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Tyunina M. Conductivity in Ferroelectric Barium Titanate: Electrons Versus Oxygen Vacancies. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2021; 68:296-302. [PMID: 32149630 DOI: 10.1109/tuffc.2020.2978901] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Mobile oxygen vacancies are increasingly widely believed to be responsible for electrical conductivity in perovskite oxide ferroelectrics. Here, this hypothesis is debated. The small-signal conductivity is investigated in oxygen-deficient films of barium titanate, where oxygen vacancies are epitaxially clamped and immobile. The observed behavior of conductivity as a function of temperature and frequency evidences pure electronic processes. Importantly, it is shown that these processes mimic motion of oxygen vacancies, which are immobile. It is also demonstrated that under the applied dc electric field, the electronic processes lead to such effects as coloration and degradation, which before were plausibly ascribed to migration of oxygen vacancies. Finally, it is concluded that the hypothesis of mobile oxygen vacancies is misleading.
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Tyunina M, Pacherova O, Nepomniashchaia N, Vetokhina V, Cichon S, Kocourek T, Dejneka A. In situ anion-doped epitaxial strontium titanate films. Phys Chem Chem Phys 2020; 22:24796-24800. [PMID: 33107506 DOI: 10.1039/d0cp03644g] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Misfit strains arising from a film-substrate mismatch can induce novel phases and properties in the epitaxial films of perovskite oxides. Here we employ yet another effect, namely, strain-assisted formation of oxygen vacancies. We demonstrate the misfit-promoted presence of oxygen vacancies and related substitutional incorporation of anion dopants in the epitaxial films of archetypal perovskite oxide SrTiO3. Both the oxygen vacancies and hydrogen or nitrogen dopants are introduced in situ during the pulsed-laser deposition of the films using compressive substrates. The films exhibit peculiar chemical expansion and optical properties, which are consistent with substitutional anion doping.
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Affiliation(s)
- M Tyunina
- Microelectronics Research Unit, Faculty of Information Technology and Electrical Engineering, University of Oulu, P. O. Box 4500, FI-90014, Finland.
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Clabel H JL, Awan IT, Lozano G, Pereira-da-Silva MA, Romano RA, Rivera VAG, Ferreira SO, Marega E. Understanding the electronic properties of BaTiO 3 and Er 3+ doped BaTiO 3 films through confocal scanning microscopy and XPS: the role of oxygen vacancies. Phys Chem Chem Phys 2020; 22:15022-15034. [PMID: 32597431 DOI: 10.1039/d0cp01010c] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photonic and electronic properties exist inherently in ferroelectric barium titanate (BaTiO3); severe luminescence quenching also exists due to the insufficient confinement of excitons. In this sense, high optical emission can only be achieved by its chemical and structural modification. Thin BaTiO3 and Er:BaTiO3 films were grown by the spin coating method on a glass substrate at room temperature. Self-trapping of excitons in the thin BaTiO3 film and its structural modification due to the doping with Er3+ ions (Er:BaTiO3) are verified using scanning confocal fluorescence microscopy (SCFM), where self-trapping excitons never occured in its pure state. By thermal treatment and doping (BaTiO3 and Er:BaTiO3) we obtained localization of the excitons, which would further induce lattice strain around the surface defects, to accommodate the self-trapped excitons. With such a self-trapped state, the structure of BaTiO3 generates broadband emission of several overlapping bands between 1.95 and 2.65 eV at room temperature, while the structure Er:BaTiO3 showed defined emission bands at 2.24 and 2.35 eV, with very weak contributions of the emission due to the self-trapping state. The influence of the variation of the excitation wavelength using 1PE and 2PE on the emission bands of BaTiO3 and Er:BaTiO3 is also investigated. The results of enhanced emission bands suggest a clear dependence of the emission intensity on the excitation energy, where a ∼3 fold enhancement in emission has been demonstrated under Er3+ (1.55 eV) excitation, which can be attributed to effective energy transfer between the Er3+ ions. As a result, it is concluded that the developed BaTiO3 and Er:BaTiO3 can pave the way for future photonic devices.
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Affiliation(s)
- J L Clabel H
- Physics Institute of São Carlos, University of São Paulo, P.O. Box 369, 13560-970, São Carlos, SP, Brazil.
| | - Iram T Awan
- Physics Institute of São Carlos, University of São Paulo, P.O. Box 369, 13560-970, São Carlos, SP, Brazil.
| | - G Lozano
- Physics Institute of São Carlos, University of São Paulo, P.O. Box 369, 13560-970, São Carlos, SP, Brazil.
| | - M A Pereira-da-Silva
- Physics Institute of São Carlos, University of São Paulo, P.O. Box 369, 13560-970, São Carlos, SP, Brazil. and University Center Central Paulista, UNICEP, P.O. Box 13563-470, São Carlos, SP, Brazil
| | - R A Romano
- Physics Institute of São Carlos, University of São Paulo, P.O. Box 369, 13560-970, São Carlos, SP, Brazil.
| | - V A G Rivera
- Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, UNMSM, Lima, Lima, Peru
| | - S O Ferreira
- Departament of Physics, Federal University of Viçosa, UFV, P.O. Box 36570-901, Viçosa, MG, Brazil
| | - E Marega
- Physics Institute of São Carlos, University of São Paulo, P.O. Box 369, 13560-970, São Carlos, SP, Brazil.
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