PTCR EFFECT IN W-DOPED KNBO3 CERAMICS SINTERED IN REDUCING ATMOSPHERE

Electrical properties of W-doped KNbO3 ceramics were studied by combin ing their diffuse reflectance measurements. In the case of samples sin tered in a reducing atmosphere, CH4/Ar=1/99, they were conductive and two step of positive temperature coefficient of resistivity(PTCR) effe cts were observed at temperatures where ferroelectric phase transition s from orthorhombic to tetragonal(lk) and successively to cubic (Tc) o ccurred, while the resistivities higher than 10(6) Omega cm were obser ved for those sintered in air, The 0.2 mol%W-doped sample sintered in the reducing atmosphere showed room-temperature resistivity of 10(1)-1 0(2) Omega cm, with PTCR jump(Log R-max/R-min) of about 1.4 order of m agnitude, Diffuse reflectance measurements for the samples sintered in the reducing atmosphere also indicated an increase of the conduction electron concentration with increasing doped amount of W.