Unraveling the effects of phason strain on the thermoelectric properties in Ag-In-Yb icosahedral quasicrystals

Abstract

This study represents the experimental comparative analysis of the thermoelectric properties in an Ag-In-Yb phason-free icosahedral quasicrystal (iQC) and four phason-strained iQCs. The aim is to understand how phason strain affects these properties. The four phason-strained iQCs are 1/1 and 2/1 approximant crystals (1/1 AC and 2/1 AC), a sample grown by the Bridgman method with a high growth rate (phason QC-1), and a sample obtained by phonon–phason coupling (phason QC-2), the magnitude of phason strain decreasing in this order. Their compositions are similar to that of iQC, and in particular, the compositions of phason QC-1 and 2 are exactly the same as that of iQC, making them suitable for clarifying the correlation between physical properties and the magnitude of phason strain. Systematic changes were observed in the electrical resistivity, Seebeck coefficient, and electronic specific heat coefficient with increasing phason-strain magnitude, which can be interpreted as due to the effect of the phason-strain blunting the pseudogap at the Fermi level in the electronic density of states. In contrast, no appreciable dependence of phonon thermal conductivity on the phason-strain magnitude was observed; very low value and a plateau feature observed consistently for all the samples do not arise directly from the quasiperiodicity or high rotational symmetry but from complex structures with a large unit cell.