Adhesive-Bonded Ca(Mg1/3Nb2/3)O3/Ba(Zn1/3Nb2/3)O3 Layered Dielectric Resonators with Tunable Temperature Coefficient of Resonant Frequency

Ca(Mg_1/3Nb_2/3)O₃ and Ba(Zn_1/3Nb_2/3)O₃ ceramic cylinders with the same diameter were bonded by adhesive with low dielectric loss to yield the layered dielectric resonators, and the microwave dielectric characteristics were evaluated with TE_01δ mode. With increasing the Ba(Zn_1/3Nb_2/3)O₃ thickness fraction, the resonant frequency ( f ₀) decreased, while the effective dielectric constant (ɛ _{r ,eff}) and temperature coefficient of resonant frequency (τ _f ) increased. Good microwave dielectric characteristics were attained for the samples with the Ba(Zn_1/3Nb_2/3)O₃ thickness fraction of 0.5: ɛ _{r ,eff}=34.33, Q × f =57 930 GHz and τ _f =2.6 ppm/°C. Finite-element method was used to predict the microwave dielectric characteristics of the layered resonators and good agreements were attained between the experimental results and predicted ones. Also, both experiment and finite-element analysis indicated that the effects of the adhesive on f ₀, ɛ _{r ,eff}, and τ _f were slight, while that on Q × f value was significant.     

Synthesis of BaCu(B2O5) Ceramics and their Effect on the Sintering Temperature and Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Ceramics

BaCu(B₂O₅) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B₂O₅) phase was formed at 700°C and melted above 850°C. The BaCu(B₂O₅) ceramic sintered at 810°C had a dielectric constant (ɛ_r) of 7.4, a quality factor ( Q × f ) of 50 000 GHz and a temperature coefficient of resonance frequency (τ_f) of −32 ppm/°C. As the BaCu(B₂O₅) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B₂O₅) was added to the Ba(Zn_1/3Nb_2/3)O₃ (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B₂O₅) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q × f =16 000 GHz, ɛ_r=35, and τ_f=22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B₂O₅) ceramic sintered at 875°C for 2 h.     

Low Loss Dielectrics in the Ca(B'1/2Nb1/2)O3 [B'=Lanthanides, Y] System

The Ca(B'_1/2Nb_1/2)O₃ [B'=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, and In] complex perovskites have been prepared by conventional solid-state ceramic route. The structure and microstructure of the ceramics have been characterized by X-ray diffraction and scanning electron microscopy methods. The ceramics have dielectric constant (ɛ_r) in the range 23–32, normalized Q -factor ( Q _u× f ) 11 000–38 000 GHz and temperature coefficient of resonant frequency (τ_f) −43–5.2 ppm/°C. The microwave dielectric properties of Ca(B'_1/2Nb_1/2)O₃ ceramics are found to depend on the ionic radii of B'-site elements and tolerance factor ( t ). The substitution of Ba²⁺ and Sr²⁺ for Ca²⁺ resulted a phase transition in Ca(B'_1/2Nb_1/2)O₃ ceramics. The (Ca_0.05Ba_0.95) (Y_1/2Nb_1/2)O₃ has τ_f close to zero (1.2 ppm/°C) with ɛ_r=35 and Q _u× f =48 500 GHz and is proposed as a useful material for base station applications. Dielectric properties of the Ca(B'_1/2Nb_1/2)O₃ ceramics were tailored by the addition of TiO₂ and CaTiO₃.     

Dielectric Characteristics of Bi- and Ti-Substituted Pb(Mg1/3Nb2/3)O3

Pb[Mg_1/3Nb_2/3]O₃ was gradually substituted by Bi[Mg_2/3Nb_1/3]O₃ (BiMN) up to 30 mol%, with an overall modification by a constant fraction of PbTiO₃ (10 mol%). Monophasic perovskite powders could be prepared via the B-site precursor route. Ceramic samples of the system showed a typical relaxor behavior of frequency-dependent dielectric dispersion. Values of the maximum dielectric constant decreased substantially with increasing BiMN concentration, whereas corresponding temperatures changed only moderately.     

Dielectric Properties of Ceramics in Ba (Co1/3 Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 Solid Solution

The dielectric properties of the Ba (Co_1/3 Nb_2/3)O₃–Ba(Zn_1/3Nb_2/3)O₃ system were determined. Ba (Co_1/3 Nb_2/3)O₃–Ba(Zn_1/3Nb_2/3)O₃ has a complex perovskite structure, a high dielectric constant, a low dielectric loss, and a low temperature coefficient of the resonant frequency. A solid-solution ceramic with 0.7Ba (Co_1/3 Nb_2/3)O₃·0.3 Ba(Zn_1/3Nb_2/3)O₃ has a dielectric constant of K=33.5, Q=11000 at 6.5 GHz, and a temperature coefficient of the resonant frequency of τ_f=0 ppm/°C. The temperature coefficient of resonant frequency can be varied by changing the composition. The Q values of the ceramics can be increased by annealing in a nitrogen atmosphere. These ceramics can be used for resonant elements and stabilized oscillators.     

