Electronic Structure and Magnetic Configuration of Ni-Substituted MnCo₂O₄ Spinel

Abstract

The electrical and magnetic structures of Nisubstituted MnCo 2 O 4 have been studied theoretically and experimentally. With the increase of Ni concentration x, the calculated results show that the bond lengths of the Mn−O and Ni−O bonds along three directions (a, b, and c axis) tend to be consistent, and the lattice symmetry of Ni x Mn 1−x Co 2 O 4 changes from tetragonal to cubic symmetry. The inverse spinel Ni x Mn 1−x Co 2 O 4 was found to have a ferrimagnetic half-metallic ground state. The Ni dopant results in the flow of holes from the e g,β 1 level of Ni 3+ at the octahedral site to the e g,β 2 level of Co 2+ at the tetrahedral site. Therefore, the calculated conductivity type of Ni x Mn 1−x Co 2 O 4 changes from n-to p-type as the Ni concentration increases. Furthermore, Ni 3+ ion substitution in the MnCo 2 O 4 spinel changed the relative position of the e g,β 1 level of Ni 3+ at the octahedral site and the e g,β 2 level of Co 2+ at the tetrahedral site, which makes the activation energy E A of Ni x Mn 1−x Co 2 O 4 obtained from our experimental results decrease first and then increases with the x value increasing. Among all the doped samples, the Ni 0.25 Mn 0.75 Co 2 O 4 has the smallest activation energy and the highest electrical conductivity. The measured room-temperature resistivity of the system is reduced by 5 orders of magnitude due to Ni doping.

Cooperative Catalysis of Polysulfides in Lithium‐Sulfur Batteries through Adsorption Competition by Tuning Cationic Geometric Configuration of Dual‐active Sites in Spinel Oxides

“…A high ELF value with 0.7 around O is mainly dominated by covalent bonds and the electron localization around Mn Oh −O is stronger than that of Co Td −O. Therefore, the bonding strength of Mn Oh −O is higher than that of Co Td −O, indicating the former possesses a higher TM−O covalency, [15] which is attributed to the head‐on overlap configuration. On this basis, the covalency of TM−S bond when S bonds to the exposed Mn Oh and Co Td is quantitatively calculated by the crystal orbital Hamilton population (COHP) analysis (Figure 1i).…”

MnCo2O4 Spinel Nanorods for Highly Sensitive Electrochemical Detection of Nitrite

“…A mixed valence of the material is beneficial to exhibit a high electrocatalytic activity . In this structure, oxygen anions form a cubic-close-packed structure, where half of the Co ions occupy tetrahedral sites and the Mn ions and the other half of the Co ions occupy octahedral sites. , …”

“…36−39 It has an inverse spinel structure, with Co cations evenly distributed over the A (tetrahedral) and B (octahedral) sites and Mn cations occupying the B sites. 40 It is an n-type semiconductor with good conductivity (600 Ω•cm at room temperature). 41 Previous exploration of MCO in electrochemical sensing applications includes nanofibers for glucose and nanosheets for hydrogen peroxide, microflowers anchored on P-doped g-C 3 N 4 nanosheets for sulfadiazine, MCO wrapped by S-doped reduced graphene oxide (rGO) for clioquinol, metal ion detection, and a composite with rGO for L-tryptophan.…”

“…Considering the distinct scope of manganese and cobalt oxides, their synergistic combination might significantly augment the electrochemical detection of nitrite. MCO spinel is widely explored for applications in fuel cells, water splitting, supercapacitors, etc. − It has an inverse spinel structure, with Co cations evenly distributed over the A (tetrahedral) and B (octahedral) sites and Mn cations occupying the B sites . It is an n-type semiconductor with good conductivity (600 Ω·cm at room temperature) .…”

“…50 In this structure, oxygen anions form a cubic-close-packed structure, where half of the Co ions occupy tetrahedral sites and the Mn ions and the other half of the Co ions occupy octahedral sites. 40,51 The Fourier transform infrared (FTIR) spectrum of MCO recorded between 500 and 4000 cm −1 reveals three peaks at the fingerprint region (Figure 4c). The strong peaks at 547 and 646 cm −1 arise from the vibrations of metal (Co/Mn)−oxygen bonds in the spinel MCO, whereas the peak at 502 cm −1 can be ascribed to the Co−O−Mn vibration.…”