Vacuum 183 (2021) 109815 Available online 30 September 2020 0042-207X/© 2020 Elsevier Ltd. All rights reserved. Design and characterization of a new (1-x)Na 1/2 Bi 1/2 TiO 3 +xBi(Ti 1/2 Fe 1/2 ) O 3 solid solution D.D. Dung a, * , M.M. Hue a , N.Q. Dung b , N.X. Duong a , L.H. Bac a , N.N. Trung a , N.A. Duc c , N. H. Thoan a a School of Engineering Physics and Multifunctional Ferroics Materials Lab., Ha Noi University of Science and Technology, 1 Dai Co Viet Road, Ha Noi, Viet Nam b Department of Chemistry, Thai Nguyen University of Education, 20 Luong Ngoc Quyen Street, Thai Nguyen, Viet Nam c Department of Physics, Faculty of Basic-Fundamental Sciences, Viet Nam Maritime University, 484 Lach Tray Road, Le Chan, Hai Phong, Viet Nam A R T I C L E INFO Keywords: Na 1/2 Bi 1/2 TiO 3 Bi(Ti 1/2 Fe 1/2 )O 3 Ferromagnetic Lead-free ferroelectric ABSTRACT A new solid solution, (1-x)Na 1/2 Bi 1/2 TiO 3 +xBi(Ti 1/2 Fe 1/2 )O 3 , was fabricated via the sol-gel method. X-ray diffraction spectroscopy revealed that the structures of Bi(Ti 1/2 Fe 1/2 )O 3 -modifed Na 1/2 Bi 1/2 TiO 3 compounds exhibited the rhombohedral symmetry of Bi 1/2 Na 1/2 TiO 3 . Optical band gap values decreased from 3.06 eV for pure Na 1/2 Bi 1/2 TiO 3 materials to 2.51 eV for 9 mol.% Bi(Ti 1/2 Fe 1/2 )O 3 -modifed Na 1/2 Bi 1/2 TiO 3 samples. The magnetic properties of Bi 1/2 Na 1/2 TiO 3 materials were tuned by controlling the amount of Bi(Ti 1/2 Fe 1/2 )O 3 as solid solution. The weak-ferromagnetism and diamagnetism of pure Na 1/2 Bi 1/2 TiO 3 materials changed into ferromagnetism and ended with ferromagnetism versus paramagnetism and/or antiferromagnetism-like as the concentration of Bi(Ti 1/2 Fe 1/2 )O 3 increased to 9 mol.%. We provided that our work will contribute to the integration of ferromagnetism at room temperature in current lead-free ferroelectric compounds for application in smart electronic devices. 1. Introduction The integration of ferromagnetic properties in lead-free ferroelectric materials is the next challenge in the development of green materials for smart electronic devices [1,2]. Lead-free ferroelectric materials are roughly divided into three main groups, namely, BaTiO 3 -based, (K,Na) NbO 3 -based, and Na 1/2 Bi 1/2 TiO 3 -based materials. BaTiO 3 -based mate- rials exhibit good piezoelectric properties, but their fabrication requires high temperature (approximately 1300 ◦ C–1450 ◦ C) and a large power of electrical energy [3]. (K,Na)NbO 3 -based materials also show high piezoelectric properties, but controlling the single phase and cost of Nb source limit their application [4]. Na 1/2 Bi 1/2 TiO 3 -based materials exhibit good properties and are comparable with PbTiO 3 -based mate- rials. As such, they can potentially replace ferroelectric Pb-based ma- terials in electronic devices because they are environment friendly and do not pose health concerns [5]. Na 1/2 Bi 1/2 TiO 3 materials were frst synthesized by Smolenskii et al. [5,6]. Na 1/2 Bi 1/2 TiO 3 materials exhibited large remnant polarization value (approximately 38 μC/cm 2 ) and high Curie temperature (approximately 320 ◦ C) [5,6]. The lone pair effect of Bi 3+ in Na 1/2 Bi 1/2 TiO 3 compounds, which originated from the strong polariza- tion in Na 1/2 Bi 1/2 TiO 3 compounds, is similar to that of Pb 2+ in PbTiO 3 -based materials [7,8]. However, the performance of electrical properties of Na 1/2 Bi 1/2 TiO 3 compounds is lower than that of PbTiO 3 -- based materials. In addition, Na 1/2 Bi 1/2 TiO 3 materials have a large co- ercive feld (E C ) of approximately 7.3 kV/mm, resulting in diffculty in the poling of samples; thus, they exhibit low performance piezoelectric properties [5]. As such, lead-based materials still remain the ideal choice for application in electronic devices. Recently, Bi(Me,Me’)O 3 -based perovskite materials have been reported as an important impurity near the morphotropic phase boundary for the strong performance enhancement of host Na 1/2 Bi 1/2 TiO 3 materials via a solid solution. Wang et al. reported that the introduction of Bi(Mg 1/2 Ti 1/2 )O 3 resulted in a decrease in the coercive electrical feld E C of Na 1/2 Bi 1/2 TiO 3 from 73 kV/cm to 40 kV/cm and an increase in piezoelectric coeffcient from 58 pC/N to 110 pC/N [9]. Zhang et al. reported that modifying Na 1/2 Bi 1/2 TiO 3 materials with Bi(Zn 1/2 Ti 1/2 )O 3 resulted in improved electrical properties, such as saturated polarization to approximately 42.0 μC/cm 2 and remnant polarization to 36.5 μC/cm 2 , and decreased coercive feld to 3.5 kV/mm [10]. Ullah et al. reported that Bi * Corresponding author. E-mail address: dung.dangduc@hust.edu.vn (D.D. Dung). Contents lists available at ScienceDirect Vacuum journal homepage: http://www.elsevier.com/locate/vacuum https://doi.org/10.1016/j.vacuum.2020.109815 Received 14 June 2020; Received in revised form 25 September 2020; Accepted 26 September 2020