Grain-boundary decorated titanate ceramics: Preparation and processing

131

The electronic and ionic conduction across grain-boundary (GB) space-charge depletion layers in acceptor-doped SrTiO 3 ceramics have been investigated by admittance analysis in the time domain. The dependence on the acceptor concentration, the oxygen partial pressure during equilibration, and the temperature dependence of the GB conductivity are discussed and interpreted in terms of a defect-chemistry model of the GB region using a numerical simulation technique.

Section: (5) Temperature Dependence Of the Grain-boundary Conductivitymentioning

confidence: 99%

Grain‐Boundary Defect Chemistry of Acceptor‐Doped Titanates: Inversion Layer and Low‐Field Conduction

Vollmann

Hagenbeck

Waser

1997

131

“…4 Ceramic processing improvements are frequently proposed in order to reach a more homogeneous dopant distribution in the final microstructure of the material. 5 ZnO additions to ceramic BaTiO 3 are reported to increase the density of the sintered body and decrease the loss tangent value. [8][9][10][11] However, heterogeneous microstructures (exaggerated grain growth) and second-phase formation are also reported.…”

Section: Introductionmentioning

confidence: 99%

“…Small amounts are usually incorporated in the material as dielectric loss controllers and/or grain growth inhibitors. 2,5,6 In an ideal microstructure, these dopants should be homogeneously distributed along grain boundaries; however, it is common to observe dopant heterogeneities, which can limit their effectiveness. During the last years, several papers have been devoted to this topic.…”

Section: Introductionmentioning

confidence: 99%

Grain Growth Control and Dopant Distribution in ZnO‐Doped BaTiO₃

Caballero

Fernández

Moure

et al. 1998

ZnO additions to BaTiO 3 have been studied in order to determine the role of this dopant on sintering and microstructure development. As a consequence of a better initial dopant distribution, samples doped with 0.1 wt% zinc stearate show homogeneous fine-grained microstructure, while a doping level of 0.5 wt% solid ZnO is necessary to reach the same effect. When solid ZnO is used as the dopant precursor, ZnO is redistributed among the BaTiO 3 particles during heating. Since no liquid formation has been detected for temperatures below 1400°C in the system BaTiO 3 -ZnO, it is proposed that dopant redistribution takes place by vapor-phase transport and grain boundary diffusion. Shrinkage and porosimetry measurements have shown that grain growth is inhibited during the first step of sintering for the doped samples. STEM-EDX analysis revealed that solid solubility of ZnO into the BaTiO 3 lattice is very low, being strongly segregated at the grain boundaries. Grain growth control is attributed to a decrease in grain boundary mobility due to solute drag. Because of its effectiveness in controlling grain growth, ZnO appears to be an attractive additive for BaTiO 3 dielectrics.

“…3(d) and Eq. (11). About 95% of the excess negative charge was present within a depth of about 20.0 nm.…”

Section: (2) Defect-related Effective Charge Distributionmentioning

confidence: 97%

“…͑ x͒ ϭ z i qC i ͑ x͒ (11) where (x) is the total charge/unit volume at x, z i is the charge number of defect i, q ϭ 1.602 ϫ 10 Ϫ19 C, and C i (x) is the concentration of defect i at x. Figure 5(a) shows the charge distribution near the grain boundaries in the ST ceramics; these were estimated with Eq.…”

Section: (2) Defect-related Effective Charge Distributionmentioning

confidence: 99%

Grain Boundaries of Semiconducting SrTiO₃ and BaTiO₃ Ceramics Synthesized from Surface‐Coated Powders

Park

Cho

2001

The chemical and electrical features of the grain boundaries in polycrystalline SrTi 0.99 Nb 0.01 O 3 (ST) and BaTiO 3 (BT) ceramics, which were synthesized by hot-press sintering Na-and Mn-coated semiconducting ST and BT powders, respectively, were investigated. Because of the excess negative electric charges formed near grain boundaries, electrostatic potential barriers were formed near the grain boundaries. The electrical features of the grain boundaries in ceramics are very sensitive to the amount of the coating material. When the amount of the coating material was increased from 0 to 5 wt%, the threshold voltage of the ST ceramics and the resistivity jump ratio of the BT ceramics increased from 0.7 to 81.0 V/cm and from 1.0 to 2.0 ؋ 10 3 , respectively. The electrical features of the grain boundaries are related to their chemical characteristics.