Search

Spinel ferrites are attractive for high frequency applications due to their larger direct current (dc) resistivity and low dielectric loss. In the present work, Co0.6Zn0.4HoxFe2-xO4 (x = 0.00 and 0.1) spinel ferrites were prepared by sol-gel method. The X-ray diffraction pattern showed that both samples had cubic spinel structure, while in sample (x = 0.1), the secondary phase (HoFeO3) was also observed. The dc resistivity was increased with the addition of holmium ions. As the temperature increased, the dc resistivity was decreased by proving their semiconducting nature. The dielectric properties were also measured as a function of temperature and frequency. The sample which was composed by the substitution of holmium ions contained low value of dielectric loss. The magnetic properties were also experimentally measured by applying the field up to 2000 oersted. The small area covered by hysteresis loop proved that both samples possessed soft nature of magnetic materials.

Mullite/TiB 2 composite has been prepared successfully by combustion synthesis from blends of fine TiO 2 –B 2 O 3 –Al–SiO 2 powders. Despite the dilution effect due to silica addition and the endothermic character of mullite formation reaction, thermodynamic calculation shows that the overall reaction between the reactants is still highly exothermic. Depending on the silica grain size and the preheating temperature, partial to full conversion of reactants into products can be achieved during the process. At 550 °C preheating temperature, complete conversion of the reactants to mullite/TiB 2 was achieved. Adiabatic combustion temperature and mullite molten fraction are calculated as a function of preheating temperature.

Calcium copper titanate CaxCu3−xTi4O12 (CCTO) nanopowders have been synthesized using the organic acid precursor method based on commercially available materials. The results revealed that cubic CCTO phase was accomplished for the formed citrate precursors annealed at 1000 °C for 2 h. The crystallite size of the formed powders was found to increase from 44.2 to 64.8 nm upon increasing the molar ratio of Ca2+ ion from 1.0 to 2.0. A slight increase in the lattice parameter “a” and unit cell volume were observed, while a slight decrease in the porosity was evidenced as a result of increasing Ca2+ ion concentration. FE-SEM observations of these powders confirmed their homogeneous regular cubic-like structure. It can be noted that the transmittance of the sample was around 85% with Ca2+ ratio 1.0. Furthermore, the band gap energy increased from 3.8 to 4.2 eV, and the DC resistivity was increased from 6.4 × 104 to 6.8 × 104 cm Ω with increasing calcium content. We demonstrate that without any dopant, only by controlling the chemistry and engineering of the interfacial regions at the grain boundaries, the dielectric loss was suppressed remarkably while retaining the giant dielectric constant. These investigations would allow the application of these materials in transparency, microelectronics and memory devices.