Dielectric behaviour and magnetoelectric effect in Ni0·25Co0·75Fe2O4-Ba0·8Pb0·2TiO3 ceramic composites

Abstract

Dielectric and magnetoelectric properties are reported in magnetoelectric (ME) composites containing lead doped barium titanate as the electrical component and a mixed Ni-Co ferrite as the magnetic component. Changes were observed in dielectric properties as well as in the ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 0·42 mV cm ^{- 1} Oe ^{- 1} (52·78 VA ^{- 1}) was observed in the composite containing 15 mol-% ferrite. Larger ME effects were observed in composites with higher contents of ferroelectric phase. This conclusion differs from earlier theoretical studies which predict a large ME interaction in composites with a 1:1 molar ratio of participating phases. Apart from the technological importance of the ME effect, some anomalies in magnetic phase transition induced by electric fields are also of scientific interest. The variation in dielectric properties with temperature resulted in two maxima, corresponding to the ferroelectric and ferrimagnetic Curie temperatures. This behaviour is unlike anything previously observed in other ME composites.     

Al2O3-3Al2O3·2SiO-ZrO2耐火材料的相组成

Al<,2>O<,3>-SiO<,2>-ZrO<,2>系耐火材料应用范围广,特别被用作陶瓷辊,具有力学强度高、抗热震性能优良、耐碱类化合物侵蚀和高温蠕变率低的特性.Al<,2>O<,3>-SiO<,2>-ZrO<,2>系耐火材料性能很大程度上取决于其结晶相和玻璃相的总量和化学成分,采用定量XRPD和XRF研究了原料中Al<,2>O<,3>/SiO<,2>比和氧化铝颗粒尺寸分布对结晶相和玻璃相的总量及其化学成分的影响.耐火材料由莫来石、刚玉、ZrO<,2>的多晶体和总量各异的玻璃相组成.莫来石含量及其晶胞参数和成分随烧成温度改变,但主要受原料中Al<,2>O<,3>/SiO<,2>比的影响.     

Phase equilibria in the CaO·SiO2Na2O·SiO2Na2O·Al2O3·6SiO2 system

Equilibrium phase relations in the system CaO·SiO₂Na₂O·SiO₂Na₂O·Al₂O₃·6SiO₂ at 40–80 wt% Na₂O·Al₂O₃·6SiO₂ composition range have been experimentally studied at temperatures between 800 °C and 1200 °C. The liquidus temperature was determined with differential scanning calorimetry. The equilibrated samples were quenched with pressurized nitrogen, and examined with electron probe X-ray microanalysis and X-ray diffraction for identification of microstructure and phase relations. Five primary phase fields, CaO·SiO₂, Na₂O·SiO₂, Na₂O·2CaO·3SiO₂, 2Na₂O·CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ were established. The ternary eutectic point of CaO·SiO₂, Na₂O·2CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ was determined to be at 1030 °C with the composition of 29.0 wt% CaO·SiO₂, 12.0 wt% Na₂O·SiO₂ and 59.0 wt% Na₂O·Al₂O₃·6SiO₂. Peritectic reaction of Na₂O·2CaO·3SiO₂, 2Na₂O·CaO·3SiO₂ and Na₂O·Al₂O₃·6SiO₂ occurred at 930 °C with the composition of 13.0 wt% CaO·SiO₂, 29.0 wt% Na₂O·SiO₂ and 58.0 wt% Na₂O·Al₂O₃·6SiO₂. The liquidus surface projection of the ternary system has been constructed in the composition region important for the bottom ash application.     

Dielectric properties of porous Ba0·997La0·003Ti1·0045O3 ceramics

An oxalate method was used in this work to produce La–BaTiO₃ materials. The obtained powders had small particle size and were disaggregated. However, the sintering process is difficult due to the presence of large pores uniformly distributed in the matrix. Grain size is not uniform, and the type of microstructure obtained suggests that clusters of particles readily sinter and densify, while leaving between them large pores. Impedance spectroscopy was done up 230°C. The variation of the permittivity with temperature showed that lanthanum changes the transition temperature of BaTiO₃, to T_o ∼115°C. One of the resistances of the proposed equivalent circuit was related to grain boundary conductance, since its associated activation energy, 0·72 eV, is too high to be assigned to a donor species. It is proposed that La substituting Ba is compensated by Ba vacancies, which turns the material highly resistive, not showing the PTC effect.     

