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.     

Low Temperature Sintering of Zn3Nb2O8 Ceramics from Fine Powders

A possibility to produce microwave (MW) dielectric materials by liquid-phase sintering of fine particles was investigated. Zn₃Nb₂O₈ powders with a grain size 50–300 nm were obtained by the thermal decomposition of freeze-dried Zn–Nb hydroxides or frozen oxalate solutions. The crystallization of Zn₃Nb₂O₈ from amorphous decomposition products was often accompanied by the simultaneous formation of ZnNb₂O₆. Maximum sintering activity was observed for single-phase crystalline Zn₃Nb₂O₈ powders obtained at the lowest temperature. The sintering of as-obtained powders with CuO–V₂O₅ sintering aids results in producing MW dielectric ceramics with a density 93%–97% of the theoretical, and a Q × f product up to 36 000 GHz at sintering temperature ( T _s)≥680°C. The high level of MW dielectric properties of ceramics was ensured by intensive grain growth during the densification and the thermal processing of ceramics.     

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.     

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.     

Crystal Structure and Microwave dielectric Properties of Ba(Zn1/3Ta2/3)O3–(Sr,Ba)(Ga1/2Ta1/2)O3 Ceramics

The microwave dielectric properties and crystal structure of Ba(Zn_1/3Ta_2/3)O₃– (Sr,Ba)(Ga_1/2Ta_1/2)O₃ ceramics were investigated in the present study. The Q value of Ba(Zn_1/3Ta_2/3)O₃ was improved by adding 5 mol% Sr(Ga_1/2Ta_1/2)O₃. The maximum Q value of Q × f = 162000 GHz was obtained at 0.95Ba(Zn_1/3Ta_2/3)O₃. 0.05Sr(Ga_1/2Ta_1/2)O₃. For this composition, a lattice super structure caused by hexagonal ordering was observed. A further improvement in the Q value was attained when some Sr was replaced with Ba, and 0.95Ba(Zn_1/3Ta_2/3)O₃· 0.05(Sr_0.25Ba_0.75)(Ga_1/2Ta_1/2)O₃ exhibited a maximum Q value such that Q × f = 210000 GHz. Despite the increased Q value with the replacement of Sr by Ba, the c/a value, which indicates the degree of lattice distortion, remained constant near 3/2. The Q value thus improved without lattice distortion in the system Ba(Zn_1/3Ta_2/3)O₃-(Sr,Ba)(Ga_1/2Ta_1/2)O₃, whereas the improvement of Q value increased with lattice distortion in the solid solution system with Ba(Zn_1/3Ta_2/3)O₃ as an end member.     

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.     

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.     

Influence of Non-Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics: I. Substitution of Ba3W2O9

A narrow region of Zn-vacancy-containing cubic perovskites was formed in the (1− x )Ba₃(ZnNb₂)O₉−( x )Ba₃W₂O₉ system up to 2 mol% substitution ( x =0.02). The introduction of cation vacancies enhanced the stability of the 1:2 B-site ordered form of the structure, Ba(Zn_{1− x} □ _x )_1/3(Nb_{1− x} W _x )_2/3O₃, which underwent an order–disorder transition at 1410°C, ∼35° higher than pure Ba(Zn_1/3Nb_2/3)O₃. The Zn vacancies also accelerated the kinetics of the ordering reaction, and samples with x =0.006 comprised large ordered domains with a high lattice distortion ( c/a =1.226) after a 12 h anneal at 1300°C. The tungstate-containing solid solutions can be sintered to a high density at 1390°C, and the resultant ordered ceramics exhibit some of the highest microwave dielectric Q factors ( Q × f =1 18 000 at 8 GHz) reported for a niobate-based perovskite.     

Temperature-Stable Dielectrics Based on Chemically Inhomogeneous BaTiO3

The dielectric properties and chemical homogeneity of BaTiO₃ ceramics sintered with additions of the pseudophase "CdBi₂Nb₂O₉" were investigated using SEM, TEM, STEM, and EDX. In materials showing the "X7R" dielectric temperature characteristic, the microstructure exhibits the grain core-grain shell structure. The perovskite material in the shell shows a temperature characteristic determined by mixed crystals of BaTiO₃ with the complex perovskites Ba(Bi_1/2Nb_1/2)O₃ and Ba(Cd_1/3Nb_2/3)O₃ having an approximate Curie point of -80°C. The chemical inhomogeneity emerges during a process of reactive liquid-phase sintering. Application of too-high sintering temperatures leads to uniform distributions of the additives via solid-state diffusion and to the loss of the X7R characteristic.     

