Pure Barium Titanate Research Articles

Obtaining the highly pure barium titanate nanocrystals by a new approach

Purity and synthesis temperature of nanocrystals are key challenges facing the scientific community. Herein a novel solid-state approach to synthesize fine BaTiO3 nanocrystals with narrow size distribution using a high-speed ball-milling process is reported. In order to improve the kinetics of this reaction, the starting materials, BaCO3 and TiO2, were milled for 10 h before mixing and initiating the synthesis reaction. The contribution of this step to the BaTiO3 formation is analyzed by XRD diffractometry and FE-SEM techniques. It was found that the use of the mechanically activated starting materials favors the decomposition of BaCO3 at low temperatures and improves the Ba2+ diffusion through the formed BaTiO3 layer. In consequence, very fine BaTiO3 nanocrystals free from the secondary phases were obtained at a lower temperature in contrast to the previous works.

Review on Preparation and Properties of High-K Dielectric Material Based on Lanthanum Doped Barium Titanate

Lanthanum doped barium titanate (BaTiO3) were studied for high-K dielectric and exhibit a relaxor ferroelectric properties and it can be prepared by using various method. Relaxor ferroelectric offers a wide temperature and frequency range of application for materials with high dielectric constant for microelectronic application. This paper reviews the preparation methods, the important features, advantages and limitation for the lanthanum doped barium titanate. Thus, the phase purity and mixture selected also been review on the second part of the article. The article concludes with a brief discussion of the methods with good dielectric behavior. The objectives of this paper are to determine the selection of suitable preparation methods and the properties of the high-K dielectric based on pure barium titanate and lanthanum doped barium titanate.

Formation mechanism and characteristics of lanthanum-doped BaTiO3 powders and ceramics prepared by the sol–gel process

Pure and lanthanum-doped barium titanate nanopowders described by two different formulae, as Ba1−xLaxTiO3, for lower La concentrations (0≤x≤0.005) and Ba1−xLaxTi1−x/4O3 for higher La concentration (x=0.025) were prepared by an alkoxide sol–gel method. Single phase compositions were obtained after annealing at 900°C for 2h, in air. The increase of the lanthanum content causes structural and morphological changes in the oxide powders, including the evolution of the unit cell from tetragonal toward a cubic symmetry, the particle size decrease and a higher aggregation tendency.SEM investigations of the ceramics sintered at 1300°C for 4h indicate significant changes of the microstructural features (strong decrease of the average grain size and increase of the intergranular porosity) with the raise of La amount. Lanthanum addition to barium titanate prepared by sol–gel induces a more significant shift of the Curie temperature toward lower values, than that one reported in literature for ceramics of similar compositions, but processed by the conventional solid state method. The compositions with smaller La amount (x≤0.005) show semiconducting properties at room temperature and high relative dielectric permittivity values, while the undoped ceramics and those doped with higher La content (x=0.025) are good dielectrics. The ceramic with x=0.025 exhibits acceptable low losses, a very diffuse ferroelectric–paraelectric transition and Curie temperature closed to the room temperature, being thus susceptible for high tunability applications.

English

We have studied the influence of a new lead-free Fe/Li incorporated H-Bt prepared by the solid state reaction method and compared it with pure hexagonal barium titanate. The hexagonal phase was stabilised at room temperature due to substitution with Fe-Li. Lattice constants were refined as a = 5.720 A.U., c = 13.96 A.U. Both XRD and IR imply that Li enters octahedral as well as Ba sites. Dielectric measurements show an increase from 800 to 105 indicating sample to be potential colossal dielectric constant (CDC) material. Abnormal grain growth (AGG) was restricted in the substituted sample and normal grain growth was observed.

Thermal, dielectric and ferroelectric properties of 0.925BaTiO3–0.075Pb(Zn1/3Nb2/3)O3 ceramic

New low-lead content 0.925BaTiO3–0.075PbZn1/3Nb2/3O3 (0.925BT–0.075PZN) ceramic was fabricated by the spark-plasma-sintering method. X-ray diffraction measurements showed that the obtained specimen possesses a pure perovskite structure. The microstructure investigation indicated a dense ceramic structure with 95% relative density determined by the Archimedes method. Composition undergoes a sequence of phase transitions as pure barium titanate (BT). Dielectric study revealed that the electric permittivity decreases at its maximum and the phase transition shifts to a higher temperature after lead zinc niobate doping of BT. Besides, the dielectric dispersion and polarization increases and decreases, respectively. Obtained results were discussed in term of the difference between ionic size and its mass and local elastic and electric fields. The results show that investigated ceramic is one of the promising low-lead materials for electronic applications.

