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 $\sim 3.9\mathrm{W}/\left(\mathrm{m}\mathrm{K}\right)$, 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.

• Received 18 November 2018

DOI:https://doi.org/10.1103/PhysRevB.99.054201