Electrical conductivity and Li self-diffusion in near-stoichiometric Li(Nb,Ta)O3 solid solutions up to 1000 °C

Lithium niobate-tantalate (LiNb 1-x Ta x O 3 , LNT) solid solutions are promising materials for high-temperature electronic and piezoelectric applications due to their tunable optical and electrical properties. While previous studies have extensively examined Li-deficient compositions, the charge transport mechanisms in near-stoichiometric LNT remain less explored. In this work, the electrical conductivity and lithium self-diffusion in near-stoichiometric LNT were investigated up to 1000 °C. Impedance spectroscopy and 6 Li tracer diffusion experiments with secondary ion mass spectrometry were performed on crystals with varying Nb/Ta ratios, prepared by the Czochralski method and post-treated by vapor transport equilibration (VTE) to achieve near-stoichiometric Li content. After VTE treatment, an additional annealing step in synthetic air was applied to lower the hydrogen content. A comparison of hydrogen-containing and hydrogen-depleted samples reveals an additional conductivity contribution below approximately 600–700 °C in the hydrogen-rich state, characterized by an activation energy of about 1.0 eV. After hydrogen depletion, the low-temperature conductivity is mainly dominated by lithium-ion transport with activation energies close to 1.3 eV. The lithium conductivity derived from Li tracer diffusivities is in good agreement with the ionic contribution obtained from impedance spectroscopy within experimental uncertainty. Above approximately 600 °C, an increasing electronic contribution is observed. This effect is most pronounced in Nb-rich compositions, where electronic conduction dominates at high temperature, but becomes progressively weaker with increasing Ta content.