Thermoelastic behavior of grain-boundary superlattices

The thermal-expansion coefficients of superlattices of twist grain boundaries on the (100) plane in fcc Cu and Au are calculated using a generalization of the Grüneisen relation. A strong anisotropy in the in-plane and out-of-plane thermal-expansion coefficients is found. The thermal expansion of these superlattices is found to be determined from a complex interplay of the structural disorder arising from the interfaces with the associated zero-temperature lattice-parameter changes. The relationship between the thermal expansion and the elastic properties is explored.