Microstructures and microwave dielectric properties of (1 − y)Nd1−xYbx(Mg0.5Sn0.5)O3–yCa0.8Sr0.2TiO3 ceramics

The (1 ? y)Nd_1?xYb_x(Mg_0.5Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of the Nd_1?xYb_x(Mg_0.5Sn_0.5)O₃ ceramics revealed that Nd_1?xYb_x(Mg_0.5Sn_0.5)O₃ is the main crystalline phase, which is accompanied by a little Nd₂Sn₂O₇ as the second phase. An apparent density of 6.87 g/cm³, a dielectric constant (? _r ) of 19.48, a quality factor (Q × f) of 117,300 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?61 ppm/°C were obtained when the Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1,600 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) increased from ?61 to ?3 ppm/°C as y increased from 0 to 0.6 when the (1 ? y)Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramics were sintered at 1,600 °C for 4 h. 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic that was sintered at 1,600 °C for 4 h had a τ _f of ?3 ppm/°C.     

Microwave dielectric properties of (Ca0.8Sr0.2)(SnxTi1−x)O3 ceramics

In this paper, we study the behavior of the B-site behavior with the incorporation of Sn⁴⁺ ion in (Ca_0.8Sr_0.2)TiO₃ ceramics. An excess of Sn⁴⁺ resulted in the formation of a secondary phase of CaSnO₃ and SrSnO₃ affecting the microwave dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics. The dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics were improved because of the solid solution of Sn⁴⁺ substitution in the B-site. The temperature coefficient of resonant frequency (τ_f) of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics also improved with increasing Sn content.     

Microwave dielectric properties of (1 − y)Nd(1−2x/3)Bax(Mg0.5Sn0.5)O3–yCa0.8Sr0.2TiO3 ceramic

The (1 ? y)Nd_(1?2x/3)Ba_x(Mg_0.5Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of the Nd_(1?2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics revealed that Nd_(1?2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ is the main crystalline phase, which is accompanied by a little Nd₂Sn₂O₇ as the second phase. An apparent density of 6.89 g/cm³, a dielectric constant (ε _r ) of 19.1, a quality factor (Q × f) of 212,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?68 ppm/°C were obtained when the Nd_2.94/3Ba_0.03(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1,550 °C for 4 h. The temperature coefficient of resonant frequency (τ _f ) increased from ?68 to +55 ppm/°C as y increased from 0 to 0.7 when the (1 ? y)Nd_2.94/3Ba_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sr_0.2TiO₃ ceramics were sintered at 1,600 °C for 4 h. 0.4Nd_2.94/3Ba_0.03(Mg_0.5Sn_0.5)O₃–0.6 Ca_0.8Sr_0.2TiO₃ ceramic that was sintered at 1,600 °C for 4 h had a τ _f of ?7 ppm/°C.     

Microstructure and dielectric properties of BaZr x Ti1−x O3 ceramics

The crystalline structure and dielectric properties of BaZr _x Ti_1−x O₃ ceramics with x = 0.05, 0.10, 0.15, and 0.20 were investigated. As zirconium increased, the a-axis lattice constant gradually increased, however, the c-axis lattice constant and c/a ratio gradually decreased. When x = 0.20, the crystal structures of the BZT ceramics are very close to cubic, different from the tetragonal structure when x < 0.20. The temperature dependence of the dielectric constant was studied and an enhanced diffuse phase transition behavior is found to be caused by the increased Zr content. The decreases of coercive electric field and remanent polarization were the result of increase of Zr/Ti ratio in BaZr _x Ti_1−x O₃.     

Influence of B2O3 on microstructure and microwave dielectric properties of 0.4Nd0.96Yb0.04(Mg0.5Sn0.5)O3–0.6Ca0.8Sr0.2TiO3 ceramic system

The effect of B₂O₃ on the microstructure and microwave dielectric properties of the 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system were investigated with a view to their use in microwave devices. A B₂O₃-doped 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system was prepared by the conventional solid-state method. The X-ray diffraction patterns of the B₂O₃-doped 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system did not significantly vary with sintering temperature. A 1.25 wt% B₂O₃-doped 0.4Nd_0.96Yb_0.04(Mg_0.5Sn_0.5)O₃–0.6Ca_0.8Sr_0.2TiO₃ ceramic system that was sintered at 1,525 °C for 4 h had a dielectric constant of 38.0, a quality factor (Q × f) of 68,600 GHz, and a temperature coefficient of resonant frequency of 2 ppm/°C.     

