Intercalation compounds of vanadyl phosphate dihydrate with rubidium ion and their electrical properties

Intercalation compounds of vanadyl phosphate with rubidium (RbxVOPO4. yH(2) O) were prepared by reacting VOPO4 with rubidium iodide solutions in aceton e/water (volume ratio 9:1) at temperatures between 18 and 40 degrees C. Two phases with interlayer distance of 0.703 and 0.644 nm were formed during t he intercalation; their composition is 0.20 less than or equal to chi less than or equal to 0.28 and chi greater than or equal to 0.48, respectively. The water content of the intercalates increases with decreasing the rubidiu m content and goes from y = 1.4 for chi = 0.557 up to y = 2.2 for chi = 0.1 10, at 58% relative humidity. Samples with chi = 0.18, 0.28, and 0.48 were investigated by ac and de conductivity measurements which were carried out on pellets at 20 degrees C as a function of relative humidity (RH). In all cases the conductivity is fully electronic up to 30% RH, The electronic con ductivity of the 0.703 nm phase is similar to 10(-7) S cm(-1) at 0% RH and reaches a maximum (similar to 10(-5) S cm(-1)) at around 5% RH, No apprecia ble change is correspondingly observed in the electronic conductivity of Rb 0.48VOPO4. yH(2)O. In all cases, at relative humidity higher than 30% the c onductivity starts being mixed, ionic-electronic, as a consequence of the i ncreasing surface hydration of the microcrystals. Electromotive force measu rements showed that the diffusion of Rb+ gives a significant contribution t o the ionic conductivity.