Relating defect concentrations to spatially fluctuating lattice strains
Measurements of lattice strain at high spatial resolution are becoming accessible and routine, owing to advances in imaging techniques such as 4D Scanning Transmission Electron Microscopy. This has the potential to enhance materials characterisation, but the data are difficult to interpret. We present a procedure for extracting local concentrations of isotropic defects, such as vacancies, from a spatially fluctuating strain field. The local dilatation is related to the defect concentration at the same point; strain fluctuations are directly proportional to concentration fluctuations by a factor determined by the Poisson ratio of the material. The inversion of strains to isotropic defect concentrations is demonstrated in molecular dynamics and finite element simulations of vacancy distributions in bcc W and fcc Au.