Probing the effect of Zn2+ on the local structure, dielectric and magnetic properties of La2CuMnO6 by solid state synthesis
Introduction
Over the last few decades, materials scientists have worked vigorously to develop multifunctional materials, reducing power consumption and giving additional functionality for the upcoming electronic age [1], [2], [3], [4], [5], [6], [7], [8], [9]. In this context, double perovskite (DP) compounds have attracted tremendous attention, which are represented as A2B′B″O6 and A′A″B2O6, where A′ and A″ sites are usually adopted by rare earth or alkaline earth elements and B′ and B″ sites mostly adopted by transition metal (TM) elements. However, very few reports showed the local structural analysis of DPs in which row-one TMs occupied both B-sites. In this context, 6s-3d-based DPs showed excellent physical properties. For example, Lanthanum-based DP compounds like La2FeCoO6, La2NiMnO6, and La2CoMnO6 showed FM structure [10], [11], [12], [13], [14], and La2CuMnO6 showed AFM structure [15]. The half-metallicity and thermophysical properties of La2CuMnO6 have been studied (theoretically) extensively by Mir et al. [15]. They have proposed a significant contribution of Mn4+- and Cu2+-ions to the magnetic response of these ceramics. Mtougui et al. studied the magnetic properties of La2CuMnO6 [16] using Monte Carlo simulation and observed a soft magnetic behavior with TC = 70 K. Palakkal et al. [17] reported orthorhombic crystal symmetry with effective magnetic moments of 4.2 μB for La2CuMnO6 ceramics. In another report, Cu-substituted La2NiMnO6 showed FM transition near room temperature [18]. Singh et al. reported the structural, morphological, and high-temperature dielectric properties of La2CuMnO6 (LCM) and La2ZnMnO6 (LZM) ceramics [19], [20], where they have shown Debye and non-Debye dielectric transition for the ceramics. In these reports, various properties of LCM are studied, but the origin of these properties and the underline physics are missing. The oxidation state of copper in LCM decides the extent of the JT distortion, which affects the physical properties of the ceramics by affecting their crystal-lattice structure, super-exchange angles, and charge exchange interaction between Cu-O-Mn and Mn-O-Mn ions. Therefore, to understand the role of Cu in the physical properties of LCM, we substitute Cu with some comparable ionic radii element, which also has the same oxidation state. Hence, Zn is used to substitute it. As, Zn has +2 oxidation state (Cu+2) and ionic radii ∼ 0.88 Å (Cu∼ 0.87 Å).
The present work highlights the effect of Cu2+-substitution by Zn2+ on the structural, electronic, dielectric, and magnetic properties of the LCM. We have prepared single-phase Zn modified La2Cu1−xZnxMnO6 (x = 0.0, 0.5 and 1.0) ceramics. The non-rigidity in BO6-octahedra and JT distortion produced an unusual trend in the dc magnetic response of these compounds. Also, the extent of the JT distortion influenced the low-temperature dielectric behavior of these oxides. We also discussed frequency-dependent relaxor dielectric features corresponding to uneven grain size distribution and electron-phonon coupling of these oxides. These ceramics appear promising candidates for fabricating electronic and magnetic devices such as energy storage, radio frequency filters, spintronic, and memory devices.
Section snippets
Sample preparation
Polycrystalline samples of La2CuMnO6 (LCM), La2Cu0.5Zn0.5MnO6 (LCZM) La2ZnMnO6 (LZM) were prepared by the solid-state reaction method. For each composition, a stoichiometric amount of pure reagents, La2O3 (by Loba Chemicals, 99.9%), CuO, ZnO, and MnO2 (by Merck, 99.99%), were mixed in acetone (by Merck) and were grinded for 6–8 hrs. Acetone is evaporated in this step. Thus, obtained grinded and mixed powder were kept in aluminum crucibles in an air furnace at 1200 ºC for 12 h for calcination,
X-ray diffraction analysis
Fig. 1 shows the Rietveld refined XRD patterns of LCM, LCZM, and LZM, confirming orthorhombic crystal symmetry with the Pnma space group for all ceramics. Atomic crystallographic positions in Wyckoff notation are La3+ ions in 4c, Cu2+/Zn2+ and Mn4+ ions in 4b, and O2--ions in ‘4c’ and ‘8d’, referred to as O1 and O2, respectively. Scale factor, zero correction, background, half-width parameters (full width at half maximum (FWHM)), lattice parameters, positional coordinates, and iso-thermal
Discussion and conclusions
The comparable ionic radius cationic substitution method is a promising approach to understanding the underline physics of local structure and physical properties of perovskite oxides. We studied the role of Cu substitution (having oxidation state 2+ and ionic radius 0.87 Å) by Zn (having oxidation state 2+ and ionic radius 0.88 Å) on the structural and physical properties of the LCM system. Cu led to JT distortion in the LCM and LCZM systems. The presence of Cu and Zn in LCZM gave high
CRediT authorship contribution statement
It should be noted that ‘All authors are contributed equally to this work.’
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors acknowledge the Directorate of (ER & IPR), DRDO, India, for providing the financial support under Grant no. ERIP/ER/1406036/M/01/1566. Officials from the University of Silesia in Katowice, Poland, and the center Director of UGC-DAE-CSR Indore for utilizing various research facilities. We acknowledge D. M. Phase and R. Sah for utilization of SXAS beamline at RRCAT Indore, India. We acknowledge V. Sathe and A. K. Rathore from UGC-DAE-CSR Indore India for Raman measurement. We are very
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