Defect structure and electrical conductivity in the Bi 3+ xNb 0.8W 0.2O 7.1+3 x/2 system

Abstract

An investigation of electrical conductivity and defect structure in the fluorite related system Bi 3 + x Nb 0.8W 0.2O 7.1 + 3 x/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.