Structure and electrical properties of Nd2O3-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 ceramics

Nd₂O₃ doped 0.82Bi_0.5Na_0.5TiO₃–0.18Bi_0.5K_0.5TiO₃ (abbreviated to BNKT) binary lead-free piezoelectric ceramics were synthesized by the conventional mixed-oxide method. The results show that the BNKT ceramics with 0–0.15 wt.% Nd₂O₃ doping possesses a single perovskite phase with rhombohedral structure. The grain size of BNKT decreased with the addition of Nd₂O₃ dopant. The temperature dependence of the dielectric constant ?_r revealed that there were two-phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. A diffuse character was proved by linear fitting of the modified Curie–Weiss law. At room temperature, the specimens containing 0.0125 wt.% Nd₂O₃ with homogeneous microstructure presented excellent electrical properties: the piezoelectric constant d₃₃ = 134 pC/N, the electromechanical coupling factor K_p = 0.27, and the dielectric constant ?_r = 925 (1 kHz).     

Effect of SrZrO3 on phase structure and electrical properties of 0.974(K0.5Na0.5)NbO3–0.026Bi0.5K0.5TiO3 lead-free ceramics

(0.974−x)(K_0.5Na_0.5)NbO₃–0.026Bi_0.5K_0.5TiO₃–xSrZrO₃ lead-free piezoelectric ceramics have been prepared by the conventional solid state sintering method. Systematic investigation on the microstructure, crystalline structures as well as electrical properties of the ceramics was carried out. With the addition of SrZrO₃, the rhombohedral–orthorhombic phase transition temperature of the ceramics increases. Both the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions of the ceramics were modified to be around room temperature when x~0.05, and as a result remarkably strong piezoelectricity has been obtained in 0.924(K_0.5Na_0.5)NbO₃–0.026Bi_0.5K_0.5TiO₃–0.05SrZrO₃ ternary system, whose piezoelectric parameters were d₃₃=324 pC/N and k_p=41%.     

Phase transition and piezoelectric properties of lead-free (Bi1/2Na1/2)TiO3–BaTiO3 ceramics

(1−x)(Bi_0.5Na_0.5)TiO₃–xBaTiO₃ ceramics (x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, and 0.90) were fabricated by a conventional solid-state reaction and their phase transitions and piezoelectric properties were investigated using XRD analyses, Curie temperature, the frequency dependance of dielectric constant, and P–E curves. A complete solid solution with a perovskite structure was formed in the whole composition range of BNT–BT and more than two phase transitions arising from a compositional change were found. With increasing BaTiO₃ content, the sequence of phase transitions from a rhombohedral structure to unknown tetragonal structures and finally a tetragonal structure with the space group P4mm has been established. While the rhombohedral–tetragonal phase transition led to superior piezoelectric properties in BNT–BT ceramics, other phase transitions between tetragonal structures had a little effect on piezoelectric properties. The d₃₃, ε_r, k_p, k_t, and Q_m and values lied in ranges of 40–130 pC/N, 400–900, 10–30%, 15–30%, and 50–250, respectively.     

Microstructure and electrical properties of (Na0.5K0.5)1−2xMgxNbO3–Bi0.5Na0.5TiO3 lead-free piezoelectric ceramics

0.975[(Na_0.5K_0.5)_1−2xMg_xNbO₃]–0.025(Bi_0.5Na_0.5TiO₃) (KNMN–BNT, x=0, 0.01, 0.02, 0.03, 0.04 and 0.05) lead-free piezoelectric ceramics were fabricated by the conventional solid-state sintering method. The dependence of Mg content on the microstructure and electrical properties of the ceramics is investigated. The X-ray diffraction (XRD) analysis revealed that an appropriate amount of Mg diffused into the KNN–BNT lattice to form a stable solid solution, the ceramics possessed a pure perovskite structure, and a morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was observed with the composition of 0.02≤x≤0.05. The orthorhombic–tetragonal transition temperature (T_O–T) is less than 95 °C and the Curie temperature (T_c) is almost unchanged (~360 °C) with the increase of MgO content. The ceramics with x=0.02 showed enhanced piezoelectric and ferroelectric properties because of close proximity to the MPB, i.e., d₃₃~210 pC/N, k_p~0.41, 2E_c~22.4 kV/cm and 2P_r~39.2 μC/cm². Moreover, the dielectric properties exhibited optimal effects with x=0.02, that is ε_r~637 and tan δ~0.09. These results indicate that the introduction of MgO is an effective method to improve the density as well as the electrical properties and the temperature stability of the KNN–BNT ceramics. As a result, the KNMN–BNT ceramic is a promising candidate for lead-free piezoelectric materials.     

