Doped Barium Titanate Ceramics Research Articles

Analysis of structural and electrical properties on rubidium doped barium titanate ceramics

Analysis of structural and electrical properties on rubidium doped barium titanate ceramics

Electrocaloric characterization of samarium doped barium titanate ceramics synthesized by sol-gel process

In this work, the effect of Sm ionic doping in BaTiO3 for electrocaloric effect has been studied. Ba1-xSmxTiO3 (x = 0, 0.02, 0.04, 0.06) ceramics were made via sol-gel method. All samples, according to XRD analysis, have a tetragonal symmetry that decreases with increasing Sm concentration. SEM micrographs revealed that, with the exception of the pure BaTiO3, all samples exhibited a dense microstructure. Compared to pure BaTiO3, thermal analysis using DSC measurement showed that as samarium content increases, the phase transition temperature decreases and the endothermic peak flattens. Dielectric measurements showed that the value of the loss tangent decreased and the value of the dielectric constant increased as the samarium doping concentration increased. Ferroelectric experiments highlighted that all samples were in the ferroelectric phase at room temperature. The remnant polarization increased with increasing Sm concentration. For Sm-doped ceramics the maximum value was Pr = 5.2 μC/cm2 for x = 6 %, under a maximum applied field of 25 kV/cm. An original customized pASC calorimeter was used in a direct method to study isothermal heat production resulting from the electrocaloric effect (ECE). According to the ECE results, the partial substitution of barium by samarium lowers the Curie temperature, which in turn lowers the temperature at which the electrocaloric effect is strongest. This extends the temperature range at which ECE can be used. For the sample Ba0.96Sm0.04TiO3, the maximum electrocaloric effect recorded is reached with a ΔT/ΔE = 0.343 K m/MV.

Investigation of structural, electrical and optical properties of lanthanum and zirconium doped barium titanate ceramics

In this work, Ba1-xLaxTi (1-y)-x/4ZryO3 (x = 0.015, y = 0.15, 0.25, 0.35) ceramics were fabricated by solid-state sintering. The structural, dielectric, and optical properties were investigated. The samples exhibited a tetragonal structure that became somewhat deformed towards pseudocubicity with increasing zirconium content. The inclusion of lanthanum created titanium vacancies and impeded the growth of grains. In y = 0.15 (BLZT15) composition, the grain size is 0.49 μm. The substitution of zirconium increased density by 3.17 gcm−3 in y = 0.25 (BLZT25), hence accelerating domain wall motion and enhancing the dielectric constant. The highest value of dielectric constant and grain size for y = 0.25 (BLZT25) ceramics was determined to be ∼3200 and 0.65 μm respectively. With increasing Zr4+ content, the optical band gap was observed to decrease from 2.75 eV to 2.40 eV. Lanthanum and Zirconium doped barium titanate ceramicswould be desirable materials for ceramic capacitors and electronic components.

Effect of sub-micron grains and defect-dipole interactions on dielectric properties of iron, cobalt, and copper doped barium titanate ceramics.

Introduction: Dilutely doped ferroelectric materials are of interest, as engineering these materials by introducing point defects via doping often leads to unique behavior not otherwise achievable in the undoped material. For example, B-site doping with transition metals in barium titanate (BaTiO3, or BTO) creates defect dipoles via oxygen vacancies leading enhanced polarization, strain, and the ability to tune dielectric properties. Though defect dipoles should lead to dielectric property enhancements, the effect of grain size in polycrystalline ferroelectrics such as BTO plays a significant role in those properties as well. Methods: Herein, doped BTO with 1.0% copper (Cu), iron (Fe), or cobalt (Co) was synthesized using traditional solid-state processing to observe the contribution of both defect-dipole formation and grain size on the ferroelectric and dielectric properties. Results and discussion: 1.0% Cu doped BTO showed the highest polarization and strain (9.3μC/cm2 and 0.1%, respectively) of the three doped BTO samples. While some results, such as the aforementioned electrical properties of the 1.0% Cu doped BTO can be explained by the strong chemical driving force of the Cu atoms to form defect dipoles with oxygen vacancies and copper's consistent +2 valency leading to stable defect-dipole formation (versus the readily mixed valency states of Fe and Co at +2/+3), other properties cannot. For instance, all three Tc values should fall below that of undoped BTO (typically 120°C-135°C), but the Tc of 1.0% Cu BTO actually exceeds that range (139.4°C). Data presented on the average grain size and distribution of grain sizes provides insight allowing us to decouple the effect of defect dipoles and the effect of grain size on properties such as Tc, where the 1.0% Cu BTO was shown to possess the largest overall grains, leading to its increase in Tc. Conclusion/future work: Overall, the 1% Cu BTO possessed the highest polarization, strain, and Tc and is a promising dopant for engineering the performance of the material. This work emphasizes the challenge of extricating one effect (such as defect-dipole formation) from another (grain size modification) inherent to doping polycrystalline BTO.

