Resistive Switching in Cr doped SrTiO3: An X-ray Absorption Spectroscopy study

TL;DR

This study uses X-ray absorption spectroscopy to investigate the microscopic mechanisms behind resistive switching in Cr-doped SrTiO3, revealing oxygen vacancy dynamics at the interface as the key factor rather than chromium valence change.

Contribution

The paper demonstrates that resistive switching in Cr:SrTiO3 is driven by oxygen vacancy redistribution at the interface, not by chromium valence change, combining spectroscopy, microscopy, and DFT calculations.

Findings

Cr valence changes from 3+ to 4+ under electric field

Oxygen vacancies localize at the interface and influence switching

Switching mechanism is due to vacancy dynamics, not valence change

Abstract

X-ray absorption spectroscopy was used to study the microscopic origin of conductance and resistive switching in chromium doped strontium titanate (Cr:SrTiO3). Differences in the x-ray absorption near edge spectroscopy (XANES) at the Cr K-edge indicate that the valence of Cr changes from 3+ to 4+ underneath the anode of our sample device after the application of an electric field. Spatially resolved x-ray fluorescence microscopy ($\mu$-XRF) maps show that the Cr4+ region retracts from the anode-Cr:SrTiO3 interface after a conducting state has been achieved. This interface region is studied with extended x-ray absorption fine structure (EXAFS) and the results are compared with structural parameters obtained from density functional theory (DFT) calculations. They confirm that oxygen vacancies which are localized at the octahedron with a Cr at its center are introduced at the interface. It is proposed that the switching state is not due to a valence change of chromium but caused by changes of oxygen vacancies at the interface.