Disruption of Dislocation Cores at Grain Boundary in Nb-Doped SrTiO 3 Bicrystals

Abstract

Bicrystals of Nb-doped SrTiO3, having tilt angles of 4°-18°with respect to [001], were prepared by joining two single crystals at 1873 K and then investigated to identify the effect of tilt angle on the grain boundary structure. The boundaries consisted of a regular array of dislocations but the positioning of cores along the boundary was found to be changed from a line to a zigzag as a tilt angle was increased up to 10°. The 14° - tilted boundary exhibited two kinds of boundary region exist at the same grain boundary; (1) the discrete cores region as observed in 4° - 10° - tilted boundaries and (2) the randomly oriented region as found in the 18° boundary. Thus it was observed that the structure of low-angle tilt boundary changed from the discrete dislocation structure to the randomly oriented structure as a tilt angle increases. These structural changes at the grain boundaries are considered to be related to a minimization of strain due to the high density of dislocations.

Full text

Disruption of Dislocation Cores at Grain Boundary
in Nb-Doped SrTiO
3
Bicrystals
S.-Y. Choi
1,a
, J. P. Buban
1,b
, N. Shibata
1,c
, T. Yamamoto
2,d
and Y. Ikuhara
1,e
1
Institute of Engineering Innovation, University of Tokyo
2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan
2
Department of Advanced Materials Science, University of Tokyo,
5-1-5, Kashiwanoha, Kashiwa, Chiba, 277-8651 Japan
a
choi@sigma.t.u-tokyo.ac.jp,
b
james@sigma.t.u-tokyo.ac.jp,
c
shibata@sigma.t.u-tokyo.ac.jp,
d
yamataka@k.u-tokyo.ac.jp,
e
ikuhara@sigma.t.u-tokyo.ac.jp
Keywords: Grain Boundary, Dislocation, Bicrystal, SrTiO
3
Abstract. Bicrystals of Nb-doped SrTiO
3
, having tilt angles of 4
o
~18
o
with respect to [001], were
prepared by joining two single crystals at 1873 K and then investigated to identify the effect of tilt
angle on the grain boundary structure. The boundaries consisted of a regular array of dislocations but
the positioning of cores along the boundary was found to be changed from a line to a zigzag as a tilt
angle was increased up to 10
o
. The 14° - tilted boundary exhibited two kinds of boundary region exist
at the same grain boundary; (1) the discrete cores region as observed in 4° ~ 10° - tilted boundaries
and (2) the randomly oriented region as found in the 18° boundary. Thus it was observed that the
structure of low-angle tilt boundary changed from the discrete dislocation structure to the randomly
oriented structure as a tilt angle increases. These structural changes at the grain boundaries are
considered to be related to a minimization of strain due to the high density of dislocations.
Introduction
Perovskite structured ceramics have been known as one of the major functional materials and have
been applied in various electronic components [1,2]. Electronic properties of the perovskite
structured materials strongly depend on the potential barrier and chemical composition state at the
grain boundary. For example, the remarkable electrical nonlinearity appears at random type
boundaries, while the electrical properties of highly coherent boundaries are similar to those of the
single crystals. However, even in the highly coherent boundary with a regular array of dislocations,
electrical nonlinearity is dependent on a tilt angle and therefore density of dislocation and dislocation
core structure can be a key-factor to understand the formation of potential barrier at grain boundary
[3,4]. Recent research [5] on dislocation-core structure in a [001] tilt boundary with a misfit angle of
5.4° exhibit two different types of cores (atomic columns of Sr-Sr and Ti-O inside the cores), which
are induced by dissociation of dislocations. However, in this research, the effect of a tilting angle was
not considered.
In this study, an analysis on the dislocation core and grain boundary structures have been
intensively carried out with symmetric [001] tilt grain boundaries with 4°
~ 18°- tilt angles which
gives the potentiality for understanding the relationship between the grain boundary characteristics
and their properties [6].
Materials Science Forum Online: 2007-10-15
ISSN: 1662-9752, Vols. 558-559, pp 869-872
doi:10.4028/www.scientific.net/MSF.558-559.869
© 2007 Trans Tech Publications Ltd, Switzerland
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
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