EFFECT OF THE BIAS FIELD ON THE THERMAL-CONDUCTIVITY OF KH2PO4 NEAR THE CURIE-POINT

The thermal conductivity of KH2PO4 (Potassium Dihydrogen Phosphate, KD P) single crystal under dc bias fields up to 2 kV/cm was measured usin g a novel technique called the 3omega method. Without a bias field, a small but definite discontinuity was observed at the Curie temperature (T(c) = 123 K), indicating the first-order nature of the transition. The value of the thermal conductivity was very small due to the proton ic scattering of phonons. The dc bias field tended to increase the the rmal conductivity of KDP only in the vicinity of T(c) and round the di scontinuity at the same time. These results clearly demonstrate the co upling between the heat carrying phonons and the soft mode associated with the ferroelectric transition.