纳米Si/C/N复相粉体的微波介电特性

MICROWAVE PERMITTIVITY OF NANO Si/C/N OMPOSITE POWDERS

研究了纳米Si C N复相粉体在 8.2— 18GHz的微波介电特性 ,采用双反应室激光气相合成纳米粉体装置 ,以六甲基二硅胺烷 ((Me3Si) 2 NH) (Me∶CH3)为原料 ,用激光诱导气相反应法合成纳米Si C N复相粉体 ,复相粉体的粒径为 2 0— 30nm .纳米Si C N复相粉体与石蜡复合体的介电常量的实部 (ε′)和虚部 (ε″)以及介电损耗角正切 (tanδ =ε″ ε′)随纳米粉体含量的增加而增大 ,ε′和ε″与纳米粉体体积分数 (v)之间符合二次函数关系 (ε′ ,ε″ =Av2 +Bv +C) ,纳米Si C N复相粉体的ε′和ε″在 8.2— 18GHz随频率的增大而逐渐减小 .纳米Si C N复相粉体中的SiC微晶固溶了大量的N原子 ,在纳米Si C N复相粉体中形成大量的带电缺陷 ,在电磁场作用下形成极化耗散电流 ,极化弛豫是损耗电磁波的主要原因 ,纳米Si C N复相粉体的介电损耗较大 。

The microwave permittivity. of nano Si/C/N composite powders suspended in paraffin wax has been studied at the frequency range of 8.2-18GHz. The nano Si/C/N composite powders were synthesized from hexamethyldisilazane ((Me3Si)(2)NH) (Me: CH3) by a laser-induced gas-phase reaction. The dissipation factors of the nano Si/C/N composite powders are high at the microwave frequencies. The microwave permittivity of the mixture of nano Si/C/N composite powders and paraffin wax (or other dielectric materials) can be tailored by the content of the composite powders. And epsilon', epsilon'' and tan delta increase with the volume filling factor (v) of nano Si/C/N composite powders. The epsilon' and epsilon'' can be effectively modeled using second-order polynomials (epsilon', epsilon'' = Av(2) + Bv + C). The epsilon' and epsilon'' of the nano Si/C/N composite powders decrease with frequency at the frequency range of 8.2-18GHz. The difference being the microwave resonance is not sharply peaked but rather smeared out over a large frequency range. The promising features of nano Si/C/N composite powders would be due to more complicated Si, C, and N atomic chemical environment. than in a mixture of pure SiC and Si3N4 phase. The SiC microcrystallines in the nano Si/C/N composite powders dissolve a great deal of nitrogen. The local structure around Si atoms changes by introducing N into SiC. Carbon atoms around Si are substituted by N atoms. So there exist a large number of charged defects and dangling bonds in the nano Si/C/N composite powders. Thus charged defects and quasi-free elections move in response to the electric field, diffusion or polarization current resulting from the field propagation. The high epsilon'' and dissipation factor tan delta(epsilon''/epsilon') of Si/C/N composite powders are due to the dielectric relaxation.