SrTi1−x Fe x O3 nanoparticle: a study of structural,optical, impedance and magnetic properties

We investigate the effects of Fe-dopant concentration on the structure, as well as optical, electrical transport and magnetic properties of SrTi_{1? x} Fe _x O₃ (x?=?0.00, 0.10, 0.20, 0.30, 0.40 and 0.50) nanoparticles prepared by sol–gel method. The dopant-induced changes are studied by X-ray diffraction (XRD), Raman, optical absorption, impedance and magnetic measurements. The results show an average particle size of about 15–30?nm, depending on the Fe-doped concentration. The decrease in lattice parameters and the change of phonon modes related to structural changes, decreasing gap with increasing dopant concentration in conjunction with increasing grain boundary contribution to the impedance. The Fe-doped content has affected the structure, absorption and Raman spectroscopy of the samples. These indicate that the Fe ion has replaced the site of Ti in unit cell. By this method, we have decreased the annealing temperature considerably than that in the conventional solid-state reaction.     

Effect of DC Biasing Field on the Dielectric Properties of High Field Treated SrTiO3 Single Crystals

Dielectric constant (K) and loss (Tan) of strontium titanate single crystals subjected to high electric fields (10 KV/cm, AC or DC) were measured as a function of frequency (10² to 10⁷ Hz). These properties were also studied as a function of time at 10³ Hz immediately after the high field treatment. The value of K and tan of the field-treated samples attained a steady value after 20 hours. Measurements of K and Tan as a function of time and frequency under small DC biasing fields (200 V/cm) were taken. The values of K and tan of the high field-treated samples decreased with time and frequencies; however under a DC biasing field, K increases slightly up to 10 minutes and then decreases slowly with time to a steady value. The inversion temperature (T_i) at different frequencies get reduced with high field treatment. However, the application of small DC-biasing field increased the T_i value with the increase of biasing field strength. On the other hand, activation energy increased with high field and decreased with biasing field. The effect of high DC field treatment on SrTiO₃ single crystal exhibits more prominent changes in K, tan , T_i and activation energy than that of high AC field treated samples.     

含氯气氛退火对CdTe薄膜性质影响的交流阻抗研究

对近空间升华制备的CdTe薄膜进行了CdCl2气氛下热处理。测量了样品在室温下的交流阻抗特性,基于恒相位角元件（CPE）等效电路拟合所测量的复阻抗谱,分析了退火工艺对CdTe薄膜的晶粒体电阻、晶界电阻、弛豫时间的影响。结果表明,随退火温度的增加,晶粒电阻增大,晶界电阻减小,弛豫时间缩短。     

Photocatalytic degradation of C.I. Direct Red 23 in aqueous solutions under UV irradiation using SrTiO3/CeO2 composite as the catalyst

The photocatalytic degradation of C.I. Direct Red 23 (4BS) in aqueous solutions under UV irradiation was investigated with SrTiO3/CeO2 composite as the catalyst. The SrTiO3/CeO2 powders had more photocatalytic activity for decolorization of 4BS than that of pure SrTiO3 powder under UV irradiation. The effects of catalytic dose, pH value, initial concentration of dye, irradiation intensity as well as scavenger KI were ascertained, and the optimum conditions for maximum degradation were determined. Under the irradiation of a 250 W mercury lamp, the best catalytic dose was 1.5 g/L and the best pH was 12.0. Light intensity exhibited a significant positive effect on the efficiency of decolorization, whereas the initial dye concentration showed a significant negative effect. Under the conditions of a catalytic dose of 1.5 g/L, pH of 12.0, initial dye concentration of 100mg/L, light intensity of 250 W, and air flow rate of 0.15 m3/h, complete decolorization, as determined by UV-visible analysis, was achieved in 60 min, corresponding to a reduction in chemical oxygen demand (COD) of 69% after a 240 min reaction. A tentative degradation pathway based on the sensitization mechanism of photocatalysis is proposed.     

