Effect of Li substitution on the structural, magnetic, and electrical properties of nanocrystalline LixNi0.6-2xZn0.4Fe2+xO4

Abstract

Nanocrystalline LixNi0.6–2xZn0.4Fe2+xO4 (where x = 0.00, 0.05, 0.10, 0.15, and 0.20) were prepared by the auto-combustion synthesis route. Each composition was sintered at different sintering temperatures, Ts, (1100–1250 °C) for 5 h. The optimum Ts for each composition was selected based on their maximum bulk density. For the first three compositions (x = 0.00, 0.05, and 0.10), the optimum Ts was 1200 °C, and for x = 0.15, Ts = 1175 °C, and for x = 0.20 Ts = 1150 °C. The Rietveld refinement of X-ray diffraction (XRD) patterns confirmed the monophasic formation of cubic spinel structure. The lattice constant was found to decrease (8.3821–8.3706 Å) slightly, complying with Vegard's law. The crystallite size calculated using Scherrer formula varied from 53 to 59 nm. However, the microstructural study showed that the average grain size has enlarged (0.53–1.39 μm) with substituting Li content up to x = 0.10. The real part of initial permeability increased up to x = 0.10, and the maximum value was 52 (at 1 MHz). The saturation magnetization, Ms, enhanced with increasing Li content, obeying the Globus model. The maximum Ms obtained for Li0.1Ni0.4Zn0.4Fe2.1O4 was 76 emu/g. The dielectric constant exhibited dispersive behavior with changing frequency. At lower frequency (<105 Hz), the dielectric constant was high, but fell down with increasing frequency. The ac conductivity and electric modulus remained low at lower frequency (<105 Hz), but ascended with increasing frequency. In contrast, the complex impedance spectra followed the reverse trend with changing frequency.