Cobalt hexacyanoferrates have a relatively low energy barrier for the charge transfer between cobalt and iron atoms. That energy barrier can be overcome by irradiation with light in the ultraviolet-blue region or through the sample heating. Such feature for that charge transfer process is determined by structural and compositional factors. In this contribution the role of a second metal partially substituting to Co in the material composition on the heat induced charge transfer is studied. Samples of the solid solution Co 3-xTx[Fe(CN)6]2yH2O with T = Mn, Ni, Cu, Zn and Cd, were prepared by a simple synthetic route and their behavior on moderate heating, from 80 to 160 °C, was evaluated. The behavior of the solid solution on heating was followed by infrared, X-ray diffraction and Mössbauer data. The heat induced charge transfer appears to be favored once the crystal water is removed, when the metal-metal interaction, through the CN bridges, reaches its maximum strength. From this fact, when a metal like Cu, Zn and Cd, with a relatively weak interaction with the coordinated water molecules and, as a consequence, with a low dehydration temperature, is present in the material structure, a lower activation energy is required to be able the heat induced charge transfer. Even in the presence of a second divalent transition metal occupying a fraction of the structural sites for Co, the charge transfer was observed, which is particularly pronounced in the 120-140 °C temperature range. The heat-induced charge transfer was also evaluated from the photo-induced inverse process in the heated samples using photo-acoustic spectroscopy. © by Oldenbourg Wissenschaftsverlag, München.
Romero, S., Jiménez-Gallegos, J., Yee-Madeira, H., & Reguera, E. (2008). Heat induced charge transfer in the solid solution Co<inf>3-x</inf>T <inf>x</inf>[Fe(CN)<inf>6</inf>]<inf>2</inf> yH<inf>2</inf>O with T = Mn, Ni, Cu, Zn and Cd. Zeitschrift fur Physikalische Chemie, 1661-1678. https://doi.org/10.1524/zpch.2008.5422