Synthesis and Characterization of Barium Titanate by Solid-State Reaction

Solid-state reactions were used to synthesize pure and doped barium titanate powder. Barium titanate formation with tetragonal perovskite structure was detected by X-ray diffraction and occurred at a temperature above 700°C for pure powder and 500°C for doped powder. However, quite crystalline samples were observed only at 800oC and 600°C for pure and doped barium titanate, respectively, what made the refinement of the synthesized powders possible. They were characterized by X-ray diffraction and Fourier transform infrared spectroscopy and scanning electron microscopy. X-ray diffraction data was analyzed by using the Fullprof Rietveld refinement approach, Thompson-Cox-Hastings pseudo-Voigt with function. The refinement method was effective in the study of the temperature influence on the microstructure of the analysis of pure and doped barium titanate.

FTIR Study of Nanostructure Perovskite BaTiO3Doped with Both Fe3+and Ni2+Ions Prepared by Sol-Gel Technique

Pure barium titanate BaTiO3 (BT) and BT doped with two di erent transition elements Fe 3+ and Ni at 5 mol.% (BT5Fe and BT5Ni, respectively) as constant concentration in powder form have been prepared by sol gel method using barium acetate, titanium(IV) n-butoxide, iron and nickel nitrates as precursor materials. The microstructure of BT and the in uence of Fe and Ni dopants on it were investigated by X-ray di raction and Fourier transform infrared spectroscopy. X-ray di raction shows that tetragonal phase is dominant for pure BT sintered for 4 h at 800 ◦C. Scanning electron microscopy and transmission electron microscopy were used to study surface morphology and particle size distribution for BT5Fe and BT5Ni, respectively. The presence of hydroxyl defects were veri ed by Fourier transform infrared spectroscopy for (BaTi1−xFexO3−x/2) (BTxFe), where x = 0.005, 0.01, 0.05, and 0.07 and (BaTi1−xNixO3−x/2) (BTxNi), where x = 0.005, 0.01, 0.03, 0.05, and 0.07.

Characteristics of BaTiO3–carbon nanotube composite synthesised by mechanical milling

Barium titanate–0.25 wt-% carbon nanotube nanocomposite was synthesised by the mechanical milling process. The nanocomposite was characterised by X-ray diffraction, SEM, thermal gravimetric analysis and LCR meter. The thermal stability of the composite was lower than that of pure barium titanate, which was attributed to the presence of trace amounts of sodium dodecyl benzene sulphonate. The relative dielectric constant of the composite was significantly greater and was attributed to the Maxwell–Wagner polarisation effect.

Dielectric Properties of Barium Zirconate Titanate Ceramics Prepared using Hydrothermal Method

Barium titanate (BT) with different content of Zr (0.001 and 0.008) is prepared using
 hydrothermal method at 150oC for 2h. It is found that with increased of Zr content, the lattice
 constant a increases while the lattice constant c decreases. It is observed also that the curie
 temperature peak shift to lower temperature and be broadened. The lattice constants have the same
 value at Zr content equal to 0.027. For BT samples sintered at 1000oC, the dielectric constant below
 Curie temperature is about 2000 and becomes 6000 at Curie temperature. With the increased of
 sintered temperature (1200oC), the dielectric constant is about 4000 and becomes 9600 at Curie
 temperature (Tc). At Curie temperature the dispersion in BZT1 (x=0.001) is distinct than that of
 pure BT. At near T1 (temperature at phase transition from tetragonal to orthorhombic) the little
 broadening is observed of BZT1 in comparing with BT. The dispersion of BZT2 (x=0.008) is more
 distinct than that of BZT1 (x=0.001) and BT. After adding gradual increasing of Zr, both T1
 (tetragonal to orthorhombic phase transition) and Tc are shifting to each other.

