ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012) P 70
SYNCHROTRON DIFFRACTION TOPOGRAPHY OF SBN (Sr
xBa
1−xNb
2O
6) AND CBN (Ca
xBa
1−xNb
2O
6) CRYSTALS
K. Wieteska1, W. Wierzchowski2∗, A. Malinowska2, M. Lefeld-Sosnowska3, M. Swirkowicz2, T. Lukasiewicz2, and C. Paulmann4
1Institute of Atomic Energy, PL 05–400 Otwock-Swierk, Poland
2Institute of Electronic Materials Technology, ul. W´olczynska 133, PL 01–919 Warsaw, Poland
3Institute of Experimental Physics University of Warsaw, Hoza 69, 00–681 Warsaw, Poland
4HASYLAB at DESY, Notkestr. 85, D–22603 Hamburg, Germany
Keywords: strontium barium niobate, calcium barium niobate, defect structure, diffraction topography
∗e-mail : Wojciech.Wierzchowski@itme.edu.pl
The crystals of ferroelectric niobates with the structure of tungsten bronze such as SrxBa1−xNb2O6 (SBN) and CaxBa1−xNb2O6 (CBN) are the subject of intense investigations in view of their very interesting non linear electro- optical, dielectric, piezoelectric and pyroelectric properties. The doping with rare earth ions ad- ditionally increases the possibility of using these crystals in the laser technology [1]. Also growth of the crystals being the mixture of SBN and CBN is possible which enables controlling the Curie tem- perature.
The published results of crystallographic perfec- tion studies of SBN and CBN crystals indicate the
Figure 1 : Representative synchrotron white beam topographs of Sr0.35Ba0.65Nb2O6 crystal: (a) back- reflection projection topograph, (b) transmission topo- graph, (c) transmission section topograph.
core, dislocations and glide bands. In some cases the dislocation loops were also observed [2].
In the present abstract we present some re- sults of synchrotron diffraction topographic inves- tigations of SBN and CBN crystals grown with the Czochralski method. The topographs were obtained both by means of white and monochromatic beam at DORIS III. The methods of characterization in- cluded the complementary use of different methods of conventional and synchrotron X-ray diffraction topography completed by polariscopic observations.
The typical elements of the defect structure re- vealed in SBN and CBN crystals were some facetted regions, particularly the core present in the mid- dle region and some linear or — stripe-like con- trasts, which are representatively shown in Figures 1 and 2 for the samples cut out respectively from Sr0,35Ba0,65Nb2O6and Ca0.26Ba0.74Nb2O6crystals.
The reported section and monochromatic beam topographs indicates a certain lattice disorientation between the regions separated by linear contrast.
It confirm the suggestion that the linear or stripe contrasts observed in the topographs are caused by
Figure 2 : Representative synchrotron topographs of Ca0.26Ba0,74Nb2O6 crystal: (a) white beam back- reflection projection topograph, (b) monochromatic beam back-reflection projection topograph.
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P 70 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)
small-angle grain boundaries formed by glide bands.
It was otherwise indicated with the use of selective etching method that the ferroelectric domains are of submicron dimension, and they cannot be directly resolved by the diffraction topography, but prob- ably contribute to the enhanced intensity in some reflections.
Acknowledgments: The measurements performed at Hasylab have received funding from the 7th Framework
Programme (FP7/2007-2013) of European Community under ELISA grant agreement No. 226716.
References
[1] J. Dec, W. Kleemannz, S. Migay, V.V. Shvartsmanz, T. Lukasiewicz, and M. ´Swirkowicz, Phase Trans. 80 (2007) 131.
[2] M. Muehlberg, M. Burianek, B. Joschko, D. Klimm, A. Danilewsky, M. Gelissen, L. Bayarjargal, G.P. G¨orler, B.O. Hildmann, J. Cryst. Growth 310 (2008) 2288.
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