In situ X-ray diffraction studies of the crystallization of layered manganese thioantimonates(III) under hydrothermal conditions

The solvothermal synthesis of the layered compound Mn2Sb2S5.DAP (DAP 1,3-di aminopropane) has been studied using in situ energy-dispersive X-ray diffra ction. The results clearly demonstrate that the induction time strongly dep ends on the reaction temperature. At lower temperatures two crystalline int ermediates 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 a suggests that a small fraction of the intermediate is either dissolved or converted into an amorphous state. The experimentally determi ned extent of reaction ct versus time was compared with various theoretical models. The reaction exponents indicate similar mechanisms for temperature s between 105 and 125 degreesC. The best agreement is obtained with a first -order reaction and/or phase-boundary-controlled mechanisms. A rigorous ana lysis reveals that it is highly likely that with increasing cr the mechanis m changes, suggesting consecutive and/or parallel kinetics as the reaction proceeds. At 130 degreesC and alpha > 0.75 a three-dimensional diffusion-co ntrolled process dominates.