Nickel substituted effect of on structural, Mössbauer and dielectric properties of spinel-type lithium ferrites

Abstract

Ni-substituted lithium ferrite Li_0.5-x/2Ni_xFe_2.5-x/2O₄, where (х=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) synthesized through sol-gel auto-combustion method was investigated for its structural, Mossbauer, and dielectric properties. At low doses of substitution, two spinels of the same composition coexist in the structure, one of spatial group P₄332, so-called spinel with superstructure, in which the iron and lithium ions are arranged along the crystallographic direction <110> and the other is a spatial group Fd3m, random spinel. The presence of both spinels is observed at low content of the doped element (x = 0.2 and 0.4). In case of increase Ni²⁺ ions, random component disappears and only the ordered phase remains. The particle sizes of the synthesized product are around 22-45 nm. According to the proposed cationic distribution of Nickel ions are localized in the A-site and lithium ions in the B-site. Iron ions are redistributed over both sites at a ratio of about 1:2. It is shown, that the conductive and dielectric properties of the synthesized powders have a frequency dependence characteristic of ferrite materials, the behavior of which is explained based on the hopping mechanism of conductivity and inter-grain polarization.