Novel optical properties and induced magnetic moments in Ru-doped hybrid improper ferroelectric Ca 3 Ti 2 O 7
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ISSN 2226-4108 CN 10-1154/TQ
Research Article
Novel optical properties and induced magnetic moments in Ru-doped hybrid improper ferroelectric Ca3Ti2O7 Xingxing WUa, Shouyu WANGb,*, Winnie WONG-NGc, Qiang GUa, Yao JIANGa, Chao WANGa, Shuang MAb, Weifang LIUa,* a
Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072, China b College of Physics and Material Science, Tianjin Normal University, Tianjin 300074, China c Materials Measurement Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA Received: March 7, 2020; Revised: September 5, 2020; Accepted: September 9, 2020 © The Author(s) 2020.
Abstract: Hybrid improper ferroelectric Ca3Ti2O7 and Ca3Ti1.9Ru0.1O7 ceramics were successfully synthesized by conventional solid-state reaction method. Two strongest diffraction peaks located around 2θ = 33° shifted towards the lower angle region with Ru substitution, reflecting structure variation. Grain growth and higher oxygen vacancy concentration after doping resulted in a reduction in the coercive field about 20 kV/cm. Optical bandgap estimated by UV−vis diffuse reflectance (DR) spectrum and X-ray photoelectron spectroscopy (XPS) valence band spectra showed a decreasing trend due to the existence of impurity energy level upon Ru doping, which was consistent with the results of first-principles calculations. The origin of the unexpected induced magnetic moments in Ru-dope Ca3Ti2O7 is also discussed. Keywords: oxides; electronic materials; optical properties; X-ray diffraction; defects; lectronic structure; ferroelectricity
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Introduction
In recent years, hybrid improper ferroelectricity (HIF) has been investigated extensively due to its promising applications in creating room-temperature multiferroic materials with strong magnetoelectric coupling [1–3]. The term “hybrid” improper ferroelectricity is used to describe the two kinds of octahedron rotations, and the main feature of HIF is the combination of coherent * Corresponding authors. E-mail: S. Wang, [email protected]; W. Liu, [email protected]
oxygen octahedral rotation (a0a0c+ in Glazer’s notation) and tilting (a–a–c0) [4,5]. Researchers have proposed that HIF widely exits in artificial superlattices such as SrTiO3/PbTiO3 and Ruddlesden–Propper structure (An+1BnO3n+1, RP) [1,2,6–9]. Liu et al. [5] and Oh et al. [10] also demonstrated experimentally that HIF existing in the RP structures at room temperature. RP structure has become the focus for HIF research since the octahedral tilting and rotation exist extensively in these materials. Ca3Ti2O7 is one of the typical RP structures (n = 2) with properties including prominent photocatalytic, special luminescence, and significant hybrid improper
www.springer.com/journal/40145
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J Adv Ceram 2020, 9(6): 0–0
ferroelectric properties [8,11–16]. Recently, researchers are working to improve the ferroelectric properties by doping or substitution. Li et al. [17] studied the preferential
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