Bi对Ba（Sn0．1Ti0．9）O3陶瓷介电性质的调节作用

采用传统的固相反应烧结工艺制备出了Ba1．3xBi2x（Ti0.9Sn0.1）O3（x=0,0．1％，0．2％，0．4％，0．6％，0．8％，1．0％，1．2％，1．4％）9种铁电陶瓷，利用XRD和介电温谱对陶瓷的物相结构与相变特性进行了研究。结果表明，产物为单相钙钛矿结构，Bi的A位轻量替代可以对陶瓷的介电性质和相变温度产生很大影响，随Bi元素在A位替代量的增加陶瓷从一般铁电体向驰豫铁电体转变，且弥散相变特征加重。     

Ba（Sn0．1Ti0．9）O3粉体的熔盐法制备与性质

采用熔盐法研究了Ba（Sn0．1Ti0．9）O3铁电体粉体的制备工艺和粉体性质。探讨了在熔盐催化下，合成温度对Ba（Sn0．1Ti0．9）O3反应完全程度及粉体形态的影响。结果表明，当反应温度达到900℃时，在熔盐环境下即可合成单相固体Ba（Sn0．1Ti0．9）O3，随着反应温度提高，粉体尺寸变化不大，但当温度超过950℃时出现晶粒异常长大趋势。烧结陶瓷的形貌和介电性质显示陶瓷粉体烧结活性好且介电性质优良。     

固相反应法研究BaTiO3粉末的相变和微观结构的转变

以国产亚微米级BaCO3和TiO2为原料,采用砂磨固相法合成粒径小、四方性高的BaTiO3粉体,同时研究煅烧温度、升温速率及保温时间对BaTiO3平均粒径和四方性的影响。结果表明,通过固相反应合成BaTiO3的反应机理可分为两个阶段:当煅烧温度低于900℃时,BaCO3和TiO2首先形成立方相的BaTiO3,当煅烧温度升至900℃时,立方相BaTiO3开始向四方相转变。在升温速率为5℃/min,煅烧温度为900℃保温5 h时,制备出粒径为180.7 nm,四方性(c/a)为1.0086的超细BaTiO3粉体。该工作为制备超薄层MLCC用高性能BaTiO3粉体提供了较好的研究思路。     

Characterization of BaSnO3-based ceramics: Part 1. Synthesis, processing and microstructural development

The compound BaSnO₃ together with its Ca- and Sr-analogs, has recently been projected as potential electronic ceramic material (thermally stable capacitor, chemical sensor for humidity, CO and NO_x, etc.). In order to fill the information gaps in the reported research, a vigorous and systematic investigation on these exotic materials has been initiated. A thorough study of BaSnO₃ with respect to its synthesis, processing and microstructural characterization has been made. In order to establish a standard methodology for low-cost mass-manufacturing with identical and beneficial microstructure and reproducible electrical characteristics, different synthesis routes (solid-state and self-heat-sustained) were adopted. Evolution of microstructure which is intimately related to the envisaged properties in the ceramics, was closely and systematically followed in terms of sintering over a wide range of temperatures and soak time. This communication forms the first of two parts in a series of investigations on MSnO₃ systems, where results on the synthesis and processing of “phase pure” barium stannate (BaSnO₃) and development of interesting microstructure are presented.     

Wet routes of high purity BaTiO3 nanopowders

High purity BaTiO₃ nanopowders were prepared in wet routes through stearic acid gel (SAG) and acetic acid gel (AAG) techniques, respectively. BaTiO₃ samples were characterized by X-ray diffraction, transmission electron microscope, Fourier transform infrared spectrometry, X-ray fluorescence spectrometry, and thermal gravimetric analysis. The present results indicate that both methods have a similar reaction process during calcination, while BaTiO₃ crystallites were initially formed at 550 °C by SAG and 800 °C by AAG. Both methods could produce BaTiO₃ powders with a cubic perovskite structure, while they had different grain size distributions within 25–50 nm for SAG and 50–80 nm for AAG. BaTiO₃ samples prepared by SAG had a lower agglomeration than those by AAG. SAG has shown many distinctive advantages in the preparation of high purity BaTiO₃ nanopowders, without Ba and Ti losses and hazardous wastes.     

