A combination of variable temperature X-ray powder diffraction, ac impedance spectroscopy and differential thermal analysis (DTA) has been used to characterise phase transitions in the Bi2ZrV1-xO5,5-(x/2)-delta, BIMEVOX system. At low substitution levels alpha-, beta-, and gamma-phase BIMEVOX structures are observed as a function of temperature with some evidence for an intermediate phase, epsilon, seen between beta and gamma phases on heating. At x=0.10 the beta-phase is observed at room temperature with a transition to the gamma-phase at around 500 degrees C. There is evidence for a subtle phase transition at around 200 to 250 degrees C in the variation of refined cell parameters and the Arrhenius plot of conductivity for this composition that may be associated with a vacancy ordering phenomenon. For the x=0.19 composition, despite near equivalence of a and b unit cell parameters, variation in the unit cell c-parameter, DTA and Arrhenius plots of conductivity show evidence of a beta <->gamma transition between 450 and 500 degrees C and that the true symmetry of the low temperature phase is likely to be orthorhombic. (c) 2005 Elsevier B.V. All rights reserved.