Substitution Effects of Gd and Mg on Cubic Structure of Barium Titanate

Barium titanate BaTiO3 is a ferroelectric oxide with low dielectric loss and high permittivity, which makes it a good insulator for industrial uses. However, the pure barium titanate is not always used for electronic devices. Gd- and Mg-doping in barium titanate is effective for the dielectrics in multilayer ceramic capacitors MLCCs, for example, to attain the uniform temperature-variation of dielectric constants in the wide temperature-range where MLCCs are practically used, while the Curie temperature is significantly decreased [1]. In this study, the structural characteristics of Gd- and Mg-substituted barium titanate (Ba,Gd)(Ti,Mg)O3 (BGTM) in the cubic phase were investigated to clarify the effects of Gd- and Mg-substitution on the crystal structure and the chemical bonding. Synchrotron radiation x-ray powder diffraction measurements were carried out using the BGTM samples with the Mg content of x = 0 ~ 0.1. Lattice parameters, substitution sites of the Gd and Mg ions, thermal parameters, and electron charge density distributions in the crystals were analyzed by using the maximum entropy method (MEM)/Rietveld method. The Curie temperature decreased with increasing x. The phase transition did not take place in BGTM with x > 0.05. The Gd ion was confirmed to be substituted for the Ba ion with larger thermal vibration amplitude than that of the Ba ion. The amplitude was almost independent of the Gd content. It was revealed that the Gd ion occupied the off-centered positions slightly form the Ba-site along the <100> directions at lower temperatures. Difference in thermal behaviors of the Gd and Ba ions can be attributed to the size difference between the smaller Gd ion and the larger Ba ion. The Mg ion was observed on the Ti-site. The substitution of the Mg ion for the Ti ion suppresses the ferroactivity of the Ti ion, which causes the lowering of the Curie temperature.

A Mechanistic Study of Nanoscale Structure Development, Phase Transition, Morphology Evolution, and Growth of Ultrathin Barium Titanate Nanostructured Films

In the present work, an improved method is developed for preparing highly pure ultrathin barium titanate nanostructured films with desired structural and morphological characteristics. In contrast to other approaches, our method can be carried out at a relatively lower temperature to obtain barium titanate ultrathin films free from secondary phases, impurities, and cracks. To reach an in-depth understanding of scientific basis of the proposed process, and in order to disclose the mechanism of formation and growth of barium titanate ultrathin film, in-detail analysis is carried out using XRD, SEM, FE-SEM, and AFM techniques aided by theoretical calculations. The effects of calcining temperature on the nanoscale structure development, phase transition, morphology evolution, and growth mechanism of the ultrathin barium titanate nanostructured films are studied. XRD results indicate that the reaction leading to the formation of the barium titanate initiates at about 873 K (600 °C) and completes at about 1073 K (800 °C). Moreover, secondary phases are not detected in the XRD patterns of the ultrathin films which this observation ensures the phase purity of the ultrathin films. The results show that the ultrathin films are nanothickness and nanostructured leading to the enhancement of rate of diffusion by activating short-circuit diffusion mechanisms. The high rate of the diffusion enhances the rate of the formation of barium titanate and also prevents from the formation of the secondary phases in the final products. SEM and AFM results indicate that the deposited ultrathin films are crack-free exhibiting a dense nanogranular structure. The results indicate that the root-mean square (RMS) roughness of the ultrathin films is in the range of 1.66 to 6.71 nm indicating the surface of the ultrathin films is smooth. RMS roughness also increases with an increase in the calcining temperature which this observation seems to be related to the grain growth process. Finally, based on the observed results, the mechanism of the formation and growth of the ultrathin barium titanate nanostructured films is deeply disclosed.

