TiO3 Samples Research Articles

Improved magnetic and ferroelectric properties of Sc and Ti codoped multiferroic nano BiFeO3 prepared via sonochemical synthesis

The room temperature multiferroic properties of bulk BiFeO3 are not exciting enough for its application in devices. Here, we report the sonochemical synthesis of scandium and titanium codoped BiFeO3 nanoparticles which exhibit improved magnetic and ferroelectric properties at room temperature. The nanoparticles have been checked for phase purity and composition using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The size and morphology of the nanoparticles have been confirmed using scanning electron microscopy (SEM), and both low and high resolution transmission electron microscopy (TEM/HRTEM). The breaking of the spin cycloid due to the smaller size and slight structural distortion caused by the doping has been found to be instrumental for the enhancement of multiferroic properties. The electrical polarization increases significantly in the case of BiFe(0.925)Sc(0.05)Ti(0.025)O3 nanoparticles. A marked reduction in the leakage current was seen compared to undoped BiFeO3. Magnetoelectric coupling was also observed in the BiFe(0.925)Sc(0.05)Ti(0.025)O3 sample. Our results demonstrate that codoping with Sc and Ti ions is an effective way to rectify and enhance the multiferroic nature of BiFeO3.

The Influence of Donor-Doped Concentration on the PTCR Characteristics of the Ba<i><sub>n</sub></i><sub>-<i>x</i></sub>Sm<sub>x</sub>TiO<sub>3</sub> Based Ceramics Sintered in Reducing Atmosphere

Positive temperature coefficient of resistivity (PTCR) effect and electrical properties of (Ban-xSmx)TiO3(BSMT ) samples with different Ba-site/Ti-site ratio (n) and various concentration of the donor-doped Sm3+(x) sintered in a reducing atmosphere and reoxidized in air are investigated. The results show that the room temperature resistivity (ρRT) of the semiconducting BSMT ceramics first decreases and then increases with increasing of concentration of the donor-doped Sm3+, especially whenxis 0.005 mol, the ρRTof the BSMT ceramics is the lowest. Moreover, the ρRTof the Ba-excess BSMT (n= 1.01) specimens reoxidized at 800 oC for 1 h after sintering at 1270 °C for 30 min in a reducing atmosphere is lower than the Ti-excess ones (n= 0.99), in addition, the ρRTof the BSMT specimens increases with an increase of both sintering temperature and reoxidized time.

Influence of Li2Co3 and V2O5 combined additions on the sintering and dielectric properties of Ca0.5Sr0.5TiO3 ceramics prepared from powders synthesized by sol-gel method

In this work, we have studied the influence of lithium carbonate (Li2CO3) associated with the vanadium oxide (V2O5) on sintering and dielectrics properties of Ca0.5Sr0.5TiO3 ceramic materials obtained from nanopowder synthesized by sol-gel method. The nanopowder was obtained by controlled mixing of titanium butoxide dissolved in butanol-2 and acetic acid with a saturated aqueous solution of calcium acetate and strontium carbonate and subsequent drying of the formed gel at 80 ?C and calcination at 1100?C. The synthesized nanopowder was mixed with different amount of additives, and then uniaxally pressed and sintered in air atmosphere at temperature determined by dilatomertic measurements. The pure Ca0.5Sr0.5TiO3 sample obtained by this process required a sintering temperature around 1500?C. The addition of Li2CO3 combined with V2O5 improved sinterability and caused a shift of dilatimeric shrinkage curve to much lower temperatures. Thus, dense ceramics (98% of theoretical density) were obtained at sintering temperature ? 1300?C. The effect of adding Li2CO3-V2O5 on the structure of ceramics and the dielectric properties is discussed and show that type I dielectric properties (linear variation of the permittivity) are conserved, but with an increase of dielectric loss.

