Investigating the ultrafast mechanisms of complete and non-reversible photo-induced phase transition in Prussian blue analogues using time-r

We propose to investigate ultrafast, complete and non-reversible photo-induced phase transitions by using the "streaming crystallography" methodology developed during our previous beamtime on ID09 (CH-6162). This enables to investigate photo-transformations within the hysteresis, by performing time-resolved X-ray diffraction on continuously-refreshed crystals. First results in Co-doped Mn(III)Fe(II) Prussian Blue Analogues microcrystals revealed full conversion towards the Mn(II)Fe(III) phase after 650 nm excitation, driven by elastic deformations involving cooperative symmetry and volume changes. A deeper analysis of the underlying mechanisms is however necessary, as both phase front propagation and global crystal expansion can intervene. Here we propose to further investigate this point by tuning the excitation wavelength, switching from surface-only to bulk absorption. Additional measurements on PBAs with different Co doping rates will allow modulating the elastic energy cost.