Broadband dielectric spectroscopy of BaTiO3–Ni0.5Zn0.5Fe2O4 composite ceramics

The behavior of three xBaTiO3–(1−x)Ni0.5Zn0.5Fe2O4 composites (x=0.50, 0.60 and 0.70M ratios) were studied using the broadband dielectric spectroscopy methods in the broad frequency and temperature ranges. x=0.70 composition clearly exhibits similar dielectric response to that of pure barium titanate, while the response of the composite with the highest concentration of nickel–zinc ferrite is largely influenced by the conductivity, especially at the highest temperatures and lowest frequencies. In the non-dispersive region the permittivity gradually increases with increasing level of high-permittivity barium titanate material as a result of the “sum property”, while the low frequency behavior described by complex contributions do not show a systematical modification with the changing composition. At around 108–1010Hz frequencies the dispersion process was observed and approximated with the Cole–Cole equation, finding the parameters describing the process. Presumably, lattices of barium titanate in close vicinity to nickel–zinc ferrite could lead to the distortion and some shifting of ions in barium titanate lattice, possibly affecting the states that Ti can occupy. The conductivity process was approximated with the recently suggested generalized Joncher’s relationship, which manages to describe both low and high frequency conductivity processes observed. The computed corresponding activation energies for all the samples were found to be similar to oxide composites containing ferrites with ionic conduction contributions.

Effect of doping on the structural parameters of pure and doped barium titanate nano powders synthesised by sol-gel emulsion technique

Ba1-xDxTiO3, ceramic powders was synthesised using sol-gel-emulsion technique. Structure of the synthesised powders was analysed using X-ray diffractometer from which the lattice parameters were deduced. Effect of doping as a function of atomic radii and the concentration of dopant (D) was studied on these parameters. XRD analysis showed the synthesised material to possess pseudocubic symmetry. Crystallite size of these powders varied between 15.98–40.72 nm. Cell volume shrinkage observed on doping pure BaTiO3 was noted to be between 0.02–2.27%. Change in % tetragonality for the synthesised powders was 16.62–21.57. The experimental lattice parameter values matched more closely when calculated using the empirical formula devised by Jiang et al. than that using Rick Ubic. The |%error| assuming six-fold coordination for the doped BaTiO3 powders was between 0.0168% to 0.9314% using the empirical formula devised by Jiang et al. and 0.0296% to 1.0852% using the formula given by Rick Ubic.

Low Temperature Synthesis of Barium Titanate Powder by a Modified Sol-Gel Method

Barium titanate (BT) is one of the most important lead-free ferroelectric materials with perovskite crystal structure and high dielectric constant. Among synthesis techniques of BT, sol-gel processing has attracted considerable interest due to the control of composition, surface morphology engineering, low temperature processing, and low equipment cost. In this research, nanocrystalline BT powders were prepared by a modified sol-gel technique. Acetic acid and water were used as solvents. The samples were heat treated at various temperatures, times, and rates for investigating the effect of heat treatment parameters on formation of single perovskite crystalline phase. According to the results of X-ray diffraction analysis, highly pure BT powder with minimum secondary phases (Magneli) was obtained after calcination at 650 °C for 1 h with the rate of 10 °C/min. The grain size and morphology of BT powders were obtained by field emission scanning electron microscopy which indicated the size of about 60 nm.

La-doped and La/Mn-co-doped Barium Titanate Ceramics

Barium titanate ceramics doped with 0.3 mol.% lanthanum and co-doped with 0.3 mol.% lanthanum and 0.05 mol.% manganese were investigated. The powders were prepared by a modi ed polymeric precursor method based on the Pechini process. The ceramics were obtained by sintering at 1300 ◦C for 8 h. The in uence of dopants on structural changes and grain size reduction was analyzed. The presence of dopants in uenced the tetragonality of the barium titanate crystal structure. Reduction of polygonal grain size with dopant addition was noticed. In the doped ceramics, characteristic phase transitions were shifted to lower temperatures in comparison with pure barium titanate. The dielectric permittivity value showed the tendency of a slight increase with lanthanum addition and further increase with adding of manganese. La as a single dopant increased the di useness of phase transitions indicating the formation of a di use ferroelectric material but in the co-doped ceramics the phase transition di useness decreased. The resistivity of the co-doped ceramics was higher than for lanthanum doped ceramics, indicating possible segregation of manganese at grain boundaries that in uenced the total resistivity of the material.

Polarization Mechanism of Fine-Grained BaTiO<sub>3</sub> Ceramics at High Temperature Region

Pure Barium titanate (BaTiO3) ceramics with grain sizes of 0.6, 1.5, and 18 μm on average were prepared by using a two-step sintering method. The wideband dielectric spectra in the range from kHz to THz were measured at 25 and 150 °C to understand the polarization mechanism of fine-grained BaTiO3ceramics. It was revealed that the dipole and ionic polarizations decreased with decreasing grain size at 25 and 150 °C when the grain size was smaller than 1 μm. These mechanisms were interpreted as a grain boundary effect.

