Thermal expansivity of Ge1-y sny alloys

The temperature dependence of the lattice parameter of Ge1-y Sny alloys deposited on Si substrates has been determined from an analysis of their x-ray reciprocal-space maps. It is found that over the range 0<y<0.03 the alloy thermal expansivity increases by up to 20% as a function of y. This implies a strong deviation from a linear interpolation between the end compounds since the thermal expansivities of pure Ge and α-Sn are nearly the same. Alternative interpolation formulas based on a Debye model and a mixed Debye-Einstein model of the phonon structure are tested and it is found that they also fail to explain the observed increase in thermal expansivity.