Characteristics of post-annealed SrTiO3 thin films prepared by mirror-confinement-type ECR plasma sputtering

SrTiO₃ films were synthesized on Pt/Ti/SiO₂/Si multilayer substrates by mirror-confinement-type ECR plasma sputtering without substrate heating. All films were found to be well crystallized at a substrate temperature below 450 K. A low temperature post-annealing of the films by electromagnetic-wave radiation drastically improved the crystallographic and electric properties of Pt/SrTiO₃/Pt/Ti/SiO₂/Si capacitors. The crystallinity of the films indicated little variation by post-annealing, but irradiation of electromagnetic wave was confirmed to be effective for decreasing the post-annealing time and temperature. The electric properties of films annealed without Pt upper electrodes were better than those with them, and the film dielectric constant reached a value of 260, which is nearly equal to thebulk one, at an annealing temperature of 573 K.     

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

Abstract

High-quality thermoelectric La_0.2Sr_0.8TiO₃ (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO₃(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10^?4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO₃ single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately –60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.     

Non-linear current–voltage characteristics related to native defects in SrTiO3 and ZnO bicrystals

SrTiO₃ and ZnO bicrystals with various types of boundaries were fabricated in order to examine their current—voltage characteristics across single grain boundaries. Their grain boundary structures were also investigated by high-resolution transmission electron microscopy. In Nb-doped SrTiO₃, electron transport behaviors depend on the type of boundaries. Random type boundaries exhibit highly non-linear current—voltage characteristics, while low angle boundaries show a slight non-linearity. On the contrary, undoped ZnO does not exhibit non-linear current—voltage characteristics in any type of boundaries including random ones. It is suggested that the differences observed in current—voltage properties between the two systems are mainly due to the difference in the accumulation behavior of acceptor-like native defects at grain boundaries. A clear non-linearity is obtained by means of Co-doping even for the highly coherent ∑ 1 boundary in a ZnO bicrystal. This is considered to result from the production of acceptor-like native defects by Co-doping.     

Investigation of ferroelectric properties on nanocrystalline barium titanate ceramics

Dense nanocrystalline BaTiO₃ (BT) ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data showed a ferropara phase transition with a maximum permittivity of 1,602 at 120°C and at 1 kHz. The polarization reversal characteristics were measured, and the typical piezoelectric hysteresis loop was recorded. The asymmetry of permanent polarization and coercive field in polarization-electric field curves were obtained and attributed to the existence of an internal electric field. The present results provide experimental evidence, indicating that if a critical grain size exists for ferroelectricity, then it is less than 50 nm for polycrystalline BT ceramics.     

Preparation and dielectric properties of BaCu(B2O5)-doped SrTiO3-based ceramics for energy storage

BaCu(B₂O₅) (BCB) was used as sintering aids to lower the sintering temperature of multi-ions doped SrTiO₃ ceramics effectively from 1300 °C to 1075 °C by conventional solid state method. The effect of BCB content on crystalline structures, microstructures and properties of the ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurements, respectively. The addition of BCB enhanced the breakdown strength (BDS) while did not sacrifice the dielectric constant. The enhancement of BDS should be due to the modification of microstructures, i.e., smaller and more homogeneous grain sizes after BCB addition. The dielectric constant of BCB-doped ceramics maintained a stable value with 1.0 mol% BCB, which was dominated by the combination of two opposite effects caused by the presence of second phases and the incorporation of Cu²⁺ and Ba²⁺, while further increase was owing to the increase of dissolved Ba²⁺ ions when the content of BCB is more than 2.0 mol%. The multi-ions doped SrTiO₃ ceramics with 1.0 mol% BCB addition showed optimal dielectric properties as follows: dielectric constant of 311.37, average breakdown strength of 28.78 kV/mm, discharged energy density of 1.05 J/cm³ and energy efficiency of 98.83%.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

The study on electrical behavior of Gd2O3-WO3 complex ceramics at high temperature

Gd₂O₃-WO₃ complex ceramics are fabricated by the conventional solid-state reaction process. The electrical characteristics and dielectric properties of the samples were measured at various ambient temperatures in a low electric field (E < 150 V/mm). As the temperature increases, the dielectric constant and the loss tangent show an obvious change at about 50 °C and 330 °C. When the temperature is above 200 °C, the samples display stable nonlinear electrical properties characterized by semiconductivity, and the nonlinearity increases along with increasing temperature. XRD analysis reveals that Gd₂W₂O₉ is the main phase and Gd₂O₃ is the secondary phase. Based on the phase transition of tungsten trioxide, these electrical properties of Gd₂O₃-WO₃ complex ceramics can be simply explained.     

