Synthesis, phase stability and electrical characterisation of BINAVOX solid solutions

Abstract

The compositional range of ‘Bi₄V₂O₁₁’ solid solutions containing Na has been determined by means of a phase diagram study using X-ray diffraction and electron probe microanalysis. The locus of the solid solution indicates that Na replaces V in the crystal structure and the BINAVOX family has the overall formula Bi_4+yV_2–y–xNa_xO_11–y–2x. The solid solution limits are temperature dependent and for samples prepared and air-cooled from 830 °C the limits are defined as 0.00<x<0.18 and 0.05<y<0.19. BINAVOX compositions with x>0.10 are thermodynamically unstable below ca. 720 °C but can be stabilised kinetically by rapid cooling from temperatures above ca. 750 °C. ac Impedance measurements demonstrate that BINAVOX materials are electrically inhomogeneous, exhibit temperature- and time-dependent conductivities and do not offer any significant advantages over the parent solid solution.