Ba2La2TiTa2O12: A new low loss microwave dielectric of A4B3O12-type cation-deficient perovskite

A new Ta-based hexagonal perovskite Ba₂La₂TiTa₂O₁₂ was synthesized by conventional solid-state reaction method. The structure and microstructure of the ceramic were characterized by X-ray diffraction and scanning electron microscopy. This compound adopts A₄B₃O₁₂ cation-deficient hexagonal perovskite structure with unit cell parameter a = 5.6825(2) Å, c = 27.860(1) Å, V = 779.10 Å³, and Z = 3. This new dielectric ceramic exhibits a moderate dielectric constant of 37.8, a high quality factor with Q × f of 36,188 GHz and a negative τ_f of ?52 ppm/°C.     

Microwave dielectric properties of a new A6B5O18-type cation deficient perovskites: Sr5LaTi2Nb3O18

A new A₆B₅O₁₈-type cation deficient perovskite Sr₅LaTi₂Nb₃O₁₈ was prepared by the conventional solid-state reaction route. The phase, microstructure, and microwave dielectric properties of the ceramic were characterized. This compound crystallizes in the trigonal system with unit cell parameter a = 5.6101(2) Å, c = 40.922(8) Å, V = 1,115.4(5) Å³, and Z = 3. It shows a high dielectric constant of 48, a high quality factors with Q _u × f of 27,806 GHz, and a small positive τ _f of +19 ppm/°C.     

Synthesis and microwave dielectric properties of Ba4Ti3P2O15 ceramics

Present work introduces a new kind of microwave dielectric ceramic, Ba₄Ti₃P₂O₁₅. Ba₄Ti₃P₂O₁₅ ceramic can be prepared by solid state reaction method and be well densified after being sintered at above 1175 °C for 4 h in air. All the XRD patterns can be fully indexed as single-phase structure. The best microwave dielectric properties can be obtained in ceramic sintered at 1200 °C for 4 h with permittivity about 20.7, Q × f about 42,210 GHz and TCF about 37 ppm °C^?1. Measurements of the microwave dielectric properties of Ba₄Ti₃P₂O₁₅ ceramic revealed the existence of a maximum in the temperature dependence of the dielectric loss because of the defect dipoles relaxation.     

Preparation and characterization of two new dielectric ceramics Ba4NdTiNb3O15 and Ba3Nd2Ti2Nb2O15

Two new cation-deficient hexagonal perovskites Ba₄NdTiNb₃O₁₅ and Ba₃Nd₂Ti₂Nb₂O₁₅ were prepared in the BaO–Nd₂O₃–TiO₂–Nb₂O₅ system by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction and scanning electron microscope (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. Ba₄NdTiNb₃O₁₅ has a dielectric constant of 38.15, a high-quality factors (Q _u ×f >18 700 at 5.4422 GHz), and a small temperature coefficient of resonant frequency ( _f )+12 ppm °C^–1 at room temperature; Ba₃Nd₂Ti₂Nb₂O₁₅ has a higher dielectric constant of 46.83 with high-quality factors Q _u ×f >19 500 at 5.0980 GHz, and _f +28 ppm °C^–1.     

Improved microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramic with Ba2+ substitution

The microwave dielectric properties of La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for wireless communications. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics contained La₂Sn₂O₇. An apparent density of 6.54 g/cm³, a dielectric constant ( $ \varepsilon_{r} $ ε r ) of 20.1, a quality factor (Q  $ \times $ ×  f) of 51,600 GHz, and a temperature coefficient of resonant frequency ( $ \tau_{f} $ τ f ) of ?82 ppm/°C were obtained for La(Mg_0.43Ba_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Effect of B2O3 additive on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

Journal of Materials Science: Materials in Electronics - This paper reported a research of the sinterability, microstructures, and microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 (BMT) ceramics...     

