δ-Phase evolution in Cd-doped lithium ferrites: Their thermal, electrical and magnetic properties

Nano-sized Cd-doped lithium ferrite LiCdxFe5−xO8 (0.0 ⩽ x ⩽ 1.0) powders were prepared using the sol–gel method. Thermal analysis showed the formation of LiFe5O8 ferrite around 440 °C and the Cd-doped lithium ferrites have been found to have better thermal stability due to the delta phase evolution. The evolution of δ-LiFe5O8 as a secondary phase has been confirmed by XRD, for all the samples above Cd content x ⩾ 0.3, with formation of pure δ-LiFe5O8 for the composition x = 0.5 only. The decrease of DC resistivity with temperature can be attributed to the semiconducting nature for all the samples. The DC resistivity also increased with Cd-content, attributing to the decrease in polaron hopping between Fe3+ and Fe2+ ions. The drift mobility showed an increasing trend with temperature, because of the hopping of charge carriers from one site to another with increasing temperature. Pure LiFe5O8 has saturation magnetization (Ms) equal to 59.55 A m2/kg, which on doping with Cd, first increases and then shows a decreasing trend. Conversely, coercivity (Hc) first decreases and then increases with Cd doping.