Microstructural changes induced by thermal treatment of cobalt(II) hexacyanoferrate(III) compound

Molecular-based magnet cobalt-iron cyanide, K0.2Co1.4 [Fe(CN)(6)] . 7H(2)O, was prepared by coprecipitation. The powder X-ray diffraction indicates a FCC crystal structure with a unit cell constant of 10.25 Angstrom. 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 structures were encountered during the course of annealing from room temperature to 600 degreesC, In the as-prepared (freeze-dried) sample, the majority of the structure was found to be Fe-III-CN-Co-II, with a minor amount of Fe-II-CN-Co-III structure. The amount of Fe-III-CN-Co-II structure decreased as a function of annealing temperature. The third structure, namely Co-II-CN-Fe-III began to show up after annealing the sample at 100 degreesC. Total decomposition of the cyanide sample occurred at 500 degreesC. A mixture of BCC Fe-Co and a significant amount of (25 wt%) amorphous carbon particles was found in the sample annealed at 600 degreesC. (C) 2001 Academic Press.