Phase composition and microwave dielectric properties of (Zn,Ni)TiNb2O8 solid solution

The Zn_1?xNi_xTiNb₂O₈ (x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were synthesized by the conventional solid-state reaction method. The crystal structure and microwave dielectric properties were investigated by XRD, SEM and dielectric measurements. The XRD patterns of Zn_1?xNi_xTiNb₂O₈ ceramics showed that (Zn, Ni)TiNb₂O₈ phase and (Ni, Zn)_0.5Ti_0.5NbO₄ phase were obtained. With the increase of sintering temperature and Ni content, the amount of the second phase [(Ni, Zn)_0.5Ti_0.5NbO₄] enhanced, resulting in the increase of dielectric constant and the decrease of Q × f value. Moreover, the temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Ni content. In conclusion, the excellent microwave dielectric properties were obtained for Zn_0.7Ni_0.3TiNb₂O₈ ceramics sintered at 1,125 °C for 4 h: ε_r = 41.36, Q × f = 31,760 GHz, τ_f = ?9.2 ppm/°C. Furthermore, to realize the zero value for τ_f, a proper adjustment of Ni doping and sintering temperature can be feasible in this system.     

Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

The effect of La³⁺ doping on Ca²⁺ sites in CaCu₃Ti₄O₁₂ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La³⁺ doping. The dielectric and impedance characteristics of Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La³⁺ substitution. The dielectric constant of CaCu₃Ti₄O₁₂ decreased drastically on La³⁺ doping. The frequency and temperature responses of dielectric constant of La³⁺ doped samples were found to be similar to that of CaCu₃Ti₄O₁₂. The effects of La³⁺ doping on the electrical properties of CaCu₃Ti₄O₁₂ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La³⁺ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La³⁺ doped CCTO ceramics were unambiguously established by modulus spectra studies.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.     

Effect of nickel on microwave dielectric properties of Ba(Mg1/3Ta2/3)O3

The dielectric and physical properties of the complex perovskite Ba(Mg_1/3Ta_2/3)O₃ system in which magnesium was substituted for nickel from 0.03–0.67 mol%, were investigated in the temperature range 20–110C, and the frequency range 10.5–14.5 GHz. As the nickel content was increased, the dielectric constant, the degree of ordering, and the unloaded Q decreased. The temperature dependence of the dielectric constant and the temperature coefficient of resonant frequency of the specimens annealed at 1500C for 20 h were found to be greater than those of the specimens sintered at 1650C for 2 h. These results are due to the increase in the density, the increase in grain size, and the lattice distortion.     

A new microwave dielectric ceramics for LTCC applications: Li2Mg2(WO4)3 ceramics

A novel microwave dielectric ceramics Li₂Mg₂(WO₄)₃ (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the Li₂Mg₂(WO₄)₃ ceramics were investigated. The optimal sintering temperature of dense Li₂Mg₂(WO₄)₃ ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: ε _r  = 7.72, Q × f = 29,600 GHz (f = 6.0 GHz), and τ _f  = ?15.5 ppm/°C. Moreover, the Li₂Mg₂(WO₄)₃ ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application.     

Structure,phase composition,and microwave dielectric properties of Ba16SnNb12O48 ceramic

Journal of Materials Science - The Ba16SnNb12O48 ceramics are prepared using a solid-state reaction method. The relationship between microstructure and dielectric properties are investigated. XRD...     

Low-firing and microwave dielectric properties of Ba[(Ni0.6Zn0.4)0 .33Nb0.67]O3 ceramics doped with Sb2O5 and B2O3

The purpose of this study was to reduce the sintering temperature of Ba[(Ni0.6Zn0.4)0.33Nb0.67]O3 ceramics by doping with Sb2O5 and B2O3. Phase formation and dielectric properties were analyzed using X-ray diffraction and the post resonator method (10 GHz), respectively. It was observed that an addition of 1 mol % Sb2O5 or 1 mol % B2O3 was very effective in reducing the sintering temperature from 1500 to 1300 °C. However, these samples showed a temperature coefficient of resonant frequency far from 0 ppm/°C. The two additions produced a temperature coefficients with opposite signs. The combination of the two dopants produced a temperature coefficient very close to 0 ppm/°C as well as a better quality factor.