Large strain of temperature insensitive in (1–x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO3) –xSr0.7La0.2TiO3 lead-free ceramics

Novel (1–x)(0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃)–xSr_0.7La_0.2TiO₃ ternary lead-free ceramics (BNBT–xSL, x?=?0.00–0.08) were fabricated by the widely used solid-state sintering technique. The crystal phase, microstructure, dielectric relaxation, piezoelectric, and electromechanical properties of each composition were systematically analyzed. It is found that the addition of SL has little effect on the crystal phase and grain morphology, but it can remarkably improved the relaxation property of the ceramic sample and gave rise to favourable dielectric properties in a wide range of temperatures. In addition, as the SL content increases, the ferroelectric to relaxor temperature (T_F-R) is adjusted to below ambient temperature. More importantly, the decay of ferroelectric phase resulted in a significant increase in strain value: the large strain of 0.5% with normalized strain of 625?pm/V was obtained at 80kv/cm and x?=?0.04. Finally, the composition exhibited high strain of temperature insensitivity range from room temperature to 100?°C, the strain value remained above 0.4% and kept within 5%. The results are due to the coexistence of rhombohedral polar-nanoregions (PNRs) and tetragonal PNRs during the relaxor region. This result is of great importance to the developments of temperature-insensitive strain sensors and actuators.     

Electrocaloric effect based on the depolarization transition in (1−x)Bi0.5Na0.5TiO3–xKNbO3 lead-free ceramics

Lead-free ferroelectric ceramics (1−x)Bi_0.5Na_0.5TiO₃−xKNbO₃ (BNT–xKN) with x=0.00, 0.04, 0.06 and 0.08 were synthesized by the conventional solid state reaction method. The effects of the KNbO₃ addition on the dielectric behavior, ferroelectric properties, as well as electrocaloric effect of the ferroelectric ceramic BNT–xKN were investigated. The results show that the depolarization temperature decreases with the increment of KN content. A high ECE of 1.73 °C is achieved at 76 °C in BNT–0.06KN. The relation between electrocaloric effect and depolarization transition was discussed. This investigation indicates that the depolarization transition below Curie transition in BNT-based ceramics is a promising approach in ECE technique.     

High electromechanical strain properties by the existence of nonergodicity in LiNbO3–modified Bi1/2Na1/2TiO3–SrTiO3 relaxor ceramics

This study investigated the effect of LiNbO₃ modification on the dielectric, ferroelectric and electromechanical strain properties of Bi_1/2Na_1/2TiO₃–SrTiO₃ (BNT–ST) lead–free relaxor ceramics. The sintering temperature for lead–free BNT–ST relaxor ceramics was slightly decreased from 1175?°C to 1050?°C by modifying with LiNbO₃. We found that the sintering temperature affects the dielectric behavior of 0.76BNT–(0.24?x)ST–xLiNbO₃ (BNST–100xLN) ceramics at high temperature (near dielectric maximum temperature, T_m). The T_m for the low–temperature sintered sample was shifted to relatively higher temperature by comparison with the high–temperature sintered samples. Furthermore, the degradation of dielectric behavior near T_m in low–temperature sintered BNST–2LN ceramics was revealed after poling treatment and seem to be related to the existence of a high temperature stabilized nonergodic relaxor phase. Accordingly, we assume that the stabilized nonergodic relaxor phase is responsible for the relatively late transition from ferroelectrics to the relaxor. Therefore, we obtained the improved d₃₃^* of 616?pm/V as the highest value in low–temperature sintered BNST–2LN ceramics.     

Piezoelectric and dielectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Ba(Zr0.04Ti0.96)O3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xBa(Zr_0.04Ti_0.96)O₃ (abbreviated as BNBT–BZT100x, wherein x from 0 to 10 mol%) were fabricated. We have studied effects of amount of BZT content on the electrical properties and microstructures. X-ray diffraction analysis indicates that a solid solution is formed when BZT diffuses into the BNBT lattice, and further the crystal structure of sintered hybrid changes from rhombohedral to tetragonal symmetry along with increasing BZT content. Piezoelectric property measurements reveal that the BNBT–BZT4 ceramics has the highest piezoelectric performance, for example, the piezoelectric constant d₃₃ reaches to 167 pC/N and planar electromechanical coupling factor k_p is up to 0.27. In addition, the effect of Bi₂O₃ on the electrical properties and microstructure of the BNBT–BZT4 ceramics have also been studied, and found that the doping of Bi enhances the piezoelectric properties of ceramics.     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

