SYNTHESIS, PHASE-STABILITY AND ELECTRICAL CHARACTERIZATION OF BINAVOXSOLID-SOLUTIONS

The compositional range of 'Bi4V2O11' solid solutions containing Na ha s been determined by means of a phase diagram study using X-ray diffra ction and electron probe microanalysis. The locus of the solid solutio n indicates that Na replaces V in the crystal structure and the BINAVO X family has the overall formula Bi4+yV2-y-xNaxO11-y-2x. The solid sol ution limits are temperature dependent and for samples prepared and ai r-cooled from 830 degrees C the limits are defined as 0.00 < x < 0.18 and 0.05 < y < 0.19. BINAVOX compositions with x > 0.10 are thermodyna mically unstable below ca. 720 degrees C but can be stabilised kinetic ally by rapid cooling from temperatures above ca. 750 degrees C. ac Im pedance measurements demonstrate that BINAVOX materials are electrical ly inhomogeneous, exhibit temperature-and time-dependent conductivitie s and do not offer any significant advantages over the parent solid so lution.