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Charge transfer drives anomalous phase transition in ceria
He Zhu1,2, Chao Yang3, Qiang Li1,2
1Beijing Advanced Innovation Center for Materials Genome Engineering, Department of Physical Chemistry, University of Science and Technology Beijing, Beijing, 100083, China.
Nature Communications
|December 1, 2018
Summary
Nanosized ceria exhibits a reversible phase transition from tetragonal to cubic, causing negative thermal expansion. This anomalous behavior is linked to oxygen vacancies and charge transfer within the material.
Area of Science:
- Materials Science
- Solid State Chemistry
- Nanotechnology
Background:
- Ceria (cerium dioxide) traditionally exhibits a stable cubic fluorite structure.
- Its properties are generally considered stable across a broad temperature spectrum.
Purpose of the Study:
- To investigate the anomalous phase transition in nanosized ceria.
- To understand the underlying mechanisms driving negative thermal expansion.
Main Methods:
- Neutron pair distribution function analysis
- Raman spectroscopy
- First-principles calculations
Main Results:
- A reversible tetragonal (P4 2 /nmc) to cubic (Fm-3m) phase transition was observed in nanosized ceria.
- Negative thermal expansion occurred between -25°C and 75°C.
- Oxygen vacancies were identified as crucial for stabilizing the tetragonal phase, involving O 2- anion displacement and charge transfer with 4f orbitals.
Conclusions:
- The study reveals an unprecedented phase transition in nanosized ceria, leading to negative thermal expansion.
- Oxygen vacancies and associated charge transfer are key to this anomalous behavior.
- Findings challenge conventional understanding of ceria's structural stability.
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