Synthesis, Microstructure Characterization And Property Research Of ZnO/SnO₂ Composites

As a novel absorbing material, ZnO/SnO₂ composite has the advantages of excellent designability, impedance matching, mutual compensation of different loss mechanisms in microwave absorption, controllable structure, broadening the absorption bands and enhance absorption etc. Hence, ZnO/SnO₂ composite has a better prospect in the field of microwave absorption and has become a hotspot in the field of stealth technology.ZnO/SnO₂ composites were prepared via two-step hydrothermal method in this paper. The first step is preparing ZnO nanorods through hydrothermal method and the second step is synthesizing ZnO/SnO₂ composite based on the primary structure of ZnO by hydrothermal method, and its crystal structure, surface morphology, atomic components, chemical bonds and electromagnetic properties were characterized. The mechanisms of nucleation and growth were established for ZnO/SnO₂ composite structure through time-dependent experiments, temperature-dependent experiments, the ratio of [Zn]/[Sn]-dependent experiments, ZnO nanorods adding-sequence experiments, and salt of Sn and NaOH adding-order experiments, respectively. Results show that the reaction source ZnO nanorods are decomposed to generate Zn（OH）42- in the first stage and then Zn（OH）42-combined with Sn4+and OH- generates perovskite structure ZnSn（OH）6. ZnSn（OH）6 crystal could be decomposed and ZnO nanorods generate again, finally the nucleation and growth of SnO₂ occurs on the ZnO nonpolar planes indicating that the formation of ZnO/SnO₂ composite structure completes. In the meantime, the electromagnetic properties of ZnO nanorods, SnO₂ nanomaterials and ZnO/SnO₂ were characterized and analyzed, the results show that ZnO/SnO₂ has higher magnetic loss than ZnO and has higher dielectric loss than SnO₂.ZnO/SnO₂ composites were prepared via two-step hydrothermal method assisted by SDS, CTAB and PAM. Mechanisms that the effects of surfactant on the growth and nucleation are explained by using the SDS micelle adsorption model, CTAB cation transport and adsorption model and PAM ionization model, respectively. In conclusion, the surfactants act as carriers of growth units, nucleation sites, dispersant and also inhibit surface growth in the hydrothermal preparation of ZnO/SnO₂ composite structure. Under the assistant of surfactants, the morphology and structure of the composite materials are changed, thus the electromagnetic performances are different, the tanδe of ZnO/SnO₂ composites are both larger than that of intrinsic ZnO/SnO₂ composites under the condition of SDS:1%, SDS:2.5%, CTAB:5% and PAM:0.0005%.Sb doping and Co, Mn doping could improve the dielectric loss and magnetic loss of ZnO/SnO₂ in Ku band. The results show that substitutional doping of Sb5+replacing Sn4+ makes ZnO/SnO₂ be a n-type semiconductor and its electromagnetic properties are controlled by its morphology and Sb doping concentration. Oxygen vacancies exist in ZnO/SnO₂ because of Co substitutional doping, the orbit coupling between Co2+and its neighbor oxygen vacancies contribute to ferromagnetism; Room temperature ferromagnetism theory of Mn doping ZnO/SnO₂ composites is put forward by using F-center model. Due to the magnetic elements doping, the magnetism is introduced into ZnO/SnO₂ composite and the magnetic loss increases, when Co and Mn doped with 3% and 5%, their tanδm are higher than that of intrinsic ZnO/SnO₂.