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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 16: Crystal Structure Defects / Real Structure / Microstructure I

KFM 16.5: Vortrag

Mittwoch, 20. März 2024, 16:30–16:50, E 124

Where is the hydrogen going? – An investigation of lithium metal oxides — •Thomas Köhler¹, Matthias Zschornak¹, Patrick Reichart², Erica Brendler¹, Christian Röder¹, Günther Dollinger², Hartmut Stöcker¹, and Dirk C. Meyer¹ — ¹TU Bergakademie Freiberg, 09599 Freiberg, Germany — ²Universität der Bundeswehr München, 85579 Neubiberg, Germany

The incorporation of hydrogen into LiNbO₃ and LiTaO₃ during crystal growth has attracted the interest of researchers for more than 50 years. Our studies address the following open points: (i) the model description of the occupation sites, (ii) the diffusion kinetics, and (iii) the hydrogen concentration determination. Hydrogen bonds to oxygen and forms hydroxyl (OH⁻) defects. Since the shape of the vibrational modes strongly depends on the crystal stoichiometry, we can use them to elucidate the presence of different hydrogen occupation sites and the associated chemical environment.

Experimental and theoretical studies indicate that the intrinsic and extrinsic defects of the crystals are crucial, as hydrogen only decorates these defects. The diffusion of hydrogen was studied using elevated temperatures and different atmospheric conditions. Differences in diffusion rate and activation energy are dependent on the dominating defect type. Finally, the question arises: What is the natural hydrogen concentration in these materials? Hydrogen microscopy using proton-proton scattering is found to be the only reliable tool for absolute quantification and can be applied to obtain a calibration factor for infrared spectroscopy.

Keywords: Hydrogen defect; Spectroscopy; Lithium niobate/tantalate; Oxides; Kinetics