# The Oxygen Partial Pressure Dependence of Space Charges at SrTiO3|Mixed Ionic Electronic Conducting Oxide Heterojunctions

## TL;DR

This study explores how oxygen levels affect electrical properties at the interface of two types of oxides, offering a model to predict these changes.

## Contribution

A new model is introduced to explain and predict p(O2) dependencies of space charge potentials at MIEC|MIEC interfaces.

## Key findings

- Space charge potentials decrease with decreasing oxygen partial pressure.
- The model successfully links Δϕ changes to p(O2) dependent defect concentrations in MIECs.
- The model can predict transitions between hole and electron depleted layers.

## Abstract

The electrical and electrochemical properties of mixed conducting oxides often depend on the oxygen partial pressure p(O2) and numerous studies have dealt with the p(O2) dependencies found in bulk materials. However, measurements regarding the properties of interfaces between two different mixed conducting oxides are much less common. This work investigates the interfacial space charge region in SrTiO3 (STO) caused by the contact with another mixed ionic and electronic conductor (MIEC), specifically La0.6Sr0.4FeO3−δ (LSF), La0.65Sr0.35MnO3−δ (LSM) and La0.9Sr0.1CrO3−δ (LSCr). The space charge regions were investigated by means of electrochemical impedance spectroscopy at 500 °C in the broad p(O2) range of 1 bar to 10−32 bar. All measurable space charge potentials Δϕ show a decrease with decreasing p(O2). A model correlates the change in Δϕ with the strongly p(O2) dependent defect concentrations of the MIECs. The measured partial pressure dependencies of Δϕ can be fully attributed to the different p(O2) dependencies of the respective bulk Fermi levels. The suggested model is broadly applicable to MIEC|MIEC interfaces in general and can also be used to predict transitions of space charges from hole depleted to electron depleted layers.

Impedance measurements of La0.6Sr0.4FeO3−δ, La0.65Sr0.35MnO3−δ and La0.9Sr0.1CrO3−δ on top of STO (100) single crystals are preformed in a broad p(O2) range between 1 and 10−32 bar. The space charge regions in STO are characterized in dependence of the varying p(O2) and a model is introduced to describe and predict p(O2) dependent trends of the space charge potential.