Electromagnetic Properties And Microwave Absorbing Properties Of TiN Nanocomposites Based On Structural Defects

As a kind of high temperature dielectric absorbing ceramics, TiN has been extensively used in thefields of electronic field, due to their high strength and hardness, good electrical and thermal conductivity.Unfortunately, few reports are currently available about thecontrol of morphology as well as evaluation ofmagnetic properties and electromagnetic performance of TiN. Particularly, the relationship between thedielectric loss and defects of nanomaterials remains unresolved. Therefore, nanotubular titanic acid (NTA)prepared at our laboratory was used as the precursor to fabricate doped and composite TiN nanoparticles.The morphology, microstructure and composition of as-prepared TiN nanoparticles were analyzed bymeans of high-resolution transmmison electron microscopy, X-ray diffraction, Laser Raman spectrometry,and X-ray photoelectron spectroscopy. The magnetic and electromagnetic properties of as-prepared TiNnanoparticles were examined with a superconducting quantum interface device and a vector networkanalyzer. Furthermore, the effects of composition, morphology, microstructure and defects of as-preparedTiN nanoparticles on their magnetic and electromagnetic properties were investigated, and the relationshipbetween the microstructure and electromagnetic properties of doped TiN or TiN nanocomposites wassystematically investigated. The main contents and results are as follows:1. TiN nanoparticles with a size of about30nmwere successfully prepared by high-temperaturenitriding of NTA precursor in the presence of ethylene diamine as the N source. The morphology,composition and electromagnetic properties of as-obtained TiN nanoparticles were investigated.2. Mn-TiN and Zn-TiN composite nanoparticles doped with Mn or Zn at different doages wereprepared by high-temperature nitriding of NTA in flowing NH3as the N source. The morphology,microstructure, as well as magnetic properties and electromagnetic properties of as-obtained Mn-TiN andZn-TiN nanocomposites were investigated. It has been found that as-prepared Mn-TiN nanocompositeexperiences a gradual diamagnetic to ferromagnetic transition at room temperature with increasing Mncontent, but Zn-TiN nanocomposite retains diamagnetism even though its Zn content is high. As-preparedMn-TiN nanocomposite (Mn dosage1.5%; mass fraction, the same hereafter) with a thickness of2mm hasa reflection loss of-38dB under a frequency of16.5GHz, while Zn-TiN nanocomposite (Zn dosage20%)with a thickness of2mm has a reflection loss of-32dB under12GHz. Besides, although Zn-TiNnanocomposites with a high Zn dosage do not possess static magnetism, they still lead to magnetic loss towards electromagnetic wave. Therefore it can be stipulated that there might exist some internal relationamong the microwave absorbing performance of as-prepared Mn-TiN and Zn-TiN nanocomposites and thetype as well as quantity of their defects. Similarly, their magnetic loss might also correspond to theirdefetcs.3. The mechanisms for materials to absorb electromagnetic wave cover dielectric loss and magneticloss, and TiN is a kind of ceramics dominated by dielectric loss. This means that incorporating magneticmaterials in TiN may endow it with magnetic loss mechanism thereby improving its electromagnetic waveabsorbing performance. For this reason and with reference to the aforementioned study on preparation ofTiN nanoparticles, we adopted Fe(NO)3·9H2O as the source of Fe to prepare TiN/Fe2N nanocompositeswith different composition by high-temperature nitriding (1000℃, nitriding time7h). The magneticproperties and electromagnetic properties of as-obtained TiN/Fe2N nanocomposites were investigated. It isfound that as-obtained TiN/Fe2N nanocomposite containing25%Fe possesses excellent electromagneticwave absorbing performance. Namely, this TiN/Fe2N nanocomposite with a thickness of3mm has areflection loss of-38dB around7GHz. Besides, the same nanocomposite with a thickness of1～5mmshows a reflection loss of below-10dB within a bandwidth of as much as4.6GHz. This means thatas-fabricated TiN/Fe2N nanocomposite is able to absorb over90%of electromagnetic wave irradiated ontoits surface within a certain range of frequency and it possesses excellent microwave absorbing performance.It can be inferred that the excellent microwave absorbing performance of TiN/Fe2N nanocomposite isclosely related to its dielectric loss mechanism and magnetic loss mechanism, as well as proper resistivityand interfacial polarization of its duak-phase nanoparticles (TiN and Fe2N) with a large surface area underalternating electric field.