Synthesis of Bi(Cu)VOx compounds by means of a monomode microwave -: Crystallographic, calorimetric, electrical and low temperature magnetic properties

BiVOx and Bi(Cu)VOx compounds exhibit various phases as a function of temperature. Syntheses performed by means of a monomode microwave allows the high copper ionic conductor gamma-Bi4CuxV2-xO11 phase to be obtained rapidly (less than 5 min). After heating at about 830 K, large crystals, characteristic of this phase. are formed. X-ray diffraction patterns show that this phase coexists with the Bi4Cu3V2O14 and BiVO4 compounds. DSC measurements show on heating the presence of an exothermic peak and two endothermic peaks. On cooling one exothermic peak occurs. Electrical conductivity (under air and oxygen) exhibits for the ionic phase a large scale of values which are close to those previously obtained for a purer material. Magnetic measurements show that the gamma-phase is strictly antiferromagnetic between 300 and 2 K. The results are discussed in terms of polytypic structures, and of performances carried out by means of the monomode microwave. (C) 2000 Elsevier Science S.A. All rights reserved.