Oxygen Vacancies in Perovskite Oxide Piezoelectrics

Tyunina, M.

doi:10.3390/ma13245596

Cited by 32 publications

(14 citation statements)

References 49 publications

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“…According to Figures 4, 5, and 7, the band gaps of individual perovskite and tungsten bronze phases were likely to be 2.5−3 and >4 eV, respectively, as shown in Figure 8 where the valence band may be contributed by O 2p states and/or trapped charges at V O that could become mobile under illumination and/or electric field and the conduction band may be contributed by Ni 3d and/or Nb 4d states. 3,16,23 In the KNBNNO perovskite-tungsten bronze composites fabricated in this research, the conduction and valence bands were possibly bent and/or misaligned at the phase interface in two ways as shown in Figure 8. Such a bent and/or misaligned band structure at the interface allowed the electrons in the valence band of the perovskite phase to be excited to the conduction band of the tungsten bronze phase with photon energy larger than 1.5−2 eV (Possibility 1 in Figure 8) or the other way round (Possibility 2 in Figure 8), resulting in largely reduced E g * values of 1.5−2 eV compared to those of individual phases as shown in Figures 5 and 7.…”

Section: Discussionmentioning

confidence: 93%

“…According to Figure , this electric field was slightly higher than the coercive fields of all samples. Such an input electric field for large-signal measurements was chosen in order to minimize the influence of mobile trapped charges/charged defects and leakage current surge during domain wall motion on the conductivity. − However, in order to validate the conductivity results, small-signal measurements (see Section 1 in the Supporting Information) were also carried out. Figure S9 shows the results of a Type C sample (10 mol % tungsten bronze phase) measured in darkness and under illuminations.…”

Section: Resultsmentioning

confidence: 99%

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Vacancy-Induced Niobate Perovskite-Tungsten Bronze Composite for Synergetic Tuning of Ferroelectricity and Band Gaps

et al. 2021

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Niobate perovskites like the (K,Na)NbO 3 (KNN) family are among the most important lead-free ferroelectrics. Ba and Ni have been co-doped into KNN to induce Ni 2+ -oxygen vacancy defect dipoles to significantly reduce the band gap while maintaining the ferroelectricity. This opens doors to novel optoferroelectric applications such as multisensors and photocatalysts. However, obtaining a single phase of the above co-doped KNN is difficult due to the sensitive stoichiometry on phase formation and arduous nickel diffusion into the KNN unit cells during synthesis. This paper reports an alternative approach to simultaneously tune the band gap and ferroelectricity. A-site vacancies are intentionally introduced into the mixtures of starting reactants. The homogeneously distributed vacancies trigger self-assembly of a niobate perovskite and niobate tungsten bronze phase and thus form a composite. The interface between the two phases, which mimics a heterojunction, rather than any individual phase, is proven to be responsible for the resultant narrow band gap and strong ferroelectricity. Hypotheses are proposed based on the results of ferroelectric, photoconductivity, and density functional theory-based studies to explain the mechanism. This paper offers an additional option to engineer polarizations and band structures in complex photoferroelectric oxides, especially alkaline niobates.

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Section: Discussionmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Vacancy-Induced Niobate Perovskite-Tungsten Bronze Composite for Synergetic Tuning of Ferroelectricity and Band Gaps

et al. 2021

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“…This smaller E opt could be linked to the crystallite size difference between the compounds nonetheless [49]. Additionally, the smaller E opt in this compound could be related to possible minor oxygen vacancies existence that could involve in the formation of the energy level of impurities within the sample band gap or lifted the Fermi energy and thus, reducing the E opt value [50]. However, as per refinement analysis, the basic lattice structure of the compound was well-formed.…”

Section: Resultsmentioning

confidence: 86%

Dielectric, AC Conductivity, and DC Conductivity Behaviours of Sr2CaTeO6 Double Perovskite

