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.     

Improved High-Q Dielectric Resonator with Complex Perovskite Structure

Microwave characteristics of the system Ba(Zn_1/3Ta_2/3)O₃-BaZrO₃ were investigated. Ba(Zn,Ta)O₃ has a perovskite pseudocell and hexagonal superstructure; the superstructure was not formed after addition of BaZrO₃. Both sintering and crystallization of Ba(Zn,Ta)O₃-BaZrO₃ were accelerated compared to those of Ba(Zn,Ta)O₃ alone, and the microwave Q value was also improved. The material optimized for the dielectric resonator, Ba(Ni,Ta)O₃-Ba(Zr,Zn,Ta)O₃, has a dielectric constant of 30, Q value of 10000 at 10 GHz, and temperature coeficient of resonant frequency of 0 ppm/°C.     

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.     

Ba(Zn1/3Ta2/3)O3 Ceramics with Low Dielectric Loss at Microwave Frequencies

The dielectric properties at microwave frequencies of Ba(Zn_1/3Ta_2/3)O₃ ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot-pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X-ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics.     

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.     

Microwave Characteristics of A(B3+1/2B5+1/2)O3 Ceramics (A = Ba, Ca, Sr; B3+= La, Nd, Sm, Yb; B5+= Nb, Ta)

Dielectric properties of A(B³⁺_1/2B⁵⁺_1/2)O₃ (A = Ba, Ca, Sr; B³⁺= La, Nd, Sm, Yb; B⁵⁺= Nb, Ta) ceramics have been investigated at microwave frequencies. Sr(B³⁺_1/2B⁵⁺_1/2)O₃ and Ca(B³⁺_1/2B⁵⁺_1/2)O₃ ceramics have relative dielectric constants (ε _r ) above 20 and negative temperature coefficients of resonant frequency (T _f ). In the group of Ba(B³⁺_1/2B⁵⁺_1/2)O₃ ceramics, T _f changes from + 118 ppm/° to nearly zero according to the kinds of B-site ions. Among the ceramics investigated, Sr(Sm_1/2Ta_1/2)O₃ ceramics have the highest Q values at microwave frequencies. For Sr(Sm_1/2Ta_1/2)O₃ ceramics Q = 7000, ε _r = 27.7, and T _f =−62.5 ppm/° at 8.5 GHz. The microstructure of Sr(Sm_1/2Ta_1/2)O₃ ceramics is composed of a matrix of the ternary compound (Sr-Sm-Ta-O system) and secondary phase grains of the binary compound (Sm-Ta-O system).     

Infrared Reflection of Ba(Mg1/3Ta2/3)O3 Ceramics

The dielectric function of the ordered Ba(Mg_1/3Ta_2/3)O₃ ceramics was investigated by the infrared reflectance spectra taken over the 50–4000-cm⁻¹ range. The detailed crystal structure of the specimen was examined by the Rietveld method. The space group of trigonal D _3d³ and the degree of long-range order of 0.97 for Mg and Ta atomic arrangement were confirmed. The reflectance spectra were analyzed on the basis of the four-parameter semiquantum model assuming 16 infrared active vibrational modes allowed for the related D _3d³ structure. The lowest-frequency optical mode was found at 60 cm⁻¹, which can be assumed to involve the motions of the heavy TaO₆ octahedra.     

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.     

The Effect of Dopants on the Dielectric Properties of Ba(B'1/2Ta1/2)O3 (B'=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In) Microwave Ceramics

Low-loss dielectric ceramics based on Ba(B'_1/2Ta_1/2)O₃ (B'=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In) complex perovskites have been prepared by the solid-state ceramic route. The dielectric properties (ɛ_r, Q _u, and τ_f) of the ceramics have been measured in the frequency range 4–6 GHz by the resonance method. The resonators have a relatively high dielectric constant and high quality factor. Most of the compounds have a low coefficient of temperature variation of the resonant frequencies. The microwave dielectric properties have been improved by the addition of dopants and by solid solution formation. The solid solution Ba[(Y_{1− x} Pr _x )_1/2Ta_1/2]O₃ has x =0.15, with ɛ_r=33.2, Q _u× f =51,500 GHz, and τ_f≈0. The microwave dielectric properties of Ba(B'_1/2Ta_1/2)O₃ ceramics are found to depend on the tolerance factor ( t ), ionic radius, and ionization energy.     

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.     

Formation and Structural Characterization of 1:1 Ordered Perovskites in the Ba(Zn1/3Ta2/3)O3–BaZrO3 System

The phase stabilities in the(1−x)Ba(Zn_1/3Ta_2/3)O₃ (BZT)-xBaZrO₃(BZ)system have been investigated using samples prepared by the mixed oxide method. The substitution of Zr⁴⁺destabilizes the 1:2 cation ordering in BZT and pro-motes the formation of a cubic, 1:1 ordered structure with a doubled perovskite repeat. The homogeneity range of the 1:1 phase extends from x = 0.04 to approximately x = 0.25; substitutions beyond this range stabilize a disordered perovskite. The limits of stability of the 1:1 ordering coin-cide with compositions previously found to exhibit anoma-lies in their dielectric loss. The range of homogeneity is consistent with a "random layer" model for the 1:1 ordered "Ba{β';_1/2β^1/2}O₃" structure. In this model the B× positions are assumed to be occupied exclusively by Ta⁵⁺, and the b× sites by a random distribution of Zn₂₊, Zr₄₊, and the remaining Ta 5+ cations. The validity of the model, where the ordered solid solutions can be represented by Ba{[Zn_{2− y /3}Ta_{(1−2 y )/3}Zr y ]_1/2[Ta]_1/2}O₃(y =2x)was con-firmed by Rietveld refinements conducted using data col-lected with a synchrotron X-ray source.     

Microwave Loss Quality of BaZn13Ta2/3O3 Ceramics

Loss of ZnO explains the improved microwave loss quality (Q) for Ba(Zn_1/3Ta_2/3)O₃ ceramics which have been sintered at high temperatures or longer times. Ordering of Zn and Ta is complete in 60 h at 1400°C, but crystallographic distortion and Q continue to increase up to 120 h. As ZnO volatilizes from the sample, Ba replaces Zn on the B sites and permits additional crystallographic distortion; meanwhile, barium tantalate phases also appear. Crystallographic compositional data are presented to confirm this interpretation.     

Solid-State Preparation of BaTiO3-Based Dielectrics, Using Ultrafine Raw Materials

BaTiO₃ and Ba(Ti,Zr)O₃ dielectric powders have been prepared from submicrometer BaCO₃, TiO₂, and ZