Controllable synthesis and growth mechanism of lead free bismuth sodium titanate nanowires

Highly uniform lead-free piezoelectric bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT) nanowires were successfully synthesized via a hydrothermal method. Synthesized at a stirring speed range of 300–1000 rpm, the compositions and orientations of BNT nanowires were well controlled. The effects of stirring speeds on the formation of BNT nanoparticles and nanowires in the hydrothermal processes were systematically investigated. The BNT nanowires with a high aspect ratio were proven to be single crystals with [110] growth direction from high-resolution TEM analysis. The mechanism of growth of BNT nanowires out of nanoparticles in the hydrothermal processes was proposed.     

催化合成柠檬酸三丁酯的新方法

研究了以钛酸四丁酯为催化剂合成柠檬酸三丁酯。探讨了催化剂用量、反应温度、酸醇摩尔比和反应时间等因素对反应结果的影响。确定最佳反应条件为：酸醇摩尔比＝1∶4.1,反应温度150 ℃,反应时间4.5 h,催化剂用量为柠檬酸质量的1.2%。在此条件下柠檬酸三丁酯的酯化率达到99%以上,产品纯度经色质联用仪(GC/MS)检测在99.5%以上。     

Low-temperature synthesis of superfine barium strontium titanate powder by the citrate method

Ba_0.6Sr_0.4TiO₃ powder was synthesized by a citrate method. The phase development was examined with respect to calcining temperature and heating rate during the calcining process. The results reveal a crucial role of the heating rate to the formation of a pure perovskite phase at low calcining temperatures. It was found that keeping relatively low heating rates ≤0.7 °C/min during the calcining process after 300 °C was favorable to a sufficient decomposition of (Ba,Sr)₂Ti₂O₅·CO₃ intermediate phase at low temperatures and consequently led to the formation of a pure perovskite phase at 550 °C. Ba_0.6Sr_0.4TiO₃ powder calcined at the temperature under the heating rate of 0.7 °C/min showed a superfine and uniform particle morphology and high sintering reactivity. As a result, the ceramic specimens prepared from the powder attained reasonable relative densities (94–95%) at sintering temperatures of 1250–1270 °C.     

Tunable structure and intensive upconversion photoluminescence for Ho3+-Yb3+ codoped bismuth titanate composite synthesized by sol-gel-combustion (SGC) method

Ho³⁺ and Yb³⁺ codoped bismuth titanate (BTO) composite powders with infrared to visible upconversion luminescence (UCL) function were prepared by SGC method. The effects of Ho³⁺ and Yb³⁺ doping content on the structure and property were investigated for BTO: xHo, 0.2 Yb (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) and BTO: 0.02Ho, yYb (y = 0.1, 0.2, 0.3, 0.5, 0.7, 0.9) samples. All the samples include three bismuth titanate phases (Bi₄Ti₃O₁₂, Bi₂Ti₂O₇, and Bi₂₀TiO₃₂), and the phase proportion can be tuned by changing Ho³⁺ and Yb³⁺ doping content. These powders are well crystalized with honeycomb-like microscopic structure, and with good absorption for 233 nm, 310 nm and 975 nm wavelength. The band gap can be tuned from 3.53 eV to 4.03 eV when increasing Yb³⁺ content from y = 0 to y = 0.9. A strong 530–580 nm green emission band and a relative weak 630–690 nm red one corresponding to Ho³⁺: ⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions appear in the UCL spectra for all the BTO: Ho, Yb samples when pumped at 980 nm. The emission intensities can well be tuned with various Ho³⁺ and Yb³⁺ content. The optimal UCL was obtained in BTO: 0.02Ho, 0.5 Yb for all the prepared samples. The energy transfer mechanism is analyzed by building a two-photon energy transfer model, which is proved by the relationship between emission intensities and pumping power measurement. The concentration quenching of Ho³⁺ is caused by cross relaxation of CR₁ and CR₂ (Ho: ⁵F₄, ⁵S₂ + ⁵I₈ → ⁵I₄ + ⁵I₇) and by CR₃ (Ho: ⁵F₄, ⁵S₂ + Yb: ²F_7/2 → Ho: ⁵I₆ + Yb: ²F_5/2) for Yb³⁺ quenching. The mean luminescence lifetime (τ_m) from Ho: ⁵S₂ decreases monotonously with the increase of Ho³⁺ and Yb³⁺ content.     

