −26 kJ mol⁻¹. The association of oxygen vacancies can significantly reduce the ionic conductivity of these materials at temperatures up to ca. 200 °C (Fe^′_Ti) or even higher (Mn^″_Ti), and must therefore be taken into account in the respective defect chemical models at moderate or low temperatures.