Uncovering the Interplay of Competing Distortions in the Prussian Blue Analogue K2CuFe(CN)6

摘要

We report the synthesis, crystal structure, thermalresponse, and electrochemical behavior of the Prussian blueanalogue (PBA) K2CuPe(CN)6. From a structural perspective,this is the most complex PBA yet characterized: its triclinic crystalstructure results from an interplay of cooperative Jahn-Tellerorder, octahedral tilts, and a collective ''slide'' distortion involvingK-ion displacements. These different distortions give rise to twocrystallographically distinct K-ion channels with different mobilities.Variable-temperature X-ray powder diffraction measurements showthat K-ion slides are the lowest-energy distortion mechanism atplay, as they are the only distortion to be switched off withincreasing temperature. Electrochemically, the material operates asa K-ion cathode with a high operating voltage and an improvedinitial capacity relative to higher-vacancy PBA alternatives. On charging, K~+ ions are selectively removed from a single K-ion channeltype, and the slide distortions are again switched on and off accordingly. We discuss the functional importance of various aspects ofstructural complexity in this system, placing our discussion in the context of other related PBAs.