Intercalation Compounds of Vanadyl Phosphate Dihydrate with Rubidium Ion and Their Electrical Properties

Intercalation compounds of vanadyl phosphate with rubidium (Rb x VOPO 4 · y H 2 O) were prepared by reacting VOPO 4 with rubidium iodide solutions in acetone/water (volume ratio 9:1) at temperatures between 18 and 40 °C. Two phases with interlayer distance of 0.703 and 0.644 nm were formed during the intercalation; their composition is 0.20 ≤ x ≤ 0.28 and x ≥ 0.48, respectively. The water content of the intercalates increases with decreasing the rubidium content and goes from y = 1.4 for x = 0.557 up to y = 2.2 for x = 0.110, at 58% relative humidity. Samples with x = 0.18, 0.28, and 0.48 were investigated by ac and dc conductivity measurements which were carried out on pellets at 20 °C as a function of relative humidity (RH). In all cases the conductivity is fully electronic up to 30% RH. The electronic conductivity of the 0.703 nm phase is ∼10 - 7 S cm - 1 at 0% RH and reaches a maximum (∼10 - 5 S cm - 1 ) at around 5% RH. No appreciable change is correspondingly observed in the electronic conductivity of Rb 0.48 VOPO 4 · y H 2 O. In all cases, at relative humidity higher than 30% the conductivity starts being mixed, ionic−electronic, as a consequence of the increasing surface hydration of the microcrystals. Electromotive force measurements showed that the diffusion of Rb + gives a significant contribution to the ionic conductivity.