Migration of Half Partial Dislocations in the Planar Fault Plane of Hexagonal Barium Titanate

Abstract

The prism plane half partials with Burgers vector bPr= 1/3 ×〈0110〉 dissociated from the perfect basal dislocations with bB= 1/3〈1210〉 embedded in an α‐type extended planar stacking fault of hexagonal (h‐)BaTiO3 have been analyzed by transmission electron microscopy. It is found that the dissociation of a series of basal dislocations occurred by glide in the fault plane (0002). However, migrating of the pair partials trailing behind in the fault plane was impeded by the leading pair. Under the applied stress in hot pressing, these partials were gradually piled up with successively decreasing separation between each pair. That has consequently led to partial separations ranging between ∼195 and 56 nm. One partial dislocation (p1) belonging initially to the leading pair partials has moved to another plane by a mixed mechanism of glide in (0002) and climb down in (0110) by 1/2[0001] (i.e., (1/2)c). The climbing partial has become an obstacle hindering dislocation migration in the fault plane. Determining the secondary pyramidal plane (0112) connecting the leading half partial allows us to propose that the p1 partial migrating by glide and climb has arrived at another planar fault plane (0005) during hot pressing. The stages of how half partials were created, separated in fault plane, and arrived gradually at the present configuration are proposed and schematically illustrated. The significance of climb‐controlled dislocation glide mechanism in the hot pressing of h‐BaTiO3 is discussed.

Dislocation‐Containing Planar Faults in Metastably Retained Hexagonal Barium Titanate

“…This has consequently produced discrepant separations between half‐partials, such as d ≈500 nm determined in the present study and ∼120 nm reported by Eibl et al 8 . and ∼47–195 nm by Wu et al 16 …”

“…This necessitates climb of partial dislocations upon dissociation in prism planes at the interface of the two stacking faults. One of a pair of half‐partials migrated by a mixed glide in (0002) and climb in has indeed been determined 16 …”

“…4(c)) if not milled off) was estimated from a lower magnification strong-beam image. When dissociation occurs by climb, such as that found by Eibl et al 8 mixed mechanism, 16 half-partials would have separated the initial fault into two fault segments consisting of different extra clayers, i.e. differing in the c component of fault vectors R F ðIIÞ .…”

“…One of a pair of halfpartials migrated by a mixed glide in (0002) and climb in ð10 10Þ has indeed been determined. 16 The glide of d 1 with b d1 ¼ 1=3½1 100 on (0002), the fault plane of F 1 , has effectively rotated R F1 ¼ 1=6½02 21 by 601 clockwise to R F 0 1 ¼ 1=6½20 21. A complex stacking fault is created extrinsically in fault segment F 0 1 with R F 0 1 .…”

“…Climb of partials must occur whenever faults with different extra c-layers are encountered in dislocation dissociation. Fault vectors of such segments suggest that the intersecting dislocations have climbed by (n/6)[0001] from one segment to the next, for example 1/2[0001] reported by Eibl et al 8 and Wu et al 16 If there are dislocations intersecting between a five-layer fault, e.g. F 1 and a six-layer fault, e.g.…”