Phase transformation of cold-sintered doped barium titanate ceramics during the post-annealing process

The cold sintering technique has been developed to densify electroceramics at significantly low temperatures to tackle high energy consumption as well as compatibility of electroceramic components in modern electronics. However, obstacles still exist since, to obtain desired electrical properties, a post-annealing procedure at elevated temperatures must follow to trigger compulsory phase formation and/or grain growth. This work investigates the BaTiO3 and (Ba,Sr)TiO3 ceramics via both the cold and conventional sintering routes, and then compares their phase transformation behaviors during the post-annealing process. Results suggest that, given similar particle and grain sizes, the cold-sintered ceramics tend to retain a substantial part of the pristine tetragonal phase at annealing temperatures of <800 °C, while the cubic phase tends to dominate when annealed at >800 °C. This indicates a process-stimulated phase transformation that may guide or limit the selection of annealing temperature in practice.

Structural and optical properties of Sb–BaTiO3 and Y– BaTiO3 doped ceramics prepared by solid-state reaction

Barium titanate ceramics synthesized employing the solid-state method were investigated for their optical properties and phase transition characteristics. X-ray diffraction method and Scanning electronic microscopy were used to reveal a typical perovskite structure. The average grain size of (Sb or Y) doped barium titanate ceramics falls considerably as the concentration of Sb2O3 or Y2O3 increases. XRD investigation revealed the creation of cubic crystal structure. The impact of (Sb, Y) concentration on structure, including the appearance of various tetragonal phases, grain size reduction, and microstructure development, was investigated. The cell parameters of the formed phases decrease from 4.05418 to 3.99385 and from 4.05418 to 3.98605 as the doping rate increases Ba1-x SbxTiO3 and Ba1-xYxTiO3 ceramics respectively,where (x = 0.00,x = 0.05, x = 0.1, x = 0.15 and x = 0.20).Crystallites sizes of Sb-doped BaTiO3 crystals changes from 34.59 to 40.47 nm when dopant concentration is changed from 0.05 to 0.20. For Y doped BaTiO3 crystallite change in size from 28.92 to 29.10 nm. Additionally, assessed were the absorption coefficient (α), extinction coefficient (k), and refractive index (n). When the concentration of Sb3+ or Y3+ ions is increased from 0.05 to 20%, the values of the energy bandgaps for Ba1-x SbxTiO3 and Ba1-xYxTiO3 increase from 3.11 to 3.17 eV and 3.07–3.14 eV, respectively. It is found that the refractive index(n) rises as wavelength rises. It has been shown that the absorption coefficient (α) increases when photon energy increases. It is found that the extinction coefficient (k) decreases with wavelength. The extinction coefficient (k) and the absorption coefficient (α) are both observed to decrease with increasing concentration for all compositions.

Microstructural tuning: A route towards realization of enhanced pyroelectric figure of merits of Sr and Zr doped barium titanate ceramics

In this article, we emphasize microstructural tuning approach to realize an enhanced pyroelectric energy conversion associated figure of merits (FOMs) in ferroelectric Ba0.85Sr0.15Zr0.1Ti0.9O3 (BSZT) ceramics. To develop porous microstructure in the ceramics, we employ BURPS (burning out of polymer sphere) technique using PMMA as a pore-forming agent. In present scenario, the porosity in the ceramics is intentionally being introduced for the noble cause of enhancement in pyroelectric figure of merits (Fe*, Fe,Fv). Here, we investigate the effect of porosity on structural, morphological, dielectric and ferroic characteristics and its correlation with pyroelectric property. We note that, in comparison to dense ceramic, the porous ceramics with 6.9% porosity level shows remarkable enhancement of 29% in Fe*, 24% in Fe, 53% in Fv at 303 K. The microstructural engineering in pyroelectric/ferroelectric ceramics opens the effective route towards the realization of high piezoelectric and pyroelectric figure of merits. Ferroic ceramics with good figure of merit are highly anticipated for their decisive role in the area of green energy harvesting, energy storage and infrared detection.

