Reduction of Thermal Conductivity for Icosahedral Al-Cu-Fe Quasicrystal through Heavy Element Substitution

Icosahedral Al-Cu-Fe quasicrystal (QC) shows moderate electrical conductivity and low thermal conductivity, and both p- and n-type conduction can be controlled by tuning the sample composition, making it potentially suited for thermoelectric materials. In this work, we investigated the effect of introducing chemical disorder through heavy element substitution on the thermal conductivity of Al-Cu-Fe QC. We substituted Au and Pt elements for Cu up to 3 at% in a composition of Al₆₃Cu₂₅Fe₁₂, i.e., Al₆₃Cu_25-(Au,Pt)Fe₁₂ (x = 0, 1, 2, 3). The substitutions of Au and Pt for Cu reduced the phonon thermal conductivity at 300 K (κ_ph,300K) by up to 17%. The reduction of κ_ph,300K is attributed to a decrease in the specific heat and phonon relaxation time through heavy element substitution. We found that increasing the Pt content reduced the specific heat at high temperatures, which may be caused by the locked state of phasons. The observed glass-like low values of κ_ph,300K (0.9-1.1 W m^-1 K^-1 at 300 K) for Al₆₃Cu_25-(Au,Pt)Fe₁₂ are close to the lower limit calculated using the Cahill model.