Studying non-reversible charge-transfer phase transition with time-resolved powder serial crystallography

We propose to develop time-resolved serial crystallography on powder to study ultrafast and non-reversible photoinduced charge-transfer transition in Prussian blue analogues nanocrystals. A previous experiment at ID09 revealed the complete phase switching within the thermal hysteresis, with volume and symmetry change towards a stable phase, precluding so usual pump-probe studies. A second experiment [CH-5458] revealed anisotropic lattice dynamics driven by photoinduced CT small-polarons. Here we propose to develop time-resolved serial crystallography for studying non-reversible processes by using a fresh powder sample for every laser shot. This will allow studying the global out-of-equilibrium dynamics, from the formation of CT small-polarons, to cooperative and macroscopic phase nucleation. Both processes involve volume expansion and symmetry change, fully characterized by shifts of the Bragg peaks, and which have to be probed by X-ray diffraction.