Effect of washing of barium titanate powders synthesized by hydrothermal method on their sinterability and piezoelectric properties

BaTiO₃ (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d₃₃ value is over 190 pC/N) was obtained from the BT powder synthesized at 250 °C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature.     

High permittivity nanocomposites fabricated from electrospun polyimide/BaTiO3 hybrid nanofibers

High dielectric permittivity, good mechanical properties, and excellent thermal stability are highly desired for the dielectric materials used in the embedded capacitors and energy‐storage devices. This study reports polyimide (PI)/barium titanate (BaTiO₃) nanocomposites fabricated from electrospun PI/BaTiO₃ hybrid nanofibers. The PI/BaTiO₃ nanocomposites were investigated using Fourier transform infrared spectroscopy, scanning electron microscope, transmission electron microscope, thermal gravimetric analysis, an electromechanical testing machine, a LCR meter and an electric breakdown strength tester. The results showed that BaTiO₃ fillers were uniformly dispersed up to 50 vol% in PI matrix. The dielectric permittivity of the composite (50 vol% BaTiO₃) was 29.66 with a dielectric loss of 0.009 at 1 kHz and room temperature. The dielectric permittivity showed a very small dependence on temperature (up to 150°C) and frequency (100 Hz–100 kHz). The nanocomposites also showed high thermal stability and good mechanical properties. The PI/BaTiO₃ nanocomposites will be a promising candidate for uses in embedded capacitors, especially in high temperature circumstance. POLYM. COMPOS., 37:794–801, 2016. © 2014 Society of Plastics Engineers     

Thermal stability and local atomic structure of (Na0.5K0.5)NbO3 doped BaTiO3 ceramics

Dielectric properties of x(Na_0.5K_0.5)NbO₃–(1−x)BaTiO₃ (x=0.00 and 0.06) specimens were investigated in terms of changes in local atomic structure, according to the phase transition by elevating the overall temperature. A 0.06(Na_0.5K_0.5)NbO₃–0.94BaTiO₃ (NKN–BT) specimen exhibited enhanced temperature stability along with an increased dielectric constant. The degree of reduction in tetragonality (c/a) at the Curie temperature was smaller in NKN–BT compared to that in pure BaTiO₃, as calculated by Rietveld refinement. From a comparison of the pre-edge region in the Ti K-edge, it was determined that the off-center displacement of the Ti atom was also raised to 13.4% through NKN substitution, with a change in local orientation from the [001] to the [111] directions. The substitution by NKN, which has a different ionic radius and electrical charge compared with BaTiO₃, causes structural distortion of the TiO₆ octahedra in the NKN–BT lattice, resulting in local polarization. These structural changes lead to the temperature stability of the dielectric constant and an overall improvement in the electrical properties of BaTiO₃.     

Fabrication and piezoelectric properties of BaTiO3/BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 composites

We fabricated xBaTiO₃ (BT)/(1-x)[BaTiO₃-Bi(Mg_1/2Ti_1/2)O₃-BiFeO₃] (BT-BMT-BF)?+?0.1?wt%MnCO₃ composites by spark plasma sintering and investigated the effect of BT content x, BT powder size, and BT-BMT-BF composition on piezoelectric properties. For xBT/(1-x)(0.3BT-0.1BMT-0.6BF) +?0.1?wt%MnCO₃ (x?=?0–0.75) composites with a 0.5-µm BT powder, the dielectric constant was increased with x, and the relative density was decreased at x?=?0.67 and 0.75, creating optimum BT content of x?=?0.50 with a piezoelectric constant d₃₃ of 107?pC/N. When a larger 1.5-µm BT powder was utilized for the composite with x?=?0.50, the d₃₃ value increased to 150?pC/N due to the grain size effect of the BT grains. To compensate for a compositional change from the optimum 0.3BT-0.1BMT-0.6BF due to partial diffusion between the BT and 0.3BT-0.1BMT-0.6BF grains, a 0.5BT/0.5(0.275BT-0.1BMT-0.625BF)?+?0.1?wt%MnCO₃ composite with the 1.5-µm BT powder was fabricated. We obtained an increased d₃₃ value of 166?pC/N. These results provided a useful composite design to enhance the piezoelectric properties.     

