The effect of Mn on the positive temperature coefficient of resistance characteristics of donor doped BaTiO3 ceramics

Abstract

BaTiO3 positive temperature coefficient of resistance (PTCR) specimens were made from commercial BaTiO3 which was mixed with 0.35 mol. % of Ho2O3 to make it semiconducting and 0.07 mol. % of MnCO3. After sintering at 1320 °C the samples were annealed in batches at 1220 °C for various periods between 0 and 5 h. The effect of Mn was studied by making direct comparison with previous results obtained from Mn free but otherwise identical specimens. Room-temperature dielectric measurements in the audio and radio frequency ranges revealed that Mn had a negligible effect on the grain bulk resistance. Mn was found to result in an increase in the minimum and maximum values of the resistivity, the temperature at which the resistivity is a maximum and the slope of the resistivity-temperature characteristic in the transition region, all of which were attributed to an enhancement of the potential barrier at the grain boundaries. The acceptor state energy of the Mn-doped samples was found to be ∼1.4 eV, while a lower value was obtained for Mn-free material (∼1.12 eV). The effective concentration of Mn acceptors was observed to increase with the annealing time. To explain this behavior a thin Mn-rich boundary layer was assumed to exist, within which there was partial compensation of the Mn ions due to the formation of ionized oxygen vacancies. During annealing in air at 1220 °C, oxidation takes place and more of these vacancies are filled resulting in an increase in the effective Mn concentration. This model is also capable of explaining other phenomena such as the disappearance of the PTCR effect in reduced samples and the effects of cooling rate and quenching on the PTCR behavior.

The influence of cooling rate and SiO2 additions on the grain boundary structure of Mn-doped PTC thermistors

“…22 Thus, during reoxidation N S (T) increases, leading to an associated increase in ϕ 0 (T), according to Eq. (2).…”

Microstructures and energy storage properties of Mn-doped 0.97Bi0.47Na0.47Ba0.06TiO3–0.03K0.5Na0.5NbO3 lead-free antiferroelectric ceramics

“…However, the Mn addition induces the inverse behavior for breakdown strength of BNBT-KNN ceramics. The reason can be that Mn dopant acts partly as a grain-boundary barrier layer in bulk ceramics as reported in most of PTCR ceramics [22,23]. In suitable composition range of Mn dopant, thus, the grain-boundary barrier height of bulk ceramics will go up with rise of Mn content and leads to the increase of breakdown strength.…”

Fabrication and positive temperature coefficient of resistivity properties of semiconducting ceramics based on the BaTiO3–(Bi1/2K1/2)TiO3 system

“…It has been reported that the BT-based semicondouting, not semicondouting ceramics sintered in a reducing atmosphere show a clear PTC property after annealing in air. [12][13][14] Hence the as-sintered semiconducting samples, BBKT5 ceramics sintered at 1350 • C in a N 2 flow with low O 2 concentration were annealed in air at various soaking temperatures and times. Fig.…”