Synthesis and electrical properties of BaBiO3 and high resistivity BaTiO3–BaBiO3 ceramics

Abstract

Ceramics of the composition BaBiO3 (BB) were sintered in oxygen to obtain a single phase with monoclinic [Formula: see text]2/[Formula: see text] symmetry as suggested by high-resolution X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states — 3[Formula: see text] and 5[Formula: see text]. Optical spectroscopy showed presence of a direct bandgap at [Formula: see text] 2.2[Formula: see text]eV and a possible indirect bandgap at [Formula: see text] 0.9[Formula: see text]eV. This combined with determination of the activation energy for conduction of 0.25[Formula: see text]eV, as obtained from ac impedance spectroscopy, suggested that a polaron-mediated conduction mechanism was prevalent in BB. The BB ceramics were crushed, mixed with BaTiO3 (BT), and sintered to obtain BT–BB solid solutions. All the ceramics had tetragonal symmetry and exhibited a normal ferroelectric-like dielectric response. Using ac impedance and optical spectroscopy, it was shown that resistivity values of BT–BB were orders of magnitude higher than BT or BB alone, indicating a change in the fundamental defect equilibrium conditions. A shift in the site occupancy of Bi to the A-site is proposed to be the mechanism for the increased electrical resistivity.