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Summary

Positron trapping at grain boundaries (GBs) is crucial in modern materials science, even for micron-sized grains. This study extends models to accurately account for GB trapping alongside intragranular defects.

Keywords:
defectsdiffusion-reaction modelgrain boundariesinterfacespositron annihilation

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Area of Science:

  • Material Science
  • Solid State Physics
  • Defect Characterization

Background:

  • Modern materials exhibit increasing structural complexity with grain sizes in the micrometer and sub-micrometer range.
  • Positron annihilation spectroscopy (PAS) is a key technique for studying free-volume defects in these materials.
  • Positron trapping at grain boundaries (GBs) can significantly influence PAS results, even when intragranular defects are the primary focus.

Purpose of the Study:

  • To extend the existing diffusion-reaction model for positron trapping and annihilation at GBs.
  • To incorporate competitive trapping at two distinct types of intragranular defects.
  • To provide a robust framework for accurate defect concentration determination in complex materials.

Main Methods:

  • Development of an extended diffusion-reaction model for positron trapping at GBs and intragranular defects.
  • Derivation of closed-form expressions for mean positron lifetime and defect-specific lifetime components.
  • Application of the model to cylindrical crystallites, with general validity for spherical symmetry.

Main Results:

  • The extended model successfully accounts for competitive positron trapping at GBs and multiple intragranular defect types.
  • Closed-form expressions enable precise calculation of positron lifetimes and intensities.
  • The study demonstrates that GB trapping is significant even for micrometer-sized crystallites.

Conclusions:

  • Positron trapping at GBs must be considered for accurate defect analysis in micro- and sub-micrometer structured materials.
  • The developed model provides a basis for reliable defect concentration measurements, even when intragranular defect lifetimes overlap with GB lifetimes.
  • Neglecting GB trapping can lead to misinterpretation of PAS data in advanced materials.