Abstract
The effects of Zn2+ ions substitutions on the Debye-Waller Factors, structure factor and other related structural properties of the Mg1-xZnxNiFeO4 (where 0.0≤x≤1.0) spinels have been investigated using the XRD, TEM, SEM and FT-IR tools. The Mg1-xZnxNiFeO4 samples were prepared using the conventional ceramic solid state sintering techniques at temperatures around 1100°C. The Mg1-xZnxNiFeO4 spinels have predominantly inverse type structure with inversion factor, λ in the range 0.69 to 0.36. The X-ray diffraction (XRD) patterns of all compositions showed the formation of cubic spinel structure. The lattice constant “a” increases from 8.3397A for MgFeNiO4 to 8.3855A for ZnFeNiO4 spinels. The increases in lattice parameters have been attributed to the replacement of small Mg2+ ions (0.66 A) with the Zn2+ (0.74 A) ions of a larger ionic radius. The IR spectra confirm the existence of two main absorption bands υ1 and υ2 in the frequency range of (400–1000 cm-1), arising due to the tetrahedral (A) and octahedral (B) stretching vibrations respectively. Values of both υ1 and υ2 decrease as Zn content increases. The scanning electron microscope (SEM) and transmission electron microscope (TEM) images showed aggregates of stacked grains. The normalized XRD intensities of the main (hkl) planes were used in the estimation of the Debye-Waller factor. Values of the Debye-Waller factors were estimated to be in the range (0.77-1.44A2). The calculated and observed relative intensities and areas of the most related plains to cation distributions (i.e.: the (220), (311), (222), (400), (422), (511) and (440) plains) were obtained by normalizing with respect to the most intensive reflection from the (311) plane. An inverse relation between the ordering, Q and inversion, λ factors exists in these partially inverse spinels. Both Q and λ decrease as Zn content (x) increases in the sample. The cation distributions indicate that the sample, MgFeNiO4 with x=0, λ=2/3 and maximum configurational entropy Sc(=15.876 J/mol, K) should represents the sample of the complete randomness of cation distributions in these spinels and can be written as (Mg1/3Fe2/3)[Mg2/3Fe1/3Ni3/3)O4. In general the variation of the different structural parameters with Zn content lie on two different regions, the first region for x values (0.0-0.6) the “highly normal” and the second region for x values (0.6-1.0) the “highly inverse” type structure.
Highlights
Spinel ferrites are characterized by many unique magnetic and electrical properties
The aims of this study are to account for the influence of the Zn2+ ions substitutions on the structural properties of the Mg1-xZnxFeNiO4 spinels for (0 ≤ x ≤ 1.0) using nondestructive tools such as the X-ray diffraction (XRD), infrared spectroscopy (IR), transmission (TEM) and scanning electron microscopy (SEM) tools
The Mossbauer tool has been used to estimate the cation distributions and other related structural and magnetic parameters [12]. These analysis indicate that these spinels are a mixture normal-inverse spinels and the degree of inversion for the pure MgFeNiO4 and ZnFeNiO4 spinels was determined to be round 0.69 and 0.36 respectively
Summary
Spinel ferrites are characterized by many unique magnetic and electrical properties. The high electrical resistivity gives rise to low eddy current and dielectric losses. Since the trivalent cations are generally smaller than the divalent ones, there should be some tendency for the trivalent cations to reside on the smallest sites, the tetrahedral sites, leading to the inverse or partially inverse type structure. This factor works in opposite direction of the electric charge factor; that the high (low) electrical charge causes the cations to occupy the larger (smaller) coordination number, the octahedral (tetrahedral) sites [8] leading to the normal (inverse) type structure
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