  Whereas exceptional mechanical and radiation performances have been found in
the emergent medium- and high-entropy alloys (MEAs and HEAs), the importance of
their complex atomic environment, reflecting diversity in atomic size and
chemistry, to defect transport has been largely unexplored at the atomic level.
Here we adopt a local structure approach based on the atomic pair distribution
function measurements in combination with density functional theory
calculations to investigate a series of body-centered cubic (BCC) MEAs and
HEAs. Our results demonstrate that all alloys exhibit local lattice distortions
(LLD) to some extent, but an anomalous LLD, merging of the first and second
atomic shells, occurs only in the Zr- and/or Hf-containing MEAs and HEAs. In
addition, through the ab-initio simulations we show that charge transfer among
the elements profoundly reduce the size mismatch effect. The observed
competitive coexistence between LLD and charge transfer not only demonstrates
the importance of the electronic effects on the local environments in MEAs and
HEAs, but also provides new perspectives to in-depth understanding of the
complicated defect transport in these alloys.
