In situ characterisation of nanostructured multiphase thermoelectric materials at elevated temperatures

Multiphase thermoelectric materials have recently attracted considerable attention due to the high

thermoelectric efficiencies which can be achieved in these compounds compared to their single-phase

counterparts. However, there is very little known on the structural evolution of these phases as a function

of temperature. In this work we performed an in situ high temperature structural characterisation of

recently reported high efficiency p-type multiphase (PbTe)0.65(PbS)0.25(PbSe)0.1 compounds by hot stage

transmission electron microscopy and high-resolution neutron powder diffraction. We observed the

microstructural evolution of precipitates and determined the lattice parameters of phases as a function of

temperature for materials, which have been heavily and lightly doped with sodium. The role of the sodium

is to optimize the concentration of charge carriers. It has been shown to distribute heterogeneously

between the phases in multiphase compounds. The dissolution of secondary phases is found to occur at

elevated temperatures. Although sodium concentration produces no significant differences between the

lattice constants of the phases and the dissolution sequence of precipitates, it affects quite significantly

the kinetics of precipitation. The heavily doped samples reach structural thermodynamic equilibrium more

quickly than the lightly doped compound. These results are a step forward in designing high performance

multiphase thermoelectric materials.