Berlin 2008 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 14: Electric, electromechanical and optical properties II

DF 14.10: Talk

Thursday, February 28, 2008, 17:00–17:20, EB 407

A model for the thermo-electric oxidization of lithium niobate crystals* — •Stephan Gronenborn¹, Boris Sturman², Matthias Falk¹, Daniel Haertle¹, and Karsten Buse¹ — ¹Institute of Physics, University of Bonn, Wegelerstr. 8, 53115 Bonn, Germany — ²Institute of Automation and Electrometry, Novosibirsk 630090, Russia

Lithium niobate is an important material for many applications in optics e.g. electro-optic modulators, holography and frequency conversion. Using LiNbO₃:Fe, concentrations of Fe²⁺ and Fe³⁺ ions are important factors determining the performance of the material. Recently, a method to strongly oxidize highly doped crystals (0.5 - 3 wt.% iron in the melt), the thermo-electric oxidization treatment, was reported [1]. The crystals are annealed in the presence of an externally applied electrical field. The iron impurities are nearly completely oxidized to the Fe³⁺ state. The concentration of Fe²⁺ is decreased by 4 to 5 orders of magnitude, compared to less than one order achieved with conventional oxidization. The oxidization starts at the cathode and forms a sharp front, which moves through the crystal. A model for the charge migration in the crystal during the treatment based on a step profile of the Fe²⁺ concentration is developed. It is experimentally verified by spatially-resolved absorption measurements and in-situ investigations of the electric potential distribution inside the crystal and the oxidation front velocity at different temperatures and doping concentrations.

*supported by the Deutsche Telekom AG

[1] M. Falk and K. Buse, Appl. Phys. B 81, 853 (2005)