Interfacial free volumes and segregation effects in nanocrystalline Pd85Zr15 studied by positron annihilation

Abstract

Positron annihilation spectroscopy on nanocrystalline Pd85Zr15 shows the segregation of Zr at the interfaces and a decrease of the fraction of nanovoids the size of 10 to 15 missing atoms upon isochronal annealing up to Ta=1100 K by which the grain size increases up to d=185 nm. In this state, the positron trapping at interfacial free volumes reversibly changes contingent upon the temperature whereas the interfacial composition is unchanged when the measuring temperature varies.

Characterization of densified fully stabilized nanometric zirconia by positron annihilation spectroscopy

“…On the other hand, it is well established that nanopores can be effective trapping centers for positrons. 11,28 In insulating materials positrons are probably trapped in the form of orthopositronium ͑o-ps͒. Pores of at least 0.3 nm in size are believed to be required in order to have an efficient trapping of o-ps.…”

Positron lifetime calculation for possible defects in nanocrystalline copper

“…Therefore the positron lifetime for those defects will be larger than the bulk lifetime. Many positron lifetime measurements have been carried out on nanocrystalline metals and alloys to investigate the microstructure of nanocrystalline metals [6,9,[14][15][16][17][18][19]. Since the positron diffusion length is typically about 100 nm in crystalline bulk metals [20], most positrons can reach the grain boundaries during the diffusion and then be trapped by vacancy-like defects or vacancy clusters in there.…”