Abstract
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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.