TiO3 Ceramic Samples Research Articles

Improving of thermoelectric figure of merit in Sr0.925Dy0.075TiO3 ceramics

Rare earth doped SrTiO3 is one of the most promising oxide materials meeting the safety and stability requirements for potential applications in thermoelectric converters. This work aims to assess the feasibility of engineering SrTiO3-based materials to improve their thermoelectric performance. A comparative analysis of the thermoelectric properties of Sr0.925Dy0.075TiO3 ceramic samples obtained from preliminarily mechanically activated Sr0.925Dy0.075TiO3 nano-powder by two methods – solid-state reaction synthesis and spark plasma sintering – was carried out. Significant differences in the morphology of the samples lead to significant differences in the temperature dependences of electrical resistivity and the Seebeck coefficient. Ceramics obtained by solid-state reaction synthesis exhibit lower porosity and lower electrical resistivity. The thermoelectric power factor of such ceramics is 2–3 times higher than that of samples obtained by spark plasma sintering. The obtained value of thermoelectric figure of merit ZT = 0.41 at T = 673 K for Sr0.925Dy0.075TiO3 is the highest value among n-type oxide thermoelectric ceramics at a given temperature and maintains a tendency to increase with increasing temperature.

Enhancement of Thermoelectric Performance of Sr0.9La0.1TiO3-Based Ceramics Regulated by Nanostructures.

La-doped strontium titanite (Sr0.9La0.1TiO3) is a promising candidate for n-type oxide thermoelectric materials. However, the ZT values of this material are low, leading to low conversion efficiency. Improvements in this efficiency are required. In this work, a high ZT value of 0.50 was obtained for Sr0.9La0.1TiO3 ceramic samples by adding 10 wt % Bi2O3 sintering aids and 20 wt % nanosized Ti powders to the matrix material. Although Ti was oxidized to TiO2 during the sintering process, nanoscale phase interfaces were beneficial for phonon scattering and thermal conductivity reduction. Nanosized metallic Bi and Bi2O3 particles were observed. These two factors played an important role in reducing the thermal conductivity from 2.5 W/(m K) at room temperature to 1.31 W/(m K) at 1073 K. Nanostructure control using nanosized metal powders as additives combined with the Bi2O3 sintering aid paves a way for enhancement of thermoelectric properties of oxide thermoelectric materials.

Investigation on dielectric properties of Al2O3, ZnO and MgO doped Ba0.7Sr0.3TiO3 ceramics

Being an insulator material with high relative permittivity, Barium Strontium Titanate (BST) ceramics can be used extensively in many applications if its dissipation factor is reduced. In this paper, we investigate dielectric properties of Ba0.7Sr0.3TiO3 ceramics when doped with Al2O3, ZnO and MgO. At first, Ba0.7Sr0.3TiO3 ceramics was synthesized using conventional solid-state reaction technique. Further the Ba0.7Sr0.3TiO3 ceramic samples were doped with 0.5, 1.0, 2.0, 4.0 and 8.0 wt% Al2O3. Similarly Ba0.7Sr0.3TiO3 ceramic samples were doped with same weight percentages of ZnO and then MgO. After making pellets of all these samples, silver paste was coated for top and bottom electrodes to form ceramic based Metal-Insulator-Metal (MIM) capacitors. The dielectric properties were measured at room temperature using Hioki 3532-50 LCR Hi-Tester. It is noted that relative permittivity increases with dissipation factor (dielectric loss) irrespective of doping material and doping concentration. The dissipation factor achieved by 2.0 wt% ZnO doped Ba0.7Sr0.3TiO3 ceramics is 0.0087, which is promisingly very low. Further it is observed that 2.0 wt% ZnO doped Ba0.7Sr0.3TiO3 ceramics possesses highest figure of merit (relative permittivity to dissipation factor ratio) and hence optimum performance among the doping materials and doping concentrations considered.

Field-induced ferroelectricity in paraelectric phase of Barium strontium titanate

The nonlinear polarization and ferroelectricity in the paraelectric region of Ba0.7Sr0.3TiO3 ceramic samples are investigated. For this, samples are poled at a finite field and field-induced phase is analyzed through XRD, SEM, dielectric, impedance, and Piezo force microscopy high-frequency studies before and after poling. The Rayleigh-like dynamics is inspected along with the switching behavior in to samples. Our study suggests field-induced ferroelectricity in Ba0.7Sr0.3TiO3 due to polar distortion.

Study of Transport Properties and Microstructure of Lithium-Conducting Li0.33La0.56TiO3 Ceramic

Methods of X-ray diffraction analysis, impedance spectroscopy, and scanning electron microscopy were used to examine how thermal treatment modes affect the transport properties and microstructure of a lithium-conducting oxide ceramic of composition Li0.33La0.56TiO3, produced from powders synthesized by the sol-gel method. It was found that the cubic structure of Li0.33La0.56TiO3 can be stabilized as a result of quenching after the high-temperature of sintering at 1150°C. The conditions were determined in which Li0.33La0.56TiO3 ceramic samples can be obtained with bulk ion conductivity of ∼1 × 10−3 S cm−1 at 20°C, which corresponds to the maximum values for the ceramic based on lithium-lanthanum titanate.

