用溶剂热方法制备CoxFe3-xO4 (0≤x≤1)亚微米球, 可看作不同比例Fe3O4和CoFe2O4的混合物.实验发现:当原料中钴铁原子比为1∶1、1∶2、1∶4和0时,反应得到的球分别为CoFe2O4、Co0.9Fe2.1O4、Co0.73Fe2.27O4和Fe3O4.Fe3O4与石蜡混合物(质量分数75wt%)厚度为5.5 mm时,反射率最低为-38 dB,对应频率为4 GHz;Co0.9Fe2.1O4与石蜡混合物在3~14 GHz频率范围内介电损耗大于磁损耗,计算出来的反射率分贝值(-41.1 dB,12.08 GHz,2 mm)低于相关报道.比较四种成分的钴铁氧体球可以看出:当x值不同时,由于成分Fe3O4和CoFe2O4的自然共振频率不同,引起磁性能随微波频率发生变化,而且由于二价铁离子被钴离子取代,结晶性也发生改变,进而改变了材料的介电和吸波性能.
CoxFe3-xO4 (0≤x≤1) spheres, a mixture of Fe3O4 and CoFe2O4, were synthesized via solvothermal reaction by changing the Co to Fe ratio in ethylene glycol solution.For the solution containing ingredients (atom ratio of Co∶Fe=1∶1,1∶2,1∶4 and 0), the obtained spheres are CoFe2O4, Co0.9Fe2.1O4, Co0.73Fe2.27O4 and Fe3O4 at 200 ℃, respectively.The calculated reflectivity indicates that for the composite containing magnetite(75wt%) and parraffin wax, the lowest reflection loss is-38 dB at 4 GHz with 5.5 mm thickness.The composite containing Co0.9Fe2.1O4 spheres displays better microwave absorption capability.The minimum reflection loss reaches-41.1 dB at 12.08 GHz and the matching thickness is 2 mm.Dielectric loss contributes even more than magnetic loss in the frequency range of 3-14 GHz.The work proves that variation of cobalt element in spheres can change the proportion of CoFe2O4 to Fe3O4, the resonance frequency together with the crystallinity of the spheres, and ultimately the dielectric character and the microwave absorption property.
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