Significant reduction in the thermal conductivity of Si-substituted Fe2VAl epilayers

We experimentally find that the substitution of Si for Al in Heusler-type ${\mathrm{Fe}}₂\mathrm{VAl}$ epilayers contributes to the significant reduction in the thermal conductivity, in which ${\mathrm{Fe}}₂\mathrm{VAl}$ is one of the next-generation thermoelectric materials without using toxic elements. Because of the low-temperature growth of the epilayers, the Si substitution induces the decrease in the degree of $L{2}₁$ ordering, giving rise to the formation of V-Si antisite defects in the epilayers. For ${\mathrm{Fe}}₂{\mathrm{VAl}}_0.57{\mathrm{Si}}_0.43$ epilayers, we can obtain a low thermal conductivity of $\ensuremath{\sim}3.9\phantom{\rule{0.16em}{0ex}}\mathrm{W}/(\mathrm{m}\phantom{\rule{0.16em}{0ex}}\mathrm{K})$, one-third less than Si-substituted ${\mathrm{Fe}}₂\mathrm{VAl}$ bulk samples [Lue et al., Phys. Rev. B 75, 064204 (2007)]. We discuss that a possible origin of the low thermal conductivity is related to the low lattice thermal conductivity due to the presence of the V-Si antisite defects.