Electronic and structural properties of micro-and nanometre-sized crystalline copper monoxide ceramics investigated by positron annihilation

Abstract

Electronic and structural properties of copper monoxide (CuO) sintered as a common ceramic and nanoceramic are studied by positron annihilation spectroscopy. A CuO nanoceramic with crystallite size ranging from 15 to 90 nm was prepared from a common one by shock-wave loading. It is found that the momentum distribution of valence electrons in CuO is shifted, as compared with metallic copper, towards higher momentum values. This result is related to the effect of the Cu 3d–O 2p hybridization in the Cu–O ionic covalent bond formation. It is found that open volumes, identified mainly as small agglomerates of oxygen vacancies, appear at the nanoceramic crystallite interfaces. The degree of the Cu–O bond covalency decreases locally at the crystallite interfaces because of an oxygen deficit. The nanocrystalline state in CuO is shown to be thermally stable up to 700 K.

Positron annihilation study of effects of Ti and plastic deformation on defect accumulation and annealing in electron-irradiated austenitic steels and alloys

“…The Fe-Ni-Ti alloy represented a supersaturated solid solution relative to titanium and underwent the radiation-induced decomposition at this irradiation temperature, which was accompanied by the formation of fine ($5 nm) particles of the Ni 3 Ti intermetallic [18]. It was shown [19] that coherent intermetallic particles retarded the accumulation of vacancy defects in austenitic alloys at the elevated irradiation temperatures.…”

Characterization of densified fully stabilized nanometric zirconia by positron annihilation spectroscopy

“…The PAS technique has been used previously for characterizing ceramics, [11][12][13][14][15] including zirconia. [16][17][18][19] The positron annihilation lifetime spectroscopy ͑PALS͒ mode has been the most commonly used, but the angular correlation of the annihilation radiation ͑ACAR͒ and Doppler broadening have been used as well.…”

“…In a study using ACAR measurements on CuO compacts, 14 it was reported that an increase in the low-momentum fraction annihilations ͑associated with an increase in the open-volume signal͒ seen in nanometric samples ͑15-90 nm͒ was attributed to positron trapping at grain boundaries. In another study on nanocrystalline SnO 2 compacts by Shek et al, 15 the average positron lifetime decreased with increasing sintering temperature, an observation attributed to the elimination of grain boundaries by grain growth during the sintering process.…”

Positron Annihilation Spectroscopy Study on Annealing Effect of CuO Nanoparticles

“…The results of theoretical calculation and experiment in cuprate superconductors have proved that the dominant positron traps were presented by oxygen vacancy defects in the Cu-O planes [38][39][40] . It was also reported that open volumes which were mainly identified as anion vacancy defects existed in the grain interfaces in the CuO nanoceramics as well as the oxygen vacancy defects led to a decrease in the degree of Cu-O bond covalency studied by PAS 30 . Therefore, in present study, we consider that the effects of positron trapping at positively charged vacancies (V O ) cannot be neglected.…”

“…Doppler broadening parameters give information about the electron momentum distribution at the annihilation site 27 . Some authors investigated defect structure of CuO nanoparticles by positron annihilation technology [28][29][30] . They found that there existed a large number of copper-and/or oxygen-related vacancies or complexes in CuO nanoparticles, which depended on the annealing environment and temperature.…”