ANALYSIS OF CHEVRON TWIN TILING OF LAALO3
Stefan Bueble , Wolfgang W. Schmahl
Institut für Mineralogie, Petrologie und Geochemie,
Universität Tübingen, Wilhelmstr. 56 Tübingen, Germany, e-mail
of corresponding author: wwschmahl@uni-tuebingen.de
Keywords: ferroelastic phase transition, twinning,
strain tensor, sponanous deformation
If cooled through the improper ferroelastic m3m
- R3_c phase transition at
544°C, single crystals of LaAlO3 develop
characteristic twin domains with {100} and {110}domain walls
referred to the pseudocubic lattice. The resulting domain
patterns on a (100)pseudocubic cut and polished
surface of a LaAlO3 wafer plate can be investigated in
a quantitative way with Scanning Force Microscopy (SFM)[1]. The
domain arrangement in different patterns indicates the stress
distribution in the initial high temperature paraelastic phase.
Fig. 1 indicates the orientation of the strain tensors for the
domains in a pattern. By integration across an area such as in
Fig.1, it is possible to calculate the orientation of the local
stress tensor in the initial cubic crystal before it was cooled
through the phase transition. The ferroelastic deformation
corresponds to a compression along one of the four <111>
directions and extension perpendicular to it. Strain tensors for
the four domain states are given in Table I. From the
rhombohedral angle of the pseudocubic unit cell a = 90.096(1)° ,
the strain coefficient at room temperature is found to be e =
8.4(1)*10-4. Table II lists the strain-compatible twin
walls between each pair of the four domain states in the system.
Fig.1 Domain pattern and section through (hopelessly exaggerated) strain tensors indicating the ferroelastic distortion within each domain on a (100) surface. The domain walls forming an angle of 18° with the vertical axis are (110) and those with a 63° angle are (010).
The arrows indicate the direction of the compressional
<111> axis pointing down into the sample.