Ion tracks and microstructures in barium titanate irradiated with swift heavy ions: A combined experimental and computational study

Tetragonally structured barium titanate (BaTiO₃) single crystals were irradiated using 635 MeV ²³⁸U⁺ ions to fluences of 1 × 10⁷, 5 × 10¹⁰ and 1.4 × 10¹² ions cm^?2 at room temperature. Irradiated samples were characterized using ion channeling, X-ray diffraction, helium ion microscopy and transmission electron microscopy. The results show that the ion-entry spot on the surface has an amorphous core of up to ～10 nm in diameter, surrounded by a strained lattice structure. Satellite-like defects around smaller cores are also observed and are attributed to the imperfect epitaxial recrystallization of thermal-spike-induced amorphization. The critical value of the electronic stopping power for creating observable amorphous cores is determined to be ～22 keV nm^?1. Molecular dynamics simulations show an amorphous track of ～1.2 nm in radius under thermal energy deposition at 5 keV nm^?1; the radius increases to ～4.5 nm at 20 keV nm^?1. A linear fit of the core diameter as a function of the square root of the energy deposition rate suggests a reduction in the diameter by an average of ～8.4 nm due to thermal recrystallization if electron–phonon coupling efficiency of 100% is assumed. The simulation also reveals details of the bonding environments and shows different densities of the amorphous zones produced at different energy deposition rates.     

The size-effect on luminescence properties of BaTiO3:Eu nanocrystallites prepared by the sol–gel method

Luminescence investigations of nanocrystalline (nc) BaTiO₃ powders doped with Eu³⁺-ions prepared by the sol–gel method is described. A stability of Eu³⁺-ions replacing Ba²⁺-sites up to 1100 °C is reported. The effect of BaTiO₃ grain sizes on luminescence properties of Eu³⁺ was noticed. To explain these differences a detailed analysis of luminescence spectra by the Judd–Ofelt theory has been performed.     

以锡酸钠为主盐的AZ91D镁合金化学转化处理工艺

利用扫描电镜(SEM)、X射线光电子能谱(XRD)和全浸蚀试验等手段,研究了AZ91D镁合金锡酸盐化学转化膜的形貌特征及耐腐蚀性。溶液主要成分包含Na2SnO3、NaOH、乙酸钠和适量添加剂。结果表明,转化膜主要由镁的α相、β相和MgSnO3.3H2O组成;该环保型化学转化新工艺可获得银白色膜层,表面由近球状颗粒构成,孔隙分布均匀,膜层厚度在微观尺寸上较均匀。该膜层可以对AZ91D镁合金提供有效的保护。     

Pyroelectric and electrocaloric effect of 〈1 1 1〉-oriented 0.9PMN-0.1PT single crystal

In this paper, the polarization vs. electric field hysteresis loops of 〈1 1 1〉-oriented 0.9PbMg_1/3Nb_2/3O₃-0.1PbTiO₃ (0.9PMN-0.1PT) single crystal at different temperatures (20-110 °C) were measured. The adiabatic temperature change ΔT of 〈1 1 1〉-oriented 0.9PMN-0.1PT single crystal due to the application or withdraw of electric field were calculated through the thermodynamic relation. The largest temperature change ΔT achieves ∼1 K with only a change of 40 kV/cm electric field, the mechanism of the electrocaloric effect (ECE) is discussed for 0.9PMN-0.1PT crystal. The pyroelectric coefficient of 0.9PMN-0.1PT under bias field was calculated according to the data of hysteresis loop. The result shows that 0.9PMN-0.1PT have large pyroelectric coefficient under bias field, the largest (∂P/∂T)_E value achieves −0.5 μC/cm² K.     

Ultrasound studies of phase transitions in tungsten bronze ferroelectric materials

Attenuation and velocity measurements at ultrasonic frequencies were performed in two ferroelectric solid solutions with tungsten bronze structure type, SBN and PBN, as a function of temperature (from 200 to 380 K). Both materials, in polycrystalline form, presented sensitive changes in the temperature dependence curves of attenuation and velocity. One of these anomalies (at 350 K for SBN and 323 K for PBN) was associated with a second-order phase transition, confirming the ferroelectric orthorhombic–ferroelectric tetragonal phase transition suggested for both systems in this temperature range.     