Effect of the valence states of titanium on the lattice structure and ionic conductivity of Li0.33La0.55TiO3 solid electrolyte

Li0.33La0.55TiO3 solid electrolytes with a pure phase were synthesized by the citric acid-supported sol-gel method and then sintered under controlled redox atmospheres of air, argon and hydrogen. Although of similar morphology and relative density, Li0.33La0.55TiO3 samples sintered under reduction atmosphere such as argon and hydrogen exhibited a tetragonal structure with lattice distortion. The distortion and volume expansion of the crystal lattice was identified as originating from the transformation of the Ti valence state, and this was more clearly observed under sintering of the hydrogen atmosphere. The qualitative analysis of the Ti valence state using an X-ray Photoelectron Spectroscopy experiment was performed and indicated that the largest amount of Ti3+(18.6%) was formed in the Li0.33La0.55TiO3 samples sintered under hydrogen atmosphere. The relationship between the lattice distortion and the lithium ion conductivity of the Li0.33La0.55TiO3 sintered under different atmospheres is also discussed on the basis of the lattice distortion.

Parameter Optimization in the Synthesis of BZT Ceramics to Achieve Good Dielectric Properties

The powder synthesis of barium zirconate titanate (BZT) (BaZrTiO3) from the mechanochemical activation of BaCO3, ZrO2, and TiO2 was studied. The grinding effect, by using a planetary ball milling, on the crystallization temperature of BZT powders was analyzed. X-ray diffractometry, differential thermal analysis, thermogravimetric analysis, and scanning electronic microscopy (SEM) were used as characterization methods. The crystallization behavior of powders activated by high-energy grinding and the effect of grinding time on the BZT crystallization were analyzed. After grinding by 4 h, the BaZr(0.05)Ti(0.95)O3 sample was almost fully crystallized at . The results of dielectric and ferroelectric properties show that high-energy ball milling is a practical and promising way to prepare BZT ceramics.

Hall mobility, electrical resistivity, and dielectric properties of reduced La0.01Ba0.99TiO3

The La0.01Ba0.99TiO3 sample was reduced at 1380 °C under about a 10−14-atmosphere oxygen partial pressure. After the sample had been reduced under these conditions, the resistivity and the Hall mobility of the reduced La0.01Ba0.99TiO3 were investigated experimentally within a temperature range of 300 to 600 K. The electrical resistivity decreased linearly with increasing measurement temperature, indicating that the conduction mechanism in this system was thermally activated. Evidence of an excess of charge carriers was observed at high temperatures. The dielectric property data showed that the known phase-transition temperature shifted to a higher temperature (425 K). Thus the reduction of the sample has an influence on both the dielectric constant and the transition temperature. In-situ high-temperature electrical-conductivity and Hall measurements are useful tools for establishing the donor-doping effect in perovskite La0.01Ba0.99TiO3 and for screening it for more industrial applications.

Fe-doped La0.5Sr0.5TiO3 nanopowders prepared by hydrothermal method

Graphical abstractThis figure shows the field dependence of magnetization (M-H curve) of the La0.5Sr0.5Ti1-xFexO3 nanopowders obtained from room-temperature VSM measurement. The undoped sample behave diamagnetic, whereas the Fe doped samples are ferromagnetic. The saturation magnetization (Ms) values of 0.00085 and 0.0166emu/g are observed for x=0.05 and x=0.1, respectively.Display Omitted Highlights? Fe-doped La0.5Sr0.5TiO3 nanopowders are prepared at 220?C by hydrothermal method. ? LRTEM reveals a cubic, plate-like and irregular shape with their size of 48-149nm. ? Undoped sample exhibits diamagnetic, whereas the doped samples are ferromagnetic. ? The saturation magnetizations are in the range of 0.00085-0.0166emu/g. La0.5Sr0.5Ti1-xFexO3 (x=0, 0.05 and 0.1) nanopowders was prepared by hydrothermal method in 2M KOH solution at 220?C for 24h. The structure and morphology of the products were characterized by X-ray diffraction, field emission scanning electron microscope and transmission electron microscope. Magnetic properties were measured at room temperature using a vibrating sample magnetometer. All product powder showed the single phase of La0.5Sr0.5Ti1-xFexO3 cubic structure without any impurity phase. The product powders consist of the cubic, plate-like and irregular particles with particles sizes in the range of 48-92, 75-149 and 25-75nm, respectively. The undoped La0.5Sr0.5TiO3 sample exhibits diamagnetic behavior, whereas the Fe-doped La0.5Sr0.5TiO3 samples are ferromagnetic having the saturation magnetizations of 0.00085-0.016emu/g.