Revisiting the structural stability and electromechanical properties in lead zinc niobate-lead titanate-barium titanate (PZN-PT-BT) ternary system

Lead zinc niobate-lead titanate (PZN-PT) system is of particular interest for scientific researches and commercial applications due to the unique relaxation feature and superior electromechanical responses. However, it is difficult to prepare polycrystalline ceramics near the morphotropic phase boundary due to the stability of a competing lead niobate pyrochlore phase. BaTiO₃ (BT) was reported to be an effective perovskite phase stabilizer at a cost of reduction in Curie temperature and piezoelectric properties. Herein, the amount of BT in PZN-PT-BT system and the sintering conditions were optimized to simultaneously stabilize the perovskite phase and maintain high dielectric and piezoelectric response. An optimum piezoelectric coefficient d₃₃ ∼ 870 pC/N along with a T_m ∼ 133 °C and an electromechanical coupling coefficient k₃₃ ∼ 0.61 was obtained in the PZN-8PT-6BT ceramics sintered at 1100 °C. The low sintering temperature, wide processing window, and improved dielectric and piezoelectric properties make PZN-PT-BT ceramics potential candidates for piezoelectric devices.     

Composition dependence of dielectric properties,elastic modulus,and electroactivity in (carbon black‐BaTiO3)/silicone rubber nanocomposites

The dielectric properties, elastic modulus, and electromechanical responses of dielectric elastomers (DEs) consisting of silicone rubber and carbon black (CB) incorporated with BaTiO₃ (BT) were studied. When compared with single filler/rubber composites, the resulting three‐component nanocomposites yielded very abnormal phenomena. They might be attributed to the interactions between the two kinds of fillers. The increase in concentration of CB (BT) would play a destructive role to the network structure formed by BT (CB) particles. The maximum electromechanical strain of the nanocomposites achieved at mass fraction m_CB = 0.03 and m_BT = 0.06. The resultant electromechanical strain would be attributed to the large dielectric permittivity in the three‐component nanocomposites, in which the BT particles themselves have a high dielectric permittivity and the electrical networks of CB particles have a contribution on the increase in dielectric permittivity of the three‐component nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Microstructure and electrical properties of Er-doped 0.67 Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 ceramics with BaTiO3 templates

In this study, [001]-oriented Er-doped 0.67 Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33 PT) textured ceramics with different BaTiO₃ (BT) template concentrations were explored. The samples were prepared by tape-casting. Er³⁺ was added to modify the electrical properties of the polycrystalline ceramics, and the BT template was used to improve the texture of polycrystalline ceramics. The 0.67PMN-0.33 PT textured ceramics contained coexisting rhombohedral and tetragonal phases. The ceramics became increasingly textured as the sintering temperature increased up to 1250 °C. The piezoelectric coefficient of 0.67PMN-0.33 PT with 5 wt% BT was 634 pC/N, which is 1.2 times than that of randomly oriented 0.67PMN-0.33 PT. The strain of the ceramic with 5 wt% BT increased by 12.5% relative to a random control specimen. Analysis of the electrical properties and microstructure suggested that the enhancement of the piezoelectric coefficient and strain may be caused by the addition of Er³⁺ and the BT template. First, the directional growth of grains along the template affected the change-of-phase distribution of the system and formed a more adaptive phase. Second, Er³⁺ was substitutionally doped on the A-site of the perovskite to form local heterostructures. Finally, the relaxation components of the templates and Er³⁺ changed in the solid solution with the matrix. The solid solution of the BT templates and Er-doped-matrix powder changed the relaxation degree, which affected the interactions at the polar nanoregions and increased the piezoelectric coefficient of the ceramics.     

Processing,Dynamic mechanical thermal analysis,and dielectric properties of barium titanate/cellulosic polymer nanocomposites

High dielectric constant BaTiO₃/ethyl cellulose (BT/EC) nanocomposites having BT loadings of up to 13 vol% were fabricated through a simple casting technique. The BT filler powder, synthesized through an ultrasonic‐assisted solid‐state route, was revealed by X‐ray powder diffractometry (XRD) and Raman spectroscopy to be dominantly tetragonal. Scanning electron microscopy (SEM) showed good dispersion of the BT nanoparticles in the EC polymer matrix at lower BT concentrations. However, at higher concentrations, the BT particles form a continuous phase or a “filler network” leading to weak BT/EC interactions. This finding is well supported by the results of the tensile strength and storage modulus. The dielectric properties of the BT/EC nanocomposites were investigated over wide ranges of frequency and temperature. The addition of BT significantly increased the permittivity (ε ′) and dielectric loss (ε ″) and improved the ionic conductivity of the EC. The electric modulus (M″ ) results were analyzed in terms of the Havriliak–Negami function through three distinct relaxation mechanisms (namely α, β*, and β relaxations) in the temperature range 30–150°C. The dc conductivity (σ _dc) results suggest that the BT/EC nanocomposites formed at low BT loading (up to 7.0 vol%) and a temperature of ≤60°C are good candidates for antistatic applications while those formed at higher concentrations and temperatures are recommended for use in electrostatic dissipation applications. POLYM. COMPOS., 38:893–907, 2017. © 2015 Society of Plastics Engineers     

