Dispersive localized Ta-rich area and Ta substitution approach ultralow lattice thermal conductivity in CrSi2

CrSi2-based thermoelectric materials with high earth abundance, low material cost, and high stability, have attracted increasing research interests. However, their performance is till off the practical application level because of high lattice thermal conductivity. Here, we discovered that the observed dispersive localized Ta-rich area and Ta substitution in the CrSi2 matrix induce significant lattice distortions and strain fields, leading to strengthened phonon scattering and in turn an ultralow lattice thermal conductivity of -0.87 W m-1 K-1 at -750 K in the Cr0.94Ta0.06Si2. Together with a power factor of -7 mu W cm-1 K-2 at -750 K, a relatively high figure of merit of 0.28 at -750 K is observed in the Cr0.94Ta0.06Si2. This figure of merit is comparable to other state-of-the-art CrSi2-based thermoelectric materials. Our understanding on the dispersive localized Ta-rich area and Ta substitution can be used to guide the development of wide thermoelectric materials.