THE EFFECT OF THERMAL RECYCLING ON THE METASTABLE STRUCTURE OF POTASSIUM FERROCYANIDE SINGLE-CRYSTALS

The electrical conductivity (sigma) and the dielectric permittivity (e psilon) of pure potassium ferrocyanide (KFCT) single crystals are meas ured in the temperature range 77-300 K. The effect of cooling and heat ing recycling on the behaviour of both sigma and epsilon is discussed. The Curie-Weiss law is found to be obeyed in a wide temperature range of the paraelectric phase with constants C0- = 352 K and T0 = 247.2 K . The ratio between the slopes of the two lines representing 1/epsilon versus T in both the ferro- and the paraelectric phases verify the th ermodynamic relations. The structural transformation from the tetragon al metastable state to the monoclinic stable state may not be complete d through the first cooling process down to about 218 K and the steady state, perhaps, needs further thermal recycling.