Extended Positron–Positronium Trapping Defects in the MgAl₂O₄ Spinel Ceramics

Abstract

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.

Defect‐Induced Effects in Nanomaterials

“…The group led by H. Klym applied the positron annihilation lifetime spectroscopy to studies of the evolution of defect-related extended free volumes in chalcogenide glasses, [10] MgAl 2 O 4 ceramics, [11] and BaGa 2 O 4 ceramics doped with Eu 3þ ions. [12] DOI: 10.1002/pssb.202200283 Agglomeration of free volumes in the initial stage of annealing with further fragmentation and shrinkage has been observed in the glasses.…”

Synthesis of MAl2O4(M = Mg, Co, Ni, Zn, Ba) Nanopowders by Liquid Impregnation of Nanofibrous Alumina

“…More recently, the use of finely monodispersed MgAl 2 O 4 nanopowders has been suggested for the sintering of small-grain (<100 nm) transparent ceramics capable of withstanding high fluxes of neutrons, which can be used in novel nuclear fusion reactors. − As a result, many recent studies have been devoted to the behavior of defects and impurities on synthetized materials and those subjected to an ionized irradiation. − At the same time, a deeper understanding of the material tolerance needs experiments on fine-grain ceramics with reproducible properties, which is connected to the availability of fine spinel powders with mean particle size ∼10 nm. Unfortunately, such commercial precursors are not available and, to the best to our knowledge, the finest commercial S25CR spinel powder has a mean crystallite size of 70 nm, which permitted obtaining transparent ceramics with a mean grain size of 135 nm via spark plasma sintering.…”