Investigation of Electric Field–Induced Structural Changes at Fe-Doped SrTiO3 Anode Interfaces by Second Harmonic Generation

David Ascienzo,Clive Randall,Thorsten Bayer,Steve Greenbaum,Jian-Jun Wang,Haochen Yuan,Yuhang Ren,Russell Maier,Haibin Zhao,Elizabeth Dickey

doi:10.3390/ma9110883

David Ascienzo, Clive Randall + Show 8 more

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https://doi.org/10.3390/ma9110883

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Abstract

We report on the detection of electric field–induced second harmonic generation (EFISHG) from the anode interfaces of reduced and oxidized Fe-doped SrTiO3 (Fe:STO) single crystals. For the reduced crystal, we observe steady enhancements of the susceptibility components as the imposed dc-voltage increases. The enhancements are attributed to a field-stabilized electrostriction, leading to Fe:Ti-O bond stretching and bending in Fe:Ti-O6 octahedra. For the oxidized crystal, no obvious structural changes are observed below 16 kV/cm. Above 16 kV/cm, a sharp enhancement of the susceptibilities occurs due to local electrostrictive deformations in response to oxygen vacancy migrations away from the anode. Differences between the reduced and oxidized crystals are explained by their relative oxygen vacancy and free carrier concentrations which alter internal electric fields present at the Pt/Fe:STO interfaces. Our results show that the optical SHG technique is a powerful tool for detecting structural changes near perovskite-based oxide interfaces due to field-driven oxygen vacancy migration.

Highlights

Perovskite-type dielectric and ferroelectric oxides have attracted significant attention for their applications in a variety of electroceramic devices such as capacitors, thermistors, actuators, and sensors [1]
Fe-doped SrTiO3 (Fe):STOinterfaces sample, we enhancements of the susceptibility as the the anode ofobserved reducedsteady and oxidized single crystals.components
The enhancements are attributed to field-stabilized electrostriction, leading sample, no obvious structural changes were observed below 16 kV/cm

Summary

Introduction

Perovskite-type dielectric and ferroelectric oxides have attracted significant attention for their applications in a variety of electroceramic devices such as capacitors, thermistors, actuators, and sensors [1]. Oxygen vacancies form in the first coordination shell of Fe3+ centers This leads to a larger oxygen vacancy concentration compared to undoped STO, making Fe:STO an excellent material for studying field-induced structural changes due to oxygen vacancy migration [5,10,11]. We report on our detection of electric field–induced structural changes at reduced and oxidized Fe-doped SrTiO3 (Fe:STO) anode interfaces using optical SHG in the reflection geometry. The EFISHG intensity changes from both anode interfaces are explained by electrostrictive distortions to the crystal structure accompanied by oxygen vacancy migrations. Differences in the EFISHG responses are explained by the presence of internal electric fields at the Pt/Fe:STO interfaces which depend on local oxygen vacancies and free charge carrier concentrations. We show that optical SHG is a powerful tool for probing electric field–induced structural changes due to oxygen vacancy electromigration in perovskite oxides

Experiment and Theory

Results and Discussion

Conclusions