High piezoelectric d33 coefficient of lead-free (Ba0.93Ca0.07)(Ti0.95Zr0.05)O3 ceramics sintered at optimal temperature

Lead-free (Ba_0.93Ca_0.07)(Ti_0.95Zr_0.05)O₃ (BCZT) ceramics were prepared using a solid-state reaction technique. The structure and electrical properties were investigated with a special emphasis on the influence of sintering temperature. Crystalline structures and microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. The BCZT ceramics sintered at 1450 °C show the highest densification and exhibit excellent piezoelectric properties of high piezoelectric coefficient d₃₃ = 387 pC/N, planar mode electromechanical coupling coefficient k_p = 44.2%, mechanical quality factor Q_m = 140 and Curie temperature T_c = 108 °C.     

Dielectric properties of Ba(Ti1 − xZrx)O3 solid solutions

This paper reports the structural and dielectric properties of Ba(Ti_1 − xZr_x)O₃ (x = 0-0.3) ceramics. Single-phase solid solutions of the samples were determined by X-ray diffraction. Microscopic observation by scanning electron microscope revealed dense, single-phase microstructure with large grains (20-60 μm). The evolution of dielectric behavior from a sharp ferroelectric peak (for x ≤ 0.08) to a round dielectric peak (for 0.15 ≤ x ≤ 0.25) with pinched phase transitions and successively to a ferroelectric relaxor (for x = 0.3) was observed with increasing Zr concentration. Compared with pure BaTiO₃, broaden dielectric peaks with high dielectric constant of 25,000-40,000 and reasonably low loss (tanδ: 0.01-0.06) in the Ba(Ti_1 − xZr_x)O₃ ceramics have been observed, indicating great application potential as a dielectric material.     

Microwave dielectric properties of Ba2 − xSrxLa3Ti3NbO15 ceramics

High dielectric constant and low loss ceramics in the system Ba_2 − xSr_xLa₃Ti₃NbO₁₅ (x = 0-1) have been prepared by conventional solid-state ceramic route. Ba_2 − xSr_xLa₃Ti₃NbO₁₅ solid solutions adopted A₅B₄O₁₅ cation-deficient hexagonal perovskite structure for all compositions. The materials were characterized at microwave frequencies. They show a linear variation of dielectric properties with the value of x. Their dielectric constant varies from 48.34 to 43.03, quality factor Q_u × f from 20,291 to 39,088 GHz and temperature variation of resonant frequency from 8 to 1.39 ppm/°C as the value of x increases. These low loss ceramics might be used for dielectric resonator (DR) applications.     

Size-dependent piezoelectric coefficient d33 of PbTiO3 nanoparticles

Size-dependent piezoelectric coefficient d₃₃(D) (D shows particle diameter) for small ferroelectrics is modeled in this paper. It is found that taking account of size effect is essential in understanding piezoelectric characteristics of nanoferroelectrics. The model prediction is in good agreement with the experimental results for PbTiO₃ nanoparticles, where d₃₃(D) increases correspondingly as D decreases. In addition, the size effect of the dielectric susceptibility coefficient η₃₃(D) is also predicted since η₃₃(D) ∝ d₃₃(D) is considered. Our model estimations for η₃₃(D) function are consistent with other theoretical evidences.     

Morphotropic phase boundary and piezoelectric properties of (Bi1/2Na1/2)1 − x(Bi1/2K1/2)xTiO3-0.03(Na0.5K0.5)NbO3 ferroelectric ceramics

Lead-free piezoelectric ceramics, (Bi_1/2Na_1/2)_1 − x(Bi_1/2K_1/2)_xTiO₃-0.03(Na_0.5K_0.5)NbO₃ (x = 0.10-0.40) were synthesized by conventional solid-state sintering. A morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases was confirmed. Two dielectric anomalies can be observed, showing diffused phase transition behavior. There is no shift of the dielectric maximum temperature with frequency due to the contribution of space charge at high temperatures, similar to pure (Bi_1/2Na_1/2)TiO₃. The materials near MPB show a strong compositional dependence with the optimal properties of a d₃₃ of 167 pC/N, a k_p of 35.5%, a P_r of 27.6 μC/cm² and a E_c of 27.9 kV/cm, suitable for future application.     

