Li-diffusion in lithium niobate - tantalate solid solutions

Among the class of ferroelectric crystals, the lithium-niobate-tantalate (LiNb_1-xTa_xO₃) system attracts growing attention for applications in the field of nonlinear optics, functional electronics and piezoelectrics. The self-diffusion of the ionic constituents, especially Li, is important for the overall electric conductivity. The aim of this investigation is to figure out how Li diffusion in lithium niobate-tantalate solid solution crystals behaves as a function of the Ta content. Specially grown LiNb_1-xTa_xO₃ single crystals with different niobium to tantalum ratios are used for this purpose. Li tracer self-diffusion is analysed using secondary ion mass spectrometry after applying an isotope-enriched ⁶LiNbO₃ tracer layer and subsequent annealing. All investigations are carried out at 250 and 600 °C, respectively. Despite of the theoretically predicted non-linear variation of the volume of the unit cell between the values of the end compounds, the results indicate no significant modification of Li diffusivities within error limits in the whole solid solution range.