Scale-Dependent Dielectric Properties in BaZr0.05Ti0.95O3 Ceramics.

In the present work, BaZr0.05Ti0.95O3 ceramics with grain sizes between 0.45 and 135 µm were prepared by solid-state reaction and classical sintering. The effect of grain size on dielectric properties was systematically explored, and it was found that dielectric permittivity reaches a maximum value for grain sizes between 1.5 and 10 µm and then rapidly drops for larger grain sizes. A numerical finite element method was employed to eliminate the effect of porosity on the effective values of permittivity. The results indicate that it is possible to have a critical size in slightly doped barium titanate ceramics with enhanced functional properties for a grain size between 1.5 and 10 µm.

Enhanced Dielectric properties of Bismuth Doped Barium Titanate Ceramics with their Structural and Compositional Studies

Several strategies have been employed to tune the functional properties of environmentally friendly Barium titanate (BaTiO3). In this work, bismuth (Bi) doped BaTiO3 with a general formula Ba1-xBi2x/3TiO3 (where x = 0.00, 0.01, 0.02, 0.03, 0.04, 0.05 and 0.06) were prepared by the conventional solid-state reaction method. The effect of Bi on the structure of BaTiO3; and their morphological and compositional studies were carried out by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) respectively. Furthermore, the effect of Bi on the transport properties of BaTiO3 was investigated. Our studies revealed that for x = 0.01, Bi doping gives rise to the highest tetragonality of the crystal with more homogeneous grains and pores distribution among all the doping concentration. Furthermore, the dielectric constant for x = 0.01 samples has been observed to be the highest, which is consistent with the structural and morphological studies. Also, the tetragonal to cubic phase transition temperature (Curie temperature) of the sample is found to increase with increasing Bi doping concentration. Our studies suggest that the higher value of the dielectric constant with higher Curie temperature can be obtained by a small amount of Bi doping (x = 0.01), which has potential applications in various electronic and energy storage devices.

Structure and morphology of yttrium doped barium titanate ceramics for multi-layer capacitor applications

Multilayer ceramic capacitors (MLCCs) are essential components in pulsed power systems (PPS) with high charging and discharging capacity for energy storage applications. Yttrium oxide (Y2O3)–doped barium titanate (BaTiO3) (BTY) ceramics with a chemical formula of 60 BaO + (40-x) TiO2 + x Y2O3 (x = 2, 8 and 15) have been synthesized by usual solid state reaction process. These ceramics are analyzed by XRD, FTIR and SEM techniques. The crystalline nature of the undoped BaTiO3 (BT) and Y2O3 doped ceramics were confirmed by XRD analysis. In addition, a doublet peak at 30.2° has been shifted to lower angles as the concentration of Y3+ ions increases. The functional groups of these BT and BTY2 ceramics were investigated using FTIR analysis. Morphological studies were performed through scanning electron microscopy (SEM), revealing the average particle size of BT 331 nm and BTY2 136 nm from Image-J software.

Defect properties of vanadium doped barium titanate ceramics

X-ray diffraction (XRD) patterns, electron probe microanalysis (EPMA), electron paramagnetic resonance (EPR) powder spectra (9 and 34 GHz) and the magnetic susceptibility of BaTiO3 + 0.04 BaO + 0.01 V2O5 ceramics were studied to investigate the valence states of V ions and their solubility in the BaTiO3 lattice. In samples sintered at 1400 °C in air, only about 0.1 mol% V is incorporated in the BaTiO3 lattice being in V4+ and V5+ valence state, respectively. 95% of the nominal V dopant content occurs in the secondary phase Ba3(V/Ti)2O8. All BaTiO3 samples investigated are in tetragonal phase at room temperature. In the as-sintered samples V4+ is detected at temperatures T < 20 K by its hyperfine structure (HFS) octet due to the nuclear spin 7/2 of 51V. Samples post-annealed in H2/Ar atmosphere at 1200 °C exhibit a further HFS octet occurring at T > 25 K and vanishing at T > 250 K, which is caused by V2+ ions. This spectrum is characterized by a simultaneous HFS and fine structure splitting constituted by allowed and forbidden transitions. Both V4+ and V2+ ions are incorporated at Ti4+ sites of the BaTiO3 lattice.