Microwave Dielectrics in the (La1/2Na1/2)TiO3–Ca(Fe1/2Nb1/2)O3 System

Dielectric properties of the system (1 − x)(La_1/2Na_1/2)TiO₃– _x Ca(Fe_1/2Nb_1/2)O₃, where 0.4 # x # 0.6, have been investigated at microwave frequencies. The temperature coefficient of resonant frequency (τ_f), nearly 0 ppm/°C, was realized at x = 0.58. These ceramics had perovskite structure and showed relatively low dielectric losses. A new dielectric material applicable to microwave devices having Q · f of 12000–14000 GHz and a dielectric constant (ε_r) of 59–60 has been obtained at 1300–1350°C for 5–15 h sintering.     

Influence of Non-Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics: III. Effect of the Muffling Environment

The effect of different muffling environments on the structure and dielectric losses of Ba(Zn_1/3Nb_2/3)O₃ (BZN) microwave ceramics was investigated. The microwave dielectric losses of stoichiometric BZN pellets heated in ZnO-rich environments were severely degraded (e.g. Q × f ∼15 000 in ZnO powder) compared with samples muffled in their own powder ( Q × f ∼80 000). Structure analyses and gravimetric measurements confirmed that the ceramics muffled in ZnO powder or vapor absorb excess ZnO to form non-stoichiometric solid solutions with reduced cation order and Q . By using starting compositions in the (1− x )BZN−( x )BaNb_4/5O₃ binary ( x =0.04), the stoichiometry can be tailored to ensure that after the uptake of ZnO, the ceramics remain well ordered and are located in a high Q region of the system. For example, ZnO-vapor-protected (0.96)BZN−(0.04)BaNb_4/5O₃ reached a very high Q × f (∼1 05 000) after sintering at 1400°C for 5 h.     

Order-Disorder Phase Formation in the Complex Perovskite Compounds Ba(Ni1/3Nb2/3)O3 and Ba(Zn1/3Nb2/3)O3

The order-disorder phase formation of the complex perovskite compounds Ba(Ni_1/3Nb_2/3)O₃ (BNN) and Ba(Zn_1/3-Nb_2/3)O₃ (BZN) was investigated using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The BNN and BZN samples were sintered over a temperature range of 1200° to 1500°C in air for 2 h. X-ray diffraction and transmission electron microscopy showed that these compounds exhibited a 1:2 ordering on the B-site within a narrow temperature range. When BNN and BZN were sintered above 1400° and 1350°C, respectively, a liquid phase formed in the grain boundary which was accompanied by disordering. The composition of the liquid phase resembled that of pyrochlore, with a small amount of nickel for BNN or zinc for BZN. The disordering with the formation of the liquid phase was attributed to the increase in defect concentration.     

Perovskite Phase Formation in the Relaxor System [Pb(Fe1/2Nb1/2)O3]1-x–[Pb(Zn1/3Nb2/3)O3]x

Phase formation and dielectric properties of the compositions in the system [Pb(Fe_1/2Nb_1/2)O₃]₁_ _x –[Pb(Zn_1/3Nb_2/3)O₃] _x were investigated as possible materials for multilayer ceramic capacitors. The formation of the phase with perovskite structure and dielectric properties of ceramics at room temperature in the entire composition range are presented. The undesirable pyrochlore phase can be suppressed up to x = 0.6 by adopting calcination of B-site oxides, followed by reaction with PbO. Compositions in the single-phase range can be sintered at less than 1000°C.     

Microwave Dielectric Properties of Ti-Substituted Bi2 (Zn2/3Nb4/3)O7 Pyrochlores at Cryogenic Temperatures

Monoclinic pyrochlore ceramic Bi₂Zn_{2/3− x /3}Nb_{4/3−2 x /3}Ti _x O₇ (M–BZN) with x =0–0.4 is synthesized and the structure and microwave cryogenic properties are scrutinized. The dielectric constant (ɛ') and loss tangent (tanδ) of these ceramics are measured at a frequency of 3 GHz and temperature range of 15–300 K. With an increase in x value from 0 to 0.4, the dielectric constant and dielectric loss tangent of the investigated materials increase from 70 to 114 and 0.009 to 0.061, respectively. The Ti-substituted ceramics show an increase in dielectric constant with temperature, and the loss tangent shows a peak around 200 K. The peak in the dielectric loss tangent becomes more prominent with an increase of Ti content. The temperature where the dielectric loss tangent peak appears is found to be decreasing slightly with an increase of titanium doping. The observed dielectric characteristics of the titanium-doped M–BZN ceramics are attributed to the presence of the relaxation in these materials, originating from the disorder caused by the Ti⁴⁺ substitution.     