电场对(Ba0.97Ca0.03)(Ti0.82Zr0.18)O3无铅压电陶瓷铁电性的影响

采用溶胶-凝胶方法制备了(Ba0.97Ca0.03)(Ti0.82Zr0.18)O3无铅压电陶瓷。在电场1～8kV/cm下,频率为0.01～10Hz范围内,对其电滞回线进行了分析。实验结果表明(Ba0.97Ca0.03)(Ti0.82Zr0.18)O3陶瓷的电滞回线随电场值和频率的变化明显,在低电场下,随着频率的增加矫顽场(Ec)单调减小,在低频下剩余极化(Pr)增加;而在高电场下,随着频率的增加Ec单调增大,电滞回线达到饱和时,电滞回线随不同测试频率无明显变化。     

KxNa1 − xNbO3 powder synthesized by molten-salt process

K_xNa_1 − xNbO₃ ceramic powders have been successfully synthesized in different salts (NaCl, KCl, NaCl-KCl). Our results reveal that K_xNa_1 − xNbO₃ powders with single-phase perovskite structure can be formed at a low temperature such as 750 °C. The type of salts has significant effects on the morphology and chemical composition of the powders. As Na⁺ has a higher diffusing rate and occupies the A-site in the perovskite structure more easily as compared to K⁺, the powder contains only a small amount of K⁺ (x ∼ 0.10) when it is synthesized according to formula K_0.5Na_0.5NbO₃ and in a flux containing the same molar content of Na⁺ and K⁺. By using a NaCl or KCl salt, the K⁺ concentration x can be adjusted to almost 0 and 0.77, respectively.     

Temperature stable high-Q microwave dielectric ceramics in (1 − x)BaTi4O9-xBaZn2Ti4O11 system

The microwave dielectric properties of (1 − x)BaTi₄O₉-xBaZn₂Ti₄O₁₁ ceramics were investigated by solid-state reaction technique for obtaining high-Q dielectric ceramics in BaO-ZnO-TiO₂ system. And they were strongly determined by the chemical composition. As x was increased from 0.05 to 0.50, BaZn₂Ti₄O₁₁ phase formed more and more. Therefore, the ε_r decreased from 37.3 to 32.8 and the Q × f values first raised from 45,300 GHz to 60,600 GHz (x = 0.30) and then started to decline to 58,700 GHz (x = 0.40), and the τ_f values varied gradually from 12 ppm/°C to − 13 ppm/°C. 0.7BaTi₄O₉-0.3BaZn₂Ti₄O₁₁ ceramics sintered at 1240 °C for 3 h had excellent comprehensive microwave dielectric properties: ε_r = 34.2, Q × f = 60,600 GHz and τ_f = − 2 ppm/°C.     

Leakage current characteristics of Bi3.15Nd0.85Ti3 − xZrxO12 thin films

Thin films of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) and Bi_3.15Nd_0.85Ti_3 − xZr_xO₁₂ (BNTZ_x, x = 0.1 and 0.2) were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a chemical solution deposition (CSD) technique at 700 °C. Structures, surface morphologies, leakage current characteristics and Curie temperature of the films were studied as a function of Zr ion content by X-ray diffraction, atomic force microscopy, ferroelectric test system and thermal analysis, respectively. Experimental results indicate that Zr ion substitution in the BNT film markedly decreases the leakage current of the film, while almost not changing the Curie temperature of the film, which is at about 420-460 °C. The decrease of the leakage current in BNTZ_x films is that the conduction by the electron hopping between Ti⁴⁺ and Ti³⁺ ions is depressed because Zr⁴⁺ ions can block the path between two adjacent Ti ions and enlarge hopping distance.     

Structure and thermal conductivity of Gd2(TixZr1 − x)2O7 ceramics

The Gd₂(Ti_xZr_1 − x)₂O₇ (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd₂(Ti_xZr_1 − x)₂O₇ were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd₂(Ti_xZr_1 − x)₂O₇ from room temperature to 1400 °C was measured by a laser-flash method. The Gd₂Zr₂O₇ has a defect fluorite-type structure; however, Gd₂(Ti_xZr_1 − x)₂O₇ (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd₂Zr₂O₇ and Gd₂Ti₂O₇ are infinitely soluable. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ is within the range of 1.33 to 2.86 W m^− 1 K^− 1 from room temperature to 1400 °C.     

