Photoinduced Phase Transition into a Hidden Phase in Cobalt Hexacyanoferrate as Investigated by Time-Resolved X-ray Absorption Fine Structure

Photoinduced dynamics in thin film of cobalt hexacyanoferrate, Na0.79Co[Fe(CN)(6)](0.90)2.9H(2)O, was investigated by time-resolved X-ray absorption fine structure (XAFS) spectroscopy around the Co K edge at 300 K. The compound remains in the low-spin (LS) phase with the electronic configuration of LS Co3+-LS Fe2+ up to 500 K. Nevertheless, the differential XAFS spectrum indicates the formation of high-spin (HS) Co2+ (similar to 0.007/Co site). The decay time (tau(decay)) of HS Co2+ is 32 ns, while the formation time is within the time resolution (<= 100 ps). Such a long decay time suggests photoinduced phase transition (PIPT) into a hidden metastable phase.