Ni/Co掺杂对二氧化锰的微波高介电响应机理研究

The one-dimensional tunnel structure of manganese dioxide makes it become an ideal candidate for the incorporation of doping ions. Many intriguing performances of manganese dioxide are derived after doping with different ions. The applicant first studied the electromagnetic characteristic of Ni/Co-doped manganese dioxide and found that the complex permittivity, especially the imaginary part of it, was significantly enhanced after Ni/Co doping, while the complex permeability was kept almost constant. Considering the above unaccustomed phenomenon, this project plans to investigate the Ni/Co-doped manganese dioxide in a deep-going way, and further explore the high dielectric response law as well as the controllable synthetic technology. The change mechanism of the microstructure, such as crystal structure, lattice distortion, energy band structure, spin magnetic moment and density of state, will be determined based on the first principle. And all these calculations are based on the search of relatively stabilized configuration by considering the doping site and magnetic coupling. Subsequently, with the study of the morphology, electromagnetic parameter and microwave reflection loss of the doped manganese dioxide, the underlying relationship between microstructure and electromagnetic property will be investigated, and the microwave attenuation mechanism of the doped manganese dioxide will also be disclosed. Finally, high dielectric response mechanics of Ni/Co-doped manganese dioxide will be clarified. The accomplishment of this project will provide theoretical foundation for developing new kinds of high performance and broad band absorbent.

二氧化锰的一维隧道晶体结构为异质离子的嵌入掺杂提供了理想的基体。经不同元素掺杂后二氧化锰不断衍生出新的特性。申请人首次对Ni/Co掺杂态二氧化锰的电磁性能进行了研究，发现掺杂后的二氧化锰复磁导率变化较小，但复介电常数特别是虚部却显著增加。基于上述有趣现象，本项目拟通过对Ni/Co掺杂二氧化锰的高介电响应规律研究，明确掺杂态二氧化锰的高介电性能可控制备工艺。具体采用第一性原理，在综合考虑掺杂位置的多组构型和掺杂离子间耦合状态的基础上，计算相对处于基态的稳定掺杂结构，进而计算掺杂后二氧化锰的晶体结构演变、晶格畸变、能带结构、自旋磁矩和电子态密度分布，结合掺杂后二氧化锰的形貌、复电磁参数和微波反射损耗特性，探究微结构和电磁性能之间的内在关联，揭示掺杂后二氧化锰的微波损耗机制，最终阐明Ni/Co掺杂二氧化锰的微波高介电响应机理。本项目的研究结果将为高性能和宽频段的新型微波吸收剂开发奠定理论基础。

二氧化锰（MnO2）以其优越的物化性质和环境友好等特性，被广泛应用于电化学、催化剂等领域。而作为典型的富有潜力的介电损耗型吸波材料，其有效吸收频宽较窄，吸收强度有限，阻碍了其在吸波材料领域的发展应用。离子掺杂作为改善材料微观结构与性能的有效途径，在提高材料的电磁学性能方面有着重要贡献。然而，掺杂作用对MnO2吸波性能的改善机制仍不完善，介电性能的增强原理并不明确。针对上述重要问题，本课题组选取Ni2+、Co2+、Fe3+、Ag+，制备了掺杂态MnO2 ，并系统研究了金属阳离子掺杂对氧化物晶体结构及形貌的影响，微波损耗性能增强的内在机制。.在δ-MnO2制备过程中进行Co2+掺杂，由于Co2+能够被氧化为Co3+，且Co3+不稳定的原因，产物中会产生α-MnO¬2，随着掺杂含量的增大，α的含量先增大后减小，生成相由呈衔尾蛇状。通过对这组样品进行吸波性能的分析可知，两相混合的样品比单独的纯相样品吸波性能更佳。最佳吸收峰值能达到-54.8 dB，吸收层厚度为2.2 mm时，有效吸收宽度能够覆盖整个Ku波段，吸收层厚度为3.1 mm时，能够覆盖整个X波段。.Ni2+掺杂对MnO2的影响则完全不同。当对δ-MnO2进行Ni2+掺杂时，产物晶型不会受到掺杂离子浓度的影响，且掺杂样品形貌仍为纳米片状。掺杂后，样品的复介电常数有显著提高，产物的介电损耗因子能够提高80%。同时，研究了Ag+掺杂的α-MnO2，掺杂之后MnO2的晶型未发生明显变化，仍为纳米线状形貌。样品的复介电常数大幅度提高，介电损耗角正切能够达到0.95，显示出更显著的介电损耗性能。.通过第一性原理计算，从微观角度明阐明掺杂原子通过增大体系磁矩、减小键能两方面提高MnO2的微波响应。. 通过本项目研究，明确了金属阳离子掺杂态MnO2的制备工艺，揭示了不同类型的掺杂离子对MnO2晶型和形貌的形成规律及内在微观机制，阐明了MnO2的微波损耗机制和高介电作用机理。本研究对高介电材料的研究提供了新思路。