Structure transformation in Ca1−x−δSrδLaxAg1−ySb (0 ≤ δ ≤ 0.7) and related thermoelectric properties

Abstract

As novel Zintl phases with the LiGaGe structure type, Ca_1−xCe_xAg_1−ySb has shown decent thermoelectric performance as well as complex structure transitions, which are closely related to the Ag defects in the anionic layers. In this report, La/Sr co-doped materials, Ca_1−x−δSr_δLa_xAg_1−ySb (0 ≤ δ ≤ 0.7), were prepared and studied regarding relevant thermoelectric properties. Interestingly, the incorporation of alkaline-earth metal Sr suggested a different structure transition mechanism from the LiGaGe type to the ZrBeSi-type, which seemed closely related to the Sr doping concentrations. Besides, significant enhancement of the thermoelectric performance resulted. For materials with a specific composition of Ca_0.55Sr_0.3La_0.15Ag_0.89Sb, a maximum zT of 0.7 has been achieved at 823 K, which also corresponded to a high average zT value of 0.66 between 774 and 1068 K.