Enhanced room-temperature magnetoelectric effect in xBi0.5Na0.5TiO3-(1-x)NiFe2O4 ceramics by magnetic field annealing

Journal of Electroceramics - The polycrystalline xBi0.5Na0.5TiO3-(1-x)NiFe2O4 solid solutions with different ratios have been synthesized by sol-gel method. The samples are respectively annealed...     

Electrochromic property of the viologen-anchored mesoporous TiO2 films

The electrochromic properties of the viologen-anchored mesoporous TiO₂ (Meso-TiO₂) films were investigated in this work. The Meso-TiO₂ films, synthesized by evaporation-induced self-assembly (EISA) process, deposited on ITO electrodes were a worm-like structure with an average pore diameter of 7.0 nm. The electrochromic devices (ECDs) fabricated from the Meso-TiO₂ demonstrated 3 times of coloration efficiency and considerably faster switching response, compared with those from the nanocrystalline films made of the 7 nm-sized TiO₂ nanoparticles. The advantage of the Meso-TiO₂ would originate from the well-organized mesopore structures, offering an efficient electrolyte transport as well as the fast electron transfer from the ITO electrode to the anchored viologen.     

Photocatalytic property of TiO2 loaded with SnO2 nanoparticles

2.5 nm-sized SnO₂ nanoparticles in rutile phase were loaded on the surface of 25 nm-sized TiO₂ (Degussa P-25) to form SnO₂/TiO₂ nano-composite structure. Up to 10 mol%, the loaded SnO₂ nanoparticles were well-dispersed on the surface of TiO₂ without mutual agglomeration. The SnO₂/TiO₂ with 1 mol% of SnO₂ demonstrated 1.5–1.7 times of photocatalytic activity compared to the pure TiO₂ in decomposing gaseous 2-propanol and in evolving CO₂. The role of SnO₂ nanoparticles on TiO₂ surface is considered to be retardation of recombination rate between electrons and holes by trapping the photo-excited electrons from the conduction band of TiO₂.     

Dielectric properties of Zn- and/or Nb-substituted Pb[(Mg1/3Ta2/3),Ti]O3 ceramics

Ceramic powders of Pb[(Mg_1/3Ta_2/3),Ti]O₃, with the octahedral components substituted separately as well as simultaneously by Zn and Nb, were synthesized by a two-step B-site precursor method. Prepared powders were examined by X-ray diffraction (XRD) to monitor the phase developments and also to determine the crystallographic aspects. The weak-field low-frequency dielectric constant and loss values of the sintered specimens were determined. Temperature-dependent dielectric constant values were further analyzed in terms of diffuseness/sharpness in the phase transition modes. The internal microstructures of the ceramics were examined by scanning electron microscopy (SEM).     

Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO

The effects of CuO and TiO₂ additives on the microstructure and microwave dielectric properties of Al₂O₃ ceramics were investigated. Al₂O₃ ceramics with CuO and TiO₂ additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti₄Cu₂O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO₂ content, due to the formation of the second phase Ti₄Cu₂O. However, the varying behaviors of the dielectric constant (ɛ _r ) and temperature coefficients (τ _f ) were associated with phase constitutions, as a result of the change of CuO and TiO₂content. The τ _f can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO₂. The specimens with 0.5 wt.% CuO and 7 wt.% TiO₂ sintered at 1,360 °C for 4 h showed ɛ _r of 11.8, Qf value of 30,000 GHz, and τ _f of −7 ppm/°C.     

Influence of anatase-rutile phase transformation on dielectric properties of sol-gel derived TiO2 thin films

The phase transformation behavior and resulting dielectric properties of sol-gel derived TiO₂ thin films were investigated. Thin films showed a typical behavior of mixture systems during the phase transformation; a kinetic investigation on the isothermal curve of pre-crystallized thin films revealed that the phase transformation was a first-order reaction with an Avrami time component of 1. Dielectric constants of TiO₂ thin films increased with the increasing amount of the rutile phase while the dielectric losses showed the opposite relationship. From a fitting process using the parallel mixing rule, dielectric constants of two end members of the mixture system were calculated to be 41.4 and 145.2 for the pure anatase and rutile phase thin films, respectively.     

Piezoelectric ceramics of (Bi1/2Na1/2)TiO3-PbTiO3-BaTiO3 system

Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi_1/2Na_1/2)TiO₃(BNT)-based solid solution, that is, (Bi_1/2Na_1/2)(_1-x)(Pb_a Ba_b)_xTiO₃(a + b = 1) [BNPB(100x-100a/100b)], are studied from the viewpoint of a new group of lead-free or low-lead content piezo-electric ceramics with a rhombohedral(F_a-tetragonal (F_β) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling. X-ray diffraction data, dielectric properties and D-E hysteresis loops show that the MPB exist near (Bi_1/2Na_1/2)TiO₃[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high-frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε₃₃Tε₀, and a high electromechanical coupling factor k₃₃, along with a high mechanical strength.     

Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTiO₃-0.8Li_0.5Nd_0.5TiO₃) have been prepared by the mixed oxide route using additions of Bi₂O₃-2TiO₂ (up to 15 wt%). Powders were calcined 1100^∘C; cylindrical specimens were fired at temperatures in the range 1250–1325^∘C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1–2 μm in size. With increasing levels of Bi₂O₃-2TiO₂ additions, needle and lath shaped second phases developed. For Bi₂Ti₂O₇ additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ _f ) increased from −28pp/^∘C to +22pp/^∘C. A product with temperature stable τ _f could be obtained at ∼2 wt% Bi₂Ti₂O₇ additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ _f becomes increasingly negative.     

TiO2用于锌空电池阴极催化剂的研究

介绍了一种应用于氧还原电极的新型催化剂--TiO2.以TiCl4一步水蒸气水解法制备在活性炭(AC)上负载均匀分布的粉状TiO2/AC,制作成空气电极并组装成空气电池,利用X射线衍射(XRD)、电化学阻抗(EIS)对催化剂粒子的大小、物相和半导体催化剂电极性能进行了分析,优化了空气电极的性能、各成分用量和工艺参数,用稳态极化曲线法和恒电流放电法测试电极性能.结果显示,400℃煅烧制得粒径约为16.5 nm的锐钛矿型TiO2,且对O2的还原有一定的催化作用,电流密度在150 mA/cm2时端电压保持在0.8 V以上.     

电解液对TiO2混合电化学电容器性能的影响

采用溶胶-凝胶法制备掺杂Ni、C改性的TiO2电极材料,并对材料的晶型结构、表面形貌及比容量、充放电效率、循环性能、阻抗、比能量和比功率等性能进行了研究.使用1mol/L MeEt3NBF4/PC电解液的电容器,具有良好的可逆性和稳定的循环性能.在500 mA/g的电流下,比容量为13.40mAh/g,放电比能量为24.12Wh/kg,比功率为1012.03W/kg.     

负载型TiO2在双脉冲放电水处理中的应用

在双脉冲放电等离子体水处理过程中,会伴有光辐射等物理效应,而光催化剂可以利用这部分的光辐射能量。为此,研究了在气液固三相混合体双极性脉冲放电条件下添加光催化剂的方式,以及其对于有机污染物降解所起到的效果。利用溶胶-凝胶法制备负载型的纳米TiO2光催化剂,选择典型的染料废水靛蓝二磺酸钠作为处理对象,检验其对于染料废水降解的催化处理效果。实验结果表明:当固相的玻璃珠上负载了纳米TiO2光催化剂时,靛蓝溶液的降解效率有了一定程度的提高,并且2次镀膜负载TiO2光催化剂时的催化处理效果优于1次镀膜时的催化处理效果。电压增大,催化处理效果提升的程度减小,气体体积流量升高,催化处理效果会略有提高。在电压为30kV、气体体积流量为1.0m3/h的条件下,放电处理3min就可以使靛蓝溶液完全褪色。     

纳米TiO2的制备及其在水处理应用方面的发展

纳米 Ti O2 作为光催化环境材料能有效降解多种有害的污染物 ,使有害物质矿化为 CO2 、H2 O及其他无机小分子物质 ,因此光催化降解水中有机污染物是一项新兴的颇有发展前途的废水处理技术。综述了纳米Ti O2 的制备、光催化降解水中有机污染物的机理、动力学规律及其研究现状和发展方向     

富钛 BaO-TiO2系微波介质陶瓷的物相分析

探讨了富钛BaO_TiO2(Ti/Ba=4~4.5)系微波介质陶瓷成分以及预烧温度对物相组成的影响。分析表明,当预烧温度为900℃时,已经有一定量的BaTi4O9相生成,但是主相仍为BaTiO3;随着预烧温度的升高,主相转变成BaTi4O9,而BaTiO3和TiO2逐渐减少直至消失;到1 200℃时,都形成了BaTi4O9单相。同时发现TiO2能促进BaTi4O9相的形成。此外,在研究的成分中都没有形成Ba2Ti9O20相。     

Optimized electrical properties of (Bi 1/2 K 1/2 )TiO 3 - bi(Mn 2/3 Sb 1/3 )O 3 lead-free ceramics in mixing phase region

A new lead-free (1-x)(Bi1/2K1/2)TiO3-xBi(Mn2/3Sb1/3)O3 (BKT-BMS) piezoelectric ceramics were prepared by conventional solid-state route. The experiments show that the addition of BMS induces the occurrence of a mixed tetragonal and pseudocubic phases, and the fraction of tetragonal to pseudocubic phases closes to 50:50 around the composition x = 0.015, at where the dielectric, ferroelectric and piezoelectric properties is optimized. It is highlighted that the Td for the composition x = 0.015 keeps at an adequately-high level around 205 °C. All these competitive properties of the composition x = 0.015 demonstrate the potential application for lead-free piezoelectric ceramics over a broad temperature range.     