Crystal structure and optimized microwave dielectric properties of (1 − x) LiZn0.5Ti1.5O4–xTiO2 ceramics for application in dielectric resonator

Microwave dielectric ceramics with the composition of (1?x) LiZn_0.5Ti_1.5O₄ (LZT)–xTiO₂ (0.05 ≤ x ≤ 0.4) were prepared by a solid-state reaction route. XRD patterns revealed that the samples consist of LiZn_0.5Ti_1.5O₄ and rutile TiO₂, and the amount of rutile TiO₂ phase increased with increasing the x values. The microwave measurements show that the dielectric properties of ceramics can be improved with increasing x values. When x = 0.1, the temperature coefficient of resonant frequency (τ _f ) of 0.9LZT–0.1TiO₂ ceramic can be adjusted to a near-zero value of ?1 ppm/°C, and permittivity (ε_r) and Q × f value are 26 and 45,000 GHz, respectively. These results indicate that 0.9LZT–0.1TiO₂ ceramic can be a candidate in microwave dielectric resonators.     

Ferroelectric and piezoelectric properties of (1 − x) (Bi0.5Na0.5)TiO3–xBaTiO3 ceramics

Lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT)–barium titanate (BaTiO₃,BT) have been prepared by solid state reaction process. The (1?x)BNT–(x)BT (x = 0.01,0.03,0.05,0.07) ceramics were sintered at 1,150 °C for 4 h in air, show a pure perovskite structure. X-ray diffraction analysis indicates that a solid solution is formed in (1?x)BNT–(x)BT ceramics with presence of a morphotropic phase boundary (MPB) between rhombohedral and tetragonal at x = 0.07. Raman spectroscopy shows the splitting of (TO₃) mode at x = 0.07 confirming the presence of MPB region. The temperature dependence dielectric study shows a diffuse phase transition with gradual decrease in phase transition temperature (T_m). The dielectric constant and diffusivity increases with increase in BT content and is maximum at the MPB region. With the increase in BT content the maximum breakdown field increases, accordingly the coercive field (E_c) and remnant polarization (P_r) increases. The piezoelectric constant of (1 ? x)BNT–(x)BT ceramics increases with increase in BT content and maximum at x = 0.07, which is the MPB region. The BNT–BT system is expected to be a new and promising candidate for lead-free dielectric and piezoelectric material.     

Microstructure and electrical properties of (1 − x)K0.5Na0.5NbO3–x(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free piezoelectric ceramics

The (1 ? x)K_0.5Na_0.5NbO₃ ? x(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (KNN–BCTZ) lead-free ceramics were fabricated by conventional solid-state sintering technique. The microstructure and electrical properties of the ceramics were investigated. The X-ray diffraction analysis revealed that the ceramics formed a single phase perovskite solid solutions with the symmetry of orthorhombic at x < 0.03. The crystal phase of the ceramics changed from orthorhombic phase to pseudocubic phase when x > 0.04. The coexistence of orthorhombic and pseudocubic (tetragonal) phases was observed near room temperature when 0.03 ≤ x ≤ 0.04. The grains grew up obviously when 2 mol% BCTZ was added, but the grain size was found to reduce gradually with further increasing BCTZ content. The T _C and T _O-T decreased with the increasing BCTZ content. The ferroelectric and piezoelectric properties were abruptly degraded as x ≥ 0.05. Optimum properties (d ₃₃ = 136 pC/N, k _p = 27 %, k _t = 26.5 %, Q _m = 25, P _r = 14.67 μC/cm², E _c = 11.23 kV/cm, T _C = 347 °C, $\varepsilon_{33}^{\text{T}} /\varepsilon_{0} = 8 6 1. 5$ ε 33 T / ε 0 = 8 6 1.5 , tan δ = 0.04) were obtained for the ceramica with x = 0.03.     

Microstructure and microwave dielectric properties of low-temperature sinterable (1 − x)Ba3(VO4)2–xCaWO4 composite ceramics

Low-temperature-sintered Ba₃(VO₄)₂–CaWO₄ composite ceramics were prepared by cofiring mixtures of pure-phase Ba₃(VO₄)₂ and CaWO₄. The thermo-mechanical analysis revealed that the CaWO₄ in the composite ceramic can significantly promote the densification process and lower the sintering temperature to ~900 °C. The X-ray diffraction results indicated that Ba₃(VO₄)₂ and CaWO₄ phases coexist in the sintered ceramics, and no secondary phases can be detected in the composite, implying the good chemical compatibility between the two phases. The near-zero temperature coefficients of the resonant frequency (τ_f) could be achieved by adjusting the relative content of the two phases owing to their opposite τ_f values. The composite ceramics with 60 wt% CaWO₄ sintered at 900 °C exhibited desirable microwave dielectric properties of the quality factor Q × f ~ 37,000 GHz, dielectric constant ε_r ~ 12, and τ_f ~ ?1.4 ppm/°C.     

