Lattice Constants of Solid Solution Microstructures: The Case of Nanocrystalline Pd-H

We present an analysis of the effect of interface stress on strain in bulk in an open system with a large interface-to-volume ratio, at equilibrium with the solute at a controlled chemical potential. The results are relations for interface stress and for solute concentration in the bulk as a function of measurable parameters: interfacial ``stretch'' and changes in the lattice constant. Stretch models a change in the average normal component of the interatomic spacing at interfaces. X-ray diffraction and dilatometry provide experimental data showing a significant variation of grain boundary stress and stretch in nanocrystalline Pd-H with hydrogen chemical potential.