Proton motion in HNbO3 and HTaO3

Proton NMR relaxation times T₁, T_1?, and T₂ are reported for the compounds HTaO₃ and HNbO₃ in the temperature range 170–540 K. The data show that for both compounds two types of motion occur. Proton diffusion occurs in both compounds above 400 K with a correlation time, τ⁰_c, of ～30 ps and an activation energy of ～50 kJ mole^?1, approximately twice that for the localized process occurring at lower temperatures. Alternating current conductivity measurements have been used to study proton diffusion above 470 K in these compounds.