  The investigation of the defect chemistry of solid oxides is of central
importance for the understanding of redox processes. This can be performed by
measuring conductivity as a function of the oxygen partial pressure, which is
conventionally established by using buffer gas mixtures or oxygen pumps based
on zirconia. However, this approach has some limitations, such as difficulty
regulating oxygen partial pressure in some intermediate-pressure regions or the
possibility of influencing the redox process by gases that can also be
incorporated into the oxide or react with the surface via heterogeneous
catalysis. Herein, we present an alternative physical method in which the
oxygen partial pressure is controlled by dosing pure oxygen inside an
ultra-high vacuum chamber. To monitor the conductivity of the oxide under
investigation, we employ a dedicated four-probe measurement system that relies
on the application of a very small AC voltage, in combination with lock-in data
acquisition using highly sensitive electrometers, minimizing the
electrochemical polarization or electro-reduction and degradation effects. By
analyzing the model material SrTiO3, we demonstrate that its characteristic
redox behavior can be reproduced in good agreement with the theory when
performing simultaneous electrical conductivity relaxation (ECR) and
high-temperature equilibrium conductivity (HTEC) measurements. We show that the
use of pure oxygen allows for a direct analysis of the characteristic oxygen
dose, which opens up various perspectives for a detailed analysis of the
surface chemistry of redox processes.
