The effect of Mn on the PTCR characteristics of La‐doped BaTiO 3 ceramics was studied. Acceptor state density was measured from a p‐1/ T graph as a function of Mn concentration. The behavior of room‐temperature resistivity with Mn concentration was explained by compensation of acceptors at grain boundaries. The valence state of Mn was analyzed by ESR, and it changed near the Curie temperature of BaTiO 3 from 3+ in tetragonal phase to 2+ in cubic phase. Therefore, the number of electron traps increased at the Curie temperature, leading to the great improvement in the PTCR effect. The valence change of Mn ions was explained by vanishing of the Jahn‐Teller effect as the phase changes from tetragonal to cubic.
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Lee et al. (1995) studied this question.
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