DIELECTRIC ANOMALIES IN LI0.4K0.6NBO3 CRYSTALS

Li0.4K0.6NbO3 (LKN) belongs to the completely filled tungsten bronze-t ype ferroelectrics and undergoes a diffuse phase transition at around 420 degrees C. LKN has two thermal hystereses in the heating and cooli ng cycles, above and below the transition point. Hysteresis above T-C is wider than the one below T-C and the width of the hysteresis decrea ses as frequency increases. The Curie range of Li0.4K0.6NbO3 is wider than that of Pb(Mg1/3Nb2/3)O-3 (PMN) and (Sr,Ba)Nb2O6 (SBN) and it imp lies that Li0.4K0.6NbO3 needs a wider temperature range to reach an eq uilibrium phase than PMN and SBN. In pyroelectric measurements using t he current method, P-s = 20 mu C/cm(2) in the ferroelectric phase, and the temperature of the pyroelectric current maximum is by 108 K highe r than that of the dielectric constant maxima. Dielectric constants do not obey Devonshire's law (Curie-Weiss law) I/epsilon proportional to (T-C - T) and in pyre-measurements, the mean field exponent (n = 0.4) is less than 1/2. These imply that Li0.4K0.6NbO3 does not satisfy the single order parameter mechanism.