Effect of zinc substitution on U-type barium hexaferrite-epoxy composites as designed for microwave absorbing applications

• Published in: Journal of alloys and compounds 2021-06, Vol.865, p.158280, Article 158280
• Main Authors: Pratap, Vivek, Soni, A.K., Abbas, S.M., Siddiqui, A.M., Prasad, N. Eswara
• Format: Article
• Language: English
• Subjects: Barium hexaferrite; C band; Complex permittivity; Composite materials; Crystal structure; Crystallinity; Electromagnetic properties; Field emission microscopy; Hexagonal phase; Lattice parameters; Magnetic properties; Magnetic saturation; Magnetometers; Measurement techniques; Microwave absorber; Microwave absorbers; Microwave absorbing materials; Microwave absorption; Network analysers; Nondestructive testing; Polymeric composite; Return loss; Sintering (powder metallurgy); Substitution reactions; Superhigh frequencies; Zinc
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.158280

•Easy and cost effective solid state reaction method has been used for synthesis of Ba4Co2−xZnxFe36O60 (0.5 ≤ x ≤ 1.5 in step of 0.5) powder.•All barium hexaferrite (BHF) powder samples demonstrate the typical characteristics of soft ferrite.•A series of BHF-epoxy composites was prepared of fix volume percentage (54.3 vol%) of BHF powder.•Complex permittivity and complex permeability were computed in the frequency range of 2–18 GHz.•The values of return loss have been successfully measured for toroidal shaped composites through metal backing technique.•Maximum absorption (›› 90%) was achieved for all prepared composites for every compositions of Ba4Co2−xZnxFe36O60. [Display omitted] In the current study, U-type barium hexaferrite (BHF) poly-crystalline powder with chemical formula Ba4Co2−xZnxFe36O60 (0.5 ≤ x ≤ 1.5 in step of 0.5) were successfully synthesized by solid state reaction route at the sintering temperature of 1400 °C in air medium. The effect of Zn+2 substitutions on the crystalline structural and magnetic properties of BHF powders were examined through nondestructive X-ray diffraction (XRD) technique and vibrating sample magnetometer (VSM) respectively. Upon increasing Zn+2 content the lattice parameters a and c decreases which is leading to the X-ray density up to a small degree, due to a smaller ionic size of Zn+2 as compared to Co+2 ions and saturation magnetization (Ms) from 56.08 emu/g for the zinc substituted sample down to 54.79 emu/g was observed. The transmission electron microscope (TEM) depicted that the particle size reached a minimum at x = 0.5 and then grown with x = 1.5 zinc content, getting a value of 103.06 nm with hexagonal phase and finer grains having the size range of ~0.51–1.0 µm thick and 5 µm long which is confirmed by field emission scanning electron microscopy (FESEM). A series of BHF-epoxy composites has been further transformed into toroidal shaped composites with fix volume percentage (54.3 vol%) of BHF powder in epoxy matrix. Electromagnetic properties; complex permittivity (εr = ε′ − jε″) and complex permeability (μr = μ′ − jμ″) of the prepared composites were computed through coaxial measurement techniques by using an Agilent E8364B vector network analyzer. Minimum return loss (RLmin) was observed as −32.98 dB (maximum absorption " 99.92) for matching frequency 10.3 GHz of the absorber with thickness of 3.1 mm and the bandwidth achieved was 7.38 GHz. Absorption values for prepared composites have potential use as