The influence of Mn on the grain-boundary potential barrier characteristics of donor-doped BaTiO3 ceramics

Abstract

Two compositions of BaTiO3 positive temperature coefficient of resistance ceramics, prepared identically except for the fact that a small addition of Mn (0.04 at. %) was made to one of them, were studied. The samples were sintered simultaneously in air at 1400 °C for 1 h and then annealed at 1200 ° for 5 h, using a muffle furnace. Room-temperature dielectric measurements in the audio- and radio-frequency ranges confirmed that Mn has a negligible effect on the bulk resistance. Arrhenius plots of resistivity vs 1/[Tε′m(T)] were found to give straight lines for Tc<T<Tmax (where ε′m is the relative permittivity of the specimen measured at a constant frequency of 30 kHz, Tc is the ferroelectric transition temperature, Tmax is the temperature corresponding to the maximum in resistivity, and T is the absolute temperature), in accordance with the well-known Heywang model. The height of the potential barriers at different temperatures, as calculated from the slopes of these plots, were found to increase by about 40% (from ∼0.34 to ∼0.50 eV) by the addition of Mn. A small increase in the acceptor-state density at the grain surfaces, which was again obtained from these plots, was observed in Mn-doped specimens (3.9×1013 cm−2 as compared to 2.7×1013 for Mn-free specimens). It was also found that the inclusion of Mn had a negligible effect on ε′m above Tc.

Characterisation of the R–T response of BaTiO3 thermistors on three different length scales

“…Illingsworth et al 7 observed a similar increase from 2.3 to 2.5 as the Mn content was raised from 0 to 0.04 at.%. Thus the observed differences in our samples could be explained by localised small changes in Mn concentration due, for example, to incomplete mixing on this scale during powder preparation.…”

“…[2][3][4] Acceptors such as Mn increase the height of the grain boundary barrier by activating deep trap states. [4][5][6][7] Isovalent substitutions of Pb or Sr for Ba are used to adjust T C 8 or are added in 'balancing' amounts to modify performance whilst maintaining T C . 9 Ca has little influence on T C , but is often also added as a grain refiner.…”

Bulk response and grain boundary microelectrical activity of high TC BaTiO3–(Bi1/2K1/2)TiO3-based positive temperature coefficient of resistance ceramics

“…A reduction in sintering temperature of BBKT10-ASTMn would presumably improve T C by reducing evaporation of volatile elements. Moreover, the increase in q max /q min by 0.6 6 0.1 and 1.9 6 0.1 orders of magnitude by AST and ASTMn additions, respectively, for both BBKT5 and BBKT10, similar to BT-based PTC ceramics, 19 can be attributed to grain boundary segregation of impurities, 1 Al 31 (20) and Mn 21 (18) acceptors, in the presence of AST.…”

Effect of fabrication routes on the microstructure, the dielectric and ferroelectric properties of the Mn-doped BaTiO3 ceramics

“…For the PTCR studies, the key role of manganese in PTCR ceramics is to modify the grain boundary layer characteristics while keeping the grain-bulk conductive; a small addition of 0.04 at. % of manganese can result in increasing the height of the grain boundary potential barriers by *40 % in the temperature range between T C and T max [23]. In this study, the manganese was added at the first stage into BaCO 3 and TiO 2 and then calcined.…”

“…Microstructure and electrical properties of Mn-doped BaTiO 3 have been extensively studied by numerous researchers [3][4][5][6][7][8][9][10][11][12][13][14][15]. For the donor-doped positive temperature coefficient of resistance (PTCR) ceramics, manganese depresses the grain size and enhances the electrical resistivity near the Curie temperature of BaTiO 3 [16][17][18][19][20][21][22][23]. For the based-metal-electrode (BME) MLCCs, undoped-perovskite BaTiO 3 materials are reduced and become semiconductors when fired in the protective atmosphere which is to prevent the internal electrodes from being oxidized.…”