Kinetics of photo-induced phase transition and relaxation in the spin-crossover complexes [FexZn1-x(phen)2(NCS)2], influence of metal dilution

• Published in: IOP conference series. Materials Science and Engineering 2009-09, Vol.5 (1), p.012025-9
• Main Authors: Lebedev, G, Pillet, S, Baldé, C, Guionneau, P, Desplanches, C, Létard, J F
• Format: Article
• Language: English
• Subjects: Activation energy; Dilution; Kinetics; Lasers; Nucleation; Phase separation; Phase transitions; Spin transition; Temperature dependence; X ray powder diffraction
• ISSN: 1757-899X; 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/5/1/012025

The kinetics of light-induced spin transition and relaxation in [FexZn1-x(phen)2(NCS)2] (phen=1,10-phenanthroline) has been investigated from time/temperature dependent x-ray powder diffraction with in situ optical excitation. We show that the phase transformation is driven by a heterogeneous nucleation and growth mechanism with phase separation, in both the thermally induced and light-induced regimes. The high spin to low spin isothermal relaxation curves strongly differ from first-order kinetics, and are interpreted using the Kolmogorov-Johnson-Mehl-Avrami model of phase transformation, from which the activation energy to domain growth is derived. Dilution tends to increase the activation energy, and slows down the whole relaxation process. Non-linear photo-induced kinetics as a function of laser power is evidenced, resulting from a light-induced phase separation process; a laser power threshold effect is pointed out. It is found that dilution speeds up the photo-conversion kinetics and reduces the laser power threshold.