Synthesis of molybdenum- and vanadium-containing mixed oxides in polymer-salt systems

Rare-earth alkaline-earth mixed oxides containing transition metals (Mo, V) were prepared via pyrolysis in polymer-salt systems. The products were cha racterized by thermal analysis, resistance measurements, dilatometry, optic al microscopy, and x-ray diffraction. The introduction of polyvinyl alcohol into the system containing lanthanum or strontium nitrate and ammonium mol ybdate was found to have a significant effect on the thermal decomposition process, testifying to changes in the bonding configurations of the constit uent components in the systems studied, capable of forming stable gels, whi ch are then used as precursors to synthesize oxide materials. The temperatu res of different stages of dehydration were shown to be lower in the polyme r-containing systems. The effect of solution acidity was assessed by examin ing thermal decomposition in systems containing a polymer and Mo or W salts and acidified with nitric acid. The reaction of nitrates (oxidants) with t he polymer was accompanied by an exotherm at similar or equal to 170 degree sC, corresponding to the melting of ammonium nitrate, resulting from an exc hange reaction. The exothermic reaction was found to reduce the decompositi on temperatures of the salts involved. The use of polymer-salt systems allo wed the mixed oxides SrMoO4 and La-2(MoO4)(3) to be synthesized at lower te mperatures in comparison with the coprecipitation of poorly soluble compoun ds. The method was also shown to be suitable for preparing perovskite oxide s in the La1-xSrxCo1-zMzO3+/-y (M = Mo, V) systems.