Ca14AlBi11-a new Zintl phase from earth-abundant elements with a great potential for thermoelectric energy conversion

The Zintl phase Ca14AlBi11 has been synthesized and structurally characterized for the first time. Its crystal structure has been carefully determined by single-crystal X-ray diffraction methods, and shown to crystallize in the tetragonal space group I4(1)/acd, No. 142 (Z = 8). Not surprisingly, Ca14AlBi11 adopts the Ca14AlSb11-structure type, although Ca14AlBi11 is the first alumo-bismuthide among the '14-1-11' family whose structure is unequivocally established. In the respective Ca-Al-Bi ternary system, so far, Ca14AlBi11 is only the second identified phase. Electronic structure calculations for this new bismuthide indicate the opening of a small gap at the Fermi level, suggestive of intrinsic semiconducting behavior. Resistivity measurements on as-synthesized single crystalline sample show temperature dependence akin to those of heavily doped semiconductors or the bad metals. In addition to the moderately high electrical conductivity (rho(300) = 1.05 m Omega cm), specimens of Ca14AlBi11 also exhibit excellent thermopower, with high-temperature (HT) values of the Seebeck coefficient approaching and possibly exceeding 200 mu V/K. These metrics, coupled with preliminary HT conductivity estimates, are comparable with the best state-of-the-art p-type Zintl thermoelectric materials and are among the best within the known bismuthides with the same atomic arrangements. Therefore, Ca14AlBi11 represents a new platform for the development of a novel, low-cost thermoelectric materials family with first-class transport properties and enhanced thermal stability. Initial data suggest that Ca14AlBi11 is amenable to doping, which opens up many opportunities for tuning charge-carrier concentration and optimizing the transport properties in this new, HT thermoelectric material. (C) 2020 The Author(s). Published by Elsevier Ltd.