Regensburg 2010 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 15: Optical and nonlinear optical properties, photonics II
DF 15.2: Vortrag
Donnerstag, 25. März 2010, 10:45–11:05, H11
Optical properties of Calcium Barium Niobate — •Urs Heine1, Klaus Betzler1, Manfred Burianek2, and Manfred Muehlberg2 — 1Department of Physics, University of Osnabrueck, D-49069 Osnabrueck — 2Institute of Crystallography, University of Cologne, D-50674 Cologne
We report on optical measurements on the novel tungsten bronze type Calcium Barium Niobate. [001]-oriented transparent and colorless single crystals were grown by the Czochralski method with dimensions of 12 mm in diameter and about 80 mm in length. With its relatively high Curie temperature of about 538 K for the congruently melting composition of 28.1 mole% calcium and its high nonlinear coefficients, CBN is a promising material for future applications. Recent experiments revealed, that the application of an external electric field of several kV/cm to CBN at room temperature leads to an increasing opacity of the sample. This might be a drawback considering the future usability of CBN in optical systems. We present investigations on the transmittance behaviour of CBN under external electric fields, demonstrating the erasement of the clouding without affecting the polarization. Experiments have been performed at temperatures ranging from room temperature to approximately 480 K. When heating up the sample, its colorless appearance changes to a light yellow, which can be attributed to a shift of the band edge to longer wavelengths with increasing temperature. To further investigate the transmittance properties of CBN, measurements of the band edge under various temperatures up to the ferroelectric phase transition have been performed.