Microstructural Changes Induced by Thermal Treatment of Cobalt(II) Hexacyanoferrate(III) Compound

摘要

Molecular-based magnet cobalt-iron cyanide, K_(O.2)Co_(1.4) [Fe(CN)_6] .7820, was prepared by coprecipitation. The powder X-ray diffraction indicates a FCC crystal structure with a unit cell constant of 10.25 A. It has a transition temperature of 11 K. The effects of heat treatment on the microstructures as well as magnetic properties in the compound were studied. Several struc- tures were encountered during the course of annealing from room temperature to 600°C. In the as-prepared (freeze-dried) sample, the majority of the structure was round to be FellI-CN-Co1l, with a minor amount of Fe1l-CN-Co111 structure. The amount of FellI-CN-Co1l structure decreased as a function of annealing temperature. The third structure, namely Co"-CN-Fe'1l began to show up after annealing the sample at 100°C. Total decompo- sition of the cyanide sample occurred at 500°C. A mixture of BCC Fe-Co and a significant amount of (25 wt%) amorphous carbon particles was found in the sample annealed at 600°C.