Formation and Annealing of BaTiO_3 and SrTiO_3 Nanoparticles in KOH Solution

Barium titanate (BaTiO3) and strontium titanate (SrTiO3) nanoparticles were synthesized separately through hydrothermal reaction of crystalline TiO2 particles and corresponding alkaline earth hydroxides, Ba(OH)2 and Sr(OH)2 respectively, in 50 mol·dm-3 KOH solution at 150℃. Each structural evolution of BaTiO3 and SrTiO3 during the hydrothermal treatment was investigated by X-ray diffraction (XRD), field emission scanning elec- tron microscopy (FE-SEM), field emission transmission electron microscopy (FE-TEM...     

Study on the microstructure and dielectric properties of X9R ceramics based on BaTiO3

This paper investigated the microstructure and dielectric properties of BaTiO₃-Pb(Sn, Ti)O₃ system ceramics. The Curie point of BaTiO₃ is 130 °C. When the temperature is higher than 130 °C, the dielectric constant of BaTiO₃ drops severely according to Curie-Weiss law. Pb(Ti, Sn)O₃(PTS) was selected to compensate the dielectric constant doping of BaTiO₃ since it has high Curie temperature (Tc) point that is about 296 °C. The Curie temperature (Tc) point of BaTiO₃ was broadened and shifted to higher temperature because of the doping of PTS, so the temperature coefficient of capacitance (TCC) curves of the ceramics based on BaTiO₃ was flattened. When 2 wt% Pb(Ti_0.55Sn_0.45)O₃ was added, the sample showed super dielectric properties that the dielectric constant was >1750 at 25 °C, dielectric loss was lower than 2.0% and TCC was <±10% from −55 °C to 200 °C. Therefore the materials satisfied EIA X9R specifications.     

Electronic Structure of Mn Acceptor Impurity Incorporated SrTiO3 Using Embedded Cluster Method

We have performed atomic-level first principle electronic structure calculations on doped grain boundaries (GB) in SrTiO₃. This was motivated by the electron holography experiments, which were able to quantify the electrostatic potential and the associated space charge distribution across the Mn-doped GB in this material. The embedded cluster Discrete Variational (DV)-X method was used to determine the charge and the densities of states for several idealized models of a single crystal and symmetrical tilt grain boundaries in SrTiO₃. Special attention was given to the role of Mn⁺² and Mn⁺³ acceptors substituting for Ti⁺⁴ resulting in charge segregation across the grain boundaries, which was shown in the electron holography experiments. We have found that Mn replacing Ti prefers to have valence charge around +2 and this picture agrees with the experimental observation of negative grain boundary charges in the GB core.     

Characterisation of oxide scales formed on nickel superalloy using impedance spectroscopy

Abstract

Impedance spectroscopy has been used to measure the electrical properties of oxide scales formed from oxidation of IN738LC superalloy at high temperature. Electrical resistance and capacitance of the oxide scales were obtained from the simulation of the measured impedance diagrams based on the equivalent circuit model, which represents the features of the oxide scales. For oxidation of IN738LC superalloy, the electrical resistance of oxide scales increased with increasing oxidation time for the specimens exposed to air at 900°C. However, for the specimens oxidised at 1,200°C, the oxide scales showed very low electrical resistance, which indicated that cracking and spallation in oxide scales occurred continuously. By using scanning electron microscopy and X-ray diffraction techniques, the composition and microstructure of the oxide scales were examined. It was found that electrical properties were determined, not only by the microstructure of oxide scales, but also by the composition of the oxide scales. By determining the relationship between electrical properties, microstructure and composition of oxide scales, impedance spectroscopy could be used as a non-destructive technique for monitoring the oxidation of metallic alloys at high temperature.     

