Composition and poling condition-induced electrical behavior of (Ba0.85Ca0.15)(Ti1−xZrx)O3 lead-free piezoelectric ceramics

Lead-free (Ba_0.85Ca_0.15)(Ti_1−xZr_x)O₃ (BCTZ) piezoelectric ceramics were fabricated by normal sintering in air atmosphere. BCTZ ceramics with x = 0.10 possess a coexistence of tetragonal and rhombohedral phases at ∼40 °C. The Curie temperature of BCTZ ceramics decreases with increasing the Zr content. Piezoelectric properties of BCTZ ceramics are dependent on the poling conditions (i.e., the poling temperature and the poling electric field), and the underlying physical mechanism is illuminated by the phase angle. The BCTZ (x = 0.10) ceramic, which locates at the existence of two phases and is poled at E ∼ 4.0 kV/mm and T_p ∼ 40 °C, exhibits an optimum electrical behavior at a room temperature of ∼20 °C: d₃₃ ∼ 423 pC/N, k_p ∼ 51.2%, 2P_r ∼ 18.86 μC/cm², 2E_c ∼ 0.47 kV/mm, ?_r ∼ 2892, and tan δ ∼ 1.53%.     

Effects of CuO addition on the structure and electrical properties of low temperature sintered Ba(Zr,Ti)O3 lead-free piezoelectric ceramics

CuO-doped Ba(Zr_0.05Ti_0.95)O₃ (BZT) ceramics were prepared using conventional solid state reaction method, and their structure and electrical properties were investigated. It was found that a small amount of CuO could lower the sintering temperature significantly and make their microstructure more densified than pure BZT. The ceramics with 1.2 mol% CuO, sintered at 1250 °C, showed excellent piezoelectric properties with d₃₃~320 pC/N and k_p=44%. The sintering temperature was decreased by 150 °C than that for pure BZT ceramics while showing comparable piezoelectric properties. Moreover, the influence of sintering temperature on the optimally 1.2 mol% CuO-doped BZT ceramics was studied. With the temperature change, different patterns of crystal growth were observed in the doped BZT ceramics. When the sintering temperature increased from 1200 °C to 1350 °C, the patterns of normal–abnormal–normal grain growth were changed accordingly.     

Photoluminescence and optical temperature sensing in Sm3+-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

A series of orange-red emitting Sm³⁺ activated Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCZT: xSm³⁺, x?=?0.001–0.007) are synthesized by a conventional solid-state reaction method. The Sm³⁺ ions composition dependent photoluminescence properties are systematically investigated. Under the excitation of a 407?nm near-ultraviolet light, the ceramics exhibit strong characteristic emission of Sm³⁺ ions with dominant orange-red emission peak at around 595?nm, which is ascribed to the transition of ⁴G_5/2 → ⁶H_7/2. The BCZT: 0.004Sm³⁺ ceramic displays the optimal emission among these Sm³⁺-doped BCZT solid solutions. Moreover, the photoluminescence intensity exhibits extremely sensitive to temperature, suggesting that BCZT: 0.004Sm³⁺ could be applicable for temperature sensing. A maximum relative sensitivity of 1.89%?K^?1 at 453?K is obtained. Furthermore, the existence of ferroelectricity in the BCZT host combined with Sm³⁺ activated photoluminescence properties could be useful for developing optical-electro multifunctional materials and devices.     

Piezoelectric behavior of (1−x)K0.50Na0.50NbO3−xBa0.80Ca0.20ZrO3 lead-free ceramics

(1−x)K_0.50Na_0.50NbO₃–xBa_0.80Ca_0.20ZrO₃ [(1−x)KNN–xBCZ] lead-free ceramics were prepared by the conventional solid-state method, and the effect of BCZ content on their phase structure and piezoelectric properties was studied. A coexistence of rhombohedral–orthorhombic phases was identified in the range 0.04<x<0.08. With increasing the BCZ content, their grain size becomes smaller, and their Curie temperature gradually decreases. An optimum piezoelectric behavior of d₃₃∼197 pC/N and k_p∼40.6% was demonstrated in the ceramic with x=0.06 because of the coexistence of two phases. As a result, the introduction of BCZ could further improve piezoelectric properties of KNN ceramics.     

