Electro-caloric behaviors of lead-free Bi0.5Na0.5TiO3-BaTiO3 ceramics

Electro-caloric (EC) properties of lead-free Ba_0.5Na_0.5TiO₃-xBaTiO₃ (BNT-xBT) ceramics prepared by citrate method are investigated at temperatures of 30–250°C. Based on thermodynamics calculations, BNT-xBT (x = 0, 0.05, 0.06, 0.1, 0.25, 0.3) are found to show EC effects different with other lead-based or lead-free ferroelectric ceramics, i.e., they absorb heats (refrigeration effect) during the processes of field application while other ferroelectric ceramics show refrigeration effect during the processes of field removal. The EC temperature change of BNT-xBT can be as large as 2.1°C under an electric field of 60 kV/cm, which is larger than most of the lead-free ferroelectric bulk ceramics. When x is close to the morphotropic phase boundary (x ~ 0.06–0.1), the EC temperature change of BNT-xBT shows a maximum near the ferroelectric to anti-ferroelectric transition temperature, which is characterized by dynamic mechanical analysis. This study suggests that these lead-free ferroelectric materials are promising in the practical application as EC coolers.     

Dielectric and piezoelectric properties of La2O3 doped (Bi0.5Na0.5)0.92(Ba0.8Sr0.2)0.08 TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.92(Ba_0.8Sr_0.2)_0.08 TiO₃+x mol% La₂O₃(x = 0, 0.1, 0.3, 0.5, 0.8) were synthesized by conventional solid state reaction. The crystal structure of all compositions is mono-perovskite ascertained by XRD. The grain size decreased and diffuse phase transition behavior was more evident with the increasing amount of La₂O₃. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p showed the maximum value of 165 pC/N and 0.322 at 0.3% and 0.1% La₂O₃ addition, respectively, and rapidly decreased when La₂O₃ addition over 0.5%. The loss tangent tanδ linearly increased and the mechanical quality factor Q_m linearly decreased with the increasing amount of La₂O₃.     

High-temperature stable dielectrics in Mn-modified (1-x) Bi0.5Na0.5TiO3-xCaTiO3 ceramics

In the current work, the bulk (1-x) Bi_0.5Na_0.5TiO₃-xCaTiO₃ [BNCT100x] system was synthesized via solid-state route. CaTiO₃ in solid solution with Bi_0.5Na_0.5TiO₃ was observed to decrease the dielectric constant at higher temperature and raise the dielectric constant at lower temperature. Polarization hysteresis measurements indicated that the ferroelectricity of Bi_0.5Na_0.5TiO₃ was weakened with an increase of CaTiO₃, resulted in the shift of the depolarization temperature (T _d) toward lower temperatures. X-ray diffraction analysis revealed that TiO₂ was produced as a secondary phase due to the losses of Bi and Na during milling and sintering processes. Moreover, the addition of Ca promoted the segregation of Ti out of BNT grains. Dielectric properties of BNCT12 ceramics with different dopant levels of Mn were characterized as a function of temperature for potential use of high-temperature capacitors. Modification of BNCT12 materials with Mn improved the temperature characteristic of capacitance (?55°C to 250°C, △C/C_25°C ≤ ±15%). Finally, by doping 1.5 wt% Mn, the dielectric constant at room temperature could reach over 900, with a low dielectric loss below 1% and a high insulation resistivity about 10¹² Ω?cm. Furthermore, a small amount of Mn influenced the microstructure in the way to inhibit the long grains and grain growth of BNCT solution ceramics. However, excess Mn caused abnormal grain growth, and therefore, rectangle grains appeared again.     

Piezoelectric ceramics of (Bi1/2Na1/2)TiO3-PbTiO3-BaTiO3 system

Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi_1/2Na_1/2)TiO₃(BNT)-based solid solution, that is, (Bi_1/2Na_1/2)(_1-x)(Pb_a Ba_b)_xTiO₃(a + b = 1) [BNPB(100x-100a/100b)], are studied from the viewpoint of a new group of lead-free or low-lead content piezo-electric ceramics with a rhombohedral(F_a-tetragonal (F_β) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling. X-ray diffraction data, dielectric properties and D-E hysteresis loops show that the MPB exist near (Bi_1/2Na_1/2)TiO₃[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high-frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε₃₃Tε₀, and a high electromechanical coupling factor k₃₃, along with a high mechanical strength.     

