Generalized Synthetic Pathway to AInS₂and AGaS₂(A = Alkali Metal) Nanoparticles

Nanoparticles of ABS₂compounds, with A = Li, Na, K, Rb, Cs and B = In and Ga, are important materials for a wide range of energy-based applications because of their useful electronic, optical, thermal, and ion-conducting properties. However, synthetic capabilities for producing these ABS₂nanoparticles remain limited due in large part to the challenge of incorporating alkali metal cations without using highly reactive reagents. Here, we report a generalizable protocol for synthesizing a nanoparticle library of ABS₂compounds that spans a range of layered and 3D-bonded crystal structures. Using reagents that are air-stable, straightforward to use, commercially available, and consistent in reactivity, we demonstrate the synthesis of LiInS₂, NaInS₂, KInS₂, RbInS₂, CsInS₂, LiGaS₂, NaGaS₂, KGaS₂, and RbGaS₂, as well as stable low-temperature and metastable high-temperature polymorphs of CsGaS₂. Across all compositions, we correlate particle morphology with the crystal structure. We also track time- and solvent-dependent morphological evolution and concentration-dependent structural evolution, identifying in situ intermediates and providing guidelines for tuning morphology and crystal phase. Using these guidelines, we then expanded the ABS₂nanoparticle library by synthesizing the mixed A-cation compositions (K,Rb)GaS₂, (Rb,Cs)GaS₂, (K,Rb,Cs)GaS₂, and (Na,K,Rb,Cs)GaS₂. The ability to synthesize compositionally and structurally diverse ABS₂nanoparticles, including solid solutions and metastable polymorphs, lays an important foundation for expanding the scope of this growing family of nanomaterials and their applications.