Structure,dielectric and piezoelectric properties of Ba0.90Ca0.10Ti1−xSnxO3 lead-free ceramics

Lead-free piezoelectric ceramics Ba_0.90Ca_0.10Ti_1−xSn_xO₃ have been prepared by a conventional ceramic fabrication technique and the effects of Sn⁴⁺ on the structure, dielectric and piezoelectric properties of the ceramics have been investigated. All the ceramics exhibit a pure perovskite structure. After the substitution of Sn⁴⁺, the crystal structure of ceramics is transformed gradually from a tetragonal to an orthorhombic phase, and becomes a pseudo-cubic phase at x≥0.14. The substitution also decreases the Curie temperature greatly from 138 °C at x=0 to 33 °C at x=0.12, and shifts the orthorhombic–tetragonal phase transition to higher temperatures. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramic at x=0.10, leading to significant improvements in the piezoelectric properties: d₃₃=521 pC/N and k_p=45.5%. Our results also reveal that the ceramics sintered at higher temperatures contain larger grains, and thus exhibit more noticeable tetragonal–orthorhombic phase transition and enhanced ferroelectric and piezoelectric properties.     

(Ba0.85Ca0.15)(Ti0.90Zr0.06Sn0.04)O3-Fe2O3无铅压电陶瓷的性能研究

采用固相法制备了(Ba0.85Ca0.15) (Ti0.90Zr0.06Sn0.04)O3-xmol％Fe2O3(简写为BCTZS-xFe)无铅压电陶瓷.研究了不同掺杂量对该陶瓷的显微结构、介电、铁电及压电性能的影响.结果表明,所有样品均具有单一的钙钛矿结构,少量掺杂能使晶粒长大,提高电性能.在x=0.025时,具有最佳的综合电性能,压电常数d33 =515 pC/N,机电耦合系数kp=48.2％,机械品质因数Qm =182,2Pr=18.2 μC/cm2,2Ec =4.3 kV/cm,介电常数εr=5175.     

Enhanced piezoelectric properties of (K0.40Na0.60)0.94Li0.06Nb0.94SbO3 lead-free ceramics by optimizing the sintering temperature

Effects of sintering temperature on the microstructure and electrical properties of (K_0.40Na_0.60)_0.94Li_0.06Nb_0.94SbO₃ (KNLNS) lead-free ceramics are investigated. The grain size gradually becomes larger with increasing sintering temperature from 1055 °C to 1105 °C, and the piezoelectric property could be enhanced by optimizing their sintering temperature. The ceramic sintered at 1075 °C has optimum electrical properties, i.e., d₃₃~272 pC/N, k_p~43.5%, ε_r~1152, tan δ~0.026, and T_C~346 °C. These results show that the sintering temperature can optimize electrical properties of KNLNS ceramics.     

Effects of sintering temperature and poling conditions on the electrical properties of Ba0.70Ca0.30TiO3 diphasic piezoelectric ceramics

The effects of sintering temperature and poling conditions on the electrical properties of tetragonal and orthorhombic diphasic Ba_0.70Ca_0.30TiO₃ (BCT) lead-free ceramics have been systematically investigated. On the one hand, with increasing sintering temperature from 1270 °C to 1400 °C, the bulk density increases monotonically and the Curie temperature keeps almost constant with the value of ∼120 °C, whereas the grain size, the maximum relative dielectric constant, room temperature polarization reach the maximum values for samples sintered at 1340 °C. On the other hand, it is found that the piezoelectric property depends on poling electric field and poling temperature significantly. An enhanced piezoelectric behavior of d₃₃=126 pC/N, k_p=0.29, and Q_m=588 is obtained for the BCT ceramics poled at 100 °C with 30 kV/cm field for 20 min. The aging behavior of the piezoelectric property is also investigated.     

Improving the oxygen permeability of Ba0.5Sr0.5Co0.8Fe0.2O3−δ membranes by a surface-coating layer of GdBaCo2O5+δ

A GdBaCo₂O_5+δ layer was coated on the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes to enhance their oxygen permeability by employing the fast oxygen adsorption/desorption surface-exchange properties of the GdBaCo₂O_5+δ material. The oxygen flux of the coated and uncoated Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes was measured in the temperature range of 600–850 °C. The results reveal that the oxygen-permeation flux of the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes coated by a GdBaCo₂O_5+δ layer shows significant enhancement. The GdBaCo₂O_5+δ layer coated on the oxygen desorption side (He side) has much effect than that coated on the oxygen adsorption side (air side). At 850 °C, the oxygen flux with a single coating layer on the air side can rise 16%, while a single coating on the helium side will result into a rise of 23%.     