ZnO·Al2O3修饰Al2O3微滤膜的研究

以硝酸锌、硝酸铝、尿素为主要原料,采用均相沉淀法对Al2O3微滤膜进行了ZnO*Al2O3涂覆改性研究.实验结果表明,在适宜的涂覆液浓度、涂覆次数条件下,ZnO*Al2O3改性后可使微滤膜的水通量提高15～20%,且具有较高耐酸碱性能.     

Humidity sensitive electrical properties of a novel ceramic heterocontact structure ZnO/BaPb0·8Bi0·2O3

The humidity dependence of the voltage-current characteristics of nonsymmetrical and symmetrical heterocontacts ZnO/BaPb_0·8Bi_0·2O₃, ZnO/BaPb_0·8Bi_0·2O₃/ZnO and ZnO/ZnO have been studied at fixed temperature in air with different relative humidity values. Nonlinear characteristics have been observed for all the contacts at any humidity values. The increase in the nonlinearity coefficient for the ZnO/BaPb_0·8Bi_0·2O₃/ZnO contact with respect to the ZnO/ZnO contact, and the voltage-current relationship at forward bias for ZnO/BaPb_0·8Bi_0·2O₃ heterocontacts are attributed to surface states. The increase in relative humidity causes the decrease in the Schottky potential barrier height, thereby resulting in a redistribution of the voltage drop at the heterocontact interface and in the current growth at lower voltages.     

Optimizing the piezoelectric properties of Ba0·85Ca0·15Zr0·10Ti0·90O3·lead-free ceramics via two-step sintering

The two-step sintering of lead-free Ba₀·₈₅Ca₀·₁₅Zr₀·₁Ti_0·9O₃·(BCZT) ceramics was investigated as a way to enhance its piezoelectric properties. The variations in grain size as a function of the calcination and sintering conditions and its effect on performance is discussed. Results indicate that as the calcination and first-step sintering temperatures increased, grain size became large and was independent of the second sintering step. Large grains were responsible for the enhanced piezoelectric properties by causing lattice distortion, larger domains, and easy motion of domain walls. The BCZT ceramic calcined at 1200 °C and sintered at 1540 °C without holding and then cooled to 1400 °C and held at 1400 °C for 4 h exhibited optimal performance with the highest remnant polarization P_r ∼13.5 μC/cm², the largest piezoelectric constant d₃₃ ∼ 529 pC/N at room temperature, and the highest Curie temperature T_c ∼125 °C. Two-step sintering has been turned out to be an effective method to realize high-performance BCZT ceramics by microstructure optimization.     

α-Al_2O_3·3H_2O热分解动力学

五十年代以来,人们采用了各种热分析法研究固体热分解反应动力学。如等温法,不等温法和循环加热法;热重法(TG),微分热重法(DTG),差热法(DTA)和差示量热法(DSC);单图法,双图法和多图法。到了七十年代,不仅常常将上述方法综合应用,而且在处理数据方面,逐渐趋向了“试差法”。其实,固相反应过程,既使是最简单的热分解:A(s)→B(s) C(g)↑,也是相当复杂的。既涉及物质及其反应的内在特性,(如键的断开,原品格的破坏,新品格的形     

Nonstoichiometry and relaxation kinetics of nanocrystalline mixed praseodymium–Cerium oxide Pr0·7Ce0·3O2−x

The oxygen deficiency and kinetics of oxygen uptake and release of nanocrystalline mixed praseodymium–cerium oxide with composition Pr_0·7Ce_0·3O_2−x were investigated by combining coulometric titration and potentiometric measurements using stabilised zirconia oxygen concentration cells. The P(O₂) versus composition isotherms indicate a two-phase region at high P(O₂) [P(O₂)>0·1 bar at 560°C] and a single-phase region at lower P(O₂). The oxygen pressure dependence in the homogeneous region can be described by a power law with an exponent (−1/6), in accordance with doubly charged oxygen vacancies as majority defects. The enthalpy of reduction amounts to (2·9±0·3) eV. The chemical diffusion coefficients are of the order of 10⁻⁶ cm² s⁻¹ at 640°C with an activation energy of ≈0·3 eV. The low activation energy for diffusion may be related to the high density of interface sites in the nanocrystalline material.     

Electrochemical characterization of BaCe0·7Zr0·1Y0·16Zn0·04O3-δ electrolyte synthesized by combustion spray pyrolysis

BaCe_0·7Zr_0·1Y_0·16Zn_0·04O_3-δ perovskite has been investigated due to its potential as an electrolyte in industrial steam electrolysis applications. The lowest area specific resistance (ASR) is achieved as 4.0 Ω cm² at 711 °C under 3% wet Ar atmosphere. The conductivity is calculated as 2.93 × 10^?2 S cm^?1 and kept stable for a ~70 h testing period. ASR increased at lower temperature (511 °C) under the same atmosphere and a new impedance arc (with 4.5 Ω cm² ASR and 2 × 10^?8 F equivalent capacitance) is formed, indicating second phase formation. No second phase formation is observed at the same temperature under dry 5% H₂ in Ar. The second phase formation/degradation of the electrolyte is attributed to Ba(OH)₂ and CeO₂ formations around 500 °C under wet atmospheres. At elevated temperatures, ~700 °C, BaCe_0·7Zr_0·1Y_0·16Zn_0·04O_3-δ exhibits both excellent protonic conductivity and stability which makes it a great candidate for both industrial fuel cells and steam electrolysers.     

Effects of humidity on the electrical behaviour of Sr0·97Ti0·97Fe0·03O3-δ

It is widely recognised that the electrical behaviour of acceptor-doped strontium titanate ceramics is often controlled by resistive grain boundaries. This work shows that the electrical behaviour of Sr_0·97Ti_1-xFe_xO_3−δ materials may also be affected by other factors such as the humidity in the atmosphere, especially for materials with open porosity. For example, the impedance of dense samples with large grain size may exceed the impedance of samples with residual porosity. The bulk and grain boundary resistivities both increase with the humidity in the atmosphere.     

矿物3CaO·3Al2O3·BaSO4 高温稳定性研究

矿物3CaO·3Al2O3·BaSO4是一种新型胶凝矿物, 而关于其高温稳定性的研究却有多种结论.本工作综合运用IR, TG-DT A,EPMA,XRD和QXDA等多种测试方法, 系统研究了3CaO·3Al2O3·BaSO4 的高温稳定性问题.研究表明, 在温度低于1 350 ℃的条件下, 矿物3CaO·3Al2O3·BaSO4的晶相结构稳定; 而温度高于1 360 ℃时, 3CaO·3Al2O3·BaSO 4发生分解并形成新的晶相.3CaO·3Al2O3·BaSO4的分解方程式可表述为: 3CaO·3Al2O3·BaSO4→CaO·Al2O3+12CaO·7Al2O3+Ba O·Al2O3+SO2↑+O2↑鉴于矿物BaO·Al2O3的形成机理与该问题紧密相关, 本文也讨论了BaO·Al2 O3的形成机理.BaO·Al2O3的形成机理有两种:温度低于1 350 ℃时, BaO·Al2O 3由原料组分发生反应而形成的; 而温度大于1 360 ℃时, 该矿物是由3CaO·3Al2O 3·BaSO4分解形成的.     

