Microwave-Assisted Solution Synthesis of Metastable Intergrowth of AgInS(2) Polymorphs

The intergrowth of stable and metastable AgInS(2) polymorphs was synthesized using a microwave-assisted synthesis. The samples were synthesized in water and in a deep eutectic solvent (DES) consisting of choline chloride and thiourea. An increase in the metal precursor concentration improved the crystallinity of the synthesized samples and affected the particle size. AgInS(2) cannot be synthesized from crystalline binary Ag(2)S or In(2)S(3) via this route. The solution synthesis reported here results in the intergrowth of the thermodynamically stable polymorph (space group I [Formula: see text] 2d, chalcopyrite structure) and the high-temperature polymorph (space group Pna2(1), wurtzite-like structure) that is metastable at room temperature. A scanning transmission microscopy (STEM) study revealed the intergrowth of tetragonal and orthorhombic polymorphs in a single particle and unambiguously established that the long-thought hexagonal wurtzite polymorph has pseudo-hexagonal symmetry and is best described with the orthorhombic unit cell. The solution-synthesized AgInS(2) polymorphs intergrowth has slightly lower bandgap values in the range of 1.73 eV–1.91 eV compared to the previously reported values for tetragonal I [Formula: see text] 2d (1.86 eV) and orthorhombic Pna2(1) (1.98 eV) polymorphs.