Microstructures and dielectric tunable properties of Ba0.5Sr0.5TiO3–MgO–Mg2TiO4 composite ceramics

Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composite ceramics were prepared by a solid-state reaction method, and the dielectric tunable properties were investigated. It is observed that the addition of MgO–Mg₂TiO₄ into the Ba_0.5Sr_0.5TiO₃ forms ferroelectric (Ba_0.5Sr_0.5TiO₃)–dielectric (Mg₂TiO₄–MgO) composites. Increasing Mg₂TiO₄ content causes an increase of Curie temperature T_c towards room temperature and a decrease of dielectric constant peak ε_max. The dielectric constant and loss tangent of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composites have been reduced and the overall tunability is maintained at a sufficiently high level. With the increase of Mg₂TiO₄ content and the decrease of MgO content, the dielectric constant and tunability of Ba_0.5Sr_0.5TiO₃–MgO–Mg₂TiO₄ composite ceramics increase and the Q × f values decrease. Ba_0.5Sr_0.5TiO₃–Mg₂TiO₄–MgO composites have dielectric constant of 123.0–156.5 and tunability of 14.4–28.5 % at 10 kHz under 3.9 kV/mm, indicating that they are promising candidate materials for tunable microwave applications requiring a low dielectric constant.     

Structure and properties of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 solid solution ceramics

The widely used piezoelectric Pb(Zr_1−x Ti _x )O₃ ceramics have been known to have Zr⁴⁺ and Ti⁴⁺ randomly distributed on the B-site lattice in the ABO₃ perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg_1/2W_1/2)O₃ − xPb(Zr_0.5Ti_0.5)O₃ (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg_1/2W_1/2)O₃ and the ferroelectric order in Pb(Zr_0.5Ti_0.5)O₃ leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, T _m, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties.     

Phase structures and microwave dielectric properties of xCaTiO3–(1 − x)Sm0.9Nd0.1AlO3 ceramics

The xCaTiO₃–(1 ? x)Sm_0.9Nd_0.1AlO₃ (0.25 ≤ x ≤ 0.85) microwave dielectric ceramics were prepared by conventional solid state reaction method. The phase structures were characterized by X-ray diffraction, scanning electron microscope and Raman spectra. Solid solutions with the orthorhombic perovskite structure with octahedral tilting were formed from the x range of 0.25 to 0.85. Microwave dielectric properties of xCaTiO₃–(1 ? x)Sm_0.9Nd_0.1AlO₃ ceramics were investigated systematically. The optimum property of the ceramics was obtained for x = 0.65 sintered at 1,415 °C for 3 h: relative permittivity ε_r = 39.70, Q × f = 50,012 GHz, τ _f  = ?6.8 ppm/°C. xCaTiO₃–(1 ? x)Sm_0.9Nd_0.1AlO₃ ceramics provide a new promising material for application in the microwave technology with relative permittivity lying within the range from 39 to 44, high quality factor and near-zero τ _f .     

The electrostrictive effect and dielectric properties of lead-free 0.5Ba(ZrxTi1−x)O3–0.5(Ba0.75Ca0.25)TiO3 ceramics

Lead-free 0.5Ba(Zr_xTi_1?x)O₃–0.5(Ba_0.75Ca_0.25)TiO₃ (x = 0.25, 0.30, 0.35, 0.40) ceramics have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and electrostrictive properties of these ceramics were studied. Based on the measured properties, these ceramics showed a typical relaxor behavior. The Curie temperature of BZT–BCT ceramics decreases with increasing the Zr content. The largest electrostrictive strain and electrostrictive coefficient are founded in BZT–BCT ceramic with x = 0.25, the value is 0.16 % and 0.079 m⁴ C^?2, respectively. The polarization, electrostrictive strain and electrostrictive coefficient (Q ₁₁) decrease with increase in Zr concentration. For samples with low Curie temperature, which have large room temperature dielectric constant (ε), electrostrictive coefficient increases (Q ₁₁) is smaller. Because doping can disrupt the long range cation order, and electrostrictive (Q ₁₁) coefficient increases with cation order from disordered, through partially-ordered, simple relaxor and then ordered perovskites, ferroelectrics with a disordered structure have a huge permittivity, but a small electrostrictive coefficient (Q ₁₁).