Low temperature sintering and properties of Ca–Al–B–Si–O glass/ceramic composites with various ceramic fillers

Low-temperature sintering and properties of low temperature co-fired ceramics materials based on a typical Ca–Al–B–Si–O glass and various ceramic fillers such as (Zr0.8Sn0.2)TiO4, (Ca0.5Mg0.5)TiO3, BaSm2Ti4O12 and CaTiO3 were investigated. Densification, crystallization and dielectric properties are found to strongly depend on the type of filler. The densification process of glass/ceramic composites with different ceramic fillers is mainly from 600 to 925 °C, and the initial compacting temperature of samples is 600 °C. The initial rapid densification of samples starts after glass softening temperature of samples. The XRD patterns of (Ca0.5Mg0.5)TiO3 and CaTiO3 samples demonstrate crystalline phases, CaTiO(SiO4) and CaTiSiO5, respectively, as a result of firing at 875 °C for 15 min. The high dielectric constant fillers produce high er values of the dielectric samples. The maximum dielectric constant of samples for (Zr0.8Sn0.2)TiO4, (Ca0.5Mg0.5)TiO3, BaSm2Ti4O12 and CaTiO3 filler is 14.02, 16.21, 18.64 and 23.78, respectively. Comparing with other samples, the specimens for (Ca0.5Mg0.5)TiO3 and CaTiO3 ceramic filler have lower dielectric loss. Especially, the sample for (Ca0.5Mg0.5)TiO3 filler exhibits the lowest dielectric loss of 0.00011.

Temperature-stable high-energy-density capacitors using complex perovskite thin films

Chemical-solution-derived thin film synthesis and dielectric characterizations of (1 - x)BaTiO(3-x)Bi(Mg,Ti) O(3) complex perovskites with compositions x <0.15 have been explored for temperature-stable high-energy-density capacitor applications. Solution chemistry has been optimized to synthesize and stabilize the precursor solution. Solution-derived (1 - x)BaTiO(3-x)Bi(Mg,Ti)O(3) thin film samples in thicknesses ranging from 250 to 500 nm were fabricated by repeated spinning and subsequent crystallization processes. These thin films showed nearly linear polarization response with high relative dielectric permittivity exceeding 900, which is beneficial for high-capacitance-density and high-energy-density capacitors. Average dielectric breakdown strengths of the dense films were as high as 2.08 MV/cm. The BaTiO(3)-Bi(Mg,Ti) O3 samples showed very low leakage current densities of the order of 10-8 A/cm(2) even at temperatures of 200°C. Based on the structural stability at high temperatures of the pseudocubic perovskite, the high dielectric permittivity and the typical P-E behaviors of the BaTiO(3)-Bi(Mg,Ti)O(3) thin films were also maintained at such high temperatures. Resulting energy density of the 500-nm-thick 0.88BaTiO(3)-0.12Bi(Mg,Ti) O(3) thin film was as high as 37 J/cm(3) at 1.9 MV/cm. The high energy density and excellent temperature stability of the Ba- TiO(3)-Bi(Mg,Ti)O(3) complex perovskite show promise for use in high-temperature pulse power capacitor applications.

Thermoelectric Properties of Dy-Doped SrTiO3 Ceramics

Sr1−x Dy x TiO3 (x = 0.02, 0.05, 0.10) ceramics were prepared by the reduced solid-state reaction method, and their thermoelectric properties were investigated from room temperature to 973 K. The resistivity increases with temperature, showing metallic behavior. The Seebeck coefficients tend to saturate at high temperatures, presenting narrow-band behavior, as proved by ab initio calculations of the electronic structure. The magnitudes of the Seebeck coefficient and the electrical resistivity decrease with increasing Dy content. At the same time, the thermal conductivity decreases because the lattice thermal conductivity is reduced by Dy substitution. The maximum value of the figure of merit reaches 0.25 at 973 K for the Sr0.9Dy0.1TiO3 sample.

Comparison of Y and La-substituted SrTiO3 as the anode materials for SOFCs

Y0.07Sr0.895TiO3 (YST) and La0.2Sr0.7TiO3 (LST) samples sintered and reduced at different temperatures were prepared. The conductivity and chemical expansion of the samples were tested. It was found that the combination of high conductivity and low chemical expansion therefore represents a conflict of material properties for YST and LST samples. The relationship between chemical expansion and sample cracking is discussed. The conductivity of the samples against redox cycles was also tested. Properties with respect to SOFC requirements were compared between LST and YST samples. Suitable preparation conditions for YST and LST as SOFC anode materials were optimized.

