University of Oulu

J. Phys. Chem. C 2021, 125, 16, 8890–8898, Publication Date:April 15, 2021,

Vacancy-induced niobate perovskite-tungsten bronze composite for synergetic tuning of ferroelectricity and band gaps

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Author: Bai, Yang1; Kistanov, Andrey A.2; Cao, Wei2;
Organizations: 1Microelectronics Research Unit, Faculty of Information Technology and Electrical Engineering, University of Oulu, FI-90014 Oulu, Finland
2Nano and Molecular Systems Research Unit, Faculty of Science, University of Oulu, FI-90014 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.6 MB)
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Language: English
Published: American Chemical Society, 2021
Publish Date: 2021-05-11


Niobate perovskites like the (K,Na)NbO3 (KNN) family are among the most important lead-free ferroelectrics. Ba and Ni have been co-doped into KNN to induce Ni2+-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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Series: The journal of physical chemistry. C
ISSN: 1932-7447
ISSN-E: 1932-7455
ISSN-L: 1932-7447
Volume: 125
Issue: 16
Pages: 8890 - 8898
DOI: 10.1021/acs.jpcc.1c01845
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Funding: This work was financially supported by the Academy of Finland (grant numbers 24302332 and 311934). The authors acknowledge the Centre for Material Analysis of the University of Oulu for the use of their facilities and for the fabrication of the electrodes and the CSC − IT Center for Science, Finland, for computational resources. The authors also acknowledge Dr. Marina Tjunina, University of Oulu, for advices on conductivity in ferroelectric oxide perovskites.
Copyright information: © 2021 The Authors. Published by American Chemical Society. Published under the CC-BY License.