Microscopic Calculation of Dielectric Loss at Microwave Frequencies for Complex Perovskite Ba(Zn1/3Ta2/3)O3

The dielectric loss tangent at microwave frequencies for the complex perovskite Ba(Zn_1/3Ta_2/3)O₃ was calculated with respect to the degree of structural disorder on B sites. Starting out from the equations of ion motion, dielectric loss was expressed in terms of the pair-correlation functions corresponding to the ordering of Zn and Ta ions on B sites. The characteristic length included in the pair-correlation functions corresponds to the average size of the region containing disorder in ion arrangements on B sites; thus the relation between the structural disorder on the B site and the dielectric loss tangent at microwave frequencies was clarified theoretically. The numerical results show that the microwave loss tangent values change their power from – 3 to – 6 with increasing degree of order on the B site, which agrees well with the experimental observations. Results obtained here confirm the physical origin of the microwave loss of complex perovskite Ba(Zn_1/3Ta_2/3)O₃.     

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.     

Dielectric and Ferroelectric Properties of Ceramics in the Pb(Zn 1/3Nb2/3)O3-BaTiO3-PbTiO3 System

The use of Pb(Zn_1/3Nb_2/3)O₃ ceramics is restricted by the formation of a pyrochlore phase detrimental to both dielectric and piezoelectric properties. Recently it has been shown that a 6 mol% addition of BaTiO₃ to PZN suppresses the formation of pyrochlore phase. Phase relations and dielectric properties of ceramics in the PZN-BT-PT system are reported here. Compositions with the perovskite structure, having high dielectric constant and low temperature coefficient of capacitance, have been identified.     

Domain-Related Phase Transitionlike Behavior in Lead Zinc Niobate Relaxor Ferroelectric Single Crystals

The relaxor ferroelectric lead zinc niobate (Pb(Zn_1/3Nb_2/3)O₃) has been intensively investigated, because of its large dielectric and piezoelectric properties for applications in actuators and transducers. In this study, the in-situ behavior of the domains in Pb(Zn_1/3Nb_2/3)O₃ single crystals has been observed using optical microscopy in combination with a charge-coupled device (CCD) camera. The temperature of the sample has been cycled between −185°C and −200°C, while applying an electric field of up to ±10 kV/cm. Many characteristics, such as the induction of birefringence, the transition between the microdomains and macrodomains, and the "freeze-in" of the macrodomains, have been optically observed. The optical and dielectric data have been collected and plotted as a function of temperature and electric field. An electric-fieldtemperature diagram showing five domain-related regions has been proposed. The microdomain-to-macrodomain phase transitionlike behavior seems to be an analog of a martensitic phase transition.     

Effects of La2O3 Addition and PbO Excess on the Transmittance of PbZrO3–PbTiO3–Pb(Zn1/3Nb2/3)O3 Ceramics by Spark Plasma Sintering

The effects of La₂O₃ addition and PbO excess on the microstructures and optical properties of PbZrO₃–PbTiO₃–Pb(Zn_1/3Nb_2/3)O₃ (PZ–PT–PZN) ceramics prepared by spark plasma sintering were investigated. When 1 mol% La₂O₃ was added, the highest transmittance of 35% at 700 nm for PZ–PT–PZN ceramics was obtained. The improved transmittance was attributed to the increased relative density and the decreased optical anisotropy. The samples containing more than 1 mol% La₂O₃ showed decreased transmittance, due to the appearance of secondary phases. The transmittance of PZ–PT–PZN ceramics increased slightly to 29% at 700 nm with increasing amount of excess PbO up to 10 mol% and thereafter decreased rapidly.     

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.     

Influence of Non-Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics. IV. Tuning τf and the Part Size Dependence of Q×f

High Q ceramics of Ba₃W₂O₉ (BW)-substituted Ba(Zn_1/3Nb_2/3) O₃ (BZN) were prepared with a zero τ_f through the partial substitution of Zn by Ni and Co. The small concentrations of B-site vacancies introduced by the substitution of BW accelerated the kinetics and stability of the cation ordering and lowered the sintering temperature. Dense, zero τ_f, ordered solid solutions such as 0.99Ba(Zn_0.3Co_0.7)_1/3Nb_2/3O₃–0.01BW with ɛ_r=34.4 and Q × f =82 000 at ∼8 GHz could be obtained after sintering at 1380°C for 5 h and annealing at 1300°C for 24 h. Partially ordered ceramics in the Zn/Co and Zn/Ni solid solutions show a large gradient in the ordering throughout the pellets, which produces a resonant frequency dependence of their Q × f value. The ordering gradient is associated with the increased constraints on the growth of the 1:2 ordered structure within the interior of larger and thicker pellets and can be minimized by extended annealing.     

