Research highlight: Elastic anomalies of relaxor ferroelectrics – evidence for Burns temperature?

Lead-free relaxor ferroelectric materials (in short relaxors) crystallizing in the partially filled tetragonal tungsten bronze structure type, as for example SrxBa1-xNb2O6 (SBN), attracted much interest in the last about 20 years because of their outstanding pyroelectric, piezoelectric, electro-optic, and photorefractive properties which are suitable for a variety of technical applications. However, as a consequence of its relatively low Curie temperature (79°C) SBN can easily depolarize near room temperature. Lead free relaxors with significantly higher Curie temperatures are the solution to overcome this problem. In this context calcium barium niobate CaxBa1-xNb2O6 (CBN) with 0.18 ≤ x ≤ 0.35 is a promising candidate. The crystals are iso-structural with SBN but possess Curie temperatures up to about 270°C.
For more than five years now, our group is working in close collaboration with the crystal growth group of Manfred Mühlberg (Köln, Germany) on CBN single crystals with the primary focus to analyze the behavior of polar nano regions which are responsible for the relaxor properties of CBN type crystal species. To this end we are employing a combination of different experimental methods including resonant ultrasound spectroscopy (RUS), dilatometry and X-ray diffraction techniques.

 

 

 Single Chrystal

Temperature
As grown single crystal of
CaxBa1-xNb2O6 with x=0.28.

Temperature dependence of elastic constants of CaxBa1-xNb2O6 (x=0.28).
Source: Phys. Rev B 84, 174102 (2011).

 

Further information can be found in:

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C. S. Pandey, J. Schreuer, M. Burianek, M. Mühlberg: Relaxor behavior of CaxBa1-xNb2O6 (0.18 x 0.35) tuned by Ca/Ba ratio and investigated by resonant ultrasound spectroscopy. Phys. Rev. B 87 (2013) 094101 (7 pp).
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C. S. Pandey, J. Schreuer, M. Burianek, M. Mühlberg: Relaxor behaviour of ferroelectric Ca0.22Sr0.12Ba0.66Nb2O6. Appl. Phys. Lett. 102 (2013) 022903 (4 pp).
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H. A. Graetsch, C. S. Pandey, J. Schreuer, M. Burianek, M. Mühlberg: Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28). Acta Crystallogr. B 68 (2012) 101 – 106.
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H.A. Graetsch, J. Schreuer, M. Burianek, M. Mühlberg: Thermally induced structural changes in incommensurate calcium barium niobateCa0.28Ba0.72Nb2O6 (CBN28). J. Solid State Chem. 196 (2012) 255 – 266.
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C. S. Pandey, J. Schreuer, M. Burianek, M. Mühlberg: Anomalous elastic behavior of relaxor ferro­electric Ca0.28Ba0.72Nb2O6 single crystals. Phys. Rev. B 84 (2011) 174102. Ca0.28Ba0.72Nb2O6 (CBN28).