Extended Positron–Positronium Trapping Defects in the MgAl2O4 Spinel Ceramics

Extended free-volume positron trapping defects (positron trapping channel) and nanopores (positronium decaying channel) in the initial and modified MgAl₂O₄ ceramics sintered at 1200, 1300, and 1400 °C are investigated using positron annihilation lifetime spectroscopy within four-component fitting procedure. It is established that the number and size of extended defects near grain boundaries (described by the second component) decrease with increasing sintering temperature of ceramics, which correlates with the content of additional phases in the materials. The agglomeration of nanopores occurs in the initial ceramics (described by the third component) and the decrease of number and size of nanopores in the modified ceramics. The corresponding processes of the evolution of nanopores described by the fourth component are reflected mainly in their reduction, except for ceramics sintered at 1400 °C. Such changes are associated with the evolution of porous structure and increased contact area between the grains of ceramics.