Key Engineering Materials Vol. 591

Abstract: The ferroelectricity of Bi_3.25Pm_0.75Ti₃O₁₂ (BPT), and Bi_3.25Pm_0.75Ti_2.97V_0.03O₁₂ (BPTV) ceramics prepared at 1200°C by a conventional ceramic technique was investigated. These ceramics possess random-oriented polycrystalline structure. The remanent polarization (P_r) and coercive field (E_c) of the BPT ceramic are 16 μC/cm² and 62kV/cm, respectively. Furthermore, V substitution improves the P_r value of the BPT ceramic up to 25 μC/cm² which is larger than that of the BPT ceramic. Therefore, co-sustitution of Pm and V in Bi₄Ti₃O₁₂ (BIT) ceramic is effective for the improvement of its ferroelectricity.

Abstract: Er₂O₃-doped bismuth titanate (Bi_4-xEr_xTi₃O₁₂, BET) and pure Bi₄Ti₃O₁₂ (BIT) thin films with random orientation were fabricated on Pt/Ti/SiO₂/Si substrates by rf magnetron sputtering technique. The experimental results indicated that Er doping into BIT also result in a remarkable improvement in ferroelectric property. The P_r and the E_c values of the BET film with x=0.75 were 21 μC/cm² and 80 kV/cm, respectively.

Abstract: In this experiment, the spinel-type lithium manganese oxide (LiMn₂O₄) prepared via solid-phase sintering method was coated with magnesium titanium composite oxide (MgTiO_x) in the presence of polyvinyl pyrrolidone (PVP) under the ultrasonic wave. The crystal structures, surface morphologies and electrochemical properties of the sample prepared were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical analysis. The X-ray diffractions indicated that the LiMn₂O₄ coated with MgTiO_x were similar to that of the pure LiMn₂O_4, and they both showed sharp and high peaks. The particles of the samples prepared with PVP did not aggregate obviously, and the samples were coated completely and homogeneously. At charge-discharge rates of 0.2C, the first discharge capacity can reach more than 120 mAh / g. Compared with pure LiMn₂O₄, the capacity attenuation of MgTiO_x-coated LiMn₂O₄ reduced after fifty cycles, and showed good electrochemical performance.

Abstract: The preparation of the BaZr_0.8Y_0.2O_3-δ solid electrolyte obtained by a nitrate-citrate combustion is reported. This synthesis method is compared with solid state reaction. The phase formation process was studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The phase evolution during the gel-combustion process and solid state process as a function of heat-treatment temperature was also studied by X-ray powder diffraction (XRD). When using nitrate-citrate combustion method a pure phase was formed at 800°C, which is much lower than that of conventional solid state reaction (at 1200°C). The sinterability of electrolyte powder was also investigated. At 1700°C very dense pellets can be obtained for both samples. The conductivity of BaZr_0.8Y_0.2O_3-δ (BZY20) electrolyte prepared using two different processes was measured by AC impedance spectroscopy. Impedance spectra analyses showed that the grain boundary conductivity is much lower than that of the bulk for BZY20. Furthermore, the grain-boundary resistance of the BZY20 prepared via nitrate-citrate combustion process was reduced markedly compared to that of the BZY20 prepared by conventional solid state reaction.

Abstract: In some applications such as automotive oxygen sensor, 5mol% Y₂O₃ stabilized zirconia (5YSZ) is generally used because it has both excellent ionic conductivity and mechanical properties. The automotive oxygen sensor would experience a cyclic change from high temperature (engine running) environment to the low temperature damp environment (in the tail pipe when vehicle stops). The conductivity change with coupled conditions of thermal cycle and dump environment in the 5mol%Y₂O₃ZrO₂ (5YSZ) system was examined by XRD,Impedance spectroscopy and transmission electron microscopy (SEM) in this paper.

Abstract: The influence of ZnO sintering aid on the structure, morphology and electrical properties of BaZr1-xYxO3-δ proton-conducting electrolyte is presented. XRD showed that all the samples mainly consisted of single-phase cubic perovskite structure. Except for BaZrO3+ 1wt% ZnO, other samples show a peak arising from a small amount of Y2O3 impurity. SEM analysis showed that all the materials have a very dense structure after being sintered at 1300 oC with ZnO sintering aid. For densified BaZr1-xYxO3-δ+ 1wt% ZnO system the ZnO addition did not lead to increase the grain size. The change of the crystal structure of BaZr1-xYxO3-δ + 1wt% ZnO system with the content of doped yttrium was investigated. The lattice parameter and unit cell volume increased sharply at x<0.2, but it was maximal and almost constant at x≥0.2. The impedance spectra for BaZr0.8Y0.2O3-δ + 1wt% ZnO sample at three different temperatures were compared. With increasing temperature the resistance for mass transfer at the electrolyte-electrode interface was reduced markedly compared to that of the grain boundary.

Abstract: Fe-based alloy is widely used for its good wear resistance and high performance-to-price ratio compared with other alloys. Laser cladding is a kind of valid method of metal surface modification, which has been successfully employed to modify the microstructure and/or composition of the near surface region to improve the wear, corrosion and oxidation resistance of a ferrite-based alloy component. In this paper, the recent research status in laser clad ferrite-based alloys is reviewed. The rules of designing laser cladding materials are introduced. The main problems and the solutions of the laser cladding materials application are analysized. The development tendency of laser cladding is forecast.

Abstract: Er³⁺ doped ZnO-TiO₂ nanofibers with diameter of 100～200 nm were prepared by electrospinning mothed after calcined at high temperature, using polyvinylpyrrolidone(PVP), Zn(NO₃)₂·6H₂O, Er(NO₃)₃·5H₂O, Ti(OC₄H₉)₄ as raw materials. The composite nanofibers were characterized by XRD, SEM, and UV-V respectively. Effects of different calcined temperatures on structure and photocatalytic degradation were investigated. The results indicated that the crystallinity becomes better with the increasing of calcination temperature. The composite nanofibers had the best effects of photocatalytic degradation of methylene blue, when Er³⁺ doping content was 0.3 wt.% and calcined temperature was 500 °C.

Abstract: In this paper, the effect of MnO₂ addition the infrared emissivity on ZrO₂-Al₂O₃-SiO₂ low thermal conductivity materials was investigated. The phase and microscopic morphology of the samples with the heat treatment at different temperatures were characterized by XRD and SEM. The results show that the infrared emissivity of ZrO₂-Al₂O₃-SiO₂ materials increased nearly 7% to 0.911 by adding 10 wt% MnO₂. After heat treatment at different temperature, the main phase of ZrO₂-Al₂O₃-SiO₂ materials were t-ZrO₂ and mullite, ZrO₂-Al₂O₃-SiO₂ materials with MnO₂ addition were molten and the phase composition was t-ZrO₂, Al₂O₃, and m-ZrO₂.

Abstract: In the experiment, the tetrabutyl titanate and lanthanum nitrate were used as raw material, lanthanum doped TiO₂ powder was prepared by sol-gel method, were characterized by using XRD, UV-vis, IR to determine the crystal structure, grain size and spectral properties. The results showed that the calcination temperature is 600 °C, lanthanum doping ratio is 0.6%, the amount of catalyst is 50mg and the visible light photocatalytic degradation time at 60min, the degradation of methyl orange solution rate of 20mg/L can reach 36%. Samples with anatase as the main, in the catalyst preparation process, due to the synergistic effects of lanthanum doping, the modified TiO₂ absorption band of different redshift, enhanced the catalytic activity of TiO₂ visible light.