Defect structure and property consequence when small Li+ ions meet BaTiO3
Date
2020
Authors
Narayanan, N.
Lou, Q.
Rawal, A.
Lu, Teng
Liu, Z.
Chen, J.
Langley, J.
Chen, H.
Hester, J.
Cox, Nicholas
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American Physical Society
Abstract
In the present work the longstanding issue of the structure and dynamics of smaller ions in oxides and
its impact on the properties was investigated on 7% Li-doped BaTiO3. The investigation combined several
techniques, notably neutron powder diffraction (NPD), nuclear magnetic resonance (7Li-NMR), electron
paramagnetic resonance (EPR), electron microprobe, electric polarization (EP) measurement, and electronic
structure calculations based on density-functional theory (DFT). Electron microprobe confirmed multiple phases,
one containing incorporated Li in the BaTiO3 host lattice and another glassy phase which breaks the host lattice
due to excessive Li accumulation. While the average structure of Li in BaTiO3 could not be determined by
NPD, 7Li-NMR revealed one broad “disordered” and multiple “ordered” peaks. Local structure models with
different defect types involving Li+ were modeled and the corresponding chemical shifts (δ) were compared
with experimental values. It is found that the closest defect model describing the ordered peaks, is with Ti4+
being replaced by four Li+ ions. The biexponential behavior of the spin-lattice relaxation of the ordered peaks
each with a short and a long relaxation discloses the existence of paramagnetic ions. Finally, EPR revealed the
existence of the paramagnetic ion Ti3+ as a charge-transfer defect. DFT calculations disclosed local antipolar
displacements of Ti ions around both types of defect sites upon insertion of Li+. This is in accordance with the
experimental observation of pinching effects of the EP in Li-doped BaTiO3. These studies demonstrate the huge
impact of the local structure of the doped smaller/lighter ions on the functional properties of oxides.
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Physical Review Materials
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