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

Abstract

Ceramics of the composition BaBiO 3 (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 BaTiO 3 (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.