Analysis of Phase Coexistence in Fe2O3-Doped 0.2PZN–0.8PZT Ferroelectric Ceramics by Raman Scattering Spectra

In this work, we suggested a method to evaluate quantitatively the effect of doping oxide on the phase coexistence of PbZr_{1− x} Ti _x O₃ (PZT)-based ceramics through the analysis of the Raman scattering spectra. Theoretically, the degenerated T _3u mode in the cubic phase of PZT will transform as A ₁(3) and E (4) modes in the tetragonal phase or as rhombohedral ( R ) modes in the rhombohedral phase below the Curie temperature, which set up the theoretical base to study the phase coexistence in ferroelectric materials. Through separation by fitting of the Raman bands, the shifts and intensities of different Raman vibration modes were determined. A calculation equation representing the phase coexistence was put forward based on the theoretical analysis of the degenerated T _3u modes. The results showed that a turning point appears at the Fe₂O₃ addition of 0.3%. The variation in the electrical properties of the Fe₂O₃-doped Pb(Zn_1/3Nb_2/3)O₃ (PZN)–PZT ceramics also affirmed the turning point of the phase evolution as the addition of Fe₂O₃.     

Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3 PbTiO3 -PbZrO3 Ceramics Modified with Certain Additives

Effects of additives on the piezoelectric properties of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-PbZrO₃ ceramics in a perovskite-type structure are described. The tetragonality of Pb(Mg_1/3Nb_2/3)_0.375-Ti_0.375Zr_0.25O₃ ceramics increased with the addition of NiO, Cr₂O₃, or Fe₂O₃ but decreased with the addition of MnO₂ or CoO. The dielectric and piezoelectric properties of the base composition were improved markedly through selection of additives in proper amounts. Addition of NiO yielded a high dielectric constant and planar coupling coefficient for compositions at the morphotropic transition boundary. High mechanical Q -factors and low electrical dissipation factors were obtained by addition of MnO₂. Addition of both NiO and MnO₂ produced a mechanical Q -factor of 2051 and a planar coupling coefficient of 0.553. The resonant frequency of Pb(Mg_1/2Nb_2/3)_0.4375Ti_0.4375 zr_0.125O₃ containing MnO₂ had very low temperature and time dependence. The microstructure indicated that ceramics with a high mechanical Q -factor had a fine, uniform grain structure. Addition of Cr₂O₃ retarded grain growth and addition of MnO₂, NiO, CoO, or Fe₂O₃ promoted grain growth in the ternary system.     

Ferroelectric Properties of Pb(Zn1/3Nb2/3)O3–PbTiO3–RNbO3(R=Na, K) Ceramics

We investigate the ferroelectric properties of Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃(PZN–PT)-based ceramics, which are stabilized by adding a small amount of NaNbO₃ (NN) and KNbO₃ (KN). As the content of alkali niobate increased, the ferroelectric properties of Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃–RNbO₃ (PZN–PT–RN; R=Na, K) became softer, which was more pronounced in PZN–PT–KN. The difference in the piezoelectric properties between PZN–PT–KN and PZN–PT–NN was explained by the cation size effect. Because the ionic size of Na is smaller than that of K, the Na ion can retain the ferroelectricity of the solid solution more effectively. The field-induced strain of 85PZN–5PT–10NN under 10 kV/cm was as high as 0.1%. Also, the addition of NN increased the tunability of dielectric constant significantly. At a composition of 85PZN–5PT–20NN, the tunability was 90% and no hysteresis was observed. In contrast to RN, the increase in the content of PT caused the transition from relaxor to normal ferroelectrics, which were accompanied by the structural change from the rhombohedral to tetragonal phase.     

Ba8ZnTa6O24: A New High Q Dielectric Perovskite

The hexagonal perovskite, Ba₈ZnTa₆O₂₄, was prepared in single-phase form and was found to be a stable secondary phase, formed as a result of the loss of ZnO from Ba(Zn_1/3Ta_2/3)O₃ microwave dielectrics. The experimental and calculated X-ray patterns of Ba₈ZnTa₆O₂₄ indicate it is isostructural with Ba₈Ta₆NiO₂₄ with an 8H (cchc)₂ close-packed BaO₃ stacking sequence and the lattice parameters, a =10.0825(14), c =19.0587(38)Å. High-density ceramics of Ba₈ZnTa₆O₂₄ could be prepared at temperatures considerably lower (1400°C) than those used to sinter pure Ba(Zn_1/3Ta_2/3)O₃, and exhibit very good microwave dielectric properties with ɛ=30.5, Q _f=62 300, and τ_f=+36 ppm/°C at 8.9 GHz.