钡过量非化学计量M型铁氧体的合成与表征

Synthesis and Characterization of Novel Non-stbichiometric M-type Hexaferrite with a Certain Barium Surplus

采用并加共沉淀工艺在900℃热处理2h的条件下合成了单相钡过量非化学计量M型铁氧体Ba1+xCoTiFe10O19+x(x=0.00、0.05、0.10、0.15、0.20),并用XRD、SEM、TEM 和VSM表征了这种新的非化学计量M型铁氧体的结构和磁学特性.结果表明:当0<x≤0.05 时,矫顽力Hc和剩余磁化强度σr均随x增大而显著增大(△σr=5.36A·m2·kg-1。,△Hc=16.99 kA·m-1),但比饱和磁化强度σs基本不变;0.05<x≤0.20时,因为Fe3+离子被稀释导致σs、Hc和σr均随x增大而持续降低.同时证实钡过量并不会导致晶体对称性破坏,0<x≤0.10时a轴长明显增大而c轴长增量很小,0.1<x≤0.20时c轴长大幅度增大而a轴长几乎无变化. 此外,还发现钡过量可导致晶粒长大和晶形由平面型向单轴型转变.这些结果说明过量Ba2+ 离子分布于平行于a轴方向的大孔隙位置,不仅具有助熔剂作用,而且对磁畴壁产生了钉扎效应.

Single-phase non-stoichiometric M-type hexaferrite with a certain barium surplus Ba1+xCoTiFe10O19+x (x=0.00, 0.05, 0.10, 0.15, 0.20) was synthesized by calcining the precursors at 900 degrees C for 2h obtained with the co-dump coprecipitation process. Structural and magnetic properties of the new non-stoichiometric M-type hexaferrite were investigated with XRD, SEM, TEM, VSM. The results show that the coercive field (H-c) and the remanent magnetization (sigma(r)) Of Ba1+xCoTiFe10O19+x are significantly increased (Delta H-c=16.99kA center dot m(-1), Delta sigma(r)=5.36A center dot m(2)center dot kg(-1)) while the specific saturation magnetization (sigma(s)) keep almost constant as the x increases in the range 0 similar to 0.05, and that sigma(s), H-c and sigma(r), all continuously decrease as the x increases in the range 0.05 similar to 0.20 since Fe (3+) ions become diluted. At the same time, it is confirmed that the crystal symmetry of Ba1+xCoTiFe10O19+x is not destroyed in the x range 0 similar to 0.20; the a-axis length is significantly increased as the x increase in the range 0 similar to 0.10 accompanying a small increase of the c-axis length, and that the a-axis length almost not change although the c-axis length stably increases as the x farther increases in the range 0.10 similar to 0.20. In addition, the phenomena of the growth of crystal grains and crystal shape transformation from plane form to uniaxial one were observed by a series of SEM and TEM images. These results imply that the excessive barium cations, which not only act as fluxing agent but. also produce the pinning effect to magnetic domainwall, are distributed in large holes along a-axis orientation of M-type barium hexaferrite.