还原气氛、助催化剂对SrTiO3光催化分解水制氢性能的影响

采用水热法制备了SrTiO3光催化材料,研究了在还原气氛下不同处理时间对SrTiO3光催化分解水制氢性能的影响;此外还研究了单一和复合助催化剂以及担载方法对光解水制氢性能的影响。结果表明:还原气氛中处理1h的样品,其制氢速率比未经处理的样品提高了近40%;担载单一助催化剂比复合助催化剂效果更好;光沉积Pt助催化剂样品具有最高的光催化活性。     

BaTiO3-SrTiO3 layered dielectrics for energy storage

BaTiO₃-SrTiO₃ (BST) thick films (~ 250-390 μm) with layered structures were fabricated by tape-casting and lamination process. Layered composites with various Ba/Sr ratios were obtained by lamination of BaTiO₃ (BT) and SrTiO₃ (ST) tapes in different spatial configurations (2-2). As-prepared BST ceramics showed much improved sinterability over the laminates of pure BT or pure ST tapes. Dielectric properties of materials were measured in the temperature range of 25 °C to 200 °C. The method of utilizing of layered structures offered flexibility to maximize the energy storage capability at specific operating conditions: (temperature and electric field) by tailoring the dielectric properties through varying the spatial configurations of BT and ST films.     

Effect of powder thermal treatment on the microstructure and electrical properties of doped ceria ceramics

Ce_0.8Sm_0.2O_2 − δ electrolytes were prepared by sol-gel methods with different thermal treatment conditions. It was found that the particle size of the powders thermally treated in N₂ could be controlled less than 10 nm, due to the fact that carbons that enwrapped the precursors could inhibit their crystallization. At the same time, the nano-sized precursors could form larger nuclei at the initial stage of sintering, resulting in the formation of electrolyte with higher density and larger grain size. At the same consent of oxygen vacancies, the enhancement of electrical properties for the electrolyte was correlated to its microstructure obtained by the N₂ thermal treatment.     

Kinetic study of Cu(II) adsorption on nanosized BaTiO(3) and SrTiO(3) photocatalysts

In this study, nanoparticles with perovskite structure (nano-SrTiO(3) and nano-BaTiO(3)) were synthesized via a co-precipitation method, and their photocatalytic and adsorption characteristics were investigated. Both of them exhibited some photocatalytic activity and possessed a high adsorption capacity for copper ions. Further, the pseudo-first-order model was found to be more suitable to fit the experimental data. Moreover, it suggested that the Langmuir model was more adequate in simulating the adsorption isotherm. The maximum adsorption capacity was 370.4 mg/g and 200.0mg/g for nano-SrTiO(3) and nano-BaTiO(3), respectively. The negative apparent free energy confirmed that the Cu(2+) adsorption onto the nano-photocatalysts was a spontaneous process. The underlying mechanism of adsorption of Cu(II) onto nano-perovskites could be due to the ion exchange and surface complexation. From the results, SrTiO(3) and BaTiO(3) nanoparticles may be an effective material for Cu(2+) removal and, together with its photocatalytic activity, may be suitable for environmental remediation applications.     

掺杂(Fe、Nb)SrTiO3晶界组成的电子能量损失谱(EELS)分析

采用高空间分辨率扫描透射电镜（STEM）对掺杂（Fe^3 、Nb^5 ）SrTiO3晶界进行了观察，并利用采集的电子能量损失谱（EELS）对晶界组成进行了分析，结果表明，掺杂Fe的SrTiO3陶瓷晶界存在1nm左右的非晶膜，同晶体内部相比晶界缺Sr；三叉晶界为钛基玻璃相，Ti、O及Fe含量明显高于晶界，掺Nb的SrTiO3陶瓷晶界同晶粒相比同样缺Sr，三叉晶界主要以SiO2非晶相为主，Fe^3 、Nb^5 对Ti^4 的替位及在晶界的偏析引起SrTiO3晶格畸变是导致晶界组成变化的主要原因。