Dielectric Properties of (1−x)CaTiO3–xCa(Zn1/3Nb2/3)O3 Ceramic System at Microwave Frequency

The microwave dielectric properties of the (1− x )CaTiO₃– x Ca(Zn_1/3Nb_2/3)O₃ ceramic system have been investigated. The ceramic samples sintered at 1300°–1450°C for 4 h in air exhibit orthorhombic pervoskite and form a complete solid solution for different x value. When the x value increased from 0.2 to 0.8, the permittivity ɛ_r decreased from 115 to 42, the unloaded quality factor Q × f increased from 5030 to 13 030 GHz, and the temperature coefficient τ_f decreased from 336 to −28 ppm/°C. When x =0.7, the best combination of dielectric properties, a near zero temperature coefficient of resonant frequency of τ_f∼−6 ppm/°C, Q × f ∼10 860 GHz and ɛ_r∼51 is obtained.     

Dielectric Behavior of the Relaxor Pb(Mg1/3Nb2/3)O3—PbTiO3 Solid-Solution System in the Microwave Region

Dielectric behavior of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃—PbTiO₃ solid-solution system was studied from—50° to 200°C in the 100 to 12 × 10⁹ Hz frequency region, and a broad dielectric relaxation was measured for compositions throughout the system. The relative microwave permittivity of the composition 0.9Pb(Mg_1/3Nb_2/3)O₃·0.1 PbTiO₃ decreased by 1 order of magnitude from the 1-MHz value of 11800, and similar decreases were observed for other compositions in the system. Dielectric loss (tan δ) values ranged from 0.5 to 1.0 at microwave frequency. The temperature of the broad dielectric constant maximum shifts toward higher values with increased frequency.     

Structural and Dielectric Characteristics in a Ca(Mg1/3Nb2/3)O3–CaZrO3 System

This study investigates the effect of CaZrO₃ (CZ) substitution on the evolution of an ordered structure in a Ca(Mg_1/3Nb_2/3)O₃ (CMN) system using Raman spectroscopy, X-ray diffractometry, and transmission electron microscopy. It indicates that a (1− x ) CMN−( x )CZ solid solution has the 1:2 and 1:1 ordered structure distorted by the antiphase, the inphase tilting of oxygen octahedra, and the antiparallel shift of A-site cation. A distinct correlation is noted between the transition of the ordered structure and microwave dielectric properties. The differences in ɛ_r and τ_f are attributed exclusively to the differences in the type of cation arrangement. The structure with the 1:2 ordering exhibits a lower relative permittivity and a more negative τ_f than the structure with the 1:1 ordering. The increased fraction of compressed Nb–O bond in the 1:2 ordered structure associated with a large NbO₆ octahedral distortion is correlated with a decrease in relative permittivity and change of τ_f toward more negative values. Simultaneously, the substitution of the Zr⁴⁺ ion causes a linear increase in polarizability, and it also results in an increase in the relative permittivity.     

Influence of Non-Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics: II. Compositional Variations in Pure BZN

The formation of non-stoichiometric cubic perovskite solid solutions based on BaZn_1/3Nb_2/3O₃ (BZN) was examined along 10 different directions in the BaO–ZnO–Nb₂O₅ ternary system. Limited ranges of non-stoichiometry were observed along several pseudo-binaries and the BZN structure can accommodate a variety of different types of defects. Although the deviations from stoichiometry are quite small, typically ∼1 mole%, they induce large changes in the extent and stability of the 1:2 B-site ordering, the sintering and microstructure, and the dielectric loss properties. The highest Q × f s (∼110 000 at 8 GHz) in the system, which coincide with the highest degree of order, were located in two regions along the BZN–Ba₅Nb₄O₁₅ and BZN–BaNb₂O₆ lines. The results of this study provide an explanation for the large variations in crystal structure and Q × f s previously reported for BZN and other related systems (e.g., Ba(Zn_1/3Ta_2/3)O₃), and demonstrate that non-stoichiometric starting compositions provide a route to the highest Q values.     

Microstructures and Microwave Dielectric Characteristics of Ca(Zn1/3Nb2/3)O3 Complex Perovskite Ceramics

Ca(Zn_1/3Nb_2/3)O₃ microwave dielectric ceramics were prepared using a solid-state reaction process, and their microwave dielectric properties were evaluated as functions of sintering and postdensification annealing conditions. The relationship between microwave dielectric properties and processing was interpreted through the variation of microstructures. The dielectric constant showed slight variation with sintering and annealing conditions, but the Q × f value increased at first and then decreased with increased sintering temperature, and annealing in oxygen indicated significant improvement in Q × f , especially for the specimens sintered at higher temperatures. The good microwave dielectric properties were obtained in the ceramics sintered at 1225°C in air for 3 h and annealed at 1100°C in oxygen for 8 h: ɛ= 34.1, Q × f = 15 890 GHz, τ_f=−48 ppm/°C.     

