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Barium titanate (BaTiO 3 ) base-metal electrode multilayer ceramic capacitors of an X7R-formulation, sintered at 12001C under low oxygen partial pressures (of pO 2 % 10 À9 and 10 À11 atm, respectively), followed by annealing at 10001C in an atmosphere containing a higher oxygen partial pressure (of pO 2 % 10 À5-10 À6 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 pO 2 % 10 À9 atm. For sample B sintered in pO 2 % 10 À11 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 /111S. The superlattice can be described by a displacive modulation with incommensurate wave vectors k 1 5 0.58a à , k 2 5 0.58b à , and k 3 5 0.58c à . It is due to the ordering of defect associates ðTi atm, but became ordered along /111S and gave rise to structural modulation.

Summary Dislocation substructure in hot‐pressed hexagonal BaTiO3 ceramics was analysed by transmission electron microscopy. Two dislocation networks each consisting of dissociated half‐partials were determined for the Burgers vectors (b) using the g · b = 0 effective invisibility criteria, and the true directions (u) by trace analysis. Each of the networks contains three partial nodes that are in the form: 1/3[010]+1/3[100]+1/3[100]+1/3[100] = 0, where four partials meet at a point and the Burgers vectors are conserved, as analysed by the weak‐beam dark field technique. Basal dislocation with bb = 1/3<110> is dissociated into two prism plane half‐partials with bhp = 1/3<100> by: 1/3<110> → 1/3<010> + 1/3<100>. Dissociation of basal dislocation by a glide mechanism creates a stacking fault when shear occurs along <100> in the c‐layer of (000l), where l = 1, 3, 4 and 6, of the (chc)1(chc)2 (or (CBC)(ABA)) stacking sequence. The slip system of 1/3<110>(0001) in hexagonal BaTiO3 has been activated at 1300 °C by hot‐pressing under ∼25.8 MPa. Plastic flow contributing to the densification of hexagonal BaTiO3 ceramics occurs through glide of half‐partials in the basal plane by a glide‐controlled dislocation glide mechanism. Dislocation motion governed by the Peierls mechanism, where velocity is determined by both correlated and uncorrelated double‐kink nucleation on two half‐partials, is discussed.

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