Composition Governed Structure Evolution and Thermoelectric Properties in Eu(Li1–2xZnx)Sb (0< x < 0.5) Zintl Phases

Abstract

In this report, a new series of Zintl phases, Eu(Li_1–2xZn_x)Sb (0 < x < 0.5), was discovered and investigated. These phases exhibit rich structural chemistry and notable thermoelectric properties. For the structures of Eu(Li_1–2xZn_x)Sb, three classes of analogues have been identified, which can be best represented by the well-known TiNiSi, LiGaGe, and ZrBeSi types, respectively. Interestingly, the structures of Eu(Li_1–2xZn_x)Sb phases are strongly dependent on the compositions varied with Li/Zn ratios. As a result, Eu(Li_1–2xZn_x)Sb features a highly complex polyanionic framework as well as inherently low thermal conductivity. In addition to the converged band structures and improved effective mass, Eu(Li_1–2xZn_x)Sb materials exhibit excellent thermoelectric performance. Demonstrated by Eu(Li_0.5Zn_0.25)Sb, exceptionally low thermal conductivity has been confirmed generally below 0.5 W/(m K), which led to a remarkable figure of merit (ZT) of 1.12 at 823 K. This value is about 14 times the maximum experimental ZT reported for the isotypic LiZnSb material. These results could bring new understandings on the structure-and-property correlations within the Zintl-phase-based thermoelectric materials since previously the performance of the p-type LiZnSb material was rather difficult to optimize. Besides, Eu(Li_1–2xZn_x)Sb phases established a very significant connection among the well-known TiNiSi, LiGaGe, and ZrBeSi structures, which classify three important thermoelectric Zintl systems represented by EuLiSb, LiZnSb, and EuZn_0.5Sb.