Title: Multi-scale chemo-mechanical evolution during crystallization of mixed conducting SrTi_0.65Fe_0.35O_3–δ films and correlation to electrical conductivity

Abstract

Recent work has demonstrated a low-temperature route to fabricating mixed ionic/electronic conducting (MIEC) thin films with enhanced oxygen exchange kinetics by crystallizing amorphous-grown thin films under mild temperatures, eluding conditions for deleterious A-site cation surface segregation. Yet, the complex, multiscale chemical and structural changes during MIEC crystallization and their implications for the electrical properties remain relatively unexplored. In this work, micro-structural and atomic-scale structural and chemical changes in crystallizing SrTi_0.65Fe_0.35O_3–δ thin films on insulating (0001)-oriented Al₂O₃ substrates are observed and correlated to changes in the in-plane electrical conductivity, measured in situ by ac impedance spectroscopy. Synchrotron X-ray absorption spectroscopy at the Fe and Ti K-edges gives direct evidence of oxidation occurring with the onset of crystallization and insight into the atomic-scale structural changes driven by the chemical changes. The observed oxidation, increase in B-site polyhedra symmetry, and alignment of neighboring B-site cation coordination units demonstrate increases in both hole concentration and mobility, thus underpinning the measured increase of in-plane conductivity by over two orders of magnitude during crystallization. High resolution transmission electron microscopy and spectroscopy of films at various degrees of crystallinity reveal compositional uniformity with extensive nano-porosity in the crystallized films, consistent with solid phase contraction expected from bothmore » oxidation and crystallization. We suggest that this chemo-mechanically driven dynamic nano-structuring is an additional contributor to the observed electrical behavior. By the point that the films become ~60% crystalline (according to X-ray diffraction), the conductivity reaches the value of dense, fully crystalline films. Furthermore, given the resulting high electronic conductivity, this low-temperature processing route leading to semi-crystalline hierarchical films exhibits promise for developing high performance MIECs for low-to-intermediate temperature applications.« less

Authors:

Buckner, Haley B. ^[1]; Ma, Qing  ^[2];

• Search DOE PAGES for author "Ma, Qing"
• Search DOE PAGES for ORCID "0000-0001-6530-9322"

Simpson-Gomez, Joshua ^[1]; Skiba, Emily J. ^[1]; Perry, Nicola H.  ^[1]

• Search DOE PAGES for author "Perry, Nicola H."
• Search DOE PAGES for ORCID "0000-0002-7207-2113"

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+ Show Author Affiliations

1. Univ. of Illinois at Urbana-Champaign, IL (United States)
2. Northwestern Synchrotron Research Center at the Advanced Photon Source Argonne, IL (United States)

Publication Date:

Wed Oct 20 00:00:00 EDT 2021

Research Org.:

Univ. of Illinois at Urbana-Champaign, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1959966

Alternate Identifier(s):

OSTI ID: 1828430

Grant/Contract Number:  

SC0018963; AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Materials Chemistry. A

Additional Journal Information:

Journal Volume: 10; Journal Issue: 5; Journal ID: ISSN 2050-7488

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE