Effects of rapid thermal annealing treatment on 0·95(Na0·5Bi0·5)TiO3-0·05BaTiO3 thin films

Abstract

Abstract

A 0·95(Na_0·5Bi_0·5)TiO₃-0·05BaTiO₃+1?wt-%Bi₂O₃ (NBT-BT3) ceramic was used as target to deposit the NBT-BT3 thin films. The excess 1?wt-%Bi₂O₃ was used to compensate the vapourisation of Bi₂O₃ during the depositing processes. The optimal deposition parameters were substrate temperature of 500°C, radio frequency power of 100?W, chamber pressure of 10?mtorr and oxygen concentration of 40%. Rapid thermal annealing treated processes were carried out on NBT-BT3 thin films from 600 to 800°C in ambient or in oxygen atmosphere for 1?min. The surface morphologies and thicknesses of NBT-BT3 thin films were characterised by field emission scanning electron microscopy, and the thickness was ～216?nm. It would be shown that the NBT-BT3 thin films annealed in oxygen atmosphere had the smaller grain size, larger memory window, smaller leakage current density, larger remanent and saturation polarisation and smaller coercive field than the NBT-BT3 thin films annealed in ambient atmosphere.     

Energy storage properties of MgO-doped 0.5Bi0·5Na0·5TiO3-0.5SrTiO3 ceramics

0.5Bi_0·5Na_0·5TiO₃-0.5SrTiO₃-x wt% MgO (x = 0, 0.5, 1.0, 1.5, 2.0, 3.0) ceramics were fabricated via solid-state method. The effect of MgO doped on energy storage properties, dielectric performance, phase structure and microstructures of 0.5Bi_0·5Na_0·5TiO₃-0.5SrTiO₃ (BNST) ceramics were studied systemically. The Mg²⁺ substituted Ti⁴⁺ site in BNST, which was confirmed by X-ray diffraction (XRD) result. The scanning electron microscope (SEM) images show that all the ceramic samples exhibit uniform and compact morphologies. The temperature dependent permittivity exhibits frequency dispersion, indicating that the ceramic samples are typical relaxor ferroelectrics. It was found that MgO doped BNST can significant improve the breakdown strength (E_b) of samples from 109 kV/cm to 227 kV/cm, which results in a great enhancement on energy storage density. The sample of x = 3.0 has the largest energy storage density (2.17 J/cm³), which is twice as much as the BNST. Consequently, we consider that MgO-doped BNST ceramics are able to be a promising candidate in the field of pulsed-power devices.     

Effects of sintering temperature on properties of Na0·5K0·5NbO3-LiSbO3-BiFeO3 lead free ceramics

Abstract

Abstract

Lead free 0·95K_0·5Na_0·5NbO₃-0·05LiSbO₃ (KNN-LS) ceramics doped with 0·4?mol.-% BiFeO₃ (BF) have been prepared by the conventional mixed oxide method with sintering temperature at 1065-1135°C in this paper. The samples are characterised by X-ray diffraction analysis and scanning electron microscopy. The dielectric and piezoelectric properties are also investigated. The results present that initially the increase in the sintering temperature is very effective in improving the density and electric properties. However, the properties of the samples would be deteriorated as they are sintered over the optimum temperature. The KNN-LS (doped with 0·4%BF) ceramics shows excellent properties with sintering temperature at 1100°C.     

Enhanced dielectric,piezoelectric properties and strengthened relaxor behavior in K-modified Na0·5Bi0·5TiO3 lead-free ceramics

The effect of K⁺ modification on the phase composition, micro structure and electrical properties of Na_0·5Bi_0·5TiO₃ ceramics prepared via solid phase reaction was investigated. The samples (Na_1-xK_x)_0.5Bi_0·5TiO₃ still present pure perovskite structure. The doping K⁺ can increase grain size and relative density, and improve the electrical properties of BNT samples. The dielectric constant of (Na_1-xK_x)_0.5Bi_0·5TiO₃ samples increased from 800 to 1844, the piezoelectric constant from 61 pC/N to 172 pC/N, and the dielectric constant at Curie temperature increased from 1950 to 7182. The samples modified by K⁺ exhibit strong relaxation performance and excellent dielectric-temperature stability at high temperatures. The mechanism of K⁺ modification was explained and analyzed in detail using domain theory, lattice theory and ferroelectric relaxation theory.     

Synthesis and characterisation of La0·95Sr0·05GaO3−δ, La0·95Sr0·05AlO3−δ and Y0·95Sr0·05AlO3−δ

The oxide-ion conducting phases La_0·95Sr_0·05GaO_3−δ (LSG), La_0·95Sr_0·05AlO_3−δ (LSA) and Y_0·95Sr_0·05AlO_3−δ (YSA) have been synthesised, either by solid state reaction or through a chemical route. Structural and microstructural characterisation was carried out using XRD and SEM/EDS techniques and a.c. impedance spectroscopy (250–1000°C) was employed to determine the electrical properties. Although low-temperature impedance results were strongly dependent on phase purity and microstructure, high temperature electrical conductivity data could be used to compare the electrical conductivities of LSG, LSA and YSA. Chemical modification from the well-known Sr-doped lanthanum gallate via replacement of different cations on the A and/or B site decreased the conductivity, increased the activation energies and decreased the ionic conductivities. From the results, there is no simple correlation between oxygen ion conductivity and geometric aspects related to unit cell parameters and cation radii. Instead, cation polarisability seems to play an extremely important role in designing improved oxygen ion conductors based on the perovskite structure.     

AC behaviour and conductive mechanisms of 2·5 mol% La2O3 doped PbZr0·53Ti0·47O3 ferroelectric ceramics

Impedance spectroscopy (IS) is an effective characterization method for the investigation of many ceramic systems including the ferroelectric systems. It is employed to analyze the properties of the intragranular and interfacial regions, their interrelations, their temperature and frequency dependences and the DC and AC phenomena in order to separate the individual contributions from the total cell impedance. Using this technique and thermally stimulated current measurements we have studied the ac behavior and the conductive mechanisms in lanthanum-doped lead zirconate titanate, a donor-doped ferroelectric ceramic system. AC and DC conductivity components were found; a Jonscher power-law behavior was obtained and a strong low frequency dispersion was observed in a wide frequency range. A mixture of ionic–electronic conductive behavior was analyzed from the experimental results and the energy activation values obtained. ©     

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.     

锂离子电池富锂正极材料0．5Li2 MnO3·0．5LiMn1／3Ni1／3Co1／3O2的研究

采用碳酸盐沉淀法合成了锂离子电池富锂正极材料0．5Li2：MnO3·0．5LiMn1／3Ni1／3Co1／3O2并对其结构、形貌以及电化学性能进行了测试。XRD测试表明富锂正极材料具有良好的层状结构,电化学测试表明材料0．5Li2：MnO3·0．5LiMn1／3Ni1／3Co1／3O2具有良好的循环特性、倍率性能,这与其结构和形貌是分不开的。     

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.     

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.     

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.     

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.     

3·5英寸软磁盘的研制

<正> 前言在计算机的发展与普及过程中,一直以微型化为其趋势。作为外部存贮设备的软磁盘,也经历了从8英寸、5.25英寸到3.5英寸的变化。目前的国际软盘市场上,3.5英寸盘和5.25英寸盘并驾齐驱,而3.5英寸盘却以更高的速度增长。3.5英寸盘的尺寸减小,但其记录容量却增加,约是5.25英寸盘的2倍,非格式化容量达到1兆字节。究其原因有下面几点:     

钛酸铋钠Bi0．5Na0．5TiO3（BNT）的制备工艺

结合钛酸铋钠Bi0．5Na0．5TiO3（BNT）的性质,介绍了钛酸铋钠Bi0．5Na0．5TiO3（BNT）的制备工艺。     

Structural,optical, electrical and dielectric properties of Bi1·5Zn0·92Nb1·5−xNixO6·92−3x/2 solid solution

Abstract

The effects of Ni content on the structural, optical, dielectric and electrical properties of Bi_1·5Zn_0·92Nb_1·5O_6·92 pyrochlore ceramics have been investigated. Nickel atoms were inserted into pure samples in accordance to the composition Bi_1·5Zn_0·92Nb_1·5?xNi_xO_6·92?3x/2, with x varying from 0·07 to 0·40. The structural analysis revealed that a single phase of the pyrochlore compound can be obtained for x values of 0·07 and 0·10 only. Further increase in Ni caused the appearance of multiple phases. The optical energy band gaps are determined as 3·30, 3·35 and 3·52 eV for Ni content of 0·00, 0·07 and 0·10 respectively. The temperature dependent electrical resistivity and the frequency dependent capacitance are observed to increase with increasing Ni content. The resonance frequency, which was determined from the capacitance–frequency dependence, was observed to shift from 12·14 to 10·47 kHz as the x values increase from 0·00 to 0·10 respectively.     

Preparation and study as positive electrode of Li0·33La0·56TiO3–PANI nanocomposite

Abstract

Abstract

A new electrode material based on the Li_0·33La_0·56TiO₃–polyaniline nanocomposite is reported. This material is prepared by in situ polymerisation of aniline in the presence of Li_0·33La_0·56TiO₃ nanoparticles. The nanocomposite and its precursors are characterised by X-ray diffraction, thermogravimetry, Fourier transform infrared, TEM, SEM, electrical conductivities and electrochemical measurements. The structural and electrochemistry study reveals the existence of relatively strong interactions between the conducting polymer and the oxide particles to assure good synergy in the transport process. The dc and ac electrical conductivities and diffusion coefficient measurements at room temperature indicate that the conductivity values are several orders of magnitude higher in the composite than in the oxide alone. This behaviour determines better reversibility for Li insertion in charge–discharge cycles compared to the pristine oxide and polymer when it is used as electrode of lithium batteries.     

（1－x）Bi0．5（Na0．8K0．2）0．5TiO3－xKSbO3压电陶瓷的制备及性能研究

采用传统固相法制备了新型（1－x）Bi0．5（Na0．8K0．2）0．5TiO3－xKSbO3无铅压电陶瓷,利用XRD、 SEM等测试技术表征了该陶瓷的晶体结构、表面形貌、压电和介电性能。研究结果表明,在所研究的组成范围内陶瓷材料均能形成纯的钙钛矿固溶体。在室温下,当KSbO3的掺杂量为1％时,该体系表现出较好的介电性能：εr和tanδ分别为2231和0．055。     

Piezoelectric and dielectric properties of Bi0 ˙ 5(Na0 ˙ 84K0 ˙ 16)0 ˙ 5TiO3–Ba(Zr0 ˙ 04Ti0 ˙ 96)O3 lead free piezoelectric ceramics

Abstract

Lead free piezoelectric ceramics (1–x)Bi_0˙5 (Na_0˙84K_0˙16)_0˙5TiO₃–xBa(Zr_0˙04Ti_0˙96)O₃ (BNKT–BZT100x, wherein x ranged from 0 to 10 mol.-%) were fabricated by a conventional mixed oxide route, whose BZT content effect on electrical properties and crystalline structures was investigated. X-ray diffraction investigation showed that BZT effectively diffused into BNKT lattice and formed a solid solution during sintering, and their crystalline structures changed from rhombohedral phase to tetragonal phase as the BZT content was increased. Piezoelectric property measurements revealed that the BNKT–BZT4 ceramics had the highest piezoelectric performance: piezoelectric constant d ₃₃ reached 178 pC N^–1 and planar electromechanical coupling factor k _p was up to 0˙33. The influence of Bi₂O₃ doped content on electrical properties and crystalline structure of the BNKT–BZT4 ceramics were also studied, and found that the piezoelectric property of the ceramics was enhanced when Bi₂O₃ was doped.     

Preparation and properties of (Ba0·7Sr0·3)TiO3 powders and thin films using precursor solutions formed from alkoxide-hydroxide

(Ba_0·7Sr_0·3)TiO₃ powders and thin films were prepared using alkoxide-hydroxide route. Solutions of Ba and Sr hydroxides dissolved in methanol were reacted with Ti-isopropoxide under conditions of stirring at room temperature for 15 h, and then dried under reduced pressure at ≦40°C to prepare precursors of (Ba_0·7Sr_0·3)TiO₃ powder. The amorphous precursors were hydrolyzed at 100°C by introducing nitrogen gas containing water vapor. The hydrolyzed products were crystalline nanosize powders of (Ba_0·7Sr_0·3)TiO₃. As-hydrolyzed (Ba_0·7Sr_0·3)TiO₃ powders showed a good crystallinity with cubic phase. (Ba_0·7Sr_0·3)TiO₃ thin films were also successfully prepared at 650°C on Pt/Ti/SiO₂/Si substrates from precursor solutions obtained by the reaction of alkoxide with hydroxides. The (Ba_0·7Sr_0·3)TiO₃ thin films exhibited the microstructure with fine grains as small as 20–60 nm. The dielectric constants of the thin films ranged from 600 to 800 at room temperature.