Diffusion mechanisms for spinel ferrite NiFe2O4 by using kinetic activation-relaxation technique

Area of Science:

• Materials Science
• Computational Materials Science
• Solid State Chemistry

Background:

• Understanding mass transport in spinel ferrites like NiFe2O4 is crucial for their application in various technologies.
• Traditional molecular dynamics methods struggle to capture complex diffusion mechanisms.
• Point defects, including vacancies and interstitials, are key to ionic diffusion in these materials.

Purpose of the Study:

• To computationally investigate mass transport phenomena in bulk nickel ferrite (NiFe2O4).
• To elucidate diffusion mechanisms driven by point defects using the kinetic activation-relaxation technique (k-ART).
• To compare the influence of different Buckingham potential parameterizations on diffusion pathways and energies.

Main Methods:

• Employed the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm.
• Investigated both cation and anion defects (vacancies and interstitials) in NiFe2O4.
• Utilized two Buckingham potential parameterizations (nominal and partial charges), corrected for short-range interactions.

Main Results:

• k-ART successfully described diffusion mechanisms often missed by molecular dynamics.
• Both potential parameterizations predicted similar diffusion mechanisms but yielded different migration energies.
• Unveiled mechanisms for normal-to-inverse spinel transformation via cation diffusion and predicted diffusion coefficients.

Conclusions:

• The study provides detailed insights into the energy landscape and pathways governing diffusion in NiFe2O4.
• Interstitial Ni diffusion involves cooperative movement of two Ni ions, while O interstitials trigger collective O ion diffusion.
• An O vacancy diffuses via an O ion moving to a cuboctahedron center, clarifying defect-mediated transport in spinel ferrites.