N₂⁻ Radical Anions Trapped in Bulk Polycrystalline MgO

Abstract

Oxidation of magnesium nitride, Mg3N2, leads to segregated nitrogen impurities within the bulk of MgO. Electron paramagnetic resonance experiments in conjunction with quantum chemical calculations allow us to identify these paramagnetic centers as N2 − radical anions trapped in anion vacancies in the bulk of MgO. The characteristics of the defect center, derived from the spin Hamiltonian parameters, exhibit similarities but also some interesting differences with respect to the classical N2 − species in KCl, a sort of prototype of molecular anions trapped in ionic crystals.

Identification of a N-related shallow acceptor and electron paramagnetic resonance center in ZnO: N2+on the Zn site

“…We also compare them with the g factors 195207-3 26 These correspond to N 2 on anion site and aligned in the [110] direction and show an orthorhombic g tensor with opposite changes in g factor from the free electron g e from that observed by Garces et al 12 We caution that we do not claim a quantitative agreement with the isolated N 2 + molecular radical, the g ⊥ in the experiment is in fact larger, −8800 ppm. However, there is a clear qualitative distinction between the N 2 + and N − 2 type g tensor, which results from the different underlying quantum state of the singly occupied molecular orbital (SOMO), which is a σ state in our case and a crystal field split π state in the other case.…”

“…26 The isotropic A iso = (A + 2A ⊥ )/3 and dipolar A dip = (A − A ⊥ )/3 hypefine terms are due to the Fermi contact term related to the s-like spin density at the nucleus and the nuclear dipole interaction respectively. The hyperfine tensor for N − 2 in MgO is orthorhombic A = A iso 1 + T with 1 the unit matrix and T a traceless diagonal matrix.…”

Nitrogen-doped semiconducting oxides. Implications on photochemical, photocatalytic and electronic properties derived from EPR spectroscopy

“…Interestingly, the same diatomic species is also found in MgO powders, an insulating oxide with rock-salt structure prepared by thermal oxidation of magnesium nitride. 80 At variance with N-TiO 2 , whose signal is visible at room temperature, the CW spectrum of polycrystalline N-ZnO is poorly resolved even at T < 20 K, due to molecular motion. However, similar to N-TiO 2 , the EPR signal intensity can be enhanced by visible light with wavelength l > 400 nm.…”

Spectroscopic Properties of Doped and Defective Semiconducting Oxides from Hybrid Density Functional Calculations

“…However, due to the intrinsic magnetic behavior of TMs, the induced magnetic properties of the doped material are often difficult to discriminate from those of other magnetic impurities . A few attempts to prepare N-doped MgO have been successful, in particular based on molecular beam epitaxy , or oxidation of metal nitrides . In this latter study, N-doped MgO samples have been prepared by direct oxidation of Mg 3 N 2 at high temperature .…”