Effects of Postdensification Annealing upon Microstructures and Microwave Dielectric Characteristics in Ba((Co0.6−x/2Zn0.4−x/2Mgx)1/3Nb2/3)O3 Ceramics

Effects of postdensification annealing upon microstructures and microwave dielectric characteristics in Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ (x = 0, 0.1, 0.2, and 0.3) complex perovskite ceramics have been investigated. Long‐time annealing at temperatures below the order–disorder transition temperature enhances the cation ordering degree and promotes the ordering domain growth. The most significant improvement of Qf value is obtained together with the suppressed temperature coefficient of resonant frequency in the samples annealed at 1400°C for 12 h, while the dielectric constant decreases slightly. The Qf value of ceramics annealed at 1400°C mainly attributes to the enhanced cation ordering degree, because their low‐energy domain boundaries are not detrimental to the Qf value. As the annealing temperature increases close to the transition temperature, coarse ordering domains with high‐energy boundaries are formed, and then the Qf value steadily decreases because of the inferior domain structure, even the cation ordering degree increases. The microwave dielectric characteristics of Ba((Co_0.6?x/2Zn_0.4?x/2Mg_x)_1/3Nb_2/3)O₃ ceramics are affected by the common function of ordering degree and domain structure. The best combination of microwave dielectric characteristics is obtained in the composition of x = 0.3 after annealing at 1400°C for 12 h: ε_r = 33.2, Qf = 117 200 GHz, and τ_f = 8.6 ppm/°C.     

Microstructures and Microwave Dielectric Properties of Ba((Co0.55Zn0.35Mg0.1)1/3Nb2/3)O3‐BaZrO3 Ceramics

Microstructures and microwave dielectric properties of (1?x)Ba((Co_0.55Zn_0.35Mg_0.1)_1/3 Nb_2/3)O₃‐xBaZrO₃ (x = 0.01, 0.02, 0.03, 0.04, 0.05, and 0.06) ceramics have been investigated. The 1:2 ordered structure remains in the solid solutions when x is less than 0.03, but the ordering is destabilized. While, the local ordering behavior, which generates from compositional inhomogeneous, is observed in the composition with x = 0.04, where the 1:1 ordered phase begins to form. For x = 0.05 and 0.06, the solid solutions are comprised of nanometer‐sized 1:1 and 1:2 ordered domains, those are dispersed in a disordered matrix. The lower Qf values of the as‐sintered ceramics mainly because of the lower ordering degrees. BaZrO₃ substitution decreases both the annealing time and temperature. The effects of annealing process upon the improvement of Qf values are significant for the lower substitution levels (x = 0.01 and 0.02), while only slight effects are determined for high substitution levels (x = 0.04, 0.05, and 0.06). The highest Qf value of 84,500 GHz is obtained for 1 mol% BaZrO₃ substituted composition, after annealing at 1300°C for 8 h.     

Determination of 1:2 Ordered Domain Boundaries in Ba[(Co,Zn, Mg)1/3Nb2/3]O3 Dielectric Ceramics

The boundaries of 1:2 ordered domains in Ba[(Co, Zn, Mg)_1/3Nb_2/3]O₃ perovskite ceramics are comprehensively studied by high‐resolution transmission electron microscopy (HRTEM) on the base of atomic position simulation. The atomic configurations for four types of twin boundaries are determined. A‐type and B‐type boundary, which lie along (001)_c and (110)_c planes, respectively, are conservative. C‐type boundary parallels to (111)_c plane, while Г‐type boundary is perpendicular to (111)_c plane. At C‐type and Г‐type boundary, atomic intersection leads to a buffer layer, among which the B‐site cations are generally disordered. The width of Г‐type boundary is larger than that of C‐type boundary, so is the perturbation to the system. The energy of four types of twin boundaries is proved to be “A‐type & B‐type < C‐type < Г‐type” according to the magnitude of the destabilization to the system. Single antiphase boundary (APB) is considered to be nonconservative. However, when combined with conservative twin boundary, an extra ordered structure with a periodicity of 1.24 nm along [001]_c direction and a periodicity of 0.87 nm along [110]_c direction forms. The boundary regions are indeed stabilized by the new superlattice.     

