Structural, electrical and dielectric properties of spinel nickel ferrite prepared by soft mechanochemical synthesis

Dielectric and magnetic properties of Nickel ferrite ceramics using crystalline powders derived from DL alanine fuel in sol–gel auto-combustion

“…Ceramics sintered at 1200 1C exhibit a high ratio of (I 220 /I 222 ¼ 4.41), and correspond to a high degree of cation inversion and support the formation of inverse spinel NiFe 2 O 4 . The intensity ratios measured in the present work are comparable to earlier reported values of (3.2 -4.412) on NiFe 2 O 4 prepared by molten salt synthesis [22], and (2.52-2.92) reported for ceramics prepared by the mechano-chemical synthesis method [21].…”

“…The appearance of this shoulder has been related to the occupancy of octahedral site by both Fe 3 þ and Ni 2 þ ions. Deconvolution of the Raman spectra clearly shows the presence of doublet peaks and is in agreement with earlier reported observations [21]. The asymmetry and the separation of the Raman modes seen prominently in samples sintered at the higher sintering temperatures (1200-1300 1C) is due to the greater degree of cation inversion and supports the formation of NiFe 2 O 4 with inverse spinel structure.…”

“…For ceramics sintered at 1100 1C the density is quite low (3.59 g/cc) in comparison to the ceramics sintered at 1300 1C which yielded the highest density of 5.11 g/cc. In many earlier reports a variation in the intensity ratio of the Bragg reflections (I 220 /I 222 ) has been used to corroborate with the changes occurring in the cation distribution [21,22] which can be influenced by varying chemical reaction rates, annealing and sintering conditions. The intensity ratio of the Bragg reflections (220) and (222) is shown to be related to the cation distribution between the tetrahedral and octahedral sites respectively.…”

“…The A 1g mode corresponds to symmetric stretching of oxygen atoms along Fe-O and Ni-O bonds in the tetrahedral site. E g mode belongs to symmetric bending of oxygen with respect to the metal ion and T 2g (3) correspond to asymmetric bending of oxygen and T 2g (2) correspond to asymmetric stretching of Fe (Ni) and O in the octahedral site, and T 2g (1) is due to translational movement of the tetrahedron (metal ion at tetrahedral site together with four oxygen atoms) [21]. All five Raman modes are asymmetric, with a prominent shoulder at lower wave number for the A 1g and T 2g (3) modes of NiFe 2 O 4 ceramics sintered at 1200 1C and 1300 1C, and the A 1g mode for NiFe 2 O 4 ceramics sintered at 1100 1C.…”

“…For example, NiFe 2 O 4 ceramics prepared with powders obtained from different fuels (glycine, alanine, poly-mediated and sol gel synthesis) show significant differences in the microstructure and exhibit a strong dispersion in the dielectric properties with frequency [20]. Similarly, powders obtained from different techniques such as (i) soft mechano-chemical synthesis using different precursor powders [21], (ii) molten salt technique [22], (iii) use of different chelating/fuel agents [23], (iv) high-energy ball milling [24], (v) sol-gel method [25], and (vi) co-precipitation methods [26] exhibit varying dielectric characteristics. Likewise the compositionally modified Ni 0.5 Zn 0.5 Fe 2 O 4 powders of varying size obtained by sol gel auto combustion method with different fuels when used for ceramic processing exhibit significant variations in the dielectric characteristics with strong dispersion in the low frequency region (o1 MHz) [4,27,28].…”