Influence of particle size on the phase behavior associated with the thermal spin transition of the Prussian blue analogue K0.4Co1.3[Fe(CN)6]·4.4 H2O

The Prussian blue analogue K0.4Co1.3[Fe(CN)6]·nH2O has previously been shown to exhibit three distinct phases at low temperature. In addition to the well-studied high-temperature ‘high spin’ and low-temperature ‘low spin’ phases, with unit cells of ∼10.3 and ∼9.95 Å, respectively, an intermediate phase with unit cell a = 10.09 Å was recently reported, although it existed as a minority constituent in a mixed-phase material. Herein we report the synthesis of 130 nm K0.4Co1.3[Fe(CN)6]·4.4 H2O particles that form solely the intermediate phase at temperatures below the normal charge transfer induced spin transition. Compared with those formed from a bulk synthesis, the nanosized particles are shown to have the same chemical composition at high temperature, but they undergo different structural transitions with thermal cycling.

Graphical abstractNanosized K0.4Co1.3[Fe(CN)6]·4.4 H2O Prussian blue analogue particles are shown to undergo different structural transitions with thermal cycling relative to bulk sized particles with the same chemical and charge-state composition at high temperature. Particle size reduction can be applied to isolate an intermediate phase in nanosized particles. This intermediate phase only occurs as a minor component in a mixture of phases in the bulk material.Figure optionsDownload full-size imageDownload as PowerPoint slide