Crystal structure, microstructure, and broadband electromagnetic response of Al3+-substituted Sr3YCo4O10+δ double perovskites

Abstract

In this work, we investigate the structural, microstructural, and broadband dielectric and magnetic properties of Sr3YCo4–xAlxO10+δ (x = 0, 0.1, 0.3, 0.5, and 1.0; δ ≤ 1) double perovskite oxides in detail. The compounds were synthesized through solid-state reaction, and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The broadband dielectric and magnetic properties of the compounds were correlated qualitatively to the multiple valence state of the cobalt ions. The real part of permittivity was found to decrease with increase in Al3+ concentration from 117.3 (x = 0) to 37 (x = 1.0) (at 900 MHz), while the dielectric loss increased from 0.36 to 1.51. The real part of permeability decreased from 1.01 for x = 0 to 0.93 for x = 1.0 (at 900 MHz) accompanied by a decrease in the magnetic loss factor from 0.43 to 0.11. The broadband electromagnetic response was found to be in good agreement with the results obtained from XPS analysis. Impedance analysis revealed that the compounds exhibit a capacitive behavior, which can be attributed to the interfacial polarization due to the pore–grain interfaces. Further, room-temperature magnetic measurements revealed that the ferromagnetic nature of the parent compound diminished with the substitution of aluminum ions as a result of the reduction in oxygen vacancy ordering, which was also evident from FTIR analysis.