Direct Observation of Short-Range Structural Coherence During a Charge Transfer Induced Spin Transition in a CoFe Prussian Blue Analogue by Transmission Electron Microscopy

Abstract

The local structure within the Co-Fe atomic array of the photoswitchable coordination polymer magnet, K0.3Co[Fe(CN)6]0.77·nH2O, is directly observed during charge transfer induced spin transition (CTIST), a solid-solid phase change, using high-resolution transmission electron microscopy (HRTEM). Along with the low-spin (LS) or thermally quenched high-spin (HS) states normally observed in CTIST solids at low temperature, slow cooling of K0.3Co[Fe(CN)6]0.77·nH2O results in an intermediate phase containing both HS and LS domains with short coherence length. By mapping individual metal-metal distances, the nanometer-scale HS domains are directly visualized within the LS array. Temperature-dependent analyses allow monitoring of HS domain coarsening along the warming branch of the CTIST, providing direct visualization of the elastic process and insight into the mechanism of phase propagation. Normally sensitive to electron beam damage, the low-temperature TEM measurements of the porous coordination polymer are enabled by using appropriate ionic liquids instead of usual conductive thin-film coatings, an approach that should find general utility in related classes of materials.

In situ Scanning Electron Microscopy of Silicon Anode Reactions in Lithium-Ion Batteries during Charge/Discharge Processes

“…Thus, the electrochemical lithiation/delithiation reactions of the Si active materials proceed in the areas where the active materials encounter the electrolyte. However, the electrolyte should be a very thin layer (up to approximately 100 nm) to obtain a clear in situ SEM image of the Si anode333435. Otherwise, only a smooth IL surface will be observed, as shown in Supplementary Fig.…”

Electroactive ion exchange materials: current status in synthesis, applications and future prospects

“…MHCFs are an important class of coordination compounds with general formula of A h M k [Fe(CN) 6 ] l ·mH 2 O (h, k, l, m = stoichiometric numbers, A = alkali metal cation, M = transition metal ion). In general, the MHCFs with different transition coordination ion exhibit similar but differently physical and chemical properties.…”

“…40 Controlling the size of the PB crystals clearly depends on the rate of nucleation (photoreduction rates and ionic concentrations). 45 A single-source precursor approach for synthesis of single crystalline nanocubes of PB was proposed by Wu et al 46 In this synthesis process, the PB nanocubes ( Figure 3D, E) were prepared through the direct dissociation of single-source precursor K 4 Fe(CN) 6 Hydrothermal synthesis method is also a useful way to prepare nanostructured PB. 45 The hollow and rigid shells can enhance the thermal stability of PB, and provide possibilities to encapsulate gust materials for various applications such as sensors, biomedicines and catalyst immobilization.…”

“…They can help to excite more electroactive sites of nanostructured PB and improve its stability. Wang et al reported a way for facile filling of MWCNTs with PB nanoparticles, 52 in which MWCNTs were first ultrasonically treated in an aqueous solution of K 3 Fe(CN) 6 followed by careful addition of FeSO 4 solution, and as such, the PB nanoparticles were formed inside the CNTs as shown in Figure 5C, D. The encapsulation of PB nanoparticles in the dispersible and multifunctional MWCNT shells creates new and valuable opportunities for quasihomogeneous phase applications of PB in liquid solutions. (1) The PB is chemically pre-synthesized and later mixed with CNTs mechanically, and subsequently this CNT/PB mixture is employed to build different kinds of electrodes.…”

“…5,6 The MHCFs possess both electric and ionic conductivity during the electrochemical redox process. 5,6 The MHCFs possess both electric and ionic conductivity during the electrochemical redox process.…”