Effect of calcination on structural and supercapacitance properties of hydrothermally synthesized plate-like SrFe12O19 hexaferrite nanoparticles

Nanocrystalline Sr1Fe22O19 hexaferrite particles were successfully synthesized via hydrothermal route from Sr and Fe nitrates at molar ratio of 1:9 (Fe/Sr). As-synthesized powders were subsequently subjected to calcination at 900, 1000, 1100 and 1200 degrees C for 4 h to evaluate their structural, morphological and supercapacitance behavioral changes with temperature. The XRD results revealed Sr1Fe12O19 phase formation in the presence of Fe2O3, SrCo3 phases in the calcined samples. The percentage of Sr1Fe12O19 phase showed an increase by increasing the calcination temperature. Furthermore, the average crystallite size was increased from 28 nm to 361 nm by increasing the calcination temperature from 900 degrees to 1200 degrees C. The formation of metal oxide (Fe-O) bonds was also confirmed from strong absorption peak between 448 and 568 cm(-1) in FT-IR analysis. The FESEM images exhibited plate-like particles, which are distributed in the range of 1-8 mu m in the as-synthesized samples calcined up to 1000 degrees C, but their shaped became almost irregular by increasing temperature to 1200 degrees C and the particles size distribution were broadened to 2-15 mu m. Electrochemical performance of the pseudocapacitor (Sr1Fe12O19)was studied by cyclic voltammetry. It was found that by increasing the calcination temperature from 900 to 1100 degrees C, the specific capacitance increased from 44.0 to 133.9 F.g(-1), respectively. Thereafter, its value decreased to 15.5 F.g(-1) by calcination at 1200 degrees C. It should be noted that the cycle stability of Sr1Fe12O19 calcined powder at 1100 degrees C was at an acceptable level, which maintains 84% of the initial capacitance after 5000 cycles.