Structure and Dielectric Properties of Pure and Zinc Oxide-Doped Barium Titanate

Abstract The effects of zinc oxide addition and sintering parameters on the structure and dielectric properties of barium titanate are observed. Different percentage of ZnO ranging from 0.30 to 1 wt. % is doped in barium titanate. Both the doped and undoped samples are sintered at temperatures ranging from 1250°C to 1325°C at different soaking times. The amount of densification of the doped and undoped samples is measured in terms of percentage theoretical density. Grain size and microstructural analysis is performed by a scanning electron microscope (SEM). Lattice parameters and tetragonality of doped and undoped barium titanate are calculated from x-ray diffraction pattern obtained from x-ray diffractometer (XRD) test. Dielectric properties of the samples are measured by an impedance analyzer. It is found that all the doped samples obtain their maximum percentage theoretical density at a lower sintering temperature compared to the undoped sample. SEM study reveals that the doped samples always show smaller grains compared to the undoped sample. Significant grain growth is observed in all of the samples at sintering temperatures above 1300°C. The evidence of surface melting is observed in 1 wt. % ZnO-doped sample soaked at 1325°C for 2 h. The presence of liquid at that sintering condition is explained by the doping mechanism of Zn2+ in BaTiO3. Correlation among the grain size, tetragonality, and dielectric properties of the doped and undoped samples are also discussed.

Influence of Oxygen Substoichiometry on the Dielectric Properties of BaTiO3‐δ Nanoceramics Obtained by Spark Plasma Sintering

Oxygen‐deficient BaTiO3‐δ nanoceramics were prepared by spark plasma sintering. Partially reduced raw nanopowders led to unusual dielectric properties. A short postsintering treatment was performed to reach a high εr/tan δ, which makes them attractive for industrial applications such as low‐frequency capacitors. Surprisingly, our ceramics also remained black even after annealing for 5 days at 850°C in air, indicating the presence of barriers against oxygen diffusion. This exceptional behavior in pure barium titanate was consistent with a core–shell structure made of semiconductive grains and insulating grain boundaries, due to the presence of Ti3+/Ti4+ and oxygen vacancies.

Fabrication and characterization of cerium doped barium titanate/PMMA nanocomposites

The cerium doped barium titanate (BaTiO3:Ce)/poly methyl methacrylate(PMMA) polymer nano-composites (PNC) were successfully fabricated via solvent evaporation method with microwaves (2.4 GHz) heating. The X-ray diffraction measurements confirm the formation of barium titanate (BT) with crystallite size ranges from 55 to 62 nm. Differential scanning calorimetry study shows that the glass transition temperature (Tg) directly affected by microwaves heat treatment and particle size of filler. The broadband dielectric spectroscopy was employed to investigate the frequency and temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 75 kHz to 5 MHz and temperature range 80–400 K. The introduction of different BT fillers in PMMA enhance the dielectric constant of PNCs drastically and give a smooth response in frequency range mentioned above. The loss factor of the composite can be suppressed by using cerium doped barium titanate filler rather than pure barium titanate filler.

Effect of vanadium doping on the electric properties of barium titanate hafnate ceramics

Pure and V-doped barium titanate hafnate (BaHf0.1Ti0.9O3, short for BHT) ceramics were prepared by sol–gel method. The microstructures, dielectric and ferroelectric properties of BaHf0.1V x Ti0.9−x O3 (x = 0, 0.02, 0.05, 0.08, 0.1) ceramics have been investigated. From the X-ray patterns it implies that V5+ ions have entered the unit cell maintaining the perovskite structure of solid solution. The a-axis and c-axis lattice constants gradually increase and the tetragonality gradually decreases with the increasing of vanadium content. The content of vanadium has an inconspicuous effect on the grain size and the Curie temperature. The addition of vanadium can decrease the dielectric loss of BHT ceramics. It is found that well-behaved hysteresis loops can be observed in all samples at room temperature. The coercive electric field gradually decreases and then increases with the increasing of vanadium content.