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Structural Metastability and Quantum Confinement in Zn1-xCoxO Nanoparticles.
G Almonacid1, R Martín-Rodríguez2,3, C Renero-Lecuna2,4
1ICMUV, MALTA-CONSOLIDER Team, Departamento de Física Aplicada, Universitat de Valencia , E-46100 Burjassot (Valencia), Spain.
Nano Letters
|July 9, 2016
Summary
The phase transition in zinc cobalt oxide nanoparticles (NPs) under pressure is gradual, unlike in bulk materials. NP size influences the transition pressure, with larger NPs exhibiting lower transition pressures.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Investigating the electronic structure and phase transitions of semiconductor nanoparticles is crucial for advanced material applications.
- Zinc cobalt oxide (Zn1-xCoxO) nanoparticles exhibit distinct crystal structures (wurtzite and rock-salt) with unique electronic properties.
Purpose of the Study:
- To explore the pressure-induced phase transition from wurtzite (W) to rock-salt (RS) in Zn1-xCoxO nanoparticles.
- To understand the influence of pressure and nanoparticle size on the electronic structure and phase stability of Zn1-xCoxO.
Main Methods:
- Optical measurements under high pressure (up to 25 GPa).
- X-ray absorption spectroscopy.
- Transmission electron microscopy.
- Synthesis of W-NPs and pressure-induced transformation to RS-NPs.
Main Results:
- Spectroscopic evidence of tetrahedral Co(2+) in NPs from ambient pressure to 17 GPa.
- A gradual and irreversible W-to-RS phase transition observed above 17 GPa, characterized by shifts in band-edge energy and absorption peaks.
- Observed metastability and gradual transition attributed to nanoparticle size distribution, with larger NPs showing lower transition pressures.
- A blue shift of 0.22 eV in the absorption edge of untransformed W-NPs after pressure cycling, attributed to quantum confinement effects.
Conclusions:
- Nanoparticle size significantly impacts the phase transition behavior of Zn1-xCoxO, leading to a gradual transition and metastability.
- Quantum confinement effects play a role in the observed optical properties of the nanoparticles.
- The findings provide insights into the pressure-dependent properties of dilute magnetic semiconductors at the nanoscale.
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