ABS-064: Grain oriented (Na0.5Bi0.5)0.94Ba0.06TiO3 piezoceramics prepared by the screen-printing multilayer grain growth technique

The texture control of polycrystalline ceramics is an important and effective way to improve the piezoelectric properties of lead-free ceramics without drastically changing the composition of the ceramics. The screen-printing multilayer grain growth (MLGG) technique is now successfully applied to perovskite-structured lead-free piezoelectric ceramics. Grain oriented (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (NBBT) ceramics with (100) orientation were fabricated. The influences of sintering time, heating rate, and pre-reaction at low temperature on grain orientation were studied. Highly textured NBBT ceramics (f?~?92%) were obtained with a high heating rate. The interface between adjacent layers, which was formed by screen-printing, was the main mechanism for the texture development in MLGG technique. Compared with other grain orientation techniques, screen-printing is a simple and effective method to fabricate grain oriented lead-free piezoelectric ceramics.     

Fabrication and electrical properties of textured Na1/2Bi1/2TiO3-BaTiO3 ceramics by reactive-templated grain growth

The <001> fiber-textured Na_1/2 Bi_1/2TiO₃-BaTiO₃ (6 mol% BaTiO₃) ceramics were fabricated by reactive-templated grain growth (RTGG), using plate-like Bi₄Ti₃O₁₄ (BiT) particles prepared by a molten salt method as templates. The effects of sintering conditions on texture development and microstructure evolvement were both studied, and the mechanisms of grain orientation and densification were discussed. High Lotgering factor (≥96%) and high density (≥96% theoretic density) textured Na_1/2 Bi_1/2TiO₃-6BaTiO₃ ceramics were prepared by using the max templates concentration supplying 100% Bi in the final product, and sintering at 1200 °C for 10 h. The NBT-6BT obtained exhibited good piezoelectric performance with piezoelectric coefficient d ₃₃ ?=?241pC/N, and electromechanical coupling factor k _p ?=?41.2%, k _t ?=?66.5% at room temperature.     

The effect of Bi4Ti3O12 particles addition in lead-free Bi0.5(Na0.75K0.25)0.5TiO3 ceramics

We studied the effect of Bi₄Ti₃O₁₂ (BiT) platelet addition in Bi_0.5(Na_0.75K_0.25)_0.5TiO₃ (BNKT) ceramics by preparing two kinds of BNKT ceramics. One type of BNKT ceramic was fabricated by a conventional solid state reaction method (normal sample), while the other by addition of 15 wt% BiT platelets to BNKT powders (BiT-added sample). In the case of BiT-added BNKT ceramics, plate like grains were formed by the reaction of BiT platelets with Na₂CO₃, K₂CO₃, and TiO₂ during the sintering process. The grain size of BiT-added BNKT ceramics was 10 times larger than that of normal BNKT ceramic. The piezoelectric strain and d₃₃ values of BiT-added BNKT ceramics were 0.135% and 225 pm/V, respectively. These values were 35% higher than those of normal BNKT ceramics. The piezoelectric properties of BiT-added BNKT ceramics were enhanced by the higher domain activity due to a decrease in domain density at larger grain sizes.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

Pyroelectric, dielectric, and piezoelectric properties of MnO2-doped (Na0.82 K0.18)0.5Bi0.5TiO3 lead-free ceramics

MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ lead-free piezoelectric ceramics were prepared by conventional solid-state reaction process and the effect of MnO₂ addition on the pyroelectric, piezoelectric and dielectric properties were studied. The experiment results showed that the pyroelectric, piezoelectric, and dielectric properties strongly depended on MnO₂ addition in the (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramics. Excellent electrical properties were obtained in (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ with 0.8?mol% MnO₂. The large dielectric loss of pure BNT ceramics was significantly reduced, the piezoelectric constant was improved, and it also showed excellent pyroelectric properties when compared with other lead free ceramics, with pyroelectric coefficient p?=?17?×?10^?4?C/m²K and figure of merit F _d ?=?6.56?×?10^?5?Pa^?0.5. With these outstanding pyroelectric properties, the 0.8?mol% MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramic can be a promising material for pyroelectric sensor applications in future.     

Sintering behavior and enhanced energy storage performance of SnO2-modified Bi0.5(Na0.8K0.2)0.5TiO3 lead-free ceramics

Journal of Electroceramics - In the present study, SnO2-modified Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) ceramics were fabricated by the conventional solid-state reaction. In order to adjust its sintering...     

