Microwave dielectric properties and microstructures of Ca(Nb1−xTax)2O6 ceramics

This study elucidates the microwave dielectric properties and microstructures of Ca(Nb_1?xTa_x)₂O₆ ceramics with a view to their potential for microwave devices. The Ca(Nb_1?xTa_x)₂O₆ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Ca(Nb_0.93Ta_0.07)₂O₆ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (? _r ) of 17.7, a quality factor (Q × f) of 117,000 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?51 ppm/°C were obtained for Ca(Nb_0.93Ta_0.07)₂O₆ ceramics that were sintered at 1,400 °C for 4 h.     

Microwave dielectric properties and applications of Ba(Zn1/3Nb2/3)O3–Ca(Zn1/3Nb2/3)O3 composite ceramics by one-step synthesis method

(1 ? x) Ca(Zn_1/3Nb_2/3) O₃ ? xBa(Zn_1/3Nb_2/3)O₃ (short for CZN/BZN, x = 0–1.0) ceramics were prepared and investigated through the “one-step synthesis method” method. The structure of the system was analyzed using X-ray diffraction. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. Dielectric constant (ε_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q × f) were measured in the microwave frequency region. Two dielectric properties were firstly in the rising tendency and then decreasing with the increased x. On the other hand, a good combination of microwave dielectric properties (ε_r = 24, Q × f = 23,510 GHz τ_f = ?9 ppm/°C) were obtained at x = 0.1. The compositions have excellent microwave dielectric properties and hence are suitable for ceramic capacitors or dielectric resonators applications.     

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti_{1 ? x} (Ln_1/2Nb_1/2) _x ]O₃. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.     

Preparation and dielectric properties of Pb[(Zn1/3Ta2/3)0.8−x(Mg1/3Nb2/3)xTi0.2]O3 ceramics

A PbTiO₃ component of 20 mol% was substituted into a Pb[(Zn_1/3Ta_2/3),(Mg_1/3Nb_2/3)]O₃ system to promote the perovskite formation, especially at Pb(Zn_1/3Ta_2/3)O₃-rich compositions. Perovskite formation yields after the heat treatments were determined by X-ray diffraction. Weak-field dielectric properties of the ceramics were investigated as functions of temperature and frequency. A quite high value of the maximum dielectric constant (37,900 at 1 kHz) was realized, whereas the dielectric maximum temperatures of the entire compositions stayed nearly constant. Microstructure developments in the sintered ceramics were also examined.     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.     

Microwave dielectric properties of flexible silicone rubber – Ba(Zn1/3Ta2/3)O3 composite substrates

Silicone rubber composites filled with Ba(Zn_1/3Ta_2/3)O₃ (BZT) were prepared by hot pressing and the effect of filler content on the microwave dielectric, mechanical and thermal properties as well as on moisture absorption were investigated. The observed relative permittivity (ɛ_r) was compared with different theoretical models. Among the different theoretical models Jayasundere Smith and Modified Lichtenecker were in good agreement with experimental values of ɛ_r. The study of the mechanical property showed that the silicone rubber – BZT composites were flexible and stretchable. The coefficient of thermal expansion and specific heat capacity decreased whereas thermal conductivity, thermal diffusivity and the moisture absorption increased with increase in filler loading.     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Microwave dielectric properties of xMgTiO3-(1 − x)(Na1/2Ln1/2)TiO3 ceramics

Na_1/2Ln_1/2)TiO₃> ceramic has a high relative dielectric constant and a positive temperature coefficient of resonant frequency (_f) (where Ln represents a lanthanide: La⁺³, Pr⁺³, Nd⁺³ and Sm⁺³). On the other hand, MgTiO₃ ceramic has a high Qf value and a negative temperature coefficient. We have investigated the microwave dielectric properties of MgTiO₃-(1 – x)(Na_1/2 Ln_1/2) TiO₃. In this system, there are no indications of a solid-solution or a secondary phase. There are mixed phases only with MgTiO₃ and Na_1/2 Ln_1/2)TiO₃ phases. Its dielectric characteristics (Q ^*f, temperature coefficient and dielectric constant) are intermediate between (Na_1/2 Ln_1/2) TiO₃ and MgTiO₃ and are predictable by the logarithmic mixing rule. The temperature coefficient of dielectric ceramic compositions approximates to zero at each Ln = La, x = 0.9, Ln = Pr, x = 0.87, and Ln = Nd, x = 0.84. At this time, there are Q ^*f values in the range of 55 000 to 28 000 GHz and relative dielectric constants in the range of 22 to 25.     