Different microstructure and dielectric properties of Ba1−xCaxTiO3 ceramics and pulsed-laser-ablated films

A comparative study of the microstructure and dielectric properties between Ba_1−xCa_xTiO₃ (BCT) ceramics and films were performed in the whole Ca concentration range of x = 0-1. The ceramics were prepared by conventional solid-state reaction technique and the films by the method of pulsed-laser deposition. X-ray diffraction (XRD) study of the BCT ceramics exhibited a pure tetragonal phase for x = 0-0.25, a tetragonal-orthorhombic diphase for x = 0.25-0.85 and a pure orthorhombic phase for x = 0.90-1.00. And the dielectric phase transition temperature from tetragonal to cubic was marginally affected by the Ca doping into BaTiO₃. However, BCT films deposited on Pt/Si/SiO₂/Si substrates showed a different microstructure and dielectric properties. Tetragonal-orthorhombic diphase was not found in the BCT films for x = 0.25-0.85, and a large decrease of the Curie point and diffuse phase transition were observed in the BCT films. Based on the compositional analysis, such phenomena were ascribed to the occupancy of some Ca²⁺ to the Ti⁴⁺ sites in the BCT films.     

Heterophase structures and their quantitative characteristics in (1 − x)Pb(Fe1/2Nb1/2)O3 − xPbTiO3 near the morphotropic phase boundary

Features of phase coexistence in solid solutions of (1 − x)Pb(Fe_1/2Nb_1/2)O₃ − xPbTiO₃ with the perovskite-type structure are studied at 0.05 ≤ x ≤ 0.08. The role of elastic matching of the tetragonal P4mm and monoclinic Cm phases of the ferroelectric nature is considered near the morphotropic phase boundary. Model concepts on the stress relief in heterophase structures are developed and applied to interpret the phase content in (1 − x)Pb(Fe_1/2Nb_1/2)O₃ − xPbTiO₃. Good agreement between the calculated and experimental dependences of the volume fraction of the tetragonal phase on x is observed. It is shown that the studied phase coexistence under conditions for the complete stress relief can take place at elastic matching of the single-domain monoclinic phase and the tetragonal phase split into two types of 90° domains.     

Effect of sintering time on crystal structure and microwave dielectric properties in aeschynite-structured (Sm1−xYx)(Ti1.5W0.5)O6 (x = 0 and 0.5) ceramics

The crystal structure and microwave dielectric properties of the (Sm_1−xY_x)(Ti_1.5W_0.5)O₆ (x = 0 and 0.5) ceramics sintered at 1375 °C for 2-50 h were investigated in this study. No secondary phase was observed in the samples sintered for various sintering times, whereas a secondary phase was formed in the (Sm_0.5Y_0.5)(Ti_1.5W_0.5)O₆ ceramic sintered at 1400 °C for 50 h. As for the microstructure analysis, the formation of the liquid phase was observed in the both of the samples sintered for 20 and 50 h. The formation of the liquid phase is related to the compositional change of Ti and W from the stoichiometric composition of the samples caused by the instability of crystal structure. The dielectric constants were increased with increased sintering time in the both of the samples, though variations in the temperature coefficient of resonant frequency of the samples were not recognized with the variation in the sintering time. Moreover, although the quality factors of the each sample increased with increasing the sintering time from 2 to 10 h, decreases in the quality factors were recognized when the sintering time was over 10 h.     

Enhancement on effective piezoelectric coefficient d33 of Bi3.15Dy0.85Ti3O12 ferroelectric thin films

Effects of annealing temperature (600-800 °C) on microstructure, ferroelectric and piezoelectric properties of Bi_3.15Dy_0.85Ti₃O₁₂ (BDT) thin films prepared by metal-organic decomposition were studied. The remnant polarization 2P_r and spontaneous polarization 2P_s (16.2 µC/cm² and 23.3 µC/cm² under 690 kV/cm), effective piezoelectric coefficient d₃₃ (63 pm/V under the bipolar driving field of 310 kV/cm) of BDT thin film annealed at 700 °C are better than those of others. The higher 2P_s and relatively permittivity ε_r induced by moderate annealing temperature should be responsible for the enhancement of piezoelectric properties. The improved d₃₃ may make BDT a promising candidate for piezoelectric thin film devices.     

Synthesis of perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) at low temperature

Gel formation was realized by adding citric acid to a solution of La(NO₃)₃·5H₂O, Ca(NO₃)₂·4H₂O, and Fe(NO₃)₂·9H₂O. Perovskite-type (La_1−xCa_x)FeO₃ (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D_1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m²/g and independent of x. The XPS measurement of the (La_1−xCa_x)FeO₃ surface indicated that the Ca²⁺ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x.     

