Influence of hydrogen and cerium dopant on structural, optical, and magnetic properties of anatase nanoparticles

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Influence of hydrogen and cerium dopant on structural, optical, and magnetic properties of anatase nanoparticles A. A. Dakhel 1 Received: 25 October 2019 / Accepted: 20 November 2020 # Springer Science+Business Media, LLC part of Springer Nature 2020

Abstract Cerium-incorporated TiO2 nano-composite powders were fabricated by a facile procedure included co-decomposition of the required chemical complexes. The structures of the synthesized composites were investigated by the X-ray diffraction (XRD) technique through Rietveld refinement method, which confirmed the formation of almost single anatase (A) phase. The formed tiny rutile (R) and Titania (B) phases were vanished with Ce doping and hydrogenation. The optical band-gap was red-shifted with Ce doping and blue-shifted with the hydrogenation. The results confirmed that the hydrogenation process was vital to create ferromagnetic (FM) properties in Ce-incorporated TiO2. A saturation magnetization of ~0.18 emu/cm3 was measured for the hydrogenated ~10 at% Ce sample. Keywords Ce-incorporated TiO2 . Ferromagnetism . Hydrogenation

1 Introduction Titanium oxide (TiO2) transparent semiconductor crystallizes into three major polymorphs; anatase [(A): tetragonal, I41/ amd, a = b = 3.785 Å, c = 9.514 Å], rutile [(R): tetragonal, P42/mnm, a = b = 4.594 Å, c = 2.959 Å], and Brookite [(Br): orthorhombic, Pbca, a = 9.184 Å, b = 5.447 Å, c = 5.145 Å] depending on the synthesis procedure and temperature. Furthermore a fourth phase called Titania-TiO2 [(B): monoclinic, 2/m, a = 12.163 Å, b = 3.735 Å, c = 6.513 Å, β = 107.29o)] was also experimentally found [1, 2]. Titanium oxide has been extensively used as a multifunctional semiconductor in many different applications, like gas sensing, photovoltaic cells, environmental treatments, photocatalysis, etc. [3–5]. The excellent photocatalytic properties of TiO2 strongly depend on its synthesis details [5]. Pure anatase has a wide band-gap (~ 3.2 eV [6]) so that its photocatalytic activity works under UV range. Therefore, it is practical to expand the response spectrum to the visible region by narrowing its band-gap to improve its photocatalytic activity. The latter is usually achieved by doping of TiO2 with suitable foreign ions [7–10]. Practically, the photocatalytic * A. A. Dakhel [email protected] 1

Department of Physics, College of Science, University of Bahrain, ZallaqP.O. Box 32038, Kingdom of Bahrain

activity of TiO 2 for the degradation of some complex chemicals was observed to be improved by doping with rare-earth ions, like Ce [11–14]. Moreover, it was found that the hydrogenation of TiO2 could control its photocatalytic activity [15], which was explained by the creation of oxygen vacancies (VOs). Generally, it has been observed that with some dopant incorporation, the photocatalytic, electrical, and optical properties of Titania could be controlled, depending on the used dopant type/amount [16, 17]. Moreover, it became known that doping of transparent conducting oxides (TCOs) could create some exotic properties, like ma