Cycling stability of lead-free BNT–8BT and BNT–6BT–3KNN multilayer actuators and bulk ceramics

This study presents the electromechanical properties and cycling stability of lead-free piezoelectric materials 0.92(Bi_1/2Na_1/2)TiO₃–0.08BaTiO₃ (BNT–8BT) and 0.91(Bi_1/2Na_1/2)TiO₃–0.06BaTiO₃–0.03(K_0.5Na_0.5)NbO₃ (BNT–6BT–3KNN). Both bulk samples as well as multilayer actuators (MLA) with internal Ag/Pd (70/30) electrodes were successfully processed from both materials. Electromechanical characteristics in the non-fatigued state and after different numbers of unipolar fatigue cycles are provided, representing the first direct comparison of the fatigue resistance of lead-free bulk ceramics and the corresponding MLAs. At a maximum field of 6 kV/mm and a frequency of 50 Hz, BNT–8BT MLA delivered a maximum strain of 0.07% and displayed excellent cycling stability. BNT–6BT–3KNN MLA provided a higher strain of 0.15% initially but degraded during cycling and exhibited break down after 10⁷ cycles. Furthermore, the frequency dependence of strain and the self-heating during cycling were investigated. The temperature increase is limited only to 2 °C in BNT–8BT MLA and 13 °C in BNT–6BT–3KNN MLA.     

Solvothermally synthesized tetragonal barium titanate powders using H2O/EtOH solvent

Multilayer ceramic capacitor (MLCC) miniaturization has increased the demand for superfine BaTiO₃ powder due to its thin dielectric layer. Hydrothermally synthesized BaTiO₃ powder has submicron size, high purity and good crystalline nature at low synthetic temperature. However, the powder has a pseudo-cubic phase resulting in poor dielectric properties due to size effect and hydroxyl ion inclusion in the BaTiO₃ lattice. We attempted a superfine (lower than 100 nm) highly tetragonal BaTiO₃ powder via a solvothermal method without precipitating agent. Solvent composition effects on the BaTiO₃ powder tetragonality were discussed.     

Enhanced piezoelectricity and high-temperature sensitivity of Zn-modified BF-BT ceramics by in situ and ex situ measuring

Effect of Zn addition on microstructure, electrical properties and temperature stability and sensitivity of piezoelectric properties for 0.7Bi_1-xZn_xFeO₃ −0.3BaTiO₃ (abbreviated as BZxF–BT) ceramics was investigated. The improved piezoelectric properties, high-temperature stability and high-temperature sensitivity by in situ and ex situ measuring were obtained by moderate Zn addition. It was demonstrated that the enhancement piezoelectric properties can be attributed to poling induced texturization degree of ferroelectric domains and increased rhombohedral structural distortions. It was proposed that the depoling temperature where the induced small signal piezoelectricity disappears stemmed from the detexturization of preferred orientation domains. The improved piezoelectric responses and high-temperature sensitivity could be attributed to the thermally activated preferred orientation domains. The good piezoelectric properties together with high-temperature stability suggest that BZxF–BT system is a promising material for high temperature piezoelectric applications.     

Effect of MgO addition on the microstructure and dielectric properties of BaTiO3 ceramics

MgO-doped BaTiO₃ (BaTiO₃/MgO) ceramics were prepared by a solid-state sintering method. The effects of MgO doping on the dielectric properties of BaTiO₃/MgO were investigated in terms of its microstructural development. The BaTiO₃/MgO was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and x-ray powder diffraction. Results show that grain growth of the BaTiO₃/MgO during sintering was inhibited by adding MgO at least 0.5 mol%. It resulted in a high resistance of the BaTiO₃/MgO sintered at high temperature. The BaTiO₃/MgO possessed a broad temperature stability and met Electronic Industries Association (EIA) ×7R specification. The improved dielectric properties of the BaTiO₃/MgO are attributed to the decreased tetragonality of BaTiO₃ lattice due to Mg²⁺ substitute for Ti⁴⁺.     

