DIELECTRIC STUDY OF KNBO3 CERAMICS OVER A LARGE RANGE OF FREQUENCY (10(2) -10(9) HZ) AND TEMPERATURE (300 -800 K)

KNbO3 ceramics were sintered at 1263 K thanks to a LiF additive. The f erroelectric-paraelectric transition is of first order and occurs at T -c similar to 670 K. A dielectric study in a large frequency range (10 (2) - 10(9) Hz) shows: a strong frequency dispersion of the permittivi ties at low frequency for T > 500 K which comes mainly from conductivi ty phenomena, a dispersion at high frequency in both ferroelectric and paraelectric regions which comes from a network relaxation of correla tion chains of Nb5+ cations. The latter effect was revealed thanks to a new high frequency-high temperature device usable up to 10(9) Hz and 800 K simultaneously.