Local structure and atomic dynamics in Fe2VAl Heusler-type thermoelectric material: The effect of heavy element doping

X-ray absorption fine structure (XAFS), x-ray fluorescence holography (XFH), and inelastic x-ray scattering (IXS) techniques were applied to an ${\mathrm{Fe}}_{2}({\mathrm{V}}_{0.95}{\mathrm{Ta}}_{0.05}$)Al Heusler-type thermoelectric material to investigate the doping effect of Ta on the local structure and the atomic dynamics. The XAFS and XFH results show that the positional correlation between Ta and surrounding Fe atoms is much more rigid than that between V and Fe. In the IXS results, we observed a broad dispersionless mode in the energy range of the acoustic phonons of undoped ${\mathrm{Fe}}_{2}\mathrm{VAl}$, which is regarded as the so-called resonant mode. These results revealed a clearly different feature of the dynamics of heavy dopants from that of the matrix element, which disturbs the coherency of phonons and should contribute to the enhancement of the thermal insulation.