Journal of Alloys and Compounds 974 (2024) 172845 Available online 14 November 2023 0925-8388/© 2023 Elsevier B.V. All rights reserved. Unveiling the effect of Gd 3+ doping on enriching the structural, magnetic, optical, and dielectric properties of biocompatible hematite nanoparticles A.M. Faramawy a, * , Hamada Elsayed b, c, ** , H.M. Elsayed a , A.A. Sattar a , Y.W. Getahun d , A.A. El-Gendy d , H. Kahil a a Department of Physics, Faculty of Science, Ain Shams University, 11566 Abbassia, Cairo, Egypt b Department of Industrial Engineering, Universit` a Degli Studi di Padova, 35131 Padova, Italy c Refractories, Ceramics and Building Materials Department, National Research Centre, P.O. Box 12622, Cairo, Egypt d Department of Physics, University of Texas at El Paso, El Paso, TX 79912, USA A R T I C L E INFO Keywords: Gadolinium doped hematite nanoparticles Hydrothermal method Band gap Dielectric loss Cytotoxicity ABSTRACT This work is an attempt to obtain gadolinium-doped hematite Gd x Fe 2x O 3 (x = 0, 0.05, and 0.1) using the hy- drothermal method followed by heat treatment. The work also studies the impact of gadolinium doping on the magnetic, electrical, and optical properties of hematite. X-ray diffraction (XRD) analysis, energy-dispersive X-ray spectroscopy (EDAX) and photoelectron spectroscopy (XPS) showed that the obtained phase for all samples was pure hematite with no evidence of secondary phases, indicating a high solubility limit of gadolinium ions in hematite lattice. The morphology and size distribution of the particles were investigated using high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). It was found that the lattice parameters increased with increasing gadolinium concentration. Magnetization was not enhanced whereas, the coercivity decreased considerably. From UV–Vis diffuse refection spectroscopy (DRS) measure- ments, the band gap energies of pure and doped α-Fe 2 O 3 decreased from 2.01 to 1.94 eV respectively. Moreover, measurements of electrical properties showed that the dielectric permittivity decreased while the resistivity increased with increasing the gadolinium content. In addition, sulforhodamine B (SRB) test against oral epithelial cell lines showed low cytotoxicity of the particles. Finally, gadolinium doped hematite is introduced as a novel, environmentally benign material for potential applications in various felds including photocatalysis for water treatment, biosensor and as an antibacterial agent. 1. Introduction Nano iron oxides (NIOs) and their derivatives are particularly interesting in both science and industry due to their usefulness for a variety of technological applications such as communications, infor- mation storage systems, data recording, biosensors, magnetic fuids, hyperthermia, microwave devices, sustainable sources and water treatment [1–4]. Their distinctive properties are infuenced by different parameters as the dopant ions, chemical composition, synthesis tech- nique, thermal treatment, particle size and morphology. Magnetic iron oxides include magnetite and maghemite with high magnetization [5–8]. These two species readily oxidize to end up in hematite [9], which contains only Fe 3+ ions in the octahedral sites [10]. Hematite is biocompatible yet shows very low magnetization at room temperature [11]. Previous studies attempted to replace Fe 3+ (5μ B ) with Gd 3+ ions (7μ B ) [12] in magnetite lattice [13], but the results showed that the solubility limit was very low because of the large radius of gadolinium ions (0.938 Å) [14] compared to (0.645 Å) Fe 3+ [15]. Hematite (α Fe 2 O 3 ) exhibits the same crystal structure as corundum (Al 2 O 3 ) [16–19] that can also be indexed as a hexagonal structure. The lattice is built up of O 2 anions and Fe 3+ cations only. O 2 with the larger radii lie in hexagonal layers forming a hexagonal close packed structure. Fe 3+ cations with the smaller radii occupy only 2 3 of the interstitial sites [9] in a symmetrical manner with each Fe 3+ ion being surrounded by six O 2 and the spacing between two adjacent oxygen planes is c/6 [20]. Hematite is antiferromagnetic below the frst tran- sition temperature; Morin temperature (T M ), which is at about 263 K in the bulk state [21]. In this state, the moments are aligned parallel to the * Corresponding author. ** Corresponding author at: Department of Industrial Engineering, Universit` a Degli Studi di Padova, 35131 Padova, Italy. E-mail addresses: ahmed_faramawy@sci.asu.edu.eg (A.M. Faramawy), hamada.elsayed@unipd.it (H. Elsayed). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom https://doi.org/10.1016/j.jallcom.2023.172845 Received 26 July 2023; Received in revised form 19 September 2023; Accepted 11 November 2023