In-situ energy dispersive X-ray diffraction studies of the crystallization of (1,2-DAPH(2))(2)Ge-9(OH)(4)O-18 center dot 2 H2O under solvothermal conditions

The solvothermal synthesis of the three-dimensional germanate (1,2-DAPH(2))(2)Ge-9(OH)(4)O-18 (.) 2 H2O has been studied with the in-situ energy dispersive X-ray powder diffraction technique (EDXRD). The temperature dependence of the extent of reaction (alpha) has been investigated at 160 degreesC, 170 degreesC and 175 degreesC. In this temperature region no crystalline precursors or intermediates could be detected. The crystallization proceeds in more than one step suggesting a change of the kinetics during the formation of the crystalline material. The evaluated reaction exponents for the different steps are in good agreement with different Avrami nucleation models. The shape of the crystals was investigated with scanning electron microscopy after quenching the products after different reaction times. In agreement with the different nucleation models significant changes of the crystal sizes and shapes were observed. For the investigation of the effect onto the crystal growth of the compound seed crystals were added to the starting material. Again, the results indicate that over the temperature range the crystallization can be modeled by nucleation-controlled processes with two or three dimensional growth of the crystals.