High performance Aurivillius-type bismuth titanate niobate (Bi3TiNbO9) piezoelectric ceramics for high temperature applications

This paper reports the significant improved piezoelectric properties of high temperature bismuth titanate niobate (Bi₃TiNbO₉, BTN) polycrystalline ceramics. The piezoelectric performance of BTN ceramics is significantly enhanced by cerium modifications. The dielectric measurements indicate that the Curie temperature T_c gradually decreases over the temperature range of 907–889 °C with cerium contents increasing up to 0.7 wt%. The BTN-5Ce (BTN+0.5 wt% CeO₂) exhibits optimized piezoelectric properties with a piezoelectric constant d₃₃ of 16 pC/N, which is five times the value of unmodified BTN (d₃₃~3 pC/N), while BTN-5Ce maintains a high Curie temperature T_c of 894 °C. The temperature-dependent electrical impedance and electromechanical coupling factors (k_p, and k_t) reveal that the BTN-5Ce exhibits thermally stable electromechanical coupling characteristics up to 500 °C but significantly deteriorates at 600 °C due to high conductivity at a higher temperature. The thermally stable electromechanical properties in combination with the ceramics׳ high electrical resistivity (10⁶ Ω cm at 500 °C) and high Curie temperature (~900 °C) demonstrate that cerium-modified BTN ceramics are good materials for high temperature sensing applications.     

The temperature-dependent piezoelectric and electromechanical properties of cobalt-modified sodium bismuth titanate

Lightly cobalt-modified, Aurivillius-type, sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) ceramics were synthesized by substituting a small amount of cobalt ions onto the Ti⁴⁺ sites using conventional solid-state reaction. X-ray photoelectron spectroscopy (XPS) analysis coupled with bond valence sum calculations show that the dopant cobalt ions substitute for Ti⁴⁺ ions in the form of Co³⁺. The resultant cobalt-modified NBT ceramics (NBT-Co) exhibit better piezoelectric and electromechanical properties by comparison with pure NBT. With only 0.3 wt% Co³⁺ substitution, the piezoelectric properties of the NBT-Co ceramics are optimal, exhibiting a high piezoelectric coefficient (d₃₃~33 pC/N), a low dielectric loss tan δ (~0.1% at 1 kHz), a high thickness planar coupling coefficient (k_t~34%) as well as a high Curie temperature (T_c~663 °C). Such NBT-Co ceramics exhibit nearly temperature-independent piezoelectric and electromechanical properties up to 400 °C, suggesting that these cobalt-modified NBT ceramics are promising materials for high temperature piezoelectric applications.     

钛酸铋纳米粉体的水热合成与分散

以四氯化钛和硝酸铋为原料,氢氧化钾为矿化剂,在220~260℃水热合成6 h,制备出发育良好的纳米级钛酸铋粉体,并对所得粉体进行了不同方式的分散。借助XRD,SEM,TEM及FT-IR等手段对钛酸铋的晶相组成、粒度、形貌等进行了分析。研究结果表明:所得钛酸铋晶粒的形状为矩形片状,宽度在30 nm左右,长度大于100 nm;未经分散的钛酸铋粉体有团聚现象,团聚体的直径可达500 nm左右,将钛酸铋粉体分散于由正硅酸乙酯、丙烯酸、无水乙醇按一定的配比配成的混合液中,然后用高剪切分散乳化机分散处理,可破坏粉体的团聚,具有很好的分散效果。     

Facile synthesis,novel structure,multicolor luminescence,and potential applications of lanthanide ions doped bismuth titanate phosphors

A variety of lanthanide ions doped bismuth titanate (Bi₄Ti₃O₁₂) luminescent materials with eminent down-conversion (DC) and up-conversion (UC) luminescence performance have been fabricated via a facile sol-gel approach. The XRD, XPS, and EDX elemental mapping results confirm the phase structure of orthorhombic Bi₄Ti₃O₁₂ (BTO), and the lanthanide activator ions occupy the Bi³⁺ lattice sites in the BTO crystal. Under UV or NIR excitation, the Eu³⁺, Yb³⁺/Ln³⁺ (Ln = Er, Tm, and Ho) doped Bi₄Ti₃O₁₂ samples exhibit characteristic red, green, blue, and green emissions. The luminescent mechanisms of the BTO:Eu³⁺ and BTO:Yb³⁺/Ln³⁺ samples are discussed based on the energy level diagrams. The doping concentrations of Eu³⁺, Yb³⁺, Er³⁺, Tm³⁺, Ho³⁺ ions and annealing temperature and time are optimized, whose optimal values are determined to be 14, 8, 1, 0.4, 1 mol% and 800 ^oC, 4 h. The as-obtained LED devices fabricated by Bi₄Ti₃O₁₂:Eu³⁺ and Yb³⁺/Ln³⁺ phosphors exhibit dazzling multicolor visible light emissions from different Ln³⁺ ions. The results indicate that the as-obtained Ln³⁺ doped BTO phosphors may be potentially utilized in LED devices and solid-state lighting. Furthermore, the Eu³⁺ and Er³⁺ co-doped BTO samples exhibit different DC and UC luminescence spectral profiles when excited at various UV, visible, or NIR wavelengths, revealing their eminent feasibility and great potential in anti-counterfeiting applications.     