Microstructure and microwave-frequency electromagnetic properties of Ni0.4Zn0.6Fe2O4/Ba0.6Sr0.4TiO3 composites

(x)Ni_0.4Zn_0.6Fe₂O₄+(1−x)Ba_0.6Sr_0.4TiO₃ composite ceramics with x=0.6, 0.7, 0.8, 0.9 and 1 were synthesized by solid state reaction method. The high dense composites have only two phases, i.e., Ni_0.4Zn_0.6Fe₂O₄ and Ba_0.6Sr_0.4TiO₃. The permittivity ε′ of the composites decreases slightly with the frequency increasing from 3 MHz to 1 GHz. The permittivity ε′′ of the composites also shows a little increase with frequency in the 3 MHz–1 GHz range. The permeability displays a relaxation resonance within the 3 MHz–1 GHz frequency range. The permeability μ′ increases while the cut-off frequency decreases with the Ni_0.4Zn_0.6Fe₂O₄ concentration, obeying the Snoek's law μ_if_r=constant. The permittivity ε′ of the composites decreases with Ni_0.4Zn_0.6Fe₂O₄ concentration. The composites have a relatively higher ε′ than the pure Ni_0.4Zn_0.6Fe₂O₄ at 1–10 GHz. In the frequency range of 1–10 GHz, the magnetic permeability μ′ reaches its maximum and μ′′ shows a minimum for the composite with x=0.6 in all ceramics. The permeability μ′ of the composites decreases with dc magnetic field at 1–10 GHz. The permeability shows a domain wall resonance, and the resonance frequency shifts to high frequency with the dc magnetic field. The permittivity was also influenced by the dc magnetic field due to a magnetodielectric effect.     

钨青铜陶瓷Sr0.6Ba0.4Nb2O6的合成、结构与介电性能

通过固相反应法合成了Sr0．6Ba0．4Nb2O6陶瓷，并对其进行了结构、介电性能的表征。结果表明Sr0．6Ba0．4Nb2O6陶瓷为四方钨青铜结构单相，其在60℃附近存在一个明显的弥散介电峰，峰值温度随频率向高温偏移，为典型的弛豫铁电相变。室温时，10kHz频率下，其介电常数约为1404，介电损耗为0．03。     

Effects of Mg/Si Ratio on Microwave Dielectric Characteristics of Forsterite Ceramics

Nonstoichiometric Mg₂SiO₄ forsterite dielectric ceramics with various Mg/Si ratios ( R =2.025, 2.05, and 2.2) were prepared and characterized. The appearance of a MgSiO₃ secondary phase could be effectively suppressed by adjusting the nonstoichiometry, and a single-phase forsterite structure was obtained in the present ceramics with Mg/Si ratios of 2.025 and 2.05. The microwave dielectric characteristics were significantly improved in the nonstoichiometric Mg₂SiO₄ ceramics on eliminating the MgSiO₃ secondary phase, where an enhanced Q × f value and a suppressed temperature coefficient of resonant frequency λ _f were obtained. The best microwave characteristics were achieved in the nonstoichiometric forsterite ceramics with an Mg/Si ratio of 2.05: ɛ _r =7.5, Q × f =114 730 GHz, and λ _f =−59 ppm/°C.     

Ti-B位置换改性Mg2SiO4陶瓷微结构与微波介电性能研究

Ti-B位置换改性Mg2SiO4陶瓷微结构和微波介电性能的研究中发现,在合成Mg2SiO4陶瓷过程中,Mg2SiO3总是作为第二相出现,Ti的引入能够有效地抑制Mg2SiO3的出现.但Ti不是进入Si-O四面体取代置换Si形成Mg2(Si1-xTixO4固溶体,而是Mg与反应形成Mg2TiO4、Mg2Ti2O5等第二相.Mg2(Si1-xTix)O4陶瓷随着值x增加,介电常数εr从6.8增加到8.1,Qf值也获得显著改善,但谐振频率温度系数不会因Ti引入而得到优化.在x=0.1时,Mg2(Si0.9Ti0.1)O4陶瓷获得优良的微波介电性能:εr=7.4,Qf=73 760GHz,τf=60·10-6/℃.     

MgSiO_3掺杂Ba_（0.4）Sr_（0.6）TiO_3陶瓷的介电调谐特性及微波性能（英文）

MgSiO3掺杂 Ba0.4Sr0.6TiO3陶瓷具有 Ba1-xSrxTiO3、（Ba,Sr）2TiSi2O8、Ba4MgTi11O27和 Mg2TiO4多相结构。MgSiO3低掺量（质量分数≤10%）陶瓷样品具有条形晶粒和细晶粒组成的微结构;随着 MgSiO3掺量增加,陶瓷样品形成晶粒细小、均匀的微结构;当 MgS...     