Electromechanical Properties of Pb(Yb1/2Nb1/2)O3-PbZrO3-PbTiO3 Ceramics

The electromechanical and electric-field-induced strain properties of x Pb(Yb_1/2Nb_1/2)O₃· y PbZrO₃·(1− x − y )PbTiO₃ ( x = 0.12, 0.25, 0.37; y = 0.10–0.40) ceramics have been studied systematically as a function of Pb(Yb_1/2Nb_1/2)O₃ (PYN) content and PbZrO₃/PbTiO₃ (PZ/PT) ratio. In addition, the effect of MnO₂ on the electromechanical properties of 0.12Pb(Yb_1/2Nb_1/2)O₃·0.40PbZrO₃·0.48PbTiO₃ was also investigated. The maximum transverse strain values of 1.6 × 10⁻³ for x = 0.12, 1.45 × 10⁻³ for x = 0.25, and 1.36 × 10⁻³ for x = 0.37 were obtained at the compositions which were regarded as the morphotropic phase boundary (MPB). The transverse strain was maximized at the MPB composition. The value of the maximum electromechanical coupling coefficient was 0.69 for y = 0.40 and x = 0.12 composition. In the 0.12Pb(Yb_1/2Nb_1/2)O₃·0.40PbZrO₃·0.48PbTiO₃ composition, the temperature of the maximum dielectric constant decreased and the grain size increased with an addition of MnO₂. The electromechanical coupling coefficient decreased while the mechanical quality factor rapidly increased with an addition of MnO₂. These resulted mainly from the acceptor effect of manganese ions that were produced by doping MnO₂ into the perovskite structure.     

Dielectric Properties and Relaxation in (1−x)BiScO3–xBa(Mg1/3Nb2/3)O3 Solid Solutions

The dielectric properties and frequency dispersion associated with a dielectric relaxation were evaluated within the perovskite (1− x )BiScO₃– x Ba(Mg_1/3Nb_2/3)O₃ solid solution systems (0.7 ≤ x ≤ 1). With increasing BiScO₃, the room-temperature dielectric permittivity at low frequency (100 Hz) increased up to 115 at x = 0.7, and a dielectric relaxation phenomenon was evident. Relaxation parameters were analyzed using several Arrhenius-type equations, and the microwave dielectric property measurement using rectangular wave-guide method enabled confirmation of the extrapolated value of the Arrhenius plot. The result of the microwave dielectric property measurement was also checked with J -function fitting based on the frequency-dependent Gaussian distribution of the associated dielectric loss data at low frequency.     

Dielectric and Electrostrictive Properties of Ferroelectric Relaxors in the System Pb(Mg1/3Nb2/3)O3:PbTiO3: Ba(Zn1/3Nb2/3)O3

Ceramic dielectrics which have been fabricated in the Pb(Mg_1/3 Nb_2/3)O₃:PbTiO₃:Ba(Zn_1/3Nb_2/3)O₃ composition system are shown to exhibit two distinct dielectric maxima, both of which show the characteristic loss spectra of ferroelectrics with diffuse phase transitions. The height of the individual maxima can be controlled by the Zn:Mg ratio in the starting material and, in suitably chosen compositions, a wide range of almost temperature-independent high dielectric permittivity is possible. These dielectrics show strong electrostrictive deformations under high electric fields but the electrostrictive strain is much less temperature-sensitive than in other relaxors.     

Cation Ordering Transformations in the Ba(Zn1/3Nb2/3)O3-La(Zn2/3Nb1/3)O3 System

Single-phase perovskites were formed in the (1−_x)Ba(Zn_1/3Nb_2/3)O₃-( _x )La(Zn_2/3Nb_1/3)O₃ system for compositions with 0.0≤ x ≤0.6. Although the stability of the trigonal "1:2" ordered structure of the Ba(Zn_1/3Nb_2/3)O₃ end member is very limited (0.0≤ x ≤0.05), low levels of lanthanum induce a transformation to a cubic, "1:1" ordered structure that has a broad range of homogeneity (0.05≤ x ≤0.6). Samples with x > 0.6 were comprised of La₃NbO₇, ZnO, and a perovskite with x = 0.6. The cubic 1:1 phases were fully ordered and no evidence was found for a compositionally segregated microstructure. These observations could not be reconciled in terms of a "space-charge" model; rather, they supported a charge-balanced, "random-site" structure for the 1:1 cation-ordered Ba(β_1/2'β_1/2")O₃ phases.