Atomic scale characterization of point and extended defects in niobate thin films

Changjian Li; Dongsheng Song; Mengsha Li; Chunhua Tang; Deqing Xue; Dongyang Wan; Stephen J Pennycook

doi:10.1016/j.ultramic.2019.03.003

Atomic scale characterization of point and extended defects in niobate thin films

Ultramicroscopy. 2019 Aug:203:82-87. doi: 10.1016/j.ultramic.2019.03.003. Epub 2019 Mar 4.

Authors

Changjian Li¹, Dongsheng Song², Mengsha Li¹, Chunhua Tang¹, Deqing Xue¹, Dongyang Wan³, Stephen J Pennycook⁴

Affiliations

¹ Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore.
² Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore; NUSNNI-Nanocore, National University of Singapore, 117411 Singapore. Electronic address: d.song@fz-juelich.de.
³ NUSNNI-Nanocore, National University of Singapore, 117411 Singapore.
⁴ Department of Materials Science and Engineering, National University of Singapore, 117575 Singapore; NUSNNI-Nanocore, National University of Singapore, 117411 Singapore. Electronic address: steve.pennycook@nus.edu.sg.

PMID: 30857652
DOI: 10.1016/j.ultramic.2019.03.003

Abstract

Niobium-based oxides have a wide range of applications owing to their rich crystal and electronic structures. Defects at the atomic scale are always unavoidable and will affect their functionalities, especially when in the form of thin films. Here, atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy have been performed on various defects (point, line, planar defects and segregated phases) in alkaline and alkaline-earth niobate thin films: CaZrO₃ modified (K, Na)NbO₃ and strontium niobate (SNO), respectively. In CaZrO₃ modified (K,Na)NbO₃ thin films, a tetragonal tungsten bronze phase was found, with a sharp boundary with the perovskite phase. In SNO thin films, several kinds of point defects and antiphase boundaries are commonly observed. In addition, a strongly Sr deficient phase, SrNb₂O₆, precipitates inside the SrNbO₃ phase with a coherent interface. The different oxidation states of Nb in SrNbO₃ and SrNb₂O₆ were revealed from the O K edge. Our characterization of the point defects and extended defects in niobate thin films offers practical guidelines for thin film deposition or discovery of defect-based novel functionalities.