Hardness and Fracture Toughness of Solid Solutions of Mg2Si and Mg2Sn

Thermoelectric material development typically aims at maximizing produced electrical power and efficiency of energy conversion, even though sometimes, this means adding expensive or toxic materials. An alternative is to use highly available and low toxic silicides. In fact, magnesium silicide and magnesium stannide have low densities (1.99 and 3.49 g/cm(3), respectively), and exhibit good thermoelectric properties with their thermoelectric figure of merit zT > 1 for n-type and near 0.6 for p-type Mg2Si-Mg2Sn solid solutions in the range of 723-773 K. These properties turn the materials into logical candidates for light-weight and efficient thermoelectric generators (TEG). The research on their mechanical properties is however lagging behind and little effort has been put into understanding them. In this work we study the effect of the composition over the Mg2Si-Mg2Sn solid solution series on hardness and fracture toughness values. Hardness ranges from 2.44-5.56 GPa whereas fracture toughness values are in a tighter range (0.64-0.88 MPa m(1/2)). However, the highest value does not belong to binary Mg2Si but a composition within the solid solution that exhibits secondary phase nanostructuring.