Correlation between nanostructural and electrical properties of barium titanate-based glass-ceramic nano-composites

Glasses in the system BaTiO₃-V₂O₅-Bi₂O₃ have been transformed into glass-ceramic nano-composites by annealing at crystallization temperature T_cr determined from DSC thermograms. After annealing they consist of small crystallites embedded in glassy matrix. The crystallization temperature T_cr increases with increasing BaTiO₃ content. XRD and TEM of the glass-ceramic nano-composites show that nanocrystals were embedded in the glassy matrix with an average grain size of 25 nm. The resulting materials exhibit much higher electrical conductivity than the initial glasses. It was postulated that the major role in the conductivity enhancement of these nanomaterials is played by the developed interfacial regions between crystalline and amorphous phases, in which the concentration of V⁴⁺-V⁵⁺ pairs responsible for electron hopping, has higher than values that inside the glassy matrix. The experimental results were discussed in terms of a model proposed in this work and based on a “core-shell” concept. From the best fits, reasonable values of various small polaron hopping (SPH) parameters were obtained. The conduction was attributed to non-adiabatic hopping of small polaron.     

有机添加剂对AZ91D镁合金锡酸盐转化膜性能的影响

采用化学转化法在镁合金表面制备锡酸盐转化膜。采用硫酸铜点滴实验、电化学交流阻抗(EIS)测试和Tafel曲线、扫描电子显微镜(SEM)测试和X射线衍射分析(XRD)等方法检测膜层的性能。研究了几种有机添加剂(Tartaric acid、Citric acid、Phytic acid、EDTA、Sodium dodecyl sulfate)对膜层耐蚀性的影响,结果表明溶液中添加SDS后,转化膜的硫酸铜点滴时间由35 s提高到了86 s,明显提高转化膜的耐腐蚀性能,膜层的形貌为呈"颗粒"状紧凑的连接到一起,该膜层的主要成分为Mg Sn(OH)6、Mg(OH)2。     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.     

Investigation of physicochemical transformation at mechanochemical, hydrothermal and microwave treatment of barium titanyloxalate

The effect of mechanochemical (in air and water) as well as hydrothermal and microwave treatment on physicochemical transformations of barium titanyloxalate was studied. The samples were examined using XRD and thermal analysis, FTIR spectroscopy, argon thermodesorption and granulometry. Barium metatitanate is already formed during mechanochemical treatment of barium titanyloxalate in air atmosphere and the following thermal treatment at 550 °C improves its crystal structure. At the same time barium metatitanate is only formed at 800 °C in the case of usual thermal decomposition of barium titanyloxalate.Hydrothermal and microwave treatment of barium titanyloxalate promotes formation of the barium orthotitanate (Ba₂TiO₄) and barium carbonate (BaCO₃) mixture.     

Monoclinic phases and stress-relief conditions in (1 − x)Pb(Mg1/3Nb2/3)TiO3–xPbTiO3 solid solutions

A comparative study on heterophase states in perovskite-type solid solutions of (1 − x)Pb(Mg_1/3Nb_2/3)TiO₃–xPbTiO₃ is carried out for compositions near the morphotropic phase boundary. The conditions for mechanical stress relief at elastic matching of phases are analysed at x = const in a wide temperature range. The heterophase states concerned with the presence of the intermediate monoclinic phase are interpreted using the domain state–interface diagrams calculated for x = 0.28, 0.32 and 0.34. It is shown that optimum volume fraction parameters of the domains in the monoclinic phase of the B type are varied in relatively wide ranges and promote complete stress relief with cubic–monoclinic phase coexistence. Two scenarios of stress relief at x = 0.32 are considered in connection with different heterophase states (either tetragonal–monoclinic of the B type or tetragonal–monoclinic of the C type) in a wide temperature range. Possibilities of elastic matching of two polydomain phases (tetragonal–monoclinic of the B type) with almost equal relative widths of the domains in these phases are shown for x = 0.34. The active role of domains of the monoclinic phases in stress relief and forming the planar unstrained interfaces is discussed.