Sub-micrometer particle size effects on metastable phases for a photoswitchable Co–Fe Prussian blue analog

Metastable phases of the photoswitchable molecular magnet K 0.3 Co[Fe(CN) 6 ] 0.77 ⋅ nH 2 O in sub-micrometer particles have been structurally investigated by synchrotron powder x-ray diffraction (PXRD) measurements. The bulk compound (studied here with a sample having average particle size 500 nm) undergoes charge transfer coupled spin transition (CTCST), where configurations change between paramagnetic Co II ( S = 3/2) –Fe III 1/2) high-temperature (HT) state and diamagnetic 0) low-temperature (LT) state. exhibits unique intermediate (IM) phase, which corresponds to mixture HT LT states that depend on cooling rate. Several hidden metastable emerge as function thermal photo stimuli, namely: (1) quench (Q) generated from flash cooling, (2) LTPX obtained photoexcitation derived relaxation Q state, (3) an IMPX accessed photo-irradiation IM A smaller size, 135 nm, is for are scale coherent domains phase within larger nm sample. PXRD studies under controlled and/or optical excitations clarified reduction profoundly affects structural changes associated CTCST. unusual also observed segregated particle, but collective transformations more hindered small particles. volume decreases 2%–3%, almost half value found (5%–8%), even though linear expansion coefficients Furthermore, does not turn into single particles, presumably because multiple interfaces internal stress coexistence lattice. Since reduced limits cooperativity domain growth lattice, CTCST becomes less sensitive external stimuli.