Composition‐Dependent Microstructures and Properties of La‐, Zn‐, and Cr‐Modified 0.675BiFeO3–0.325BaTiO3 Ceramics

Pure and 1.0 mol% La₂O₃, ZnO, and Cr₂O₃‐modified 0.675BiFeO₃–0.325BaTiO₃ (BF–BT) multiferroic ceramics were prepared and comparatively investigated. For pure and La‐, Zn‐, and Cr‐modified BF–BT, the average grain size is 415, 325, 580, and 395 nm, and the maximum dielectric constant temperature is 460°C, 430°C, 465°C, and 445°C, respectively. All additives weaken the ferroelectricity slightly. Zn‐ and Cr‐modifications dramatically enhance the room‐temperature magnetic properties, whereas La‐modification has almost no effect on magnetic property. Especially, the Cr‐modified BF–BT ceramics show switchable polarization and magnetization of 4.9 μC/cm² and 0.27 emu/g at room temperature, the magnetoelectric coupling is confirmed by the magnetization‐magnetic field curves measured on ceramics before and after electric poling. The mechanism responsible for the different effects of additive on microstructures and properties are discussed based on additive‐induced point defect and second phase as well as diffusion‐induced substitution. These results not only provide a promising room‐temperature multiferroic material candidate, but also are helpful to design new multiferroic materials with enhanced properties.     

High piezoelectric properties of BaTiO3-xLiF ceramics sintered at low temperatures

BaTiO₃-xLiF ceramics were prepared by a conventional sintering method using BaTiO₃ powder about 100 nm in diameter. The effects of LiF content (x) and sintering temperature on density, crystalline structure and electrical properties were investigated. A phase transition from tetragonal to orthorhombic symmetry appeared as sintering temperatures were raised from 1100 °C to 1200 °C or as LiF was added from 0 mol% to 3 mol%. BaTiO₃-6 mol% LiF ceramic sintered at 1000 °C exhibited a high relative density of 95.5%, which was comparable to that for pure BaTiO₃ sintered at 1250 °C. BaTiO₃-4 mol% LiF ceramic sintered at 1100 °C exhibited excellent properties with a piezoelectric constant d₃₃ = 270 pC/N and a planar electromechanical coupling coefficient k_p = 45%, because it is close to the phase transition point in addition to high density.     

Dispersion and Rheology of Aqueous Suspensions of Nanosized BaTiO3

The zeta potential and the rheological behavior of aqueous suspensions of a commercial nanosized BaTiO₃ powder were studied. The influence of the volume fraction of solids, the kind and concentration of dispersant, the homogenization technique, and times were investigated. Because the as-received powder contained ∼5 wt% organics, the powder was calcined to 350°C/0.5 h. After calcination, a good dispersion was achieved for suspensions with up to 80 wt% solids using a polyacrylic-based dispersant combined with tetramethylammonium hydroxide and 10 min of ultrasound. Green bodies obtained by slip casting had relatively low densities (2.6 g/cm³, 43% TD), but homogeneous, agglomerate-free microstructures.     

Effect of mechanical milling on structural,dielectric and magnetic properties of BaTiO3–Ni0.5Co0.5Fe2O4 multiferroic nanocomposites

The coexistence of ferroelectricity and ferromagnetism has triggered great interest in multiferroic materials. Multiferroic with strong room temperature magnetoelectric (ME) coupling can provide a platform for future technologies. In this paper, we have investigated the effect of mechanical milling on the properties of multiferroic nanocomposites synthesized by mixing barium titanate (BaTiO₃) (BT) and nickel cobalt ferrite (Ni_0.5Co_0.5Fe₂O₄) (NCF). This process has resulted into reliable disposal of a given quantity of NCF nanoparticles in BT grid and composite samples of different particle sizes (<500 nm) have been obtained by varying the duration of ball-milling for 12, 24, and 48 h. The presence of NCF within BT powder has been confirmed by X-ray Diffraction (XRD) and magnetization measurements (MH). Structural analysis was performed by using Reitveld refinement method that shows that the tetragonality of BaTiO₃ structure get reduced in submicron range. Variations in ferroelectric and dielectric properties with reduction in particle size/milling duration have been studied by P-E loop tracer and Impedance analyzer. The dielectric constant value of 400 has been observed for BT-NCF0 that increases to 9.7 K for composite sample ball mill at 48 h whereas remnant polarization increases to 4.2 μC/cm². These composites with high dielectric constant that changes with temperature and particles size find application in energy storage devices, sensor and memory devices.     

