Effects of Ba/Ti Ratio on Positive Temperature Coefficient of Resistivity Characteristics of Donor-doped BaTiO₃ Fired in Reducing Atmosphere

Abstract

The positive temperature coefficient (PTC) of resistivity characteristics of donor-doped BaTiO 3 fired at 1350 C in a reducing atmosphere of 1 Â 10 À7 MPa at the partial pressure of oxygen is investigated. The result reveals that BaTiO 3 ceramics fired in such a reducing atmosphere usually exhibit low PTC characteristics, whereas La-doped BaTiO 3 with compositions in the range of ðBa þ LaÞ=Ti = 1:02 exhibit pronounced PTC characteristics. A La content of less than 0.4 mol % is suitable for the PTC characteristics, while samples doped with more than 0.8 mol % La do not show the PTC characteristics. The PTC characteristics of semiconducting BaTiO 3 fired in a reducing atmosphere are enhanced with a decrease in the ion radius of a donor ion in the order La < Nd < Sm, therefore, semiconducting BaTiO 3 doped with Sm shows pronounced PTC characteristics with a resistivity increase of more than 6 orders of magnitude. However, the resistivity of BaTiO 3 ceramics doped with Y, whose ion radius is less than that of Sm, is extremely high resistivity that decreases with increasing temperature, thereby indicating only a negative temperature coefficient (NTC) characteristics.

Influence of Reoxidation on Silica-Containing Barium Titanate Ceramics for PTCR Thermistors Prepared by Tape Casting

“…Consequently, the reoxidized ceramics show their PTCR effect when the temperature is higher than the Curie's point, above which the permittivity of the ceramic follows Curie-Weiss law. Similarly, the addition of Y may have a negative effect on the PTCR jump, as reported by Niimi et al [9]. They proved that some of the reduced ceramics may have a PTCR effect when donor additives other than Y were introduced, provided that the Ba/Ti ratio was above 1.02.…”

Reoxidation Effects of Ba‐Excessive Barium Titanate Ceramics for Laminated Positive Temperature Coefficient Thermistors

“…proved that BaTiO 3 ceramics with excessive Ba element had a more significant PTC effect than those rich in Ti element . It was also found out that several kinds of reduced BaTiO 3 ceramics have PTCR effects but the Y‐doped sample reveal no resistivity jump at all . The behavior of oxygen had been traced on reoxidized PTC ceramics, showing that the scale of the PTCR jump depends on the amount of the oxygen penetrated into grain boundary region .…”

“…9 It was also found out that several kinds of reduced BaTiO 3 ceramics have PTCR effects but the Y-doped sample reveal no resistivity jump at all. 10 The behavior of oxygen had been traced on reoxidized PTC ceramics, showing that the scale of the PTCR jump depends on the amount of the oxygen penetrated into grain boundary region. 11 Moreover, Ho et al focused on calculating acceptor-state density at grain boundaries.…”

Abnormal reoxidation effects in Ba‐excess La‐doped BaTiO3 ceramics prepared by the reduction‐reoxidation method

“…Ba‐excess BaTiO 3 ceramics was frequently used because it showed higher PTCR jump than Ti‐excess one . Generally, PTCR ceramics fired in a protective or reducing atmosphere showed poor PTCR effect, which could be enhanced through reoxidation .…”