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Title: Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films

Abstract

The ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 degrees C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by approximate to 30%, resulting in a tunable oxygen defi cient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Basic Energy Sciences - Scientific User Facilities Division; USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division
OSTI Identifier:
1253606
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Advanced Functional Materials (Online); Journal Volume: 26; Journal Issue: 10
Country of Publication:
United States
Language:
English

Citation Formats

Petrie, Jonathan R., Mitra, Chandrima, Jeen, Hyoungjeen, Choi, Woo Seok, Meyer, Tricia L., Reboredo, Fernando A., Freeland, John W., Eres, Gyula, and Lee, Ho Nyung. Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films. United States: N. p., 2016. Web. doi:10.1002/adfm.201504868.
Petrie, Jonathan R., Mitra, Chandrima, Jeen, Hyoungjeen, Choi, Woo Seok, Meyer, Tricia L., Reboredo, Fernando A., Freeland, John W., Eres, Gyula, & Lee, Ho Nyung. Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films. United States. doi:10.1002/adfm.201504868.
Petrie, Jonathan R., Mitra, Chandrima, Jeen, Hyoungjeen, Choi, Woo Seok, Meyer, Tricia L., Reboredo, Fernando A., Freeland, John W., Eres, Gyula, and Lee, Ho Nyung. Tue . "Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films". United States. doi:10.1002/adfm.201504868.
@article{osti_1253606,
title = {Strain Control of Oxygen Vacancies in Epitaxial Strontium Cobaltite Films},
author = {Petrie, Jonathan R. and Mitra, Chandrima and Jeen, Hyoungjeen and Choi, Woo Seok and Meyer, Tricia L. and Reboredo, Fernando A. and Freeland, John W. and Eres, Gyula and Lee, Ho Nyung},
abstractNote = {The ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 degrees C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by approximate to 30%, resulting in a tunable oxygen defi cient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.},
doi = {10.1002/adfm.201504868},
journal = {Advanced Functional Materials (Online)},
number = 10,
volume = 26,
place = {United States},
year = {Tue Mar 08 00:00:00 EST 2016},
month = {Tue Mar 08 00:00:00 EST 2016}
}
  • In this study, the ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoO x) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 °C. By applying a small biaxial tensile strain (2%), the oxygen activation energy barrier decreases by ≈30%, resultingmore » in a tunable oxygen deficient steady-state under conditions that would normally fully oxidize unstrained cobaltite. These strain-induced changes in oxygen stoichiometry drive the cobaltite from a ferromagnetic metal towards an antiferromagnetic insulator. The ability to decouple the oxygen vacancy concentration from its typical dependence on the operational environment is useful for effectively designing oxides materials with a specific oxygen stoichiometry.« less
  • Epitaxial thin films of Cr2-xTixO3 were deposited by oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) for 0.04 ≤ x ≤ 0.26. Ti speciation is verified by both x-ray photoelectron spectroscopy (XPS) and Ti K-edge x-ray absorption near-edge spectroscopy (XANES) to be Ti4+. Substitution of Ti for Cr in the corundum lattice is confirmed by modeling of the Ti K-edge extended x-ray absorption fine structure (EXAFS). Room temperature electrical transport measurements confirm the highly insulating nature of Ti-doped Cr2O3, despite the presence of aliovalent Ti4+. The resistivity of highly pure, undoped Cr2O3 was measured to be three orders of magnitude higher than formore » Ti-doped Cr2O3. Although the formation of Cr vacancies in Ti-doped Cr2O3 is found by density functional theory (DFT) calculations to be the energetically preferable defect compensation mechanism to maintain charge neutrality, an analysis of the XPS and EXAFS data reveal the presence of both Cr vacancies and oxygen interstitials at intermediate and high Ti concentrations, with a weak trend towards Cr vacancies as the Ti concentration increases. At low Ti concentrations, a strong dependence of the XPS Ti 2p core level peak width on concentration is observed. This dependence is attributed to the presence of widely spaced Ti dopants, which renders compensation of two or three Ti by a single oxygen interstitial or Cr vacancy, respectively, less probable. Instead, defect clusters of unknown type occur, although they may involve Cr vacancies. The defect compensation model developed here provides insight into previous, conflicting reports of n-type versus p-type conductivity in Ti-doped Cr2O3 at high temperature, and will inform future studies to exploit the wide variety of electronic and magnetic properties of corundum-structure oxides.« less
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  • High quality single-crystal fcc-Co x (Mg y Zn 1-y ) 1-x O 1-v epitaxial thin films with high Co concentration up to x = 0.5 have been fabricated by molecular beam epitaxy. Systematic magnetic property characterization and soft X-ray absorption spectroscopy analysis indicate that the coexistence of ferromagnetic regions, superparamagnetic clusters, and non-magnetic boundaries in the as-prepared Co x (Mg y Zn 1-y ) 1-x O 1-v films is a consequence of the intrinsic inhomogeneous distribution of oxygen vacancies. Furthermore, the relative strength of multiple phases could be modulated by controlling the oxygen partial pressure during sample preparation. Armed withmore » both controllable magnetic properties and tunable band-gap, Co x (Mg y Zn 1-y ) 1-x O 1-v films may have promising applications in future spintronics.« less