The Role of Microstructure on Microwave Dielectric Properties of (Ba,Sr)TiO3 Ceramics

Microstructural effects on the microwave dielectric properties of (Ba_0.4Sr_0.6)TiO₃ (BST) polycrystalline ceramics were investigated, focusing on the grain size. Sintering temperatures between 1350°C and 1500°C have a strong effect on the permittivity (880 < ε_r < 990), quality factor (570 GHz < Q×f < 1150 GHz), and temperature coefficient of resonant frequency (3920 ppm/°C < τ_f < 4560 ppm/°C) at microwave frequency (≈1.4 GHz). The tunable permittivity characteristics (measured at 10 kHz), were also found to be sensitive to the sintering process, demonstrating the possibility of tailoring material property by designed processing. In addition, the effect of the sintering process on grain structure was investigated by XRD calculation and Raman scattering characterization. Less confined phonons were believed to contribute to the enhanced microwave performance as an intrinsic effect (grain size effect), for samples with higher sintering temperature and longer dwell time. On the contrary, the macroscopic properties tend to saturate (or deteriorate), for samples at intensified sintering condition, being thought to be dominated by the extrinsic factors (such as the abundant defects in large grains), as confirmed by the SEM observations.     

Dielectric Properties and Low‐Temperature Sintering of the Ba0.6Sr0.4TiO3 Ceramics with B2O3/CuO Additions

The sintering behaviors and dielectric properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated as a function of B₂O₃ and CuO content. The addition of both B₂O₃ and CuO reduced the sintering temperature of Ba_0.6Sr_0.4TiO₃ about 500°C. It was suggested that a liquid phase BaCu(B₂O₅) was formed and assisted the densification of Ba_0.6Sr_0.4TiO₃ ceramics. Ba_0.6Sr_0.4TiO₃ ceramics co‐doped with 3.0 mol% B₂O₃, and 2.0 mol% CuO, sintered at 950°C for 5 h, had a dense microstructure and showed good microwave dielectric properties of a moderate dielectric constant (ε = 1048), low dielectric loss (0.0090) and high tunability (42.2%) at dc electric field of 30 kV/cm.     

Impedance Spectroscopy,Broadband, and Microwave Dielectric Properties of Mechanically Alloyed Ba5Nb4O15 Ceramics

Ba₅Nb₄O₁₅ (BNO) ceramics were synthesized by the mechanical alloying method. The transmission electron microscope images of BNO powders revealed rod‐shaped grains. Mechanically alloyed BNO exhibited maximum density of 97.3% and is explained on the basis of Herring's scaling law. Both the dielectric constant and loss tangent show a stable response up to 0.2 GHz. Further, the dielectric response of BNO ceramics measured above 350°C shows relaxation behavior and is explained using Havriliak–Negami equation. The obtained stable dielectric response of BNO is suitable for type I capacitor and dielectric resonator applications.     

Y3+取代对(Bi1.5Zn0.5)(Nb0.5Ti1.5)O7陶瓷显微结构与介电性能的影响

研究了Y3 取代的(Bi1.5Zn0.5)(Nb0.5Ti0.5)O7(BZNT)基陶瓷(Bi1.5-xYx Zn0.5)(Nb0.5Ti1.5)O7(0≤x≤1.5,BYZNT)的显微结构和介电性能。采用传统的固相反应法制备陶瓷样品,XRD分析样品的相结构。结果表明:BZNT陶瓷的相结构中主相为立方焦绿石相;在整个取代范围内,BYZNT陶瓷的结构仍然保持主相为立方焦绿石的相结构。同时,随着Y3 取代的增加,晶胞体积减小,介电性能随结构的变化而呈现有规律的变化。其介电性能为:εr≈73-180,tanδ≈1.6％-0.4％,αε≈(-583-89)× 10-6／℃(1MHz)。     

Dielectric and Magnetic Properties of Sr(Fe1/2Ta1/2)O3 Complex Perovskite Ceramics

The dielectric and magnetic properties of Sr(Fe_1/2Ta_1/2)O₃ complex perovskite ceramics were systematically investigated together with the structure. The X‐ray powder diffraction analysis confirmed a B‐site disordered orthorhombic structure in space group Pbnm. Only one broadened dielectric peak with strong frequency dispersion was observed in the present ceramics, which was significantly different from that for the analogue Ba(Fe_1/2Nb_1/2)O₃ and Ba(Fe_1/2Ta_1/2)O₃. The strong dependence of sample thickness and electrode material indicated that the dielectric relaxation behavior at lower frequency was due to the interface effects. The present ceramics were spin glass state with slight ferromagnetic behavior below the Néel temperature (20 K). The co‐presence of Fe³⁺ and Fe²⁺ was confirmed by the μ_eff value.     

