摘要
Ceramics of the composition BaBiO_(3)(BB)were sintered in oxygen to obtain a single phase with monoclinic I2/m symmetry as suggested by high-resolution X-ray diffraction.X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states—3þand 5þ.Optical spectroscopy showed presence of a direct bandgap at-2.2 eV and a possible indirect bandgap at-0.9 eV.This combined with determination of the activation energy for conduction of 0.25 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.
基金
the National Science Foundation under Grant No.DMR-1308032
Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,under Contract No.DE-AC02-06CH11357.