水热合成掺镧钛酸铋粉体及其光催化性能探讨

以硝酸铋、四氯化钛和硝酸镧为原料,以氢氧化钾为矿化剂,采用水热法合成了不同镧掺杂量的钛酸铋粉体.用X射线衍射(XRD)和透射电镜(TEM)对所得粉体进行了表征,借助紫外-可见分光光度计考察了样品降解甲基橙的光催化性能.实验结果显示:在水热合成温度为220～280 ℃、保温时间为6 h的条件下,可得到各向异性、短轴为30 nm、长轴大于100 nm的掺镧钛酸铋粉体,且该方法所制备的掺镧钛酸铋(Bi 4-xLaxTi3O12)粉体具有一定的光催化效果.     

Anisotropic effects of oxygen vacancy defects on the electrical properties of highly oriented bismuth titanate ferroelectric ceramics

Bismuth titanate (Bi₄Ti₃O₁₂, BIT) exhibits a high Curie temperature and anisotropic electrical performance owing to its layered perovskite structure, and hence, it is an important ferroelectric material for high-temperature piezoelectric applications. It is crucial to understand the effects of the anisotropy in BIT-based ferroelectrics for developing novel high-temperature piezoelectric materials. In this study, a highly textured BIT ceramic was fabricated using the tape-casting technique from highly grain-oriented BIT platelets prepared by the molten salt method. The textured BIT ceramic showed a dense microstructure and high grain orientation along the (00l) plane with a texturing degree F_00l = 0.86. It exhibited significant anisotropy in the electrical properties along the directions parallel and perpendicular to the axis of the tape-casting plane. Double ferroelectric hysteresis P–E loops and normal ferroelectric P–E loops were observed in the parallel and perpendicular samples, respectively. In addition to the layered crystal structure and domains, the anisotropy in the arrangement of the oxygen vacancy defects and their transport in the structure led to a significant anisotropy in the ferroelectric properties of the textured BIT ceramics. This work demonstrates the anisotropic arrangement of the oxygen vacancy defects and its effect on the electrical properties of high-temperature bismuth layer-structured ferroelectrics.     

Glycothermal法制备钛酸铋镧纳米晶

以分析纯Bi2O3、La2O3、TiCl4为原料,NaOH为矿化剂,通过Glycothermal法制备了具有板状形貌的钛酸铋镧(BLT)纳米晶。采用X线衍射(XRD)和场发射扫描电镜(FESEM)等测试手段对纳米晶的微结构进行了表征,并研究了醇水体积比、反应时间和矿化剂加入量等因素对晶粒尺寸、形貌及结晶性的影响关系。结果表明:BLT纳米晶尺寸随醇水体积比增加而减小;随着反应时间的延长,晶粒尺寸与结晶度逐渐增大;随着矿化剂量的增加,晶粒宽厚比逐渐增大。当醇水体积比为1∶5、反应时间为24 h、矿化剂引入量为0.266 mol/L时,BLT纳米晶宽厚比可达2.67。     

水热法制备NaY型分子筛及其催化合成柠檬酸三丁酯

以正丁胺为模板剂,采用水热法制备了NaY型分子筛,用XRD、SEM和TG-DTA等手段对分子筛进行表征,研究了晶化时间、晶化温度、投料顺序和添加NaCl对制备的分子筛性能的影响,原料中添加NaCl,423 K晶化50 h,制备的NaY型分子筛结晶度高,颗粒均匀,粒径约1 μm.用制备的分子筛分别负载CuO-ZnO<,2...     

Low-temperature synthesis of nanosized bismuth ferrite by the soft chemical method

This paper describes research on a simple low-temperature synthesis route to prepare bismuth ferrite nanopowders by the polymeric precursor method using bismuth and iron nitrates. BiFeO₃ (BFO) nanopowders were characterized by means of X-ray diffraction analyses, (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy (Raman), thermogravimnetric analyses (TG-DTA), ultra-violet/vis (UV/Vis) and field emission scanning electron microscopy (FE-SEM). XRD patterns confirmed that a pure perovskite BiFeO₃ structure with a rhombohedral distorted perovskite structure was obtained by heating at 850 °C for 4 hours. Typical FT-IR spectra for BFO powders revealed the formation of a perovskite structure at high temperatures due to a metal–oxygen bond while Raman modes indicated oxygen octahedral tilts induced by structural distortion. A homogeneous size distribution of BFO powders obtained at 850 °C for 4 hours was verified by FE-SEM analyses.     

