Effect of rare earth on structural, morphological, vibrational, magnetic and dielectric properties of RFe0.5Cr0.5O3 (R = Nd, Eu) perovskites

Abstract

RFe0.5Cr0.5O3 (R = Nd,Eu) perovskites were synthesized through solid-state reaction. The structural analysis evidences the orthorhombic symmetry of these materials in accordance with their tolerance factor. The lattice parameters, bond lengths, and bond angles, as obtained by Rietveld refinement, vary systematically with the size of R3+ cations. The structural stability and thermally activated expansion of the crystal lattice are affirmed by means of a high-temperature X-ray diffraction (HT-XRD) study. The microstructure of the prepared powders is investigated using scanning electron microscopy (SEM), as well as X-ray diffraction (XRD) through the calculation of the crystallite size. Diffuse reflectance spectra indicate that these materials behave as semiconductors, and the gap energies are calculated. Room-temperature Mössbauer spectroscopy highlights the presence of magnetic frustration phenomenon in both materials. The frequency-dependent dielectric study reveals a colossal dielectric constant in agreement with the Maxwell-Wagner relaxation mechanism resulting from intergrain boundaries, as asserted by impedance spectroscopy. The conductivity mechanism is provided by the correlated barrier hopping model for EuFe0.5Cr0.5O3 perovskite, and the non-overlapping small polaron tunneling mechanism for NdFe0.5Cr0.5O3 material. High-temperature dielectric measurements reveal two anomalous features attributed to the magnetodielectric effect and the onset of ferroelectric-paraelectric transition, respectively. Metallic behavior is identified at higher temperatures for both materials.