Effect of Acceptors on the Segregation of Donors in Niobium-Doped Barium Titanate Positive Temperature Coefficient Resistors

Small amounts of niobium (donor) doping in barium titanate (BaTiO3) cause semiconductivity in this material. When the amount of niobium is increased slightly, the BaTiO3 is converted back to an insulator. This phenomenon is attributed to donor segregation. Such an insulating material can recover its semiconductivity when specific amounts of acceptors are introduced. The space-charge segregation theory explains that such acceptors can prevent the segregation of donors. Impedance/modulus analysis of BaTiO3 with a slightly increased niobium content and with no or a minimal amount of magnesium (acceptor) show a response of a third resistance–capacitance (RC) network, in addition to the two that have been thought to be caused by the grains and grain boundaries. The response of the third RC network is not observed at greater magnesium concentrations that give a recovery of the semiconductivity. This study suggests that acceptors can inhibit the donor segregation.