Expanding the I–II–V Phase Space: Soft Synthesis of Polytypic Ternary and Binary Zinc Antimonides

Abstract

Soft chemistry methods offer the possibility of synthesizing metastable and kinetic products that cannot be obtained through thermodynamically controlled, high-temperature reactions. A recent solution-phase exploration of Li–Zn–Sb phase space revealed a previously unknown cubic half-Heusler MgAgAs-type LiZnSb polytype. Interestingly, this new cubic phase was calculated to be the most thermodynamically stable, despite prior literature reporting only two other ternary phases (the hexagonal LiGaGe-type LiZnSb and the cubic full-Heusler Li2ZnSb). This surprising discovery, coupled with the intriguing optoelectronic and transport properties of many antimony-containing Zintl phases, required a thorough exploration of synthetic parameters. Here, we systematically study the effects that different precursor concentrations, injection order, nucleation and growth temperatures, and reaction time have on the solution-phase synthesis of these materials. By doing so, we identify conditions that selectively yield several unique ternary (c-LiZnSb vs h*-LiZnSb), binary (ZnSb vs Zn8Sb7), and metallic (Zn and Sb) products. Further, we find one of the ternary phases adopts a variant of the previously observed hexagonal LiZnSb structure. Our results demonstrate the utility of low-temperature solution-phase—soft synthesis—methods in accessing and mining a rich phase space. We anticipate that this work will motivate further exploration of multinary I–II–V compounds and encourage similarly thorough investigations of related Zintl systems by solution-phase methods.