Space-phase 2D simulation of electromechanical transformation in electrical machines

A space-phase method for the mathematical simulation of electromechanical energy transformation in electrical machines of rotational motion is proposed. Results of numerical experiments with two-dimensional space-phase models of a reverse-design valve machine with constant magnets are presented.     

Preparation of Si doped molecularly imprinted TiO2 photocatalyst and its degradation to antibiotic wastewater

TiO₂, molecularly imprinted TiO₂ (TiO₂/OTC) and a novel Si doped molecularly imprinted TiO₂ (TiO₂/SiO₂/OTC) nano photocatalytic materials were prepared by liquid phase deposition method. The products were characterized by XRD and SEM. The photocatalytic activities of the samples were evaluated by the photocatalytic degradation of oxytetracycline wastewater under a xenon lamp irradiation. The results showed that TiO₂/SiO₂/OTC and TiO₂/OTC could improve both the photocatalytic activity and the molecular recognition ability, while the photocatalytic activities of TiO₂/SiO₂/OTC sample was more effective than TiO₂/OTC sample with 5 times reuse. The photocatalytic activity of TiO₂/SiO₂/OTC photocatalyst sample had a greater improvement and its photocatalytic degradation of oxytetracycline wastewater reached 80.79% in 120 minute reaction.     

Effect of nano-sized TiO2 powder on Ag-electrode in piezoelectric multilayer devices

The objective of this study is to present sintering shrinkage behavior of Ag-Pd electrode powders with TiO₂ nano-particle addition and the matching characteristics to a piezoelectric ceramics, Pb(Zr,Ti)O₃. The densification of the nanoparticle TiO₂-added electrode paste followed the TiO₂ solid state diffusion-controlled mechanism upon sintering process. Reaction between ceramic and electrode layers with the TiO₂ nano-particle powder allows internal stress to be reduced and mechanical bonding strength to be increased. High adhesive strength and good electrical conductivity of more than 10⁴/Ω cm could be obtained in the multilayer ferroelectric structure. In order to understand the effectiveness of the nano-TiO₂ doped electrode for multilayer device, the multilayer ceramic actuators containing Ag-based electrode without and with nano-sized TiO₂ powder were fabricated and evaluated each other. Both the samples exhibited similar piezoelectric and dielectric properties.     

Dielectric and piezoelectric properties of La2O3 doped (Bi0.5Na0.5)0.92(Ba0.8Sr0.2)0.08 TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.92(Ba_0.8Sr_0.2)_0.08 TiO₃+x mol% La₂O₃(x = 0, 0.1, 0.3, 0.5, 0.8) were synthesized by conventional solid state reaction. The crystal structure of all compositions is mono-perovskite ascertained by XRD. The grain size decreased and diffuse phase transition behavior was more evident with the increasing amount of La₂O₃. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p showed the maximum value of 165 pC/N and 0.322 at 0.3% and 0.1% La₂O₃ addition, respectively, and rapidly decreased when La₂O₃ addition over 0.5%. The loss tangent tanδ linearly increased and the mechanical quality factor Q_m linearly decreased with the increasing amount of La₂O₃.     

Sb_2S_3/TiO_2纳米棒的构筑及其在杂化太阳电池中的应用

采用水热法在FTO导电玻璃基底上,制备了一维有序的TiO_2纳米棒阵列。采用化学浴沉积方法在TiO_2纳米棒有序阵列上沉积Sb_2S_3纳米粒子,形成壳核式Sb_2S_3/TiO_2复合纳米棒阵列结构。通过控制化学浴的沉积时间,可以得到不同厚度Sb_2S_3纳米粒子壳层。通过电子扫描电镜(SEM)、X射线衍射(XRD)、能谱分析(EDS)、以及紫外-可见漫反射吸收光谱(UV-Vis DRS)等对样品形貌、结构组成以及光性能进行了测定和分析。最终基于P3HT/Sb_2S_3(3 h)/TiO_2为光电极所组装的杂化太阳电池能量转换效率最高,获得了1.15%的能量转换效率。     

Fabrication of amorphous bulk and multi-phase ceramics by melting method in the HfO2-Al2O3-Gd2O3-Eu2O3system

Ceramics have generally been fabricated from powders by shape forming & sintering methods except for glasses and glass ceramics. Glasses and glass ceramics can be fabricated by melting methods. The melting method has not only higher productivity but also higher shape forming ability than powder processes via forming & sintering methods. Thus we have reinvestigated melting methods in binary and ternary oxides systems to fabricate amorphous bulk ceramics and bulk nano composites. We have successfully fabricated amorphous phases by simple melt solidification methods in ternary eutectic melts in the HfO₂-Al₂O₃-Gd₂O₃system. The present study demonstrates the formation of the amorphous phases in quaternary systems HfO₂-Al₂O₃-Gd₂O₃-Eu₂O₃. Furthermore, we have also succeeded to fabricate nano-structured bulk ceramics, which consisted of constituent oxide grains with 20–100 nm in size, by post annealing of the amorphous phase.