Kinetics of light-induced first-order phase transformation in molecular solids:: Fe(btr)2(NCS)2•H2O

The mechanism and kinetics of the thermally and light-induced spin transition of the highly cooperative spin crossover material Fe(btr)(2)(NCS)(2)center dot H2O (btr=4,4'-bis-1,2,4-triazole) have been investigated by single crystal x-ray diffraction techniques. The key role of like-spin domains is quantitatively analyzed through a nucleation, growing, and coarsening mechanism whose kinetics follow the Kolmogorov-Johnson-Mehl-Avrami model with low dimensional characteristics.