Structural Defects in Magnesium Aluminate Spinel Crystals with Different Stoichiometry

Latvijas Universitātes Cietvielu fizikas institūta, Doktorantūras skolas „Funkcionālie materiāli un nanotehnoloģijas” zinātniskais seminārs uzstājās Dr. Aleksandr Lushchik (Institute of Physics, University of Tartu).

Insufficient radiation tolerance is a serious limitation for the use of wide-gap materials in the environment of future fusion reactors (PROTO, DEMO, industrial). Presently, the search for the materials with optical window capabilities and a high tolerance to neutron radiation in fusion devices is an urgent task in the research programs of the EUROfusion consortium. MgAl2O4 spinel crystals and ceramics exhibit very little swelling and belong to attractive candidates for window materials.

A comparative study of radiation damage caused by ~MeV fission neutrons, ~GeV swift heavy ions and 100-keV protons in MgAl2O4, the equimolar mixture of MgO and Al2O3 binary oxides, has been performed. The damage was analyzed using the methods of electron paramagnetic resonance, induced optical absorption (region of 1.4-9 eV), cathodo- and photo-luminescence and thermoactivation spectroscopy. The thermal annealing of F-type center absorption, measured in a stepwise regime, was compared to that of the EPR signal for new paramagnetic hole centers in a neutron-irradiated spinel crystals with different stoichiometry. In addition, the optical and EPR characterization of as-grown structural defects in these spinel crystals has been performed as well. Taking into account the determined models of paramagnetic centers, the tentative scenario of the thermal annealing process of neutron-induced defects (hole-type and complementary electron F-type ones) has been proposed.