Abstract:
The effect of structure and size parameters on the formation of intrinsic and impurity paramagnetic centers in nanoceramics of aluminum–magnesium spinel is studied. The studied samples (grain size ∼ 30 nm) are obtained by thermobaric synthesis. Microcrystalline ceramics and MgAl2O4 single crystal are used as the reference samples. Characteristic paramagnetic centers of Mn2+ (hyperfine structure constant (HFS) A = 82 G) are present in both single crystal and microceramics. In the studied samples of nanoceramics in the initial state, both impurity Mn2+ and intrinsic F+ centers exist. Unlike the nanoceramics, the centers of F+ type in the reference sample appear only after the irradiation with accelerated electrons (130 keV). The parameters of Mn2+ centers in nanoceramics significantly differ on that in microceramics and single crystal. EPR signal of Mn2+ centers in nanoceramics is characterized by two anomalous constant HFS (A1 = 91.21 G, A2 = 87.83 G) caused by two types of octahedrally coordinated manganese ions
([Mn2+]Al3+ antisite defects). The features of spectral parameters of manganese centers correlate with a decrease in the cell parameter of MgAl2O4 in the nanostructural state. The observed effects are interpreted based on the assumed scheme of [Mn2+]Al3+ charge compensation by the aluminum antisite defect and F+ center.
This work was financially supported by the Ministry of Education and Science (state assignment no. 3.1485.2017/4.6) and the Government of the Russian Federation (act 211, contract no. 02.A03.21.0006), as well as the project “New functional materials for advanced technologies АААА-А19-119031890025-9”.
Citation:
A. F. Zacepin, A. N. Kiryakov, D. R. Bajtimirov, T. V. D'yachkova, A. P. Tyutyunnik, Yu. G. Zainulin, “Paramagnetic mn antisite defects in nanoceramics of aluminum–magnesium spinel”, Fizika Tverdogo Tela, 62:1 (2020), 94–100; Phys. Solid State, 62:1 (2020), 137–143