La^(3+)掺杂SiC纳米线的电磁性能与第一性原理计算

Electromagnetic Properties and First-Principles Calculation ofLa^(3+)^(3+) Doped SiC Nanowires

SiC纳米线具有吸波性能强、作用频带宽、密度低的优点,但是由于SiC较差的阻抗匹配条件和较低的电导率,影响了其吸波性能的进一步提高。为了调节SiC的电子结构,改善其电磁性能,以硅微粉、活性炭、La_(2)O_(3)粉末为原料通过碳热还原法在1600℃合成了La^(3+)掺杂SiC纳米线。结果表明:掺杂La^(3+)能够增大SiC纳米线的长径比和堆垛层错密度,增强其形成三维网状结构和界面极化的能力,其介电性能得到了提高。在2~18 GHz范围内,其介电实部由3.08~13.48(x=0)提升至3.33~19.75(x=1.0%),介电虚部由3.45~6.98(x=0)提升至5.03~11.56(x=1.0%)。同时La^(3+)掺杂提高了SiC纳米线的电导率,增强了其电导损耗。由于SiC纳米线界面极化和电导损耗的同时增强,掺杂2.0%的La^(3+)的SiC纳米线在厚度为2.0 mm时达到了最小反射损耗(R)-31.46 dB,有效吸收带宽(R<-10 dB)为7.18 GHz。通过第一性原理计算研究了SiC纳米线及La^(3+)掺杂SiC纳米线的电子结构,结果表明,La掺杂后SiC纳米线的带隙减小,验证了其导电性的增强。La掺杂能够在引入掺杂元素的同时增大SiC纳米线的堆垛层错密度,克服了掺杂元素时堆垛层错密度降低的现象,为合成高吸波特性SiC纳米线提供了思路。

As one of microwave absorbing materials, SiC nanowires have a good microwave absorbing property, a wide microwave absorbing bandwidth and a low density. However, the poor impedance matching condition and low conductivity of SiC affect the improvement of its microwave absorbing property. To adjust the electronic structure of SiC and improve its electromagnetic properties,Ladoped SiC nanowires were synthesized via carbothermal reduction at 1 600 ℃ with silicon powder, activated carbon andLa^(3+)_(2)O_(3)powder as raw materials. The results show that dopingLa^(3+)can increase the aspect ratio and stacking fault density of SiC nanowires,and enhance their ability to form three-dimensional network structure and interface polarization, and improve their dielectric properties. At 2-18 GHz, the real part of permittivity increases from 3.08-13.48 (x = 0) to 3.33-19.75 (x = 1.0%), and the imaginary part of permittivity increases from 3.45-6.98 (x = 0) to 5.03-11.56 (x = 1.0%). Also,La^(3+)doping improves the conductivity of Si C nanowires and enhances its conductivity loss. SiC nanowires doped with 1.0%La^(3+)achieve a minimum reflection loss (R) of -31.29 dB with the thickness of 2.0 mm and the effective absorption bandwidth with R<–10 dB of 7.18 GHz due to the simultaneous enhancement of interface polarization and conductivity loss of SiC nanowires. The electronic structures of SiC nanowires andLa^(3+)doped SiC nanowires were analyzed via the first-principle calculations. The results show that the band gap of SiC nanowires decreases afterLa^(3+)doping, verifying the enhancement of their conductivity.La^(3+)doping can increase the stacking fault density of SiC nanowires and solve a problem that the stacking fault density decreases. The results of this study can provide an idea for the synthesis of SiC nanowires with a high electromagnetic absorbing capability.