Synthesis, Structural Characterization, and Hirshfeld Surface Analysis of AgCd2InSe4: A New Member of the I-II2-III-VI4 Chalcogenide Family

A new quaternary chalcogenide compound, AgCd2InSe4, belonging to the I-II2-III-VI4 family of diamond-like semiconductors, has been synthesized using the melt and annealing technique. The stoichiometric composition was confirmed by energy-dispersive X-ray spectroscopy (EDS), yielding elemental ratios consistent with the nominal 1:2:1:4 proportions. Powder X-ray diffraction (PXRD) data revealed a single-phase material with an orthorhombic crystal structure and successfully refined using the Rietveld method in the Pmn21 space group with unit cell parameters a = 8.5817(6) Å, b = 7.4099(9) Å, c = 6.9953(6) Å, and V = 444.83(7)(5) Å3. This quaternary compound crystallizes in a wurtzite-stannite structure where tetrahedrally coordinated cations (Ag+, Cd2+, In3+) and anions (Se2–) form a three-dimensional honeycomb structure. Interatomic distances suggest enhanced ionic contributions to bonding, consistent with other related chalcogenides. A Hirshfeld surface analysis (HSA) indicates that the most important contributions to the crystal packing are from Cd-Se (39.4%), In-Se (31.93%), and Ag-Se (19.9%) interactions, suggesting that the Ag+ ion is the most labile species and making this material a promising candidate for applications requiring fast ion transport. Additionally, Debye temperature and heat capacity estimations point to soft lattice dynamics, indicating potential for use in thermoelectric and optoelectronic devices.