Defect association in acceptor-doped SrTiO 3 : case study for Fe′TiV˙˙O and Mn″TiV˙˙O

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 ΔassH0eff and entropies ΔassS0eff are determined, and ΔassH0eff 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.