Sintering of glass-added BaZn1/3Nb2/3O3 ceramics

The complex perovskite oxide Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?_r of 39, low dielectrics losses (tan(δ) < 10⁻³) and a temperature coefficient of permittivity τ_? of 45 ppm/°C⁻¹. The 2 wt.% ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of B₂O₃-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?_r = 38, tan(δ) < 10⁻³) and it is more interesting in terms of temperature coefficient of the permittivity (τ_? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications.     

Microwave dielectric properties of SnO2-doped CaSiO3 ceramics

SnO₂-doped CaSiO₃ ceramics were successfully synthesized by a solid-state method. Effects of different SnO₂ additions on the sintering behavior, microstructure and dielectric properties of Ca(Sn_1−xSi_x)O₃ (x=0.5–1.0) ceramics have been investigated. SnO₂ improved the densification process and expanded the sintering temperature range effectively. Moreover, Sn⁴⁺ substituting for Si⁴⁺ sites leads to the emergence of Ca₃SnSi₂O₉ phase, which has a positive effect on the dielectric properties of CaO–SiO₂–SnO₂ materials, especially the Qf value. The Ca(Sn_0.1Si_0.9)O₃ ceramics sintered at 1375 °C possessed good microwave dielectric properties: ε_r =7.92, Qf =58,000 GHz and τ_f=−42 ppm/°C. The Ca(Sn_0.4Si_0.6)O₃ ceramics sintered at 1450 °C also exhibited good microwave dielectric properties of ε_r=9.27, Qf=63,000 GHz, and τ_f=−52 ppm/°C. Thus, they are promising candidate materials for millimeter-wave devices.     

Long-term degradation of Ta2O5-doped Bi2O3 systems

Bismuth oxide in δ-phase is a well-known high oxygen ion conductor and can be used as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). 5-10 mol% Ta₂O₅ are doped into Bi₂O₃ to stabilize δ-phase by solid state reaction process. One Bi₂O₃ sample (7.5TSB) was stabilized by 7.5 mol% Ta₂O₅ and exhibited single phase δ-Bi₂O₃-like (type I) phase. Thermo-mechanical analyzer (TMA), X-ray diffractometry (XRD), AC impedance and high-resolution transmission electron microscopy (HRTEM) were used to characterize the properties. The results showed that holding at 800-850 °C for 1 h was the appropriate sintering conditions to get dense samples. Obvious conductivity degradation phenomenon was obtained by 1000 h long-term treatment at 650 °C due to the formation of α-Bi₂O₃ phase and Bi₃TaO₇, and 〈1 1 1〉 vacancy ordering in Bi₃TaO₇ structure.     

Effect of TiO2 doped Ni electrodes on the dielectric properties and microstructures of (Ba0.96Ca0.04)(Ti0.85Zr0.15)O3 multilayer ceramic capacitors

The effects of TiO₂-doped Ni electrodes on the microstructures and dielectric properties of (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ multilayer ceramic capacitors (MLCCs) have been investigated. Nickel paste with a TiO₂ dopant was used as internal electrodes in MLCCs based on (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ (BCTZ) ceramic with copper end-termination. The microstructures and defects were analysed by microstructural techniques (SEM/HRTEM) and energy-dispersive spectroscopy (EDS). The continuity of the electrode of the MLCC was measured using a scanning electron microscope, which showed that the continuity of the electrode for the MLCC with a TiO₂-doped Ni electrode was approximately 90%. However, continuity of the electrode for a conventional MLCC was below 80%. The continuity of the TiO₂-doped Ni electrode showed significant improvement in the MLCC, which was due to no reaction between Ni and BCTZ.     

Dielectric and piezoelectric properties of (Ba0.95Ca0.05)(Ti0.88Zr0.12)O3 ceramics sintered in a protective atmosphere

(Ba_0.95Ca_0.05)(Ti_0.88Zr_0.12)O₃ (BCTZ) ceramics have been produced in a protective atmosphere of industrial N₂ gas for potential piezoelectric applications. For comparison, the ceramics were also sintered at 1200–1400 °C in air. The results revealed that the reducing atmosphere of pO₂ = 5 × 10² Pa had no substantial effect on the phase structure or the microstructure of the BCTZ ceramics. The XRD patterns suggested a tetragonal to pseudocubic phase transition at sintering temperatures above 1300 °C in both atmospheres. The nitrogen-sintered BCTZ samples had higher dielectric constants _r but lower electromechanical coupling coefficients k_p than the air-sintered samples. The piezoelectric constant d₃₃ for the BCTZ ceramics was not significantly influenced by the reducing atmosphere of pO₂ = 5 × 10² Pa. The correlation of dielectric and piezoelectric properties of the BCTZ ceramics with the sintering temperature was explained based on a competing mechanism between phase structure and microstructure.     