Effect of Grain Size on the Microwave Dielectric Characteristics of High‐Energy Ball‐Milled Zinc Magnesium Titanate Ceramics

Using solid‐state reaction route and high‐energy ball milling technique Zn1−xMgxTiO3 (x = 0–0.5) compositions were synthesized. These ball milled samples were sintered at 1100°C for 2 h and microwave dielectric properties such as dielectric constant (ε’), quality factor (Q), and temperature coefficient of resonant frequency (τf) were studied. Significant improvement in quality factor of ~ 65% was observed for x = 0.3. To understand the effect of sintering duration on the microwave dielectric properties, single phase Zn0.7Mg0.3TiO3 samples were sintered at 1100°C for different durations from 2 to 20 h. The grain size increases with sintering duration and it influences to enhance the microwave dielectric properties and as a result, the quality factor further improved by three times. The dielectric constant and temperature coefficient of resonant frequency showed a slight improvement of ~ 10%–15% with sintering duration.

Structure and composition-dependent optical properties of (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotube arrays

AbstractLead strontium titanate (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes were synthesized by sol-gel template method via spin coating. The structures and morphology of the as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the chemical composition of the sample and the valence state of elements. Raman spectroscopy of the as-prepared (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes at room temperature was also investigated. The results indicate that as-prepared (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes are perfectly crystallized and there is a trend of structure change from PST40 to PST60. A weak peak at 508 cm−1 assigned to E(3TO) mode can be seen in the Raman spectrum of (Pb0.6Sr0.4)TiO3 sample. Photoluminescence spectra of samples at room temperature reveal three intense emission bands centered at 356, 400 nm for (Pb0.4Sr0.6)TiO3 and 413, 433, 451 nm for (Pb0.6Sr0.4)TiO3 nanotubes, respectively. The peak positions of the emission band have a significant blue shift as Pb content increases.

Light-induced structural changes in Eu-doped (Pb,La)(Zr,Ti)O3 ceramics

Fluorescence spectra of poled and unpoled Eu-doped (Pb,La)(Zr,Ti)O3 ceramics with various compositions were measured using 580 nm excitation. The ratio of the intensities of the Eu3+ D50→F72/D50→F71 fluorescence transitions was used as an indicator for the symmetry of the Eu3+ site. As the symmetry decreases, the ratio increases. Increasing the Zr content in (Pb,La)(Zr,Ti)O3 increases the ratio, indicating that the symmetry of the Eu3+ site decreases. Exposure of the Eu-doped (Pb,La)(Zr,Ti)O3 samples to UV light also increases the intensity ratio, indicating that UV light exposure leads to structural distortions in Eu-doped (Pb,La)(Zr,Ti)O3 samples, lowering the Eu3+ site symmetry.

Preparation and Thermoelectric Properties of La-Doped SrTiO3 Ceramics

Single-phase polycrystalline LaxSr1−xTiO3 (x = 0, 0.04, 0.06, 0.08, and 0.12) ceramics were prepared by the conventional solid-state reaction method using high-activity hydroxides as the raw materials. The electrical conductivity of all the samples increased with increasing x value and decreased with measurement temperature, while the thermal conductivity decreased with increasing x value and measurement temperature. The La0.12Sr0.88TiO3 sample showed the lowest thermal conductivity of 2.45 W m−1 K−1 at 873 K and the largest ZT of 0.28 at 773 K. The present work revealed that hydroxides with high activity as raw materials are beneficial to improve the thermoelectric properties, especially to decrease the thermal conductivity.

