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Overlapping large polaron tunnelling in lanthanum silicate oxyapatite
Ashishkumar Yadav1, Priyanka A Jha1, Pardeep K Jha1
1Department of Physics, Indian Institute of Technology (Banaras Hindu University) Varanasi, Varanasi 221005, India.
Journal of Physics. Condensed Matter : an Institute of Physics Journal
|December 20, 2022
Summary
Calcium substitution in lanthanum silicate oxyapatite enhances oxide ion conductivity by altering ion transport mechanisms. This study reveals Ca affects hopping and tunnelling, crucial for fast ion conductor development.
Area of Science:
- Materials Science
- Solid-state Chemistry
- Ionics
Background:
- Lanthanum silicate oxyapatite exhibits promising fast ion conductivity.
- Lanthanum vacancies increase activation energy, hindering ionic transport.
- Understanding ion conduction mechanisms is key for advanced materials.
Purpose of the Study:
- Investigate the effect of calcium (Ca) substitution on lanthanum (La) sites in lanthanum silicate oxyapatite.
- Analyze the hopping/tunnelling mechanism in Ca-substituted samples.
- Determine the role of Ca on ionic transport and activation energy.
Main Methods:
- Synthesis of Ca-substituted lanthanum silicate oxyapatite: (La1-xCa_x)9.67(SiO4)6O2+δ (x=0.0-0.15).
- Rietveld refinement of X-ray diffractograms for elemental and structural analysis.
- X-ray Photoelectron Spectroscopy (XPS) and Thermogravimetric Analysis (TGA) to confirm sample composition.
- Temperature and frequency-dependent AC conductivity measurements (548–973 K).
Main Results:
- Rietveld refinement confirmed La deficiency with minimal oxygen deficiency in synthesized samples.
- XPS and TGA validated the formation of La-deficient Ca-substituted samples.
- AC conductivity measurements indicated conduction via overlapping large polaron tunnelling.
- Ca substitution altered tunnelling distance and polaron radii, affecting the ion-conducting channel.
- Elongation of La(6 h) triangles was observed due to Ca substitution.
Conclusions:
- Calcium substitution in lanthanum silicate oxyapatite influences the ion transport mechanism.
- Overlapping large polaron tunnelling is the dominant conduction mechanism.
- Phononic contributions are pivotal in the ionic transport of these materials.
- Ca substitution offers a route to tune the properties of fast ion conductors.
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