microstrain

noun2

1. •
   A strain expressed in terms of parts per million.
2. •
   The root mean square of the variations in the lattice parameters across the individual crystallites, usually across microscopic distances, <ϵ²>^(1/2). By definition, it cannot be negative. In contrast, macrostrain refers to the overall change in the lattice parameters caused by a composition change or temperature change or pressure change.

   • Thus, a Gaussian shape for the microstrain-broadened diffraction-line profile occurs for a Gaussian microstrain distribution. — 2013