Tetragonally Distorted Thio-Spinel Cu _<i>x</i> Co _{(3- <i>x</i> )} S ₄ ( <i>x</i> = 0.60): A Structural and Computational Study

We present a unique Jahn–Teller (J.T.)-distorted phase Cu x Co (3- x ) S 4 ( x = 0.60) in the Cu–Co–S ternary system. The phase was synthesized using molten-flux-mediated high-temperature seal-tube synthesis, and its structure was characterized by single-crystal X-ray diffraction. The compound Cu x Co (3- x ) S 4 ( x = 0.60) crystallizes in the tetragonal I 4 1 / amd ( tI 28) space group, and the structure is made up of Co 3+ centered tetragonally distorted S 6 -octahedral units and (Cu/Co) 2+ centered flattened S 4 tetrahedral units. Magnetic measurements and computational studies suggest a possible reorganization of the electronic environment at the octahedral site, supported by temperature-dependent X-ray crystallographic studies. The phase exhibits spin-canted ferrimagnetism with an indirect band gap of 1.3 eV. Heat capacity measurements, supported by density functional theory (DFT) calculations, reveal that the compound undergoes a ‘Lifshitz’ transition in one spin channel.