Investigation on the Correlation between Structural and Electrical Properties of Lanthanum Doped Barium Titanate Ceramics

The structure-property relationship of 0.3, 0.5 and 0.7mole% lanthanum (La2O3) doped Barium titanate (BaTiO3) ceramics prepared by solid state sintering under different sintering conditions were investigated in this research. The raw materials were La2O3 (grain size=~80nm) and BaTiO3 (grain size=100nm) powders. Field Emission Scanning Electron Microscope (FE-SEM) was used to examine grain size and surface morphology of sintered pellets &amp; X-Ray Diffraction analysis was conducted to identify crystal structure. The results showed significantly improved grain size and electrical properties of BaTiO3 for 0.5 mole% La2O3 with desired grain size (0.8-1.3μm), high densification (&gt;90% theoretical density) and stable dielectric constant (12700) at room temperature (f=100Hz) by lowering curie temperature around 30oC by sintering at 1300oC for 8 hrs. A gradual deterioration follows with increased doping concentration. So the research revealed that proper La3+ concentration can inhibit grain size and lower Curie temperature hence significantly improving the electrical properties of BaTiO3 ceramics.

Chemical bonding and charge density distribution analysis of undoped and lanthanum doped barium titanate ceramics

A-site deficient, Lanthanum substituted Ba1−xLa2x/3TiO3 (x =0.000, 0.005, 0.015, 0.020 and 0.025) ceramics have been synthesized by chemical route. The effects of lanthanum dopant on the BaTiO3 lattice and the electron density distributions in the unit cell of the samples were investigated. Structural studies suggested the reduction in cell parameters and shrinkage in cell volume with the increase in lanthanum content. Chemical bonding and electron density distributions were examined through high resolution maximum entropy method (MEM). The mid bond electron density values revealed the enhancement of covalent nature between titanium and oxygen ions and predominant ionic nature between barium and oxygen ions. Average grain sizes were estimated for the undoped and doped samples. SEM investigations showed the existence of smaller grains with large voids in between them.

Structural, dielectric and electrical analysis of Ba2−xLa4 + 2x/3Ti8O24ceramics system with frequency and temperature

In the present investigation, the study of structural, dielectric, and electrical properties of lanthanum doped barium titanate ceramics with structural formula Ba2−xLa4 + 2x/3Ti8O24 (x = 0.0, 0.2, 0.4, 0.6) was reported. The target samples were obtained by mixed oxide route technique. Preliminary X-ray diffraction studies revealed the single phase formation in the orthorhombic crystal structure. The surface morphology of the samples showed that there were well-defined grains of different sizes and shapes that were homogenously distributed on the surface of samples. The approximate grain size was also calculated. The dielectric properties like dielectric constant (er), loss tangent (tan δ), and AC conductivity (σac) and temperature coefficient of resonant frequency were studied in the temperature range of 298—623 K and frequency range of 10 KHz–1 MHz. Dielectric response showed low temperature dispersion in dielectric properties at low frequency. This showed the space charge phenomenon arising due to defects. DC resistivity measured at room temperature for different compositions decreased with increase in substitution. All four samples gave very small value of temperature coefficient of resonant frequency. Sample with x = 0.6 showed minimum value of τf. Thus, the prepared samples could be the dielectric materials for the practical applications like resonators, filters, antennas, etc. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1679–1686, 2016

Conductivity relaxation experiments on donor doped barium titanate ceramics: Effect of microstructure

The re-equilibration kinetics of n-conducting BaTiO3 ceramics upon a sudden change of the oxygen partial pressure of the surrounding gas phase has been investigated by application of conductivity relaxation experiments at 900°C using the van der Pauw method. The relaxation curves show two distinct equilibration processes. The first (fast) relaxation refers to diffusion of oxygen most probably via oxygen vacancies along the core regions of grain boundaries. The second (sluggish) relaxation process is related to slow diffusion of cation vacancies from the grain boundaries into the bulk. Even after 1000h, disk-shaped samples with an average grain size of 4μm and thicknesses between 0.5 and 1.0mm are not fully equilibrated with the gas phase. A modified Schottky barrier model, taking account of diffusion profiles of cation vacancies at the grain boundaries, enables a phenomenological interpretation of the conductivity relaxation curves. In addition, the defect chemistry of core regions of grain boundaries in n-type BaTiO3 ceramics has been studied by conductivity measurements as a function of oxygen partial pressure [0.5>p(O2)/bar>0.001].

