CHANGES OF PTCR PROPERTIES DURING ANNEALI NG IN REDUCING GASES IN NB(W)-MN-CODOPED BATIO3 CERAMICS

The degradation behaviors of Nb(W)-doped BaTiO3 and Nb(W)-Mn-codoped p ositive temperature coefficient of resistivity (PTCR) BaTiO3 during an nealing in reducing gases were studied by measuring their electrical p roperties, diffuse reflectance and ESR spectroscopies. The decrease of PTCR effects during the annealing is consistent with the decrease of the grain-boundary resistivity and density of surface acceptor states, and the increase of conduction electrons. The results also indicated that durability to reducing-atmosphere of Nb (W)-Mn-codoped PTCR BaTiO 3 was enhanced by adding Mn after calcination of the Nb (W)-doped BaTi O3 powders. It is assumed that Mn ions concentrated in the grain bound aries contribute to the enhancement of the durability to reducing-atmo sphere by stabilizing the chemisorbed oxygens through Nb5+(W6+)-Mn pai rs or forming high valence Mn(Mn3+, Mn4+) which trap electrons release d from the chemisorbed oxygens. Thus Mn ions in grain boundaries suppr ess the lowering of the potential barrier during annealing in reducing atmosphere.