Synthesis of barium strontium titanate nanopowders by microwave hydrothermal method

Barium strontium titanate (BST) powders of high purity, good crystallinity and well dispersed with a diameter of 50–90?nm are prepared by microwave hydrothermal method using tetrabutyl titanate, barium nitrate and strontium nitrate as the main raw materials. The phase composition, element composition and microstructure of the powders are characterised by X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive spectroscopy and transmission electron microscopy. The results show that Ba_0.6Sr_0.4TiO₃ powders could be synthesised under the conditions that the reaction temperature is 70°C, the reaction time is 10?min, and the value of pH is 14, which indicates that the reaction temperature, time and the value of pH have a great effect on the crystallinity of nanopowders, and the dispersant (OP-10) plays a role in the dispersion of the nanopowders.     

pH对溶胶-凝胶法合成钛酸镍纳米晶的影响

以无机镍盐和钛酸四丁酯为起始原料,乙醇为溶剂,柠檬酸为螯合剂,乙酰丙酮为络合剂,采用溶胶-凝胶法在不同的pH下制备了钛酸镍纳米晶。采用X射线衍射(XRD) 、综合热分析仪（TG-DSC）以及透射电子显微镜（TEM）对制备的纳米晶进行了测试和表征。结果表明：NiTiO3的合成温度为550～700 ℃;在酸性条件下更易获得单一物相的钛酸镍纳米晶;并且随着pH的增加,粉体的纯度降低,平均粒径有增大的趋势;当pH为0.5时,粉体为单一物相的钛酸镍纳米晶,且晶粒形貌为六方形。     

柠檬酸三辛酯的合成

以硫酸作催化剂,柠檬酸和辛醇(2 乙基己醇)酯化反应生成柠檬酸三辛酯,其最佳工艺条件为:酯化温度150～155℃,催化剂加入量0 20%,过量醇含量17%,碱洗碳酸钠溶液的浓度为4%,碱洗温度为90℃,脱醇真空为20kPa,脱醇温度为145℃,活性炭加入量为0 10%,产品收率大于98%。     

钛酸锶钡压电陶瓷超细粉体的水热法合成

采用水热工艺制备不同组成的BaxSr1-xTiO3(BST)，利用FT-IR，XRD，TEM等技术分析了水热反应转变机理及相结构转变情况，同时对影响合成的工艺参数以及不同组成材料的居里温度变化进行了研究。结果表明：获得的BST粉体颗粒粒度较细，粒径为20～40nm。其最佳的工艺参数为n(Ba)／n(Ti)=3，n(Sr)／n(Ti)=1／4或者n(Ba)／n(Ti)=1／3，n(Sr)／n(Ti)=4／5，cKOH=1．5～2mol／L。制得不同组成粉体的居里温度呈规律性变化。     

草酸法超细钛酸钡的工业化生产

介绍了草酸共沉淀法工业化生产BaTiO3过程中TiCl4的精制,TiCl4的稀释及化合共沉淀过程等工艺条件的控制,生产的BaTiO3完全达到电子行业及汽车反光材料的要求。     

Enhanced piezoelectric properties of Aurivillius-type sodium lanthanum bismuth titanate (Na0.5La0.5Bi4Ti4O15) by B-site manganese modification

The Aurivillius-type bismuth layer-structured ferroelectrics (BLSFs) sodium lanthanum bismuth titanate (Na_0.5La_0.5Bi₄Ti₄O₁₅, NLBT) polycrystalline ceramics with 0.0–0.4 wt% MnO₂ were synthesized using conventional solid-state processing. Phase analyses were performed by X-ray powder diffraction (XRPD), and the microstructural morphology was assessed by scanning electron microscopy (SEM). The dielectric and piezoelectric properties of the manganese-modified NLBT ceramics were investigated in detail. The results show that manganese is very effective in promoting the piezoelectric activities of NLBT ceramics, and the reasons for piezoelectric activities enhancement by manganese modification are explained. The NLBT ceramics modified with 0.2 wt% MnO₂ (NLBT-Mn2) possess good piezoelectric properties, with a piezoelectric coefficient d₃₃ of 28 pC/N. This value is the highest value among the modified NLBT-based piezoelectric ceramics examined. The temperature-dependent dielectric spectra show that the Curie temperature T_c of the manganese-modified NLBT ceramics is slightly higher than that of the pure NLBT ceramics. Thermal annealing analysis revealed that the manganese-modified NLBT ceramics possess good thermal stabilities up to 500 °C. These results demonstrate that the manganese-modified NLBT ceramics are promising materials for high temperature piezoelectric applications.