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 I2/m symmetry as suggested by high-resolution X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of bismuth in two valence states -3þ and 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.

Defect mechanisms in BaTiO3‐BiMO3 ceramics

“…The edge energy of 25BZT was found to be very similar to Bi 2 O 3 , with no noticeable shift to higher energy values, and the pre‐edge bump was also absent. Thus, there was no evidence of Bi 5+ in 25BZT ceramics, within the resolution of the instruments used.…”

“…In separate reports on macroscopic transport properties, it was shown that on forming solid solutions with small amounts of Bi M O 3 to BT, their insulation properties improve by multiple orders of magnitude. There is also a corresponding transition from p‐type behavior for BT towards n‐type for BT‐Bi M O 3 ceramics without any deliberate donor doping, indicating a drastic change in underlying defect equilibrium conditions . A thorough study of the complex defect mechanisms in BT‐Bi M O 3 has been performed in this article, which intends to explain the observed change in transport properties on adding Bi‐perovskites to BT.…”

“…There is also a corresponding transition from p-type behavior for BT towards n-type for BT-BiMO 3 ceramics without any deliberate donor doping, indicating a drastic change in underlying defect equilibrium conditions. [13][14][15][16] A thorough study of the complex defect mechanisms in BT-BiMO 3 has been performed in this article, which intends to explain the observed change in transport properties on adding Biperovskites to BT. The defect chemistry is expected to be strongly influenced by factors such as solubility limits of different cations, volatile nature of Bi and other cations, oxygen stoichiometry, bonding characteristics of cations sharing the same sublattice position, enthalpies associated with specific defect species in a given condition, microstructure and others.…”

Revisiting the BaBiO3 semiconductor photocatalyst: synthesis, characterization, electronic structure, and photocatalytic activity

“…The past two decades have witnessed a significant renaissance of the bismuthate BaBiO 3 from both a technological and scientific viewpoint [1][2][3][4][5][6][7][8][9][10][11], especially as a superconductor [1,3,[5][6][7] because of its electronic properties, and as a promising photocatalyst toward the degradation of organic pollutants [2], water splitting [9,10], CO 2 reduction [4], and as a prospective photovoltaic material [11]. The unique properties of BaBiO 3 are largely the result of the occurrence of both Bi 3+ and Bi 5+ oxidation states that have tended to complicate studies of this bismuthate.…”

“…Their comparison of the photoemission, optical absorption, and transport data on BaBiO 3 suggested the existence of polaron energy levels within the bandgap of BaBiO 3 that accommodate thermally excited charge carriers. Kumar and coworkers [5] synthesized this bismuthate from Bi 2 O 3 and BaCO 3 via a two-step solid-phase heating method that, when sintered in oxygen, yielded a singlephase BaBiO 3 with monoclinic I 2/mm symmetry from high-resolution XRD, while XPS confirmed the presence of two valence states of bismuth: Bi 3+ and Bi 5+ . Optical spectroscopy revealed a direct bandgap of ∼2.2 eV and a possible indirect bandgap of ∼0.9 eV, which when combined with the activation energy for conduction of 0.25 eV (ac impedance spectroscopy) led Kumar et al [5] to infer a polaron-mediated conduction mechanism to prevail in BaBiO 3 .…”