Synthesis and Characterization of Isovalent Substituted BaTiO3 Ceramics by Modified Chemical Route

Iso-valent ion substituted barium titanate (Ba0.96Sr0.04TiO3 & Ba0.96Mg0.04TiO3) ferroelectric samples were synthesized in single perovskite phase by modified chemical route. For single perovskite phase and dense grain morphology formation, 900°C and 1300°C temperatures were optimized as calcination and sintering temperatures, respectively. Room temperature (RT) dielectric constant (ϵr) and dielectric loss (tanδ) of Ba0.96Mg0.04TiO3 & Ba0.96Sr0.04TiO3 systems at 1 kHz frequency were found to be ∼ 576 & 0.019 and 2300 & 0.13, respectively. Curie temperature, Tc, of Ba0.96Sr0.04TiO3 and Ba0.96Mg0.04TiO3 samples were found to be around ∼105 and 75°C, respectively.

Phase formation and dielectric properties of Ba0.5Sr0.5TiO3 by slow injection sol–gel technique

A simple sol–gel process incorporating slow precursor injection technique was employed to synthesize homogeneous Ba0.5Sr0.5TiO3 nano powders. The Ba0.5Sr0.5TiO3 samples were subjected to calcination temperatures from 600 to 1,100 °C and sintering temperatures from 1,250 to 1,350 °C for the study of phase formation, crystallite size, particle distribution, and dielectric properties. Single phase Ba0.5Sr0.5TiO3 with a cubic perovskite structure was successfully synthesized after calcination at 800 °C. The average size of the nano particles is 42 nm with a narrow size distribution, and a standard deviation of 10%. The highest values recorded within the investigated range for dielectric constant, and dielectric loss measured at 1 kHz are 1,164 and 0.063, respectively, for Ba0.5Sr0.5TiO3 pellets calcined at 800 °C and sintered at 1,350 °C. Leakage current density measured at 5 V for the Ba0.5Sr0.5TiO3 pellet was found to be 49.4 pA/cm2.

A method of material design for systematic absence of X-ray diffraction

Materials with systematic absence of X-ray diffraction (XRD) peaks are desirable for conducting some special researches using X-ray diffraction or time-resolved X-ray scattering. This paper proposes a method for designing this kind of materials. It utilizes solid solution to reduce the structure factor of a selected reflection to zero by choosing proper components and their contents to let the reflection amplitudes from different atomic layers in a unit cell of the solid solution cancel each other completely. This method on how to select a solid solvent and how to calculate its content was illustrated using SrTiO3 as an example. A solid solution Sr1−xCaxTiO3 with a systematic absence of the (001) diffraction can be designed, and the value of x can be determined to be x=0.54 using an iteration calculation process. This result was verified by the experimental XRD pattern of a Sr0.46Ca0.54TiO3 sample.

A large thermoelectric figure of merit of La-doped SrTiO3 prepared by combustion synthesis with post-spark plasma sintering

We investigated figures of merit of La-doped SrTiO3 prepared by combustion synthesis (CS) with post-spark plasma sintering (SPS), focusing mainly on the effect of sintering time. Sr0.92La0.08TiO3 samples prepared by CS from oxides, carbonates, metals, and sodium perchlorate were SPSed at 1573 K for 1, 5, 15, and 30 min to measure their thermoelectric properties from room temperature to 1173 K. The 5-min-sintered sample recorded the largest figure of merit of 0.37 at 1045 K.

Thermoelectric Properties of Rare Earth-doped SrTiO3 Using Combination of Combustion Synthesis (CS) and Spark Plasma Sintering (SPS)

Thermoelectric properties of combustion synthesized and spark plasma sintered rare-earth-doped (La, Sm, Gd, Dy and Y) SrTiO3 was investigated from room temperature to 870 K from viewpoint of energy and time saving without deterioration in thermoelectric properties. All single phases of rare-earth-doped SrTiO3 were successfully synthesized and sintered with high densities. With temperature increasing, the absolute value of Seebeck coefficient of all the samples increased and the electric conductivity decreased; the power factor of all the samples decreased except Y-doped sample in the considering temperature range. In all the samples, the La-doped sample and the Y-doped sample had the highest and lowest power factor, respectively. The figure of merit of La-doped samples with different doping amounts was evaluated and the maximum figure of merit 0.22 was obtained at 800 K from Sr0.92La0.08TiO3 sample. Comparing Y and La-doped samples prepared by our synthesis method with that of conventional solid-state reaction method, the thermoelectric properties of our samples were relatively higher. Thus the combination of combustion synthesis and spark plasma sintering has a potential to prepare perovskite-oxide materials with relatively higher thermoelectric properties for high-temperature application.