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Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P153
X-ray diffraction study of BiB3O6 crystals in an external electric field
Oleg Schmidt 1 , Semen Gorfman 1 , Wolfgang Morgenroth 2 , Ullrich Pietsch 1
1 Solid state physics department, Siegen University, Germany – 2 Department for Inorganic
Chemistry, University of Göttingen, Germany, Department of Chemistry, Aarhus,
Denmark and HASYLAB at DESY, Hamburg, Germany
The application of a permanent external electric field to a single crystal induces deformations,
visible on both atomic and macroscopic levels. Microscopic deformations
are associated with displacements of atomic positions in a fixed unit cell [1], and result
in dielectric polarization of a media. In addition non-centrosymmetrical crystals are
deformed under electric field, showing thus converse piezoelectric effect.
The information about atomic displacements within a unit cell is obtained from Bragg
diffraction intensities. Macroscopic deformation can be simultaneously quantified from
angular positions of diffraction maxima.
In the present work we performed X-ray diffraction study of monoclinic BiB3O6 crystal
under external electric field. This crystal is interesting because of its extraordinary
piezoelectric effect, at least 10 times stronger than in α-quartz. For the first time
the piezoelectric constants of BiB3O6 were measured by means of a Michelson interferometer
[2]. We have determined piezoelectric constants from shifts of rocking curves
by means of synchrotron X-ray diffraction experiment.
The measurements were performed with three differently oriented samples of BiB3O6
parallel to (100), (010), (001) Miller planes using the four circle HUBER diffractometer
at the D3 beamline at HASYLAB. External high voltage was applied via two silver
contacts deposited on the opposite sample faces. The peak shift and intensity variation
of more than 100 reflections were measured. We used the following equation
to calculate eight independent constants of the piezoelectric tensor dijk.
∆θ(H) = tan θdijkEiHj
Hk
H 2 + dijkEiYj
Hk
H + RijkEiYj
Hk
H
This equation relates the tensor dijk, the antisymmetric rotation tensor Rijk and the
electric field vector Ei with the observed peak shift ∆θ. Hi is the scattering vector
and Yi is the Y-axis of the diffractometer in a crystal Cartesian system as the basic
system. We compare the calculated piezoelectric constants to those, obtained in the
work [2].
To get an information about structural reasons for observed physical properites of
BiB3O6 we measured electric field induced diffraction intensity variations. With the
measured data qualitative statements are made concerning atomic displacements related
to high piezoelectric properties.
The authors acknowledge the support of DFG (priority program 1178) and L. Bohat´y,
P. Becker (University of Cologne) for providing the samples of BiB3O6.
[1] Gorfman, S., Tsirelson, V., Pietsch, U. Acta. Cryst. A61, p. 387-396 (2005)
[2] Haussühl, S., Bohat´y, L., Becker, P. Appl. Phys. A82, p. 495-502 (2006)