Enhanced energy storage density and high efficiency of lead-free Ca1-xSrxTi1-yZryO3 linear dielectric ceramics

Ca1-xSrxTi1-yZryO3 (0.40 ≤ x ≤ 0.60, 0.1 ≤ y ≤ 0.4) ceramic samples were fabricated by conventional solid state method. The microstructure of ceramic samples were studied by XRD and SEM, and the influence of Zr4+ doping on the electric properties and energy storage performances were systematically studied. The results showed that the introduction of Zr4+ results in an inhibition of interfacial polarization and enhancement of grain boundary barrier effect. Ca0.5Sr0.5Ti1-yZryO3 ceramic samples exhibit excellent energy storage properties, with breakdown strength being on the order of 390 kV/cm versus 280 kV/cm for the counterpart Ca0.5Sr0.5TiO3 ceramic samples, together with energy efficiency above 95%. Meanwhile, a maximum breakdown strength of 390 kV/cm, a high energy storage density of 2.05 J/cm3 and an ultrahigh energy efficiency of 85% at high temperature of 125 ℃ were obtained in the sample with y = 0.1 as well, indicating it as a good candidate for linear energy storage fileds.

Size effect in nanocrystalline lithium-ion conducting perovskite: Li0.30La0.57TiO3

To investigate the nanometer size effect in nanocrystalline lithium-ion conducting perovskite, dense Li0.30La0.57TiO3 ceramic samples with average grain sizes in the range of 25 to 860nm were prepared by means of the spark plasma sintering. The microstructure of the samples was characterized by TEM, and their electrical properties were investigated by AC impedance spectroscopy as a function of grain size. When the grain size of Li0.30La0.57TiO3 decreases from 860 to 25nm, the lithium-ion conductivity decreases from 1.9×10−6 to 9.8×10−10S/cm at 0°C, while the grain boundary conductivity decreases by two to three orders of magnitude. According to the Schottky barrier model, the low grain boundary conductivity can be ascribed to the severe lithium-ion depletion in the space-charge layers. The low grain boundary conductivity, together with the very high grain boundary density, contributes to the significantly decreased lithium-ion conductivity.

Dielectric relaxation and conduction mechanism studies of BNT-BT-BKT ceramics

Electrical properties of 0.884Bi0.5Na0.5TiO3-0.036BaTiO3-0.08Bi0.5K0.5TiO3 ceramic samples were investigated in 100Hz to 1 MHz frequency range and in 200–450 °C temperature range using impedance spectroscopy technique. Real part of impedance versus frequency plots in lower frequency region revealed its PTCR behavior and NTCR behaviors in higher frequency region. Impedance study also suggested the presence of non-Debye type relaxation mechanism. Cole-Cole plots suggested two relaxation regions, in which grain and grain, grain boundary effects were prominent in lower and high temperature regions, respectively. DC conductivity followed Arrhenius law with an activation energy of ∼0.79 and 1.2 eV, which suggested that the charge carrier were cation vacancies in lower temperature region whereas cation vacancies and oxygen vacancies in higher temperature region.

Effect of sintering temperature on structural and dielectric properties of Bi and Li co-substituted barium titanate ceramic

Bi and Li co-substituted barium titanate, Ba0.98(Bi,Li)0.02TiO3 ceramic samples were sintered at different temperatures using conventional solid state sintering technique. X-Ray Diffraction patterns confirm tetragonal phase in all the sintered samples. Microstructure analysis using Scanning Electron Microscopy (SEM) reveals increasing grain sizes with an increase in sintering temperature. Dielectric spectroscopy performed in the range of 40Hz to 2MHz at room temperature shows that the dielectric constant increases with increasing sintering temperature, reaching a maximum of value of 1200 at 40Hz where the dielectric loss observed was less than 0.02 for samples sintered at 1300°C. Temperature dependant impedance spectroscopy data in the range of 30–300°C was used to measure AC conductivity. The activation energy of grains was deduced through Arrhenius plots. Loss tangent at different frequencies for 1300°C sintered samples was less than 0.1 over the entire temperature range. The high dielectric constant with a low dielectric loss at elevated temperatures make Ba0.98(Bi,Li)0.02TiO3 samples suitable for Multi-Layer Ceramic Capacitors (MLCC)s used in high-temperature applications.

Microwave sintered sol–gel derived BaTiO3 and Ba0.95La0.05TiO3 ceramic samples for capacitor applications

Sol–gel derived BaTiO3 and Ba0.95La0.05TiO3 powders were calcined at 700°C for 40min and sintered at 1100°C for 1h in a microwave furnace to obtain single-phase perovskite ceramic samples. About 98% of the theoretical density was obtained in the sintered BT ceramic samples. Room temperature (RT) dielectric constant (εr) and dielectric loss (tanδ) at 1kHz frequency of the BLT ceramic samples were found to be ~2220 and 0.005, respectively. High value of εr, low value of tanδ and negligible temperature coefficient of capacitance from RT to 60°C suggested the suitability of BLT ceramic samples for multi-layer capacitor applications.

High-temperature dielectric properties of incipient ferroelectric Gd0.5Na0.5TiO3

Gd0.5Na0.5TiO3 ceramic samples were prepared by the solid-state reaction method. Incipient ferroelectricity was confirmed in the sample. Dielectric properties were investigated at temperatures from room temperature to 1073K and the frequency range of 20 Hz–10 MHz. By means of electric modulus and impedance analysis, the sample was found to show two thermally activated relaxations with the high-frequency (low-temperature) one being the relaxation caused by hopping motion of oxygen vacancies and the low-frequency (high-temperature) one being the interfacial relaxation.

Pulsed electron emission of (Ba,Pb)TiO3ceramics

Pulsed, field-excited electron emission from the surface of (Ba,Pb)TiO3ceramic samples with hollow electrode has been investigated. The electron emission is observed in the temperature regions below as well as above the ferroelectric phase transition; it occurs, however, only during every other half-period of the exciting ac electric field. The time distribution of electrons emitted from (Ba,Pb)TiO3ceramics during the emissively active half-period of the field, consits of two current components which lie nearly in the middle and at the end of this half-period, respectively. The mechanism of this electron emission is discussed.