Role of non-magnetic dopants (Ca, Mg) in GdFeO 3 perovskite nanoparticles obtained by different synthetic methods: struc
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Role of non-magnetic dopants (Ca, Mg) in GdFeO3 perovskite nanoparticles obtained by different synthetic methods: structural, morphological and magnetic properties Antonia Ruffo1, Maria Cristina Mozzati2, Benedetta Albini2, Pietro Galinetto2, and Marcella Bini1,* 1 2
Department of Chemistry, University of Pavia, viale Taramelli 16, 27100 Pavia, Italy Department of Physics, University of Pavia, via Bassi 6, 27100 Pavia, Italy
Received: 10 June 2020
ABSTRACT
Accepted: 27 August 2020
GdFeO3 perovskite attracted large interest in different fields thanks to peculiar magnetic and optical properties that are further tunable by means of doping processes and achievable on both Gd and Fe sites or by properly choosing the synthesis routes. In this paper, nanometric GdFeO3 compounds, undoped and doped with diamagnetic Ca2? and Mg2? ions, were synthesized by microwave assisted, sol–gel, and polyol syntheses and characterized by X-ray diffraction, showing solid solutions formation. Raman spectroscopy allowed us to confirm, from peak enlargements, the Ca and Mg substitution on Gd and Fe sites, respectively. The magnetic data showed the presence of magnetic domains as consequence of doping with diamagnetic ions, which seem to play a crucial role in the magnetic activity of the compounds. A superparamagnetic behaviour is evidenced; nevertheless, its intrinsic character is not definitely demonstrated. Indeed, the possible presence of traces of magnetic impurities, which are easily obtainable in these samples, such as iron oxides, must be taken into account.
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The Author(s) 2020
1 Introduction GdFeO3 is one of the most important members of the lanthanide metal oxide perovskites ABO3 (A = La, Sm, Eu, Gd) class. An ideal perovskite has a cubic crystal structure, composed of a three-dimensional framework of corner-sharing BO6 octahedra. It was
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https://doi.org/10.1007/s10854-020-04374-8
demostrated that the formation of regular perovskites is mainly governed by the Goldschmidt ‘‘tolerance p factor’’ ðt ¼ rA þ rO= 2ðrB þ rOÞÞ, where rA, rB, and rO are the ionic radii of A, B, and O atoms, respectively [1]. The t value of an ideal perovskite should be equal to 1.0, even if, based on the analysis of tolerance factor values, the perovskite structure is hexagonal, cubic, and orthorhombic for
J Mater Sci: Mater Electron
1.00 \ t \ 1.13, 0.9 \ t \ 1.0, and 0.75 \ t \ 0.9, respectively. It seems, however, that proper t values are a necessary, but not a sufficient condition for the formation of the perovskite structure. In addition, the octahedron BO6, i.e. the basic unit for perovskite structure, has a great importance and an ‘‘octahedral factor’’ can be defined as rB/rO. By considering both these factors, the perovskites formability can be reliably predicted. GdFeO3 with a t value of 0.86 crystallizes in the orthorhombic space group Pnma showing a distorted perovskite-type structure, as a result of the FeO6 octahedra tilting, with Gd3? in a eightfold coordination [1, 2]. GdFeO3 is on
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