Multiferroic ceramics in BaO–Y₂O₃–Fe₂O₃–Nb₂O₅ system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba₂YFeNb₄O₁₅, and minor phases of monoclinic YNbO₄ and hexagonal Ba₃Fe₂Nb₆O₂₁. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe³⁺ and Nb⁵⁺ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics.     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

Effect of sintering temperature on ferroelectric properties of 0.94(K0.5Na0.5)NbO3–0.06LNbO3 system

Lead free 0.94(K_0.5Na_0.5NbO₃)–0.06(LiNbO₃) (KNN–LN) system was synthesized by conventional solid state reaction route (CSSRR). The KNN–LN system was calcined at 850 °C for 6 h for the formation of single perovskite phase whereas the sintering was done at 1050 °C, 1080 °C and 1100 °C for 4 h, respectively. The KNN–LN samples sintered at 1080 °C show better properties: room temperature (RT) dielectric constant (?_r) ∼936, dielectric loss (tan δ) ∼0.016 at 1 MHz, a relatively high bulk density (ρ) ∼4.385 g/cm³, which is 97.5% of the theoretical density (TD ∼ 4.51), remnant polarization (P_r) ∼6.4 μC/cm² and coercive field (E_c) ∼9.6 kV/cm have been observed.     

Influences of La and Er on structure and properties of Bi2O3–B2O3 glass

Bi₂O₃·2B₂O₃ glasses doped with La₂O₃ and Er₂O₃ were prepared by the melting-quenching method with AR-grade oxides. IR analysis was used to investigate the glass network structure. The characteristic temperatures including the glass transition temperature (T_g), crystallization temperature (T_p), and melting temperature (T_m) were estimated by DSC. The coefficient of thermal expansion (α), mass density (D), and Vickers hardness (H_v) were also measured. The results show that the basic network structure of Bi₂O₃·2B₂O₃ glasses doped with rare-earth oxides consists of chains composed of [BO₃], [BO₄], and [BiO₆] units. La₂O₃ and Er₂O₃ act as network modifiers. As the doping concentrations of the rare-earth oxides were increased, T_g increased and α decreased, indicating that a more rigid glass was obtained. Er₂O₃ reduces the melting temperature and prevents glass crystallization. La₂O₃ contributes to the improvement of the microhardness of Bi₂O₃·2B₂O₃ glass.     

NaNbO3–CaZrO3–Bi0.5Na0.5TiO3三元系陶瓷的相结构与储能性能

铌酸钠(NaNbO₃)无铅陶瓷由于其无毒和出色的储能性能,在脉冲功率电容器领域吸引了越来越多的关注。然而,由于较大的有效储能密度(W_rec)和高的储能效率(η)不能同时实现,限制了其商业化。通过构建局域随机场,增加弛豫特性来提高储能性能的策略。采用传统固相法制备了(1–x)(0.96Na Nb O₃–0.04CaZrO₃)–x Bi_0.5Na_0.5TiO₃ (x=0.05、0.10、0.15、0.20)反铁电储能陶瓷,研究了不同含量Bi_0.5Na_0.5TiO₃对0.96Na Nb O₃–0.04CaZrO₃陶瓷的相结构、微观形貌、介电性能和储能特性的影响。结果表明：随着Bi_0.5Na_0.5TiO₃含量的增加,(1–x)(0.96NaNbO₃...     

Microwave dielectric characteristics of Nb2O5-added 0.9Al2O3–0.1TiO2 ceramics

The sintering characteristics, phase composition, and microwave dielectric properties of Nb₂O₅-added 0.9Al₂O₃–0.1TiO₂ ceramics sintered at 1300–1500 °C have been investigated. Results show that Nb⁵⁺ and Al³⁺ can co-substitute for Ti⁴⁺ and form Ti_0.8Al_0.1Nb_0.1O₂, which can lower effectively the sintering temperature, and improve the quality factor of 0.9Al₂O₃–0.1TiO₂ ceramics.     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

Effects of PbO and SrO contents on crystallization and dielectric properties of PbO–SrO–Na2O–Nb2O5–SiO2 glass–ceramics system

PbO–SrO–Na₂O–Nb₂O₅–SiO₂ glass–ceramics were prepared via roll-quenching followed by controlled crystallization from 700 °C to 900 °C. The effects of PbO and SrO contents on crystallization and dielectric properties were investigated. The results show that Pb₂Nb₂O₇, Sr₂Nb₂O₇ and their solid solutions crystallize at 700 °C, NaNbO₃ is the primary phase at 800 °C, Pb₂Nb₂O₇ disappears and PbNb₂O₆ forms at 900 °C. The dielectric properties of the glass–ceramics formed through controlled crystallization has a strong dependence on the phase compositions that were developed during heat treatment. The highest dielectric constants (∼600) are found in samples with 6.0 mol% SrO annealed at 900 °C for 3 h. The dielectric–temperature characteristics of the samples show stability over the range from −60 °C to 180 °C, except the sample without SrO heated at 900 °C.     

