Properties of non-stoichiometric PTCR ceramics

BaO- and TiO/sub 2/-rich BaTiO/sub 3/ (BT) ceramics were studied to disclose the relations among nonstoichiometry, phase formation, microstructure evolution and the positive temperature coefficient of resistance (PTCR) property. Both La/sup 3+/ and Sb/sup 3+/ make BT ceramics semiconducting by way of A-site substitution. The available range of doping amount to obtain minimum resistivity increased with increasing TiO/sub 2/ excess up to 7 mol.%. The second phase for TiO/sub 2/ -rich compositions was Ba/sub 6/Ti/sub 17/O/sub 40/ which promoted grain growth and increased conductivity. The elimination of the grain boundary in the grain growth controls the PTCR jump. Better crystalline BT grains were provided by increasing the sintering temperature and TiO/sub 2/ excess. For BaO-rich compositions, the second phase Ba/sub 2/TiO/sub 4/ was formed and retarded grain growth. High resistivity (>10/sup 8/ Omega -cm) was usually found. A nonstoichiometric composition with a slight TiO/sub 2/-rich content results in a better PTCR property.<
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