Hydrogen Diffusion in Li(Nb,Ta)O₃Single Crystals Probed by Infrared Spectroscopy and Secondary Ion Mass Spectrometry

High Resolution Image Download MS PowerPoint Slide Hydrogen is an impurity that is incorporated into LiNb 1– x Ta x O 3 crystals during crystal growth or during thermal treatment in a humid atmosphere and may influence the physical properties in different ways. In this context, diffusion of hydrogen is an important process because it may enhance the ion conductivity of the material. We investigated the diffusion of hydrogen in LiNbO 3, LiTaO 3, and LiNb 0.15 Ta 0.85 O 3 single crystals in the temperature range between 311 and 606 °C using deuterium from a gaseous D 2 O source as a tracer. Diffusivities were determined by analyzing the relative deuterium fraction in the crystal with infrared spectroscopy or secondary ion mass spectrometry. The results are in good agreement with each other. The diffusivities in LiNbO 3 can be described by the Arrhenius law with an activation energy of 0.98 eV. The diffusivities in LiTaO 3 and LiNb 0.15 Ta 0.85 O 3 are nearly identical to those in LiNbO 3 within a maximum factor of 2. A direct interstitial diffusion mechanism is suggested where hydrogen migrates in the energy landscape of the crystal. From a comparison of the partial H and Li ion conductivities calculated from diffusivities to electrical conductivities measured by impedance spectroscopy, we conclude that hydrogen may contribute to the overall conductivity below 400 °C.