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 tempe rature. Syntheses performed by means of a monomode microwave allows the hig h copper ionic conductor gamma-Bi4CuxV2-xO11 phase to be obtained rapidly ( less than 5 min). After heating at about 830 K, large crystals, characteris tic of this phase. are formed. X-ray diffraction patterns show that this ph ase coexists with the Bi4Cu3V2O14 and BiVO4 compounds. DSC measurements sho w on heating the presence of an exothermic peak and two endothermic peaks. On cooling one exothermic peak occurs. Electrical conductivity (under air a nd oxygen) exhibits for the ionic phase a large scale of values which are c lose to those previously obtained for a purer material. Magnetic measuremen ts show that the gamma-phase is strictly antiferromagnetic between 300 and 2 K. The results are discussed in terms of polytypic structures, and of per formances carried out by means of the monomode microwave. (C) 2000 Elsevier Science S.A. All rights reserved.