First-principles investigation of boron defects in nickel ferrite spinel

TL;DR

This study uses first-principles calculations combined with experimental data to analyze boron incorporation in nickel ferrite, revealing it is thermodynamically unfavorable for B to form defects within NFO, favoring secondary phase formation instead.

Contribution

It provides a detailed first-principles analysis of boron defect formation in nickel ferrite, highlighting the thermodynamic limitations and secondary phase formation.

Findings

Boron incorporation into NFO is thermodynamically unfavorable.

Secondary phases like B2O3 and Fe3BO5 are more likely to form.

Defect formation energies depend on NFO's electronic type (n-type or p-type).

Abstract

The accumulation of boron within the porous nickel ferrite (NiFe2O4, NFO) deposited on fuel rods is a major technological problem with important safety and economical implications. In this work the electronic structure of nickel ferrite is investigated using first-principles methods, and the results are combined with experimental data to analyze B incorporation into the NFO structure. Under thermodynamic equilibrium the calculations predict that the incorporation of B into the NFO structure is unfavorable. The main limiting factors are the narrow stability domain of NFO and the precipitation of B2O3, Fe3BO5, and Ni3B2O6 as secondary phases. In n-type NFO, the most stable defect is Ni vacancy while in p-type material lowest the formation energy belongs to tetrahedrally coordinated interstitial B . Because of these limiting conditions it is more thermodynamically favorable for B to form secondary phases with Fe, Ni and O than it is to form point defects in NFO