cm0c02698_si_001.pdf (1.44 MB)
Download fileRevealing the Structure and Oxygen Transport at Interfaces in Complex Oxide Heterostructures via 17O NMR Spectroscopy
journal contribution
posted on 2020-09-10, 14:16 authored by Michael
A. Hope, Bowen Zhang, Bonan Zhu, David M. Halat, Judith L. MacManus-Driscoll, Clare P. GreyVertically aligned nanocomposite (VAN) films, comprising nanopillars
of one phase embedded in a matrix of another, have shown great promise
for a range of applications due to their high interfacial areas oriented
perpendicular to the substrate. In particular, oxide VANs show enhanced
oxide-ion conductivity in directions that are orthogonal to those
found in more conventional thin-film heterostructures; however, the
structure of the interfaces and its influence on conductivity remain
unclear. In this work, 17O NMR spectroscopy is used to
study CeO2–SrTiO3 VAN thin films: selective
isotopic enrichment is combined with a lift-off technique to remove
the substrate, facilitating detection of the 17O NMR signal
from single atomic layer interfaces. By performing the isotopic enrichment
at variable temperatures, the superior oxide-ion conductivity of the
VAN films compared to the bulk materials is shown to arise from enhanced
oxygen mobility at this interface; oxygen motion at the interface
is further identified from 17O relaxometry experiments.
The structure of this interface is solved by calculating the NMR parameters
using density functional theory combined with random structure searching,
allowing the chemistry underpinning the enhanced oxide-ion transport
to be proposed. Finally, a comparison is made with 1% Gd-doped CeO2–SrTiO3 VAN films, for which greater NMR
signal can be obtained due to paramagnetic relaxation enhancement,
while the relative oxide-ion conductivities of the phases remain similar.
These results highlight the information that can be obtained on interfacial
structure and dynamics with solid-state NMR spectroscopy, in this
and other nanostructured systems, our methodology being generally
applicable to overcome sensitivity limitations in thin-film studies.