X-Ray Diffraction and Dielectric Constant of Lanthanum Doped Barium Titanate Ceramics

Undoped barium titanate and lanthanum (La) doped barium titanate (BaTiO3) were studied for ferroelectric properties with the formula of Ba1-xLaxTi1-x/4O3 for x=0.1 and being prepared by using conventional solid state method reaction. The pure phase of this composition which x=0 were found at final heating temperatures starting from 1300°C and x=0.1 at 1350°C for overnight in air with intermittent grinding. The changes in the crystal structure of the composition were detected by using X-ray diffraction. Impedance Spectroscopy analysis is carried out to determine the dielectric properties for undoped BaTiO3 and La doped BaTiO3 for x=0.1.

Dielectric and Piezoelectric Properties of Microwave Sintered Ba1-xRexTiO3 Ceramics

Lead free piezoelectric ceramic Ba1-xRexTiO3 (Re = Ce and Pr with x = 0.003) were prepared through microwave sintering route using 5% SiO2 as sintering aid. The dielectric, impedance and piezoelectric properties were studied over a wide range of temperature. Pr doped barium titanate showed higher value of dielectric constant around 15,099. The electromechanical coupling factors at 225°C are 0.9985 and 0.9978 for Ce and Pr doped barium titanate ceramics respectively. The d33 values for Ce and Pr doped barium titanate ceramics at 225°C are 368 nm.V−1 and 470 nm.V−1 respectively. The d33 value decreased with the increase of temperature and the values at 600°C are 10 nm.V−1 and 8 nm.V−1 for Ce and Pr doped barium titanate ceramics respectively.

Study of the Dielectric Properties of Europium Doped Barium Titanate Ceramics by an Impedance Spectroscopy

The barium titanate (BaTiO3) and the BaTiO3 + 0.1wt.% Eu2O3 ceramics were prepared by a conventional ceramic method. The structural studies were carried out by means of an X-ray diffraction technique. The influence of the grains and the grain boundaries on the electrical properties was investigated using a impedance spectroscopy. This technique enables us to determine the values of grain and grain boundary resistance. The results show that the Eu doping leads to a significant reduction in the resistance value of the grains (˜105Ω) with respect to the pure BT ceramics (˜107Ω). The conductivity processes were determined from the Arrhenius behaviour of grain and grain boundary resistances.

Double hysteresis loop in BaTi1−xHfxO3 ferroelectric ceramics

Hafnium doped barium titanate ceramics were prepared by the conventional solid-state reaction method. The structural, microstructure and ferroelectric properties were analyzed with varying Hf concentration. It is found that the crystal structure of the solid solution remains in tetragonal phase with the decrease of tetragonality by increasing of Hf ion concentration. The grain growth habit is significantly depending upon Hf ion concentration. The remnant polarization and coercive field is decreased along with narrowing of the central portion of the ferroelectric hysteresis loop with the increasing of Hf ion concentration. The double hysteresis loops are associated with the onset of an antiferroelectric order and it is increased with increasing of Hf ion concentration.

Nonlinear properties of antimony-doped BaTiO3 ceramics

Barium titanate nanopowders doped with various concentrations of antimony were synthesized by polymeric precursors method based on modified Pechini process. Obtained powders were pressed and sintered at 1,573 K for 8 h. The temperature dependence of dielectric permittivity pointed on the significant influence of added antimony on dielectric properties of obtained materials. The analysis of impedance spectrum in the temperature range 250–445 K has shown the presence of one semicircle that corresponds to the grain contribution but impedance spectrum at 773 K showed possible overlapping of two semicircles indicating also grain boundary resistivity. The total specific resistivity obtained from impedance analysis showed modest PTCR jump in the heavily doped barium titanate ceramics. The electric field dependence of permittivity of the ceramics was investigated in detail. The experimental data were analyzed using Johnson model.