Direct Preparation of the Nanocrystalline MnZn Ferrites by Using Oxalate as Precipitant

Oxalate was generally used as a precipitant for synthesis of MnZn ferrites during the co-precipitation process. However, the MnZn ferrite couldn’t be directly obtained and a calcination process was needed. In this research, we reported a direct preparation of the MnZn ferrite nanoparticles by using co-precipitation method, together with refluxing process. XRD measurements proved that crystallite size of the obtained samples increased with an increase in pH value of the co-precipitation solution, and that the crystallite size of about 25 nm was obtained for the sample at a pH of 13. This sample showed the maximum Ms of 58.6 emu/g, which was about one times larger than that of 12 (pH value). Calcination to the obtained samples result in an enlargement in their crystal size and an improvement in their magnetic properties with an increase in temperatures. The samples calcinated in CO2 + H2 atmosphere presented good stability, and the maximum Ms value of 188.2 emu/g was obtained for the 1100。C-heated sample. Unfortunately, precipitation of some Fe2O3 at 800。C suggested poor stability of the nanocrystalline MnZn ferrite in N2 atmosphere.

Improved electrochemical properties in the Li_3Fe_2(PO_4)_3 by titanium and vanadium doping

The nominal Li_(3-x)Fe_(2-x)Ti_x(PO_4)_(2.55)(VO_4)_(0.45)(x=0～0.3) compounds were synthesized by a sol-gel process.Different from the single V043 doping, further introduction of Ti^(4+) ion was easy to result in precipitation of a little secondary phases, besides the main NASICON products. The simultaneous substitution of Ti^(4+)and VO_4~3 for Fe^(3+) and PO_4~3,respectively, in the Li_3 Fe_2(PO_4)_3 resulted in a net improvement in the rate capability and cycling performance, as compared with the single Ti^(4+) or VO_4~3-substituted compound.The sample with x=0.2 presented a high initial discharging capacity of 125.4 mAh/g at the rate of 0.5 C,about 25% higher than the Ti^(4+)-substituted Li_(2.8)Fe_(1.8)Ti_(0.2)(PO_4)_3, and 102.6 mAh/g after 60 cycles at 2 C,about 12% higher than the single VO_4~3-substituted one. The high rate performance between 0.5 C to 10 C suggested that this sample had a good stability and reversibility. These results proved that the combination of the Ti^(4+) substitution for Fe^(3+) with the V043 substitution for PO_4~3 was a promising method of improving electrochemical performance of the studied Li_3 Fe_2(PO_4)_3 cathode material.