ELECTRICAL-PROPERTIES IN THE BI-RICH PART OF THE BI,MO O SYSTEM/

Mixed [(1-x)BiO1.5-x MoO3] oxides in the composition range x=0 to 0.25 have been prepared by solid state reaction at different temperatures and their electric transport properties have been characterised as a f unction of temperature and oxygen partial pressure P-O2. Broad-range s olid solutions belonging to the fluorite-related structure of delta-Bi 2O3 are formed at high temperatures, and their high conductivity can b e partially retained during fast cooling, but it is not reproducible d uring successive heating runs. Reproducible electrical properties have been obtained as a result of long thermal annealing at 800 degrees C. Materials so prepared show a conductivity maximum of similar to 10(-3 ) or 10(-2) Ohm(-1) cm(-1) (respectively at 500 or 700 degrees C) for compositions near x=0.125. For x=0.125 (Bi/Mo=7) the total bulk conduc tivity is independent of oxygen partial pressure in the range 1 less t han or equal to P-O2 less than or equal to 10(-13) atm. Below the latt er pressure, an irreversible conductivity jump occurs, due to formatio n of a reaction layer on the electrode surface.