Correlation between crystal structures and vibration modes of Ba[(Zn1−x Mg x )1/3Nb2/3]O3 ceramics as a function of sintering temperatures

Ba[(Zn_1?x Mg _x )_1/3Nb_2/3]O₃ (short for BZMN, x = 0.4, 0.6, 0.8) solid solution ceramics were sintered by conventional solid-state sintering technique at different temperatures. Effects of sintering temperatures on phonon modes and crystal structures of BZMN ceramics were investigated by X-ray diffraction and vibration spectra (Raman spectroscopy as well as Fourier transform far-infrared reflection spectroscopy) techniques. The results reveal that sintering temperatures have an obviously influence on phonon modes, which are closely related to the 1:2 ordered structures. For the samples where x = 0.4, they possess the cubic structure (Pm3m), and the ordering degree decreases with the increase in the temperature. For the samples where x = 0.6, phase transition occurs after sintered at 1,500 °C, i.e., a 1:2 ordered monoclinic unit cell is formed. For the samples where x = 0.8, they possess the hexagonal structures ( $P\bar{3}m1$ ), and the ordering degree increases with the increase in the temperatures.     

Microwave dielectric properties of new SrLa4−xNdxTi5O17 ceramics

New microwave dielectric ceramics in the SrLa_4?xNd_xTi₅O₁₇ (0 ≤ x ≤ 4) composition series were prepared through a solid state mixed oxide route. All the compositions formed highly dense (～95%) single phase ceramics upon sintering at 1500–1580 °C. The molar volume and theoretical density decreased due to the substitution of small (1.27 Å) Nd ions for large (1.36 Å) La ions. This decrease was associated with a decrease in the dielectric constant (?_r), temperature coefficient of resonant frequency (τ_f) and quality factor (Q_uf_o). An analysis of properties achieved in the present study indicated that ceramics exhibiting nearly zero τ_f corresponding to ?_r ～ 54 could be fabricated in the SrLa_4?xNd_xTi₅O₁₇ composition series at x ～ 1.6; however, further work is required to improve Q_uf_o (～6000 GHz) for possible practical applications.     

Microstructure and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3–MgO composite ceramics with nano-silica added

Ba(Mg_1/3Nb_2/3)O₃–MgO composite ceramics were prepared by solid-phase method. The ceramic exhibited the 1:2 ordered structure. By adding a proper amount of MgO, the permittivity decreased rapidly compared with other Ba(Mg_1/3Nb_2/3)O₃-based ceramics. The Q?×?f values of the samples were greatly improved by nano-silica. Raman spectra showed that the permittivity and Q?×?f value showed a strong correlation with Raman shift and full width at half maximum of the A_1g(O) phonon mode, respectively. The Raman shift of A_1g(O) was consistent with the variation trend of permittivity. And the full width at half maximum of the A_1g(O) phonon mode had a negative correlation with the Q?×?f value. The results showed that upon adding 1.5 wt% nano-silica to the ceramics, the ceramics sintered at 1550 °C for 5 h had the lowest Raman shift and the narrowest full width at half maximum, achieving the best microwave dielectric properties: ε_r?=?22.22, Q?×?f?=?80,436 GHz, τ_f?=?–?5.89 ppm/°C.

