Crystal structure, phase transition and properties of indium (III) sulfide

Poly- and single-crystalline samples of In0.670.33In2S4 thiospinel were obtained by various powder metallurgical and chemical vapor transport methods, respectively. All synthesized samples contained β-In0.670.33In2S4 modification only, independent from synthesis procedure. High-resolution powder X-ray diffraction (PXRD) experiment at 80 K enabled observation of split tetragonal reflections (completely overlapped at room temperature), which proves the correctness of crystal structure model accepted for β-polymorph. Combined single-crystal XRD, transmission electron microscopy and selected-area electron diffraction confirmed the presence of three twin domains in as-grown crystals. High temperature PXRD study revealed both abrupt (in full width at half maximum) and gradual (in intensity of satellites, c/a ratio and unit-cell volume) changes in the vicinity of the α-β phase transition. On the other hand, clear thermal effect in heat capacity, magnitude of enthalpy/entropy change and temperature dependence of electrical resistivity, associated with hysteresis, hinted towards the 1st order type of the transition. Two scenarios, based on Rietveld refinement analysis, were proposed for the description of crystal structure evolution from β- to α-modification. Seebeck coefficient, electrical resistivity and thermal conductivity were shown to be influenced not only by phase transition, but also by annealing conditions (S-poor or S-rich atmosphere). Theoretical density functional calculations predicted n-type semiconducting behavior of In0.670.33In2S4, as well as instability of fictitious InIn2S4 thiospinel.