Defect Chemistry, Phase Transitions, and Thermoelectric Properties of Ca1–xCexAg1–ySb (0 ≤ x ≤ 1; 0 ≤ y ≤ 1)

Zintl phases Ca1–xCexAg1–ySb (0 ≤ x ≤ 1; 0 ≤ y ≤ 1) have exhibited high-temperature thermoelectric potentials in previous studies. In this work, defect chemistry and thermoelectric properties related to the Ca1–xCexAg1–ySb series were carefully investigated. The results revealed that the Ce contents in Ca1–xCexAg1–ySb were very critical in governing the formation of various Ag-defect structures. With the Ce concentrations increased, several phase transition processes were observed, corresponding to closely related but obviously different [Ag1–ySb] anionic superlattices. Such a defect model makes these compounds very flexible in the optimization of thermoelectric properties. For a material with the nominal composition of Ca0.83Ce0.17Ag0.85Sb, a high figure of merit (ZT ∼ 0.6) can be maintained over a wide temperature range from 800 to 1025 K, which is a favorable characteristic for practical applications.