     

Microwave dielectric properties of Mg2SiO4–Ca1−ySm2y/3TiO3 composite ceramics

In this work, (1?x)Mg₂SiO₄–xCa_1?ySm_2y/3TiO₃ ceramics were fabricated using the conventional solid-state reaction method. When y?=?0.2, the effects of Ca_1?ySm_2y/3TiO₃ contents on microstructure, phase evolution, and microwave dielectric properties of the samples were studied. The X-ray diffraction showed that Mg₂SiO₄ and Ca_0.8Sm_0.4/3TiO₃ co-existed in composite ceramics. The dielectric constant (ε_r) and temperature coefficient of resonant frequency (τ_f) increased with the increasing content of Ca_0.8Sm_0.4/3TiO₃, while the quality factor (Q?×?f) decreased. At x?=?0.22, the (1?x) Mg₂SiO₄–xCa_0.8Sm_0.4/3TiO₃ ceramics sintered at 1325?°C for 3?h possessed optimal microwave dielectric properties: ε_r?~?11.89, Q?×?f value?~?32,703?GHz and τ_f?~?+?0.49?ppm/°C. As a result, the ε_r of (1?x) Mg₂SiO₄?+?xCa_1?ySm_2y/3TiO₃ ceramics could be adjusted in the range of 10.83 to 13.88 while the τ_f is near-zero.

     

Microwave dielectric properties of BaCu2−xMnxSi2O7 (x = 0–0.04) ceramics

Journal of Materials Science: Materials in Electronics - BaCu2?xMnxSi2O7 (x?=?0–0.04) microwave dielectric ceramics were synthesized through solid-state reaction method....     

Effect of sintering parameters on the microstructure and microwave dielectric properties of Ba(Zn1/3Nb2/3)O3–ZnNb2O6 Ceramics

Ba(Zn_1/3Nb_2/3)O₃–ZnNb₂O₆(BZNZ) composite ceramics were fabricated by conventional solid solution processing. After optimizing the composition, the effects of the sintering parameters, such as the heating rate, the soaking time, and the cooling rate on densities, microstructure, and microwave dielectric properties were investigated using orthogonal experimental design method. The results show that with increasing the content of Ba(Zn_1/3Nb_2/3)O₃, the ε _r increases, while the Q × f value increases first, then decreases, and τ _f shifts to the negative value. The BZNZ ceramics with composition of 0.3Ba(Zn_1/3Nb_2/3)O₃–0.7ZnNb₂O₆ show the optimal dielectric properties. The results of orthogonal experimental design show that sintering parameters play an important role in the microstructure and dielectric properties. The ceramics show obvious duplex-grain structure. The importance sequence of the sintering parameters is: cooling rate > heating rate > soaking time. The sintering parameters were optimized, with 0.3Ba(Zn_1/3Nb_2/3)O₃–0.7ZnNb₂O₆ ceramic sintered at a heating rate of 2 °C/min, soaking time of 8 h, and cooling in the air. Samples have the excellent dielectric properties: ε_r = 32.75, Q × f = 34,100, and τ _f  = ?10.2 ppm/°C.     

Microwave dielectric properties and low temperature sintering of Ba3Ti4?x(Mg1/3Nb2/3)xNb4O21 ceramics with BaCu(B2O5) addition

Microwave dielectric ceramics of Ba₃Ti_4?x(Mg_1/3Nb_2/3)_xNb₄O₂₁ solid solutions (BTMNN-x, x?=?0–4) were prepared via the conventional solid-state reaction method. The X-ray powder diffraction analysis revealed that the BTMNN-x ceramics formed complete solid solutions with hexagonal structure. The dielectric constant (ε_r) and the temperature coefficient of the resonant frequency (τ_f) of BTMNN-x ceramics decreased with the increase of x, while the quality factor (Q?×?f) enhanced with increasing the substitution content. In addition, a small amount of BaCu(B₂O₅) (BCB) additive can effectively lower the sintering temperature of BTMNN ceramics. The 1.5?wt% BCB doped BTMNN-2 ceramics can be sintered at 950?°C and have good microwave dielectric properties of ε_r?=?50, Q?×?f?=?10,500?GHz and τ_f?=?18?ppm/°C, which makes it possible to be a promising candidate for mid-permittivity low temperature co-fired ceramic materials.     

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.     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.