The spacing of atoms in crystal lattices of nanomaterials initially contracts as the grain size falls, but expands again below a critical value, as a team of researchers headed by Eric Mittemeijer from the Max Planck Institute for Intelligent Systems has established. Accordingly, surface stress and excess volume compete in nanopowders as the ratio of surface to volume increases in the individual nanoparticles, so that the crystals become distorted.
stress and excess volume compete with one another and the latter wins the upper hand