Effects of Barium Substitution on Perovskite Formation, Dielectric Properties, and Diffuseness Characteristics of Lead Zinc Niobate Ceramics

Perovskite-phase developments in partially/fully substituted (Ba,Pb)(Zn_1/3Nb_2/3)O₃, synthesized via B-site precursor routes, were investigated. The pyrochlore structure, present at no barium content, was immediately replaced by perovskite with a small amount (≥8 at.%) of barium substitution. Variations in the lattice parameters of the pyrochlore and perovskite structures were studied. The weak-field radio-frequency dielectric constants and losses of the system ceramics were examined. A highest maximum dielectric constant of 9000 (76°C, 1 MHz) was observed at 8 at.% barium substitution. The dielectric-constant spectra were analyzed further in terms of diffuseness characteristics (e.g., diffuseness exponent and degree of diffuseness). The dielectric hysteresis loops of the ceramics were measured. The microstructures of the sintered ceramics also were observed.     

(Mg4-xLi2x)(Nb1.92V0.08)O9陶瓷微波介电性能

采用固相合成法制备了(Mg_(4-x)Li_(2x))(Nb_(1.92)V_(0.08))O_9系列微波介质陶瓷。通过XRD、SEM以及HP网络分析仪等测试手段对其烧结特性、晶体结构和微波介电性能进行了系统研究。结果表明:x<0.3时形成了(Mg_(4-x)Li_(2x))(Nb_(1.92)V_(0.08))O_9固溶体;x≥0.3时,除主相(Mg_(4-x)Li_(2x))(Nb_(1.92)V_(0.08))O_9外,还有少量第二相Li3Mg2NbO6生成。微波介电常数ε随x的增大持续升高,品质因数Q则先增大后减小。x=0.2,950℃,5h烧结样品的微波介电性能达到最佳:ε=12.7,Q.f=14078GHz(f0=8GHz)。     

Ferroelectric to Relaxor Transition in BaTiO3–Bi(Zn2/3Nb1/3)O3 Ceramics

The (1?x)BaTiO₃–xBi(Zn_2/3Nb_1/3)O₃ (x = 0.01–0.30) ceramics were synthesized by solid‐state reactions. The solubility limit was determined to be x = 0.20. A systematic structural transition from a tetragonal phase (x ≤ 0.034), to a mixture of tetragonal and rhombohedral phases (0.038 ≤ x ≤ 0.20), and finally to a pseudocubic phase (x ≥ 0.22) at room temperature was identified. Dielectric measurement revealed a ferroelectric (x ≤ 0.04) to relaxor (x ≥ 0.06) transition with permittivity peak broadening and flattening, which was further verified by Raman spectroscopy and differential scanning calorimetry (DSC). Activation energies obtained from the Vogel–Fulcher model displayed an increasing trend from ~0.03 eV for x ~ 0.05, to unusually high values (>0.20 eV) for the compositions with x ≥ 0.15. With the increase in Bi(Zn_2/3Nb_1/3)O₃ content, the polarization hysteresis demonstrated a tendency from high nonlinearity to sublinearity coupled with the reduction in remnant polarization and coervice field. The deconvolution of the irreversible/reversible polarization contribution was enabled by first‐order reversal curve distributions, which indicates that the decreasing polarization nonlinearity with the increase in Bi(Zn_2/3Nb_1/3)O₃ concentration could be related with the change from the ferroelectric domain and domain wall contributions to the weakly coupled relaxor behaviors.     

