  The control of solute segregation at grain boundaries (GBs) is essential in
engineering alloy properties, however the structure-activity relationship of
the key parameter-the segregation energies-still remains elusive. Here we
propose the electronic and geometric descriptors of GB segregation based on the
valence, electronegativity and size of solutes and the non-local coordination
number of free surfaces, with which we build a predictive framework to
determine the segregation energies across different solutes, matrices, GB
structures and segregation sites. This framework uncovers not only the coupling
rule of solutes and matrices in GB segregation, but also the origin of
solute-segregation determinants. The contribution of solutes essentially stems
from their d- and s-state coupling in alloying, whereas that of matrix GB
interfaces is determined by matrix free surfaces. Our scheme builds a novel
picture for the solute segregation at GBs and provides a useful tool for the
design of advanced alloys.
