Rationalization of Diversity in Spinel MgFe₂O₄ Surfaces

Abstract

Spinel magnesium ferrite (MgFe 2 O 4) is a prospective anode material for lithium ion batteries (LIBs). Here, using density functional theory (DFT) we report the first systematic study of diverse MgFe 2 O 4 surfaces in three types of spinel structures: normal, mixed, inverse, which can have significant impact This article is protected by copyright. All rights reserved. 2 on the initial lithiation. Our results show that the faceting and therefore the shape of MgFe 2 O 4 crystals strongly depend on the bulk structures. Upon going from normal, mixed to inverse spinel, the energetically preferred facets of MgFe 2 O 4 vary from the combination of (1 0 0) and (3 1 1), solely [1] to a combination of (1 0 0), (0 0 1), (1 1 1) and (3 1 1), respectively, depending on the distribution of Mg 2+ in the spinel structure. However, there is one common descriptor to the stable surfaces among all three MgFe 2 O 4 systems: high density of Mg 2+ exposed to the surface. Our study rationalizes the essential effect of the substitution of Zn 2+ for Mg 2+ in ferrites and provides new insights on how to control the shape of ferrite materials and thus tune the performances of LIBs.

Mg‐Zn Ferrite Nanoparticles: A Brief Review on Synthesis, Characterizations, and Applications

“…The majority of mixed spinel ferrites are inverse spinel [100]. In an inverse spinel structure, Fe 3+ (ferric ions) equally occupy both the A-and B-sites while metal ions take up only the B-site [101,102]; [Fe 3+ ]A[M 2+ Fe 3+ ]B. NiFe 2 O 4 is an example of inverse spinel structure [103][104][105][106][107][108][109][110][111][112][113]. Cubic spinel ferrites have drawn great attention of researchers during the last five decades due to their intriguing properties like low coercivity and dielectric losses, high permeability and Curie temperature, low loss eddy current, and high saturation magnetization and mechanical hardness.…”

Essential Role of Spinel MgFe2O4 Surfaces during Discharge

“…Here, building on our previous studies of pristine MgFe 2 O 4 surfaces, 7 we investigated the adsorption and transport of the Li + ions on the stable facets of three spinel structures using DFT: (1 0 0) and (3 1 1) in normal-spinel, {1 0 0} in mixed-spinel and (1 0 0), (0 0 1), (1 1 1) and (3 1 1) in inverse-spinel. These DFT-identified surfaces agreed well with previous high-resolution transmission electron microscope (HR-TEM) results.…”

“…4 In the present study, we move from ZnFe 2 O 4 to MgFe 2 O 4 , which necessitates consideration of the increase in diversity of spinel going from a single normal-spinel as the case of ZnFe 2 O 4 to three spinel structures, including normal-spinel, mixed-spinel and inversespinel for the MgFe 2 O 4 system. 1,5,7 Bulk MgFe 2 O 4 is not limited to normal-spinel (O 2− : octahedral 32e; Fe 3+ : octahedral 16d; Mg 2+ : tetrahedral 8a sites) as the case of ZnFe 2 O 4 ; Rather, it can also adopt mixed-and inverse-spinel structures, where 16d Fe 3+ ions partially or completely intermix with 8a Mg 2+ ions depending on synthesis methods. [8][9][10][11][12][13][14][15][16] As a consequence, the preferential surface orientations also vary from dominant (1 1 1) in normal-spinel ZnFe 2 O 4 to the combination of (1 0 0) and (3 1 1) in normal-spinel, {1 0 0} in mixed-spinel and a combination of (1 0 0), (0 0 1), (1 1 1) and (3 1 1) in inverse-spinel of MgFe 2 O 4 according to our previous study.…”

“…[8][9][10][11][12][13][14][15][16] As a consequence, the preferential surface orientations also vary from dominant (1 1 1) in normal-spinel ZnFe 2 O 4 to the combination of (1 0 0) and (3 1 1) in normal-spinel, {1 0 0} in mixed-spinel and a combination of (1 0 0), (0 0 1), (1 1 1) and (3 1 1) in inverse-spinel of MgFe 2 O 4 according to our previous study. 7 However, all the stable surfaces feature a high density of stable Mg 2+ ions exposed to the surface, which significantly lowers the surface energy. The impact on the capture of Li + ions on these surfaces and the differences in transport properties from surface to bulk are still underexplored and deserve considerable attentions.…”

Exploring the Synergistic Structural and Optical Properties of Co-Precipitated BiCr2O4/GO Nanocomposite

“…28,29 Inverse spinal is a subordinate feasible structures that also has all tetrahedral coordination places A +2 taking one half of the tetrahedral sites while B +3 another half of the octahedral sites. 30,31 BiCr 2 O 4 possess a tetragonal distorted spinel structure due to condensation along single axes and rotation along all axes. 32 Extensive studied on various parameters of Bismuth chromite (BiCr 2 O 4 ) including photocatalytic activity, pollution control, contaminant removal, hydrogen production and many more synthesized using variety of methods including sol-gel, thermal decomposition, co-precipitation, hydrothermal method, reaction of solid-state and combustion method.…”