Direct and converse piezoelectric grain-size effects in BaTiO3 ceramics with different Ba/Ti ratios

The grain-size effects of the direct piezoelectric coefficient (d₃₃) and the converse piezoelectric coefficient (d₃₃*) of BaTiO₃ ceramics with different Ba/Ti ratios were systematically explored. It was found that both d₃₃ and d₃₃* exhibited strong grain size (g) dependences for BaTiO₃ ceramics with various Ba/Ti ratios. Although d₃₃ showed similar grain-size dependence for all the Ba/Ti ratios except a subtle shift of the critical grain size from 1?μm to 3?μm, two entirely different grain-size dependence of d₃₃* were observed. By carefully examining the microstructure and ferroelectric properties of the ceramics, the variations of domain configurations and maximum polarization of BaTiO₃ ceramics with different Ba/Ti ratios were considered to be responsible for the different grain-size dependence of d₃₃ and d₃₃*, respectively.     

Grain size effect on piezoelectric and ferroelectric properties of BaTiO3 ceramics

A series of dense barium titanate (BaTiO₃, BTO) ceramics with different grain sizes (GS) were prepared by two-step sintering method. The effect of GS on piezoelectric coefficient (d₃₃) and planar electromechanical coupling factor (k_p) displayed a trend similar to that on relative permittivity (ɛ′). The values of d₃₃, k_p, and ɛ′ increased significantly with decreasing GS, reaching maximum values (ɛ′ = 6079, d₃₃ = 519 pC/N and k_p = 39.5%) at approximately 1 μm, and then decreased rapidly with further decreasing GS. The results revealed that high-performance BTO ceramics could be effectively prepared by controlling GS. Polarization–electric field hysteresis loops and temperature dependence of ɛ′ were also investigated.     

Enhancement of piezoelectric and ferroelectric properties of BaTiO3 ceramics by aluminum doping

Ferroelectric and piezoelectric properties of BaTiO₃ and Al-doped BaTiO₃ ceramics were investigated. The ferroelectric study demonstrated that, by doping Al³⁺ ions in the A-site of BaTiO₃, the polarization–electric field loop exhibited enhanced remnant polarization (from 12 to 17.5  μC/cm²), saturation and switching. In addition, the piezoelectric constant (d₃₃) increased with Al-doping for both static and dynamic strain values (from 75 to 135 and from 29.2 to 57.9 pC/N, respectively, at a maximum applied electric field of 16 kV/cm). Furthermore, the dielectric constant values increased and both the dielectric loss factor and leakage current decreased, even though the transition temperature shifted to lower temperature (from 121 to 113 °C) for the Al-doped sample. Therefore, the Al-doped BaTiO₃ has adjustable piezoelectric and ferroelectric properties.     

Microstructure,dielectric, piezoelectric,and ferroelectric properties of fine-grained 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

For preparing fine-grained 0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃ lead-free ferroelectric ceramics, the precursor powders were synthesized via sol-gel method and calcined at various temperatures. The precursor powders calcined at 520 °C, 550 °C, and 600 °C exhibit mean grain sizes of 30 ± 4 nm, 54 ± 3 nm, and 78 ± 5 nm, respectively. By optimizing the synthesis parameters, the fine-grained ceramics with high relative densities (>97%) and mean grain size around 100 nm were prepared. The ferroelectric, dielectric, and piezoelectric behavior were investigated. The ceramics prepared using the different precursor powders show different piezoelectric, ferroelectric, and dielectric behavior. The ceramic calcined at 550 °C and sintered at 900 °C exhibits the breakdown strength higher than 85 kV/cm, which exhibits the maximum polarization of 38.4 ± 0.3 μC/cm², remanent polarization of 20.6 ± 0.4 μC/cm².     

Temperature dependence of piezoelectric properties on Nd and V co-substituted Bi4Ti3O12 ceramics for ceramic resonator applications

The temperature dependences of the piezoelectric properties of (Bi_4−yNd_y)_1−(x/12)(Ti_3−xV_x)O₁₂ [BNTV-x, y (x = 0.01, y = 0.00–1.00)] were investigated for environmentally friendly lead-free piezoelectric ceramic resonators with low-temperature coefficients of resonance frequency, TC-f. The |TC-f| in the (33) mode improved with increasing concentration of modified Nd ions, y, and exhibited the smallest |TC-f| value of 77.4 ppm/°C at y = 0.75 (BNTV-0.75). The |TC-f| in the other vibration mode (t), was also investigated for the BNTV-0.75 ceramic, and a smaller value of 42 ppm/°C was obtained. The (t) mode of the BNTV-0.75 ceramic showed excellent piezoelectric properties: Q_m = 4200, Q_e max = 31 and TC-f = −49.8 ppm/°C. These properties are very similar to those of commercialized hard PZT ceramics for resonator applications. The BNTV-0.75 ceramic seems to be a superior candidate material for lead-free piezoelectric applications of ceramic resonators.     

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.     