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.     

Preparation, characterization and dielectric properties of CaCu3Ti4O12 ceramics

CaCu₃Ti₄O₁₂ nano-sized powders were successfully prepared by sol-gel technique and calcination at 600-900 °C. The thermal decomposition process, phase structures and morphology of synthesized powders were characterized by IR, DSC-TG, XRD, TEM, respectively. It was found that the main weight-loss and decomposition of precursors occurred below 450 °C and the complex perovskite phase appeared when the calcination temperature was higher than 700 °C. Using above synthesized powders as starting materials, CCTO-based ceramics with excellent dielectric properties (?₂₅ = 5.9 × 10⁴, tan δ = 0.06 at 1.0 kHz) were prepared by sintering at 1125 °C. According to the results, a conduction mechanism was proposed to explain the origin of giant dielectric constant in CCTO system.     

Structural, thermal and mechanical properties of transparent Yb:(Y0.97Zr0.03)2O3 ceramic

Yb doped (Y_0.97Zr_0.03)₂O₃ transparent ceramics were fabricated by solid state reaction and vacuum sintering. The microstructure, thermal and mechanical properties of Y₂O₃ ceramic, as well as the effect of Yb doping concentration on these properties were investigated in detail. The lattice parameter and unit cell volume decrease with the increasing of Yb content, whereas thermal expansive coefficient increases. With Yb content increasing from 0 to 8 at.%, the mean grain size increases from 15.82 μm to 26.54 μm, and the thermal conductivity at room temperature (RT) decreases from 11.97 to 6.39 W/m/K. The microhardness decreases with Yb content, and the microhardness and fracture toughness of (Y_0.97Zr_0.03)₂O₃ transparent ceramic is 11.11 GPa and 1.29 MPa m^1/2, respectively.     

Role of sintering on magneto-electric effect in CuFe1.8Cr0.2O4–Ba0.8Pb0.2Ti0.8Zr0.2O3 composite ceramics

Magnetoelectric composites containing CuFe_1.8Cr_0.2O₄–Ba_0.8Pb_0.2Ti_0.8Zr_0.2O₃ phases have been prepared by sintering them at different firing temperatures. The particle size for either phase of the composite was found to increase, whereas porosity decreases with increase in sintering temperature. This is due to the increase in the grain size with increase in sintering temperature. Resistivity of the composite decreases with increase in either sintering temperature or with increase in CuFe_1.8Cr_0.2O₄ content. The variation of dielectric constant (′) with temperature reflects DPT type behaviour. The peak value of dielectric constant (′_max) for a composite decreased with increase in its sintering temperature. The maximum value of the magnetoelectric conversion factor (dE/dH)_max equal to 182.7 μV/(cm*Oe) is obtained for 70% Ba_0.8Pb_0.2Ti_0.8Zr_0.2O₃–30% CuFe_1.8Cr_0.2O₄ composite when sintered at 1000°C.     

Piezoelectric properties of Pb(Mn1/3Nb2/3)O3–PbZrO3–PbTiO3 ceramics with sintering aid of 2CaO–Fe2O3 compound

Since the electromechanical devices move towards enhanced power density, high mechanical quality factor (Q_m) and electromechanical coupling factor (k_p) are commonly needed for the high powered piezoelectric transformer with Q_m≥2000 and k_p=0.60. Although Pb(Mn_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PMnN–PZ–PT) ceramic system has potential for piezoelectric transformer application, further improvements of Q_m and k_p are needed. Addition of 2CaO–Fe₂O₃ has been proved to have many beneficial effects on Pb(Zr,Ti)O₃ ceramics. Therefore, 2CaO–Fe₂O₃ is used as additive in order to improve the piezoelectric properties in this study. The piezoelectric properties, density and microstructures of 0.07Pb(Mn_1/3Nb_2/3)O₃–0.468PbZrO₃–0.462PbTiO₃ (PMnN–PZ–PT) piezoelectric ceramics with 2CaO–Fe₂O₃ additive sintered at 1100 and 1250 °C have been studied. When sintering temperature is 1250 °C, Q_m has the maximum 2150 with 0.3 wt.% 2CaO–Fe₂O₃ addition. The k_p more than 0.6 is observed for samples sintered at 1100 °C. The addition of 2CaO–Fe₂O₃ can significantly enhance the densification of PMnN–PZ–PT ceramics when the sintering temperature is 1250 °C. The grain growth occurred with the amount of 2CaO–Fe₂O₃ at both sintering temperatures.