Aqueous Solution–Gel Preparation and Dielectric Properties of Ba(Mg1/3Nb2/3)O3 Thin Films with Long‐Range Order

In the present research, the Ba(Mg_1/3Nb_2/3)O₃ (BMN) thin films with high 1:2 long‐range order (LRO) were prepared by an entire aqueous solution–gel route and a heat treatment at low temperature. The BMN precursor solutions used for spin‐coating consist of tri‐metal ions citrate complexes, which are formed through the combination of three single citrate complexes with NH₄⁺ acting as crosslinks. The metal‐coordinated bonds of the citrate complexes can be easily broken by heat treatment, which can result in the crystallization of BMN films at low annealing temperature. The crystalline structure and LRO degree of BMN films were also investigated. It is shown that the LRO degrees increase with the increase in annealing temperature. The dielectric constant increases and the dielectric loss decreases with the annealing temperature up to 750°C due to the improvement of the film densification and the LRO degree. The further increase in annealing temperature slightly decreases the dielectric constant and increases the dielectric loss due to the appearance of large aggregates. It is shown that the charge carriers mainly contribute to the dielectric response below 100 KHz, while the dipolar response starts to take effect for the frequency higher than 100 KHz.     

Main Source of Microwave Loss in Transition‐Metal‐Doped Ba(Zn1/3Ta2/3)O3 and Ba(Zn1/3Nb2/3)O3 at Cryogenic Temperatures

Microwave resonator measurements were performed on high‐performance microwave ceramics Ba(Zn_1/3Ta_2/3)O₃ (BZT) and Ba(Zn_1/3Nb_2/3)O₃ (BZN) containing additives commonly used by commercial manufacturers (i.e., Co, Mn, and Ni). We find that the loss tangent, even in ambient magnetic fields, is dominated by electron paramagnetic resonance (EPR) absorption by exchange‐coupled 3d electrons in transition metal clusters at cryogenic temperatures. The large orbital angular momentum in Co²⁺ and Ni²⁺ ions of L = 3 causes strong anisotropic‐broadened dipolar interactions that extend EPR losses to zero applied field. This effect is greatest in BZN with Co concentrations greater than 0.5 mol%, dominating the losses at liquid nitrogen temperatures (77 K) and below. In samples containing Mn²⁺ ions with L = 0, the dipolar interactions and associated EPR losses in ambient fields are smaller. We show the magnetic‐field‐dependent changes in the EPR losses (i.e., tan δ) and magnetic reactive response (i.e., μ_r) are from the same mechanism, as they follow the Kramers–Kronig relation. Finally, we note that these materials can make ultra‐high Q passive microwave devices with externally controlled transfer functions, as the quality factor (Q) of the composition Ba(Co_1/15Zn_4/15Nb_2/3)O₃ at 77 K can be tuned from 1 100 to 12 000 at 10 GHz by applying practical magnetic fields.     

Structure and Microwave Dielectric Characteristics of Ca[(Ga1/2Nb1/2)1−xTix]O3 Ceramics

The microwave dielectric characteristics of Ca[(Ga_1/2Nb_1/2)_1?xTi_x]O₃ ceramics were investigated together with the structure evolution. The excellent microwave dielectric characteristics were achieved by forming solid solution between Ca(Ga_1/2Nb_1/2)O₃ and CaTiO₃ in the present ceramics. The solid solutions in space group Pbnm with antiphase and inphase tilting were determined for all compositions where minor secondary phase was detected for x = 0–0.47, whereas no B‐site ordering was detected. Owing to the structural modification, the dielectric constant (ε_r) increased with increasing x, and the temperature coefficient of resonant frequency (τ_f) could be tuned from negative to positive, while the decrease of Qf value was acceptable. The best combination of microwave dielectric properties was obtained at x = 0.47: ε_r = 51.6, Qf = 34 100 GHz and τ_f = ?0.3 ppm/°C.     

二步法合成低温烧结(Mg,Zn)TiO3介电陶瓷

首先采用固相法合成了(Mg,Zn)2TiO4粉体,然后将钛酸丁酯水解制备出TiO2溶胶,再利用TiO2溶胶对已合成的(Mg,Zn)2TiO4粉体进行包覆。包覆后的粉体经500℃预烧后在1 150℃烧结成瓷,采用XRD、SEM分别做了样品的物相和显微结构分析,测试结果表明:当TiO2/(Mg,Zn)2TiO4为1.1时,合成产物为纯的(Mg,Zn)TiO3相。在1 MHz下测试了样品的介电性能,结果表明:当TiO2/(Mg,Zn)2TiO4为1.1,烧结温度为1 150℃时,陶瓷介电性能最好。