Defect structure and electrical conductivity in the Bi3+xNb0.8W0.2O7.1+3x/2 system

An investigation of electrical conductivity and defect structure in the fluorite related system Bi3 + xNb0.8W0.2O7.1 + 3x/2 (0.0 ≤ x ≤ 2.0) using a.c. impedance spectroscopy and powder neutron diffraction is presented. All compositions exhibit incommensurate ordering of the cubic fluorite sublattice, with only the x = 2.0 composition showing evidence for an order-disorder transition above 650 °C. Non-linear behaviour in the thermal expansion of the cubic lattice parameter and the Arrhenius plot of total conductivity are discussed in terms of the defect structure.