The {111}-Modulated Domains in Tetragonal BaTiO3

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Abstract:

Barium titanate (BaTiO3) base-metal electrode multilayer ceramic capacitors of an X7R-formulation, sintered at 1200°C under low oxygen partial pressures (of pO2≈10−9 and 10−11 atm, respectively), followed by annealing at 1000°C in an atmosphere containing a higher oxygen partial pressure (of pO2≈10−5–10−6 atm), have been analyzed for crystalline phases using X-ray diffractometry, for microstructure using transmission electron microscopy, and for microchemistry using energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. The classical core–shell structure characterized by a core consisting of tetragonal ferroelectric {011) domains and featureless shell (designated type I) was observed only in sample A sintered in pO2≈10−9 atm. For sample B sintered in pO2≈10−11 atm, the core–shell structure is predominantly type II, consisting of a featureless shell similar to type I, but a core of modulated domains. The core of type II contained incommensurately modulated {111} superlattice domains along 〈111〉. The superlattice can be described by a displacive modulation with incommensurate wave vectors k1=0.58a*, k2=0.58b*, and k3=0.58c*. It is due to the ordering of defect associates , generated extrinsically from sintering in low pO2. Shell thickness was determined by the lattice diffusion of Ca2+ solute cations into BaTiO3 grains during sintering. The core–shell interface became less distinguishable in type II because defect associates , unlike those in type I, were not completely eliminated by re-oxidizing in pO2≈10−5–10−6 atm, but became ordered along 〈111〉 and gave rise to structural modulation.

Document Type: Research Article

DOI: http://dx.doi.org/10.1111/j.1551-2916.2006.01124.x

Affiliations: 1: Centre for Nanoscience Institute of Materials Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan 2: Ferro Electronic Material Systems, Penn Yan, New York, USA

Publication date: September 1, 2006

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