In Situ X-ray Diffraction Studies of the Crystallization of Layered Manganese Thioantimonates(III) under Hydrothermal Conditions

The solvothermal synthesis of the layered compound Mn 2 Sb 2 S 5 ·DAP (DAP = 1,3-diaminopropane) has been studied using in situ energy-dispersive X-ray diffraction. The results clearly demonstrate that the induction time strongly depends on the reaction temperature. At lower temperatures two crystalline intermediates could be detected. The decay of the second intermediate and the product growth show a strong correlation. A detailed analysis of the extent of reaction α suggests that a small fraction of the intermediate is either dissolved or converted into an amorphous state. The experimentally determined extent of reaction α versus time was compared with various theoretical models. The reaction exponents indicate similar mechanisms for temperatures between 105 and 125 °C. The best agreement is obtained with a first-order reaction and/or phase-boundary-controlled mechanisms. A rigorous analysis reveals that it is highly likely that with increasing α the mechanism changes, suggesting consecutive and/or parallel kinetics as the reaction proceeds. At 130 °C and α > 0.75 a three-dimensional diffusion-controlled process dominates.