Phase structure and nano-domain in high performance of BaTiO3 piezoelectric ceramics

BaTiO₃ ceramics were prepared by conventional sintering technique with a special emphasis on the effects of sintering temperature (1100-1230 °C) on the crystalline structure and piezoelectric properties. XRD patterns indicated that the crystallographic structure changed from tetragonal phase to orthorhombic one with raising sintering temperature from 1160 °C to 1180 °C. Domains were shaped in a stripe and a herringbone in orthorhombic samples for BaTiO₃ ceramics. The domain width and domain density increased with raising sintering temperature. The BaTiO₃ ceramic sintered at 1190 °C showed the excellent electrical properties, d₃₃ = 355 pC/N, k_p = 40%, P_r = 10.2 μC/cm², respectively, which are originated to the contributions of both the crystallographic structure transition and nano-domain.     

Structural,electrical, magnetic and magnetoelectric properties of Fe doped BaTiO3 ceramics

In the present work structural, electrical, magnetic and magnetodielectric properties of BaTi_1−xFe_xO₃ (0%≤x≤10%) ceramics have been investigated. X-ray diffraction (XRD) study reveals that the coexistence of tetragonal and hexagonal phases is strongly influenced by Fe doping concentration. The increase in Fe-doping content leads to the development of hexagonal phase along with an increase in average grain size. A reduction in the dielectric properties is also observed. All BaTi_1−xFe_xO₃ (BTFO) compositions exhibit ferroelectric behavior at room temperature. Remnant polarization (P_r) for pure BaTiO₃ (BTO) has been found to be 7.50 µC/cm² and further decreases with an increase in the Fe concentration. All Fe doped samples exhibit ferromagnetic ordering with saturation magnetization (M_s) being 26 memu/g for x=2.5%. Further, at x=5%, it decreases and thereafter again increases with Fe concentration. The magnetodielectric coefficient increases with Fe doping concentration and highest value found to be 2.80 at x=2.5%.     

Size effect on dielectric properties of fine-grained BaTiO3 ceramics

The effect of grain size on the dielectric behavior of high-purity, fine-grained BaTiO₃ ceramic has been investigated. It was found that the dielectric constant and dissipation factor changed much with the decreasing of average grain size. The specimen with grain size of 280 nm had a high dielectric constant at room temperature, and the _r-T and tanδ-T curves remarkably changed with the grain size. Part of the grains remaining ferroelectric structure was ascribed to the high value of dielectric constant. ©     

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.     

LCD-SLA 3D printing of BaTiO3 piezoelectric ceramics

Stereolithography-based 3D printing is a promising method to produce complex shapes from piezoceramic materials. In this study, LCD-SLA 3D printing was used to create lead-free piezoceramics based on barium titanate (BaTiO₃, BT). Three types of BT powders (micron, submicron and nanoscale) were tested in LCD-SLA 3D printing, and a technique for the preparation of a ceramic slurry suitable for LCD-SLA printing has been developed. Using TGA-DSC analysis, the thermal debinding parameters to obtain crack-free samples were determined, followed by further sintering and the study of the piezoelectric properties (ε_r = 1965, d₃₃ = 200 pC/N, tan = 1,7 %). The results of the study demonstrate high potential for the production of complex piezoceramic elements that can be used in aviation, in particular, aviation radio equipment; in the marine industry for transceiver modules of hydroacoustic antennas; and in the nuclear industry for pressure control sensors in the steam–water path.     

Structural and luminescence properties of RE (RE = Eu, Tb):(MgCa)2Bi4Ti5O20 ceramics

Rare-earth ions (Eu³⁺, Tb³⁺) activated magnesium calcium bismuth titanate [(MgCa)₂Bi₄Ti₅O₂₀] ceramics were prepared by conventional solid state reaction method for their structural and luminescence properties. By using XRD patterns, the structural properties of ceramic powders have been analyzed. Emission spectrum of Eu³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ_exci = 393 nm and Tb³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown green emission at 542 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 376 nm. In addition, from the measurements of scanning electron microscopy (SEM), Fourier transform-infrared (FTIR) and energy dispersive X-ray analysis (EDAX) results the morphology, structure and elemental analysis of these powder ceramics have been studied.     

Enhancement of the dielectric,piezoelectric, and ferroelectric properties in BiYbO3-modified (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 lead-free ceramics

Lead-free (1−x)(Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃−xBiYbO₃ [(1−x)BCTZ−xBYO] piezoelectric ceramics in the range of BYO concentrations were prepared by the conventional oxide-mixed method, and the effect of BYO content on their microstructure, crystalline structure, density and electrical properties was investigated. A dense microstructure with large grain was obtained for the ceramics with the addition of BYO. The ceramics with x=0.1% exhibit an optimum electrical behavior of d₃₃~580 pC/N, r~10.9 Ω, k_p~56.4%, and tan δ~1.12% when sintered at a low temperature of ~1350 °C. When the measuring electric field is 40 kV/cm, the well-saturated and square-like P–E loops for the ceramics were observed with P_r~12.2 μC/cm² and E_c~1.83 kV/cm.     