The influence of In2O3 on electrical characteristics of iron mixed Li2O–PbO–B2O3–SiO2–Bi2O3 multi-component glass system

Glasses of the composition 19Li₂O–20PbO–20B₂O₃–30SiO₂–(10−x) Bi₂O₃–1Fe₂O₃: xIn₂O₃ with six values of x (0 to 5.0) were synthesized. Dielectric properties viz., dielectric constant, ε′(ω), loss, tan δ, ac conductivity, σ_ac, electric modulus, M(ω) over wide ranges of frequency and temperature and also dielectric break down strength have been studied as a function of In₂O₃ concentration. The temperature dispersion of real part of dielectric constant, ε′(ω) has been analyzed using space charge polarization model. The dielectric loss (and also the electric moduli) variation with frequency and temperature exhibited relaxation effects and these effects were attributed to the divalent iron ion complexes. The ac conductivity exhibited maximal effect, whereas the activation energy for the conductivity demonstrated minimal magnitude at about 1.0 mol% of In₂O₃. The conductivity mechanism is understood due to the polaronic transfer between Fe²⁺ and Fe³⁺ ions. The low temperature ac conductivity mechanism is explained following the quantum mechanical tunneling model. Spectroscopic studies viz., optical absorption and ESR spectra have revealed that the redox ratio (Fe²⁺/Fe³⁺) is maximal when the concentration of In₂O₃ is ~1.0 mol%. The higher values of dielectric parameters observed at 1.0 mol% of In₂O₃ are attributed to the presence of iron ions largely in divalent state and act as modifiers. The analysis of these results together with spectroscopic studies has indicated that when In₂O₃ is present in the glass matrix in higher concentrations (more than 1.0 mol%) iron ions predominantly exist in trivalent state, occupy substitutional positions and make the glass more rigid. Such enhanced rigidity of the network is causing the decrease of dielectric parameters with the concentration of In₂O₃. Finally it is concluded that In₂O₃ mostly participate in the glass network in octahedral positions and make act as reducing agent (for iron ions) in the studied glass matrix when its concentration is ≤1.0 mol%.     

Bi2O3对K2O–B2O3–SrO–Al2O3–Nb2O5–SiO2玻璃陶瓷介电储能性能的影响

随着电力电子系统的不断发展,高功率脉冲电容器的需求增多。电介质电容器因具有放电功率大、充放电速度快及性能稳定等优点,在电力系统、电子器件、脉冲电源等方面发挥着重要作用,广泛应用于民用领域及军事领域。通过熔融压延制备玻璃基体,采用可控结晶工艺研究了不同含量的Bi₂O₃ (x=0.0%、1.0%、2.0%、4.0%,摩尔分数)对K₂O–B₂O₃–Sr O–Al₂O₃–Nb₂O₅–SiO₂玻璃陶瓷物相演化、微观结构、介电和储能性能的影响。在该玻璃陶瓷中,KSr₂Nb₅O₁₅为主要析出晶相,当Bi₂O₃的加入量为x=2.0%(摩尔分数)时,热处理温度为950℃时,玻璃陶瓷样品的储能密度最大可达到1.27 J/cm³,室温下介电常数可达342,是热处...     

Effect of ceramic bonding phases on the thermo-mechanical properties of Al2O3–C refractories

Ceramic bonding phases of non-oxide whiskers can enhance the hot strength and the thermal shock resistance of Al₂O₃–C refractories. In this paper, the effect of different metals on the microstructure and thermo-mechanical properties of Al₂O₃–C refractories has been investigated. Thermodynamic calculation of Al–Si–O–C–N systems shows that Al₄C₃, AlN, SiC and β-Sialon are stable at elevated temperature. AlN with the shape of short column can be generated in Al₂O₃–C refractories with metallic Al, which leads to high hot modulus of rupture (HMOR) and poor resistance to thermal shock. SiC whiskers formed in Al₂O₃–C refractories with metallic Si give rise to low HMOR and good resistance to thermal shock. When metallic Si and Al are added together in the refractories, β-Sialon (z=2) with plane structure can be generated under the action of catalyst (nano-sized Ni). The existence of the catalyst promotes the diffusion of Al and O in Si₃N₄ crystals and contributes to the generation of plane-shaped β-Sialon. The corresponding HMOR and residual cold modulus of rupture respectively increase to about 20 MPa and 10.3 MPa. The plane-shaped β-Sialon can significantly enhance both hot strength and thermal shock resistance of Al₂O₃–C refractories.