Formation of sodium bismuth titanate—barium titanate during solid‐state synthesis

Phase formation of sodium bismuth titanate (Na_0.5Bi_0.5TiO₃ or NBT) and its solid solution with barium titanate (BaTiO₃ or BT) during the calcination process is studied using in situ high‐temperature diffraction. The reactant powders were mixed and heated to 1000°C, while X‐ray diffraction patterns were recorded continuously. Phase evolutions from starting materials to final perovskite products are observed, and different transient phases are identified. The formation mechanism of NBT and NBT–xBT perovskite structures is discussed, and a reaction sequence is suggested based on the observations. The in situ study leads to a new processing approach, which is the use of nano‐TiO₂, and gives insights to the particle size effect for solid‐state synthesis products. It was found that the use of nano‐TiO₂ as reactant powder accelerates the synthesis process, decreases the formation of transient phases, and helps to obtain phase‐pure products using a lower thermal budget.     

BaTiO3 nanotubes by co-axial electrospinning: Rheological and microstructural investigations

BaTiO₃ (BT) nanotubes (NT_s) were synthesized using a co-axial electrospinning process. BT precursor/PVP-ethanol and heavy mineral oil were used as the shell solution and core liquid, respectively. The rheological studies indicated that NT_s could be formed by a stable jet at a range of viscosities of the shell solution. Due to the shear thinning behavior of the shell solutions, their actual viscosity values at the time of jet formation will be lower than the viscosity of the core liquid. The morphology of the obtained NT_s was strongly influenced by the viscosity of the shell solution. By increasing the concentration of BT precursor, the morphology of the BT NT_s was changed from porous to more dense structure. XRD analysis revealed that the crystallization of BT NT_s occurs at 550–630 °C calcination temperature range. Raman spectra confirmed the presence of tetragonal phase at early stage of crystallization.     

Comparative structural and optical studies on pellet and powder samples of BaTiO3 near phase transition temperature

In order to investigate the possible effect of inter-granular strain on the physical properties of Barium titanate (BaTiO₃), comparative studies have been carried out on the polycrystalline pellet and its corresponding powder samples. For this purpose, the polycrystalline pellet sample of BaTiO₃ has been prepared via conventional solid-state reaction route and powder is obtained by crushing the part of the prepared BaTiO₃ pellet. The comparative room temperature structural studies, temperature dependent optical and Raman spectroscopy measurements have been carried out on the prepared pellet and powder samples. Room temperature X-ray diffraction and Raman analysis confirms the presence of extra amount of strain in pellet sample compared with that of the powder sample. Temperature dependent Raman analysis also suggests the difference in the high temperature tetragonal to cubic transition temperature in both cases. Temperature dependent optical absorption properties measured in terms of Urbach energy (E_U), Urbach focus (E₀) and Urbach relaxation clearly indicates the significant change in these quantities for both types of samples on BaTiO₃. Present results strongly reveal the difference in structural, optical and vibrational properties of BaTiO₃ especially across phase transition in pellet and its corresponding powder which clearly shows the importance of inter-granular strain at the grain boundaries.     

Remarkable piezoelectricity and stable high‐temperature dielectric properties of quenched BiFeO3–BaTiO3 ceramics

Effects of quenching process on dielectric, ferroelectric, and piezoelectric properties of 0.71BiFeO₃?0.29BaTiO₃ ceramics with Mn modification (BF–BT?xmol%Mn) were investigated. The dielectric, ferroelectric, and piezoelectric properties of BF–BT?xmol%Mn were improved by quenching, especially to the BF–BT?0.3 mol%Mn ceramics. The dielectric loss tanδ of quenched BF–BT?0.3 mol%Mn ceramics was only 0.28 at 500°C, which was half of the slow cooling one. Meanwhile, the remnant polarization P_r of quenched BF–BT?0.3 mol%Mn ceramics increased to 21 μC/cm². It was notable that the piezoelectric constant d₃₃ of quenched BF–BT?0.3 mol%Mn ceramics reached up to 191 pC/N, while the T_C was 530°C, showing excellent compatible properties. The BF–BT?xmol%Mn system ceramics showed to obey the Rayleigh law within suitable field regions. The Rayleigh law results indicated that the extrinsic contributions to the dielectric and piezoelectric responses of quenched BF–BT?xmol%Mn ceramics were larger than the unquenched ceramics. These results presented that the quenched BF–BT?xmol%Mn ceramics were promising candidates for high‐temperature piezoelectric devices.