Grain size effect on electrical and reliability characteristics of modified fine-grained BaTiO3 ceramics for MLCCs

Fine-grained BaTiO₃-based ceramics of different grain sizes (118–462 nm) with core–shell structures were prepared by a chemical coating method, having good dielectric properties and gentle temperature stability. The grain size effect on the dielectric properties and insulation resistivity of modified fine-grained BaTiO₃ ceramics under high temperatures and electric fields were investigated. The DC bias shows a strong effect on the dielectric properties with decreasing grain size. In the finest ceramics, the absolute value of the capacitance stability factor was the smallest, indicating that the modified-BaTiO₃ ceramic capacitor with smaller grains had higher reliability under the DC bias voltage. The highly accelerated lifetime test results showed that with decreasing the grain size, samples exhibited higher insulation resistance under elevated temperatures and high voltages. Impedance analysis proved that the finer-grained ceramic with core–shell structure had higher activation energy for both grain and grain boundary, whereas the proportion of ionic conductivity was lower.     

Structural origin of size effect on piezoelectric performance of Pb(Zr,Ti)O3

Grain size effect plays a vital role in piezoelectric performance from both scientific and technological view. However, the underlying structural mechanism related to grain size is still unclear. In the present study, the structural mechanism of grain size effect on piezoelectric performance has been revealed in the prototype Pb(Zr,Ti)O₃ system by using in-situ synchrotron X-ray diffraction. The miniaturization of grain size tends to favor the appearance of higher symmetric tetragonal phase, while a single monoclinic phase is determined in the coarse-grained ceramics. The direct structural evidence reveals that both tetragonal and monoclinic phases in the fine-grained ceramics are less sensitive to the electric field, corresponding to the inferior piezoelectric performance, while the single monoclinic phase in the coarse-grained ceramics is more active to be driven by the electric field, generating good piezoelectric behavior. Both domain switching ability and lattice strain are suppressed with decreasing grain size, which directly leads to the deterioration in piezoelectric performance. The current results will benefit the structural understanding of the size effect of piezoelectric and other related systems.     

Dielectric characteristics of donor-acceptor modified BaTiO3 ceramics

Sm/Mn codoped BaTiO₃ ceramics were investigated for their microstructure and dielectric characteristics. The powders were prepared by the conventional solid state procedure. The concentration of Sm₂O₃ as a donor dopant has been kept from 0.1 up to 5.0 at%. The content of MnO₂ as acceptor was kept constant at 0.05 at% Mn in all samples. The specimens were sintered at 1290 °C, 1320 °C and 1350 °C in an air atmosphere for two hours.A mainly uniform and homogeneous microstructure with average grain size ranging from 0.3 µm to 2.0 µm was observed in low doped samples. In highly doped samples, apart from the fine grained matrix, the appearance of local area with secondary abnormal grains was observed.The dielectric properties were investigated as a function of frequency and temperature. The low doped samples exhibit the high value of dielectric permittivity at room temperature and the greatest change at the Curie temperature. The highest value of dielectric constant (ε_r=6800) was measured for 0.1Sm/BaTiO₃ samples sintered at 1350 °C. A nearly flat permittivity-temperature response and lower values of ε_r were obtained in specimens with 2.0 and 5.0 at% additive content. The dielectric constant increases with the increase of sintering temperature. The dissipation factor ranged from 0.01 to 0.22 and decreases with the increase of sintering temperature. The Curie constant (C), Curie-Weiss temperature (T₀) and critical exponent of nonlinearity (γ ) were calculated using a Curie-Weiss and modified Curie-Weiss law. The highest value of Curie constant (C=9.06·10⁵ K) was measured in 0.1 at% doped samples. The Curie constant decreased with increasing dopant content. The γ values, ranging from 1.001 to 1.58, point out the sharp phase transition in low doped samples, and the diffuse phase transition in heavily doped BaTiO₃ samples.     

Enhanced piezoelectric properties by reducing leakage current in Co modified 0.7BiFeO3-0.3BaTiO3 ceramics

Co modified lead-free 0.7BiFeO₃??0.3BaTiO₃ (0.7BFO-0.3BT-xCo₂O₃;x?=?0, 0.3, 0.6, 0.9 and 1.2) piezoelectric ceramics were prepared by a conventional solid-state reaction. The effect of Co doping on the structural, piezoelectric properties and leakage current was investigated. A greatly reduced leakage current and dramatically improved piezoelectric properties were achieved in x?=?0.3 Co doped ceramic. The maximum d₃₃ =?151 pC/N and k_p =?0.32 were obtained at x?=?0.3 addition due to the co-effect of maximum applied poling electric field and large grain size. The X-ray photoelectron spectroscopy (XPS) analysis and complex impedance data indicated that the greatly reduced leakage current could be attributed to the effect of suppressing Fe²⁺ ion formation and promoting grain boundary resistance by Co doping. These results strongly suggest that low concentration of Co doping is a good strategy to improve the resistance and piezoelectric properties simultaneously in BFO-based lead-free piezoceramics.