Halizan

Mohamed

2022

Materials

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Relatively new double perovskite material, Sr2CaTeO6, has been prepared through conventional solid-state procedures. Structural, dielectric, and optical characteristics of this exquisite solid-state material were analysed in this study. The single-phase monoclinic P21/n structure of this prepared compound was well correlated with the literature review. Good distribution of grain sizes and shapes was observed in the morphological study of this compound. The discussions on its optical and dielectric properties are included in this manuscript. High dielectric real permittivity, low dielectric loss, and good capacitance over a range of temperatures possessed by this compound, as shown in dielectric and electrical modulus studies, indicated good potential values for capacitor applications. The Ro(RgQg)(RgbQgb) circuit fitted well with the impedance and electrical modulus plot of the compound. Its relatively high electrical DC conductivity in grain at high frequencies and its increasing value with the temperature are typical of a semiconductor behaviour. This behaviour might be attributed to the presence of minor oxygen vacancies within its lattice structure and provides a long-range conduction mechanism. A small difference between activation energy and Ea of DC conductivity indicates that the same charge carriers were involved in both grains and the grain boundaries’ long-range conduction. The electrical AC conductivity of this compound was found to contribute to the dielectric loss in grain structure and can be related to Jonscher’s power law. The presence of polarons in this compound was exhibited by non-overlapping small polaron tunnelling (NSPT) and overlapping large polaron tunnelling (OLPT) conduction mechanisms over a range of temperatures. Wide optical band gap and Eopt in the range of 2.6 eV to 3.6 eV were determined by using an indirect and direct allowed mechanism of electrons transitions. These values supported the efficient semiconducting behaviour of the grain in this material and are suitable for applications in the semiconductor industry.

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“…Because of O-vacancies levels above the Fermi level in Bi:BT, the entire electronic structure may have been altered. We guess that the presence of O-vacancies in the band structure near the Fermi level decreased the effective bandgap [64,65]. Consequently, this mechanism enhanced the absorption spectra and decreased the bandgap energy of irradiated samples as illustrated in Figure 6a,b.…”

Section: Resultsmentioning

confidence: 99%

Effect of Gamma Irradiation on the Structural, Optical, Electrical, and Ferroelectric Characterizations of Bismuth-Modified Barium Titanate Ceramics

2022

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Materials with ferroelectric properties, low bandgap energies, high polarization, low loss, and thermal stability are essential for future solar-cell applications. Researchers have attempted to obtain such materials by using several approaches. In this vein, a novel approach is reported in this work using gamma ray irradiation. The effect of gamma radiation on the structural, optical, and ferroelectric characterizations of bismuth (Bi)-doped barium titanate (BaTiO3 (BT)), namely Ba0.95Bi0.05TiO3 ceramics (abbreviated as (Bi:BT)), was investigated. X-ray diffraction, structure refinement, and Raman study revealed the presence of a perovskite structure with a tetragonal phase in all investigated samples. Morphological study revealed a nonuniform grain size and some porosity. Gamma irradiation-induced combined effects were proved by a detailed analysis of bond lengths, bond angles, octahedral distortions, oxygen vacancies, and charge compensations. Electron paramagnetic resonance (EPR) study gave direct evidence of oxygen vacancies in the irradiated samples. After gamma irradiation, UV–vis study indicated a decrease in the bandgap from 3.14 to 2.80 eV and a significant increase in visible light absorption. Cole–Cole plots confirm as an increase in gamma-ray dose results in higher levels of electron hopping. Study of the P–E hysteresis loop demonstrated that ferroelectric properties could be maintained after gamma irradiation, with a slight decrease in remnant polarization. The behaviour of the P–E was correlated with increasing gamma dose in the investigated ceramics, demonstrating a strong gamma dependence in the loops’ profile. We guess that the present approach may be a promising technique for enhancing the multifunctionality of electronic devices.

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Oxygen Vacancies in Perovskite Oxide Piezoelectrics

Cited by 32 publications

References 49 publications

Vacancy-Induced Niobate Perovskite-Tungsten Bronze Composite for Synergetic Tuning of Ferroelectricity and Band Gaps

Vacancy-Induced Niobate Perovskite-Tungsten Bronze Composite for Synergetic Tuning of Ferroelectricity and Band Gaps

Dielectric, AC Conductivity, and DC Conductivity Behaviours of Sr2CaTeO6 Double Perovskite

Effect of Gamma Irradiation on the Structural, Optical, Electrical, and Ferroelectric Characterizations of Bismuth-Modified Barium Titanate Ceramics

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