Effect of BiAlO3 concentration on the dielectric and piezoelectric properties of lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

In this paper, lead-free (1-x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-xBiAlO₃ (BNBT-BA, x?=?0, 0.010, 0.015, 0.020, 0.025, and 0.030) piezoelectric ceramics were synthesized using a conventional solid-state reaction method. The effect of BiAlO₃ concentration on dielectric, ferroelectric and piezoelectric properties were investigated. The ferroelectric and piezoelectric properties of BNBT ceramics are significantly influenced by the presence of BA. In the composition range studied, X-ray diffraction revealed a perovskite phase with the coexistence of rhombohedral and tetragonal phases. The temperature dependence of dielectric properties showed that the depolarization temperature (T _d) shifted towards lower temperatures and that the degree of diffuseness of the phase transition around T _d and T _m became more obvious with increasing BiAlO₃ content. The remanent polarization increased with increasing BA, and reached a maximum value of 30 μC/cm² at x?=?0.020. As a result, at x?=?0.020, the piezoelectric constant (d ₃₃) and the electromechanical coupling factor (k _p) of the ceramics attained maximum values of 188 pC/N and 34.4 %, respectively. These results indicate that BNBT-BA ceramics is a promising candidate for lead-free piezoelectric materials.     

Microstructure and electrical properties of the rare-earth doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 piezoelectric ceramics

Phase structure, microstructure, piezoelectric and dielectric properties of the 0.4 wt% Ce doped 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (Ce-BNT6BT) ceramics sintered at different temperatures have been investigated. The powder X-ray diffraction patterns showed that all of the Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The morphologies of inside and outside of the bulk indicated that the different sintering temperatures did not cause the second phase on the inside of bulk. However, the TiO₂ existed on the outside of the bulk due to the Bi₂O₃ and Na₂O volatilizing at higher temperature. The ceramics sintered at 1,200 °C showed a relatively large remnant polarization (P _r) of about 34.2 μC/cm², and a coercive field (E _c) of about 22.6 kV/cm at room temperature. The permittivity ? _r of the ceramics increased with the increasing of sintering temperature in antiferroelectric region, the depolarization temperature (T _d) increased below 1,160 °C then decreased at higher sintering temperature. The resistivity (ρ) of the Ce-BNT6BT ceramics increased linearly as the sintering temperature increased below 1,180 °C, but reduced as the sintering temperature increased further. A maximum value of the ρ was 3.125?×?10¹⁰ ohm m for the Ce-BNT6BT ceramics sintered at 1,180 °C at room temperature.     

Enhanced physical properties of Bi 4 Ti 3 O 12 modified Bi 0.5 (Na 0.4 K 0.1 )TiO 3 lead-free piezoelectric ceramics using crystallographic orientation techniques

In this study, bismuth titanate (Bi4Ti3O12) templates were synthesized through the molten salt method in Na2CO3 and K2CO3 fluxes. The prepared Bi4Ti3O12 te     

Effect of annealing temperature on the electrostrictive properties of 0.94(Na0.5Bi0.5)TiO3-0.06BaTiO3 thin films

0.94(Na_0.5Bi_0.5)TiO₃-0.06BaTiO₃ (NBT-BT6) thin films were fabricated by metal-organic decomposition (MOD) at the different annealing temperatures. Based on the electrostrictive effect and converse piezoelectric effect, the phenomenological approach is provided to characterize the electrostrictive properties of the perovskite relaxor, and it is used to determine the effective electrostriction coefficients $ Q_{33}^{\mathrm{eff}} $ and electrostrictive strains $ {S_3} $ of NBT-BT6 thin films annealed at the range of 650?C800?°C. After the microstructure, ferroelectric, dielectric and piezoelectric properties of the thin films were determined, the maximum values of $ Q_{33}^{\mathrm{eff}} $ and $ {S_3} $ of NBT-BT6 thin film annealed at 750?°C are respectively determined as 0.0289?m⁴/C² and 0.26?% under the bipolar driving field of 391?kV/cm. They are strongly influenced by annealing temperature due to the bismuth evaporation and crystallization of perovskite phase, and the enhanced electrostrictive properties could make NBT-based thin film a promising candidate to the design and application of stacked actuators, microangle-adjusting devices, and oil pressure servo valves.     

