This paper presents an increase to x = 0.67 of the zirconium content in the conductive Bi2-xZrxO3+delta solid solution. Complete incorporation of Zr in the beta(III)-Bi2O3 structure, confirmed by X-ray powder diffraction, has produced a phase with a lower volume and superior conductivity than those predicted by an earlier study. The observed beta(III)-delta Bi2-xZrxO3+delta phase transition around 730 degreesC has been characterised for the first time and shows a segregation of a mixture of predominantly gamma-Bi2O3 and approximately 30% of the ZrO2, before total reincorporation of the Zr in the high temperature delta-phase. (C) 2004 Elsevier Ltd. All rights reserved.