Decomposition of (Ti2xFe1−xSb1−x)O4 solid solutions below 1673 K

The pseudo-binary TiO₂-FeSbO₄ system was investigated by means of thermogravimetric analysis below 1673 K in O₂. Rutile-type solid solutions were synthesised at 1373 K in O₂ by means of a solid state reaction between the two pure end members TiO₂ (rutile) and FeSbO₄ mixed in stoichiometric amounts. Thermal stability of the (Ti_2xFe_1−xSb_1−x)O₄ solid solution increases with rutile content; equimolar (Ti_1.00Fe_0.50Sb_0.50)O₄ solid solutions decompose at about 1673 K forming a TiO₂-enriched solid solution and FeSbO₄, that subsequently decomposes into Fe₂O₃ (hematite) and a volatile Sb oxide, probably Sb₄O₆. For compositions characterised by higher Ti content the decomposition temperature is higher than 1673 K.     

Magnetic and electrical properties of Ba2CrMo1 − xWxO6 double perovskite

Effects of the partial substitution of W^5+,6+ for Mo^5+,6+ on the structural and physical properties of Ba₂CrMoO₆ have been investigated. Polycrystalline Ba₂CrMo_1 − xW_xO₆samples have been prepared by sol-gel method in a stream of 5% Ar/H₂ gas at various sintering temperatures. Rietveld analysis of X-ray diffraction patterns shows a partial disorder of Mo/W and Cr on the B sites of the double perovskite, which plays a dominant role in the structural and magnetic properties of these compounds. The symmetry is cubic (Fm3?m) for all samples, and no phase transition was detected for Ba₂CrMo_1 − xW_xO₆. The Curie temperature T_C has been analyzed by two methods: a linear extrapolation of M(T) to zero magnetization and the thermodynamic model. The experimental results indicate that T_C decrease from 335 K (x = 0) to 285 K (x = 0.5) with increasing W substitution independently of the method used to obtain T_C. A systematic decrease in saturation magnetization, M_s with increasing W substitution has been observed in this solid solution series. This decrease of magnetization arises from the disorder at the Cr and Mo/W sites. Electrical properties change as well strongly along the series.     

Phase evolution and magnetic property of Bi1 − xDyxFeO3 ceramics

Rare-earth ion Dy was substituted at the bismuth site in BiFeO₃ to produce Bi_1 − xDy_xFeO₃ (x = 0, 0.1, 0.2 and 0.3) polycrystalline ceramics. A two-stage solid-state reaction method was adopted in synthesizing the materials. The effects of varying the Dy doping concentration on the crystalline structures, morphologies and magnetic properties of the final products have been investigated. It is found that Dy doping resulted in a sequence of structural phase transitions and led to small grain sizes in the materials. As a result, the magnetic property of the doped samples was much enhanced. Therefore, it seems a promising way to improve the weak ferromagnetic property of BiFeO₃ based materials by Dy doping.     

Synthesis and luminescence properties of color-tunable Ba1−ySryLa4−xTbx(WO4)7 (x = 0.02-1.2, y = 0-0.4) phosphors

Ba_1−ySr_yLa_4−xTb_x(WO₄)₇ (x = 0.02-1.2, y = 0-0.4) phosphors were prepared via a solid-state reaction and their photoluminescence properties were investigated. An analysis of the decay behavior indicates that the energy migration between Tb³⁺ ions is conspicuous in the ⁵D₃ → ⁷F₄ transition due to the cross-relaxation in BaLa₄(WO₄)₇. A partial substitution of Ba²⁺ by Sr²⁺ can not only enhance the emission intensity but also increase the solid solubility of Tb³⁺ in Ba_1−ySr_yLa_4−xTb_x(WO₄)₇. The emission intensity of the ⁵D₄ → ⁷F_J (J = 4, 5, 6) transitions can be enhanced by increasing Sr²⁺ and Tb³⁺ concentrations, with the optimal conditions being x = 1.2, y = 0.4 (Ba_0.6Sr_0.4La_2.8Tb_1.2(WO₄)₇). Under near-UV excitation at 379 nm, the CIE color coordinates of Ba_1−ySr_yLa_4−xTb_x(WO₄)₇ vary from blue (0.212, 0.181) at x = 0.04, y = 0, to green (0.245, 0.607) at x = 1.2, y = 0.4.