Effects of co-doped CaO/MnO on the piezoelectric/dielectric properties and phase transition of lead-Free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

The piezoelectric properties of (1?x)(Bi_0.5Na_0.5)TiO₃-xBaTiO₃ ceramics were reported and their piezoelectric properties reach extreme values near the MPB (about x?=?0.06). The X-ray analysis of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics for all compositions exhibited a pure perovskite structure without any secondary phase. Within a certain ratio of contents, the co-doped ceramics enhanced piezoelectric coefficient (d ₃₃ ), lowered the dielectric loss, and increased the sintered density. The temperature dependence of relative dielectric permittivity (K ₃₃ ^T ) reveals that the solid solutions experience two phase transitions, ferroelectric to anti-ferroelectric and anti-ferroelectric to relaxor ferroelectric, which can be proven by P-E hysteresis loops at different temperatures. In addition, the specimen containing 0.04/0.01 wt.% CaO/MnO showed that the coercive field E _c was a minimum value of 26.7 kV/cm, while the remnant polarization P _r was a maximum value of 38.7 μC/cm², corresponding to the enhancement of piezoelectric constant d₃₃ of 179 pC/N, electromechanical coupling factor k _p of 37.3%, and relative dielectric permittivity K ₃₃ ^T of 1137. (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics co-doped with CaO/MnO were considered to be a new and promising candidate for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties, which are superior to an un-doped BNBT system.     

Dielectric and piezoelectric properties of (K0.5Na0.5)(Nb0.97Sb0.03)O3 ceramics doped with Bi2O3

In this study, to develop the optimal composition of ceramics for low loss piezoelectric actuator and ultrasonic motor applications, (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃?+?0.009 K_5.4Cu_1.3Ta₁₀O₂₉?+?0.1wt%Li₂CO₃?+?xwt%Bi₂O₃(x?=?0?~?0.9) lead-free piezoelectric ceramics with a fixed quantity of 0.009 K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) were manufactured using the conventional solid-state solution processes. The effects of Bi₂O₃ addition on the dielectric and piezoelectric properties were then investigated. From the X-ray diffraction analysis result the specimens demonstrated orthorhombic symmetry when Bi₂O₃ was less 0.6?wt%, a pseudo-cubic phase appeared when Bi₂O₃ was 0.9?wt%. SEM images indicate that a small amount of Bi₂O₃ addition affect the microstructure. The piezoelectric properties of (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃ ceramics were greatly improved by a certain amount of Bi₂O₃ addition. Excellent properties of density?=?4.54?g/cm³, relative densities?=?98.5?%, k _p?=?0.468, Q _m?=?1,715 and d ₃₃?=?183 pC/N were obtained with a composition of 0.3?wt% Bi₂O₃     

Effect of reoxidation on positive temperature coefficient of resistance behavior for BaTiO3-K0.5Bi0.5TiO3 ceramics

As a positive temperature coefficient of resistivity (PTCR) material, (1-x)BaTiO₃-xK_0.5Bi_0.5TiO₃ (BT-KBT, 0.05≦ x ≦0.15) ceramics without any donor doping were prepared by a conventional oxide mixing method. All samples were sintered in an Ar atmosphere at 1280?~?1350°C, subsequently, reoxidized at 800?~?1100°C in a gas mixture (99 %Ar–1 %O₂). The PTCR behavior of BT-KBT ceramics were investigated in terms of KBT content, reoxidation temperature and time. The results showed that the BT-KBT ceramics exhibited an abrupt increase in their resistivity near the Curie temperature (Tc) after annealing in gas mixture, Tc of 0.9BT-0.1KBT ceramic was shifted to a higher temperature (~150°C). Furthermore, the room-temperature resistivity (ρ_RT) of ceramic samples sintered in Ar and reoxidized in a gas mixture decreased to 10² Ω·cm. The jump in resistivity (maximum resistivity [ρ_max]/minimum resistivity [ρ_min]) was enhanced by three orders of magnitude through a suitable reduction–reoxidation method without sacrificing the ρ_RT.     

Thermal Expansion Behavior of (Bi0.5Na0.5)Zr1-x Ti x O3 Ceramics

(Bi_0.5Na_0.5)Zr_1-xTi_xO₃ with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 ceramics were fabricated by a conventional sintering technique at 850–950°C for 2 h. From X-ray diffraction study, three regions of different phases were observed in the ceramic system; i.e., orthorhombic phase region (0 ≤ x ≤ 0.2), mixed-phase region (0.3 ≤ x ≤ 0.4), and rhombohedral phase region (0.5 ≤ x ≤ 0.6). The thermal expansion coefficient data indicated the phase transition in the temperature range from 100°C–150°C of the ceramics. The thermal strain curve of all compositions suggested a decrease of local polarization with temperature increment up to the Burns temperature.