YUE Lulu, DONG Weixia, BAO Qifu, LI Ping, GU Xingyong

(Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended Abstract:[Background and purpose] As a key filler in antistatic materials, conductive powder plays a role in rapidly transmitting charges by forming conductive pathways, endowing certain antistatic and electromagnetic shielding capabilities. Currently, conductive powders are composed of carbon-based materials (carbon black, graphite, carbon nanotubes, etc.), metal powders (Au, Cu and their mixed powders) and metal oxides (SnO₂, TiO₂, ZnO, Sb₂O₃, In₂O₃, etc.). However, carbon-based powders have poor dispersibility and adhesion, making it difficult to clean. Metal powders have problems such as deep color and easy oxidation, which limit their applications. Metal oxides have electrical conductivity, stability, dispersibility and relatively light color, thus having the most wide applications. Among them, ZnO, as a Ⅱ-Ⅳ group wide bandgap semiconductor with a wurtzite structure, has been widely utilized in fields such as antistatic coatings, transparent conductive films, solar cells and ultraviolet semiconductor lasers, due to its excellent physical properties and chemical stability. To our knowledge, there are problems for ZnO, such as doping with noble metals and expensive equipment. In this paper, Al and Ce co-doped ZnO conductive powder (ACZO) with high electrical conductivity was prepared by using a simple one-step hydrothermal method, while the essential reasons for the improvement of electrical conductivity were analyzed based on the first-principles.[Methods] One-step hydrothermal method was employed to prepare Al and Ce co-doped ZnO conductive powder (ACZO). Keeping Al doping concentration of 1.5%, the doping concentration of Ce ranged from 0 to 0.7%. A white suspension was obtained according to the raw material ratio and stirred for 30 min. Then, the suspension reacted in a hydrothermal autoclave at 180 ℃ for 12 h. After the product was filtered and washed, it was dried at 80 ℃ for 12 h. Subsequently, it was heated at 550 ℃ for 2 h at a rate of 3 ℃·min⁻¹ to obtain ACZO powder. Phase composition of the sample was tested by using X-ray diffractometer (XRD). Morphology of the sample was analyzed by using a scanning electron microscope (SEM). The particle size and distribution of the sample were measured by using a MS2000 laser particle size analyzer. Infrared spectrum of the sample was analyzed by using a Fourier-transform infrared spectrometer. The spectrum of the sample was analyzed by using an ultraviolet-visible spectrophotometer. The resistivity of the sample was measured by using a digital multimeter. The first-principles calculations were based on the density-functional theory (DFT), with the generalized gradient approximation and the Perdew-Burke-Ernzerhof (PBE) correlation-gradient-corrected functions. The ultrasoft pseudopotential method in the CASTEP module of Materials Studio 2020 software was used to calculate the band structures of different doping concentrations by constructing different supercell structures.[Results] XRD and SEM analysis results indicate that all the samples are pure ZnO, with nanorod morphology (PDF# 75-0576). Compared with pure ZnO, as the Ce doping concentration increases, the crystallinity and particle size of the Ce, Al co-doped samples (ACZO) decrease. However, the diffraction peak intensity at the wave number of 3460 cm⁻¹ increases, suggesting that more OH^- ions are adsorbed on the crystals. Therefore, there will be a significant steric hindrance effect on the force between the ACZO crystal nucleus and OH⁻. The steric hindrance effect blocks the lateral growth of the crystal plane and 1D anisotropic growth becomes dominant, resulting in the growth of nanorods and a decrease in grain size. TEM and EDS results show that the samples are mainly composed of Zn and O, with a Zn:O atomic ratio of 1:1, which is consistent with the atomic ratio of ZnO and XRD results. As the Ce doping concentration increases, the D₅₀ particle size of the samples first decreases and then increases (Tab. 1). When Ce³⁺ doping concentration is 0.4%, the D₅₀ particle size of the ACZO sample reaches a minimum of 1.176 μm and the overall particle size distribution shows a normal distribution trend, indicating that the particle size distribution of the powder is relatively uniform. Compared with that of pure ZnO (Eg=3.37 eV), after doping Al and Ce, Eg of ACZO samples significantly decreases. When Ce doping concentration is 0.4%, Eg and the resistivity of the sample reaches a minimum of 3.085 eV and 13.67 Ω·m, respectively, which is consistent with the first-principles calculation results.[Conclusions] Uniformly dispersed and rod-shaped ZnO conductive powder was prepared by using a one-step hydrothermal method. Compared with that of pure ZnO, the conductivity of the doped modified ZnO samples was significantly increased, especially after co-doping with Ce and Al. The appropriate Ce content could significantly reduce the particle size, band gap width and resistivity of the Al-doped ZnO samples. With increasing content of Ce, the resistivity and band gap width of the samples first decrease and then increase. When the Ce³⁺ content was 0.4%, the band gap width and resistivity of the sample reached the minimum values of 3.085 eV and 13.67 Ω·m, respectively. Based on the experimental and first-principles calculation results, doping reduces the band gap width, increases the free carrier concentration, and shortens the transmission path with smaller particle size, which are more conducive to the transport of free carriers.

Key words: hydrothermal method; without surfactant; Al and Ce co-doped; nano ZnO; resistivity