Coherent Domain Growth under Photo-Excitation in a Prussian Blue Analogue

We have investigated the structural properties of the photo-induced metastable phase of a Prussian blue analogue (Na0.42Co[Fe(CN)(6)](0.78).4.64H(2)O), which shows the photo-magnetization phenomenon, as revealed by means of the high angle-resolved synchrotron-radiation X-ray powder diffraction technique. We have found that (1) the structural domain size is larger than the quenched high-temperature phase and (2) the lattice constant a (= 10.287(1) Angstrom) is larger than that of the quenched phase (a = 10.187(3) Angstrom). These observations indicate that photo-excitation coherently increases the size of the photo-induced metastable region even at low temperature (91 K much less than T-c).