Structural phase transition of spinel to hematite of as-prepared Fe2+-Cr nanoferrites by sintering temperature

Abstract

This investigation presents effect of sintering temperature on the transition processes of as-synthesized cubic spinel Fe2+Cr0.4Fe1.6O4 nanoferrites by the co-precipitation method. In addition to parts of as-synthesized sample were sintered at the temperatures T = 300, 500, 700, 900 or 1100 °C in ambient air for 4 h, other parts were sintered at 250 °C for 1, 2 and 3 h. The structural phase of sample crystal was converted from cubic spinel–to- maghemite–to-hexagonal hematite with T. The effect of the sintering temperatures and transition process on the different properties of the samples was investigated. The threshold frequency and energy of transition electrons showed decrease against T. The specific surface area S revealed decrease against the crystallite size R, while the saturation magnetization MS was affected by R and porosity P. The density indicated effect on elastic wave velocities, VS and VL, while increase of strain ε enhanced the band gap energy Eg.