Electro-degradation and resistive switching of Fe-doped SrTiO3 single crystal

Abstract

In this work, the results of the electrocoloration of strontium titanate single crystals with different iron concentrations are presented. The samples of SrTiO3(100) doped with 0.06 at. % and 0.13 at. % of iron were electroreduced at low pressure (10−8 mbar) and elevated temperature (250 °C) using a DC voltage of 200 V. This led to the migration of oxygen vacancies and subsequent electrocoloration of the samples, which was confirmed by optical analysis and electrical measurements. Evolution of the color front was compared with finite element calculations of electric potential indicating good agreement. Both macroscopic and nanoscopic measurements showed insulator-metal transition at several hundreds of seconds (0.06%Fe) and resistive switching behavior. We found that the resistive switching is clearly modified by the oxygen partial pressure of the ambient atmosphere. Moreover, after electroreduction, in the region between the electrodes, stripes can be found following simple crystallographic directions connected with the extended defects and easy diffusion paths also observed in the single crystals of undoped strontium titanate. Furthermore, migration of negatively charged oxygen ions towards the anode led to the formation of oxygen bubbles trapped between the surface of the crystal and the electrode. Using atomic force microscopy, we were able to measure the geometry of a bubble and calculate the oxygen pressure necessary for the formation of such bubbles and the total amount of oxygen ions trapped within.