Significant ion conduction in Cu acceptor-substituted bismuth titanate polycrystalline ceramics

Abstract

This paper reports that Cu acceptor substitution at the Ti site has significant effects on structure and electrical properties of Aurivillius-phase Bi4Ti3O12 polycrystalline ceramics. Phase purity, microstructure and defect chemistry of Bi4Ti3−xCuxO12−x (BiT–100xCu, x = 0–0.12) are characterized by XRD, SEM, EDS and EPR measurements. Neutron diffraction refinement indicates that BiT–8Cu has an orthorhombic symmetry [space group: B2cb; lattice parameters: a = 5.4116(1) A, b = 32.833(1) A, c = 5.4479(1) A and V = 967.98(5) A3]. Impedance spectra of BiT–100xCu were measured under variable oxygen partial pressure (pO2). Bi4Ti3O12 shows mixed electronic (hole) and ionic conduction owing to the existence of oxygen vacancies ($$ {\text{V}}_{\text{O}}^{ \cdot \cdot } $$) arising from the loss of Bi2O3 during sintering. Interestingly, bulk conductivity in Cu-substituted Bi4Ti3O12 ceramics is predominately ionic due to the fact that there are considerably additional oxygen vacancies introduced into the perovskite lattices. The optimum composition of BiT–8Cu shows high ionic conductivity in the bulk with a value of ~ 0.007 S/cm at 650 °C.