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

Author:

Restrepo Oscar A.1ORCID,Becquart Charlotte S.2ORCID,Mousseau Normand3ORCID

Affiliation:

1. Biophysics Group, Institute of Physics, University of Antioquia 1 , 050010 Medellín, Colombia

2. Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 - UMET - Unité Matériaux et Transformations 2 , F-59000 Lille, France

3. Département de physique, Regroupement québécois sur les matériaux de pointe, and Institut Courtois, Université de Montréal 3 , Case Postale 6128, Succursale Centre-Ville, Montréal, Quebec H3C 3J7, Canada

Abstract

Mass transport in bulk spinel ferrites NiFe2O4 is studied computationally using the kinetic activation–relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Diffusion mechanisms—difficult to observe with molecular dynamics—are described by k-ART. Point defects are assumed to be responsible for ionic diffusion; thus, both cation and anion defects are investigated. This work focuses on vacancies and interstitials by comparing their properties with two Buckingham potential parameterizations: one with nominal charges and the other with partial charges. Both potentials are corrected at short distances, thus allowing interstitial diffusion and avoiding the catastrophic infinite energies appearing with Buckingham at short distances. The energy landscape along different pathways is described in detail. Both potentials predict the same mechanisms but different migration energies. Mechanisms by which a normal spinel is transformed to an inverse spinel via cation diffusion are unveiled, and diffusion coefficients are predicted. We find that interstitial Ni diffusion involves the movement of two Ni ions and that O interstitials trigger a collective diffusion of O ions, while an O vacancy diffuses by an O ion moving to the center of a cuboctahedron.

Publisher

AIP Publishing

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