矿物3CaO·3AI2O3·BaSO4高温稳定性研究

矿物3CaO·3Al2O3·BaSO4是一种新型胶凝矿物, 而关于其高温稳定性的研究却有多种结论.本工作综合运用IR, TG-DT A,EPMA,XRD和QXDA等多种测试方法, 系统研究了3CaO·3Al2O3·BaSO4 的高温稳定性问题.研究表明, 在温度低于1 350 ℃的条件下, 矿物3CaO·3Al2O3·BaSO4的晶相结构稳定; 而温度高于1 360 ℃时, 3CaO·3Al2O3·BaSO 4发生分解并形成新的晶相.3CaO·3Al2O3·BaSO4的分解方程式可表述为: 3CaO·3Al2O3·BaSO4→CaO·Al2O3+12CaO·7Al2O3+Ba O·Al2O3+SO2↑+O2↑鉴于矿物BaO·Al2O3的形成机理与该问题紧密相关, 本文也讨论了BaO·Al2 O3的形成机理.BaO·Al2O3的形成机理有两种:温度低于1 350 ℃时, BaO·Al2O 3由原料组分发生反应而形成的; 而温度大于1 360 ℃时, 该矿物是由3CaO·3Al2O 3·BaSO4分解形成的.     

Preparation and properties of (Ba0·6Sr0·4)Bi2Ta2O9 ceramic

(Ba_0·6Sr_0·4)Bi₂Ta₂O₉ (BSBT) ceramic materials with plate-like grains were prepared by the conventional mixed oxide method. The microstructures of BSBT ceramic sintered at different temperatures were studied. The variations of the saturation polarization (P_s), remanent polarization (P_r) and coercive field (E_c) with applied electric field and temperature were studied by hysteresis (D–E loop) measurements. The permittivities, piezoelectric and pyroelectric coefficients of BSBT ceramic poled at various electric fields and temperatures were measured.     

Al2O3-MgO·1.35Al2O3复合浆料的流变特性研究

测试了高纯板状刚玉粉(Al2O3)、富铝尖晶石粉(MgO@1.35Al2O3)及其复合粉料(Al2O3-MgO@1.35Al2O3)在水溶液中不同pH值下的ζ电位,三者的等电点分别为7.4、～3和5.3.研究了分散剂三聚磷酸钠对复合浆料的ζ电位和流动性的影响,结果表明外加1 wt%溶剂量的三聚磷酸钠可降低复合浆料的ζ电位约40 mV;制备Al2O3-MgO@1.35Al2O3复合浆料的理想pH值范围为9～11;复合浆料中MgO@1.35Al2O3对流变特性的影响比Al2O3的大.     

Al2O3、Fe2O3、Si O2、Ti O2

选用氢氧化钠-过氧化钠熔融样品,热水浸取,酸化后用电感耦合等离子体发射光谱法测定几内亚红土型铝土矿中Al2O3、Fe2O3、SiO2、TiO2含量。对溶矿条件、分析谱线的选择和光谱干扰等各种因素进行了讨论,确定了试验的最佳条件。用本法测定国家标准物质和实际样品,测定值与标准值和其他化学方法测定值相符,方法的精密度5%(n=7),加标回收率在94. 96%～103. 07%。适合批量红土型铝土矿样品中硅铝铁钛的快速测定。     

Na_2CO_3·10H_2O生产方法

摘１５０５Ｎａ＿２ＣＯ＿３·１０Ｈ＿２Ｏ生产方法－ＦＭＣＣＯＲＰ，美国专利ｕｓ５２６２１３４，申请６期：１９９２．２．２１．公布６期：１９９３．１１．１６。ＴＯ１１４．１７２含有Ｎａ＿２ＣＯ＿３和ＮａＨＣＯ＿３的卤水加工处理：①加热蒸发Ｈ＿２Ｏ，使Ｎ...     

TiO2·Al2O3复合氧化物载体研究进展

TiO2.Al2O3多孔复合氧化物是新型的催化剂载体材料,因其在加氢精制工艺上能够显著增加催化剂的脱硫、脱氮活性而逐渐受到重视。本文综述了国内外关于TiO2·Al2O3多孔材料的制备方法,分析了制备方法对材料的比表面积、孔结构、表面酸性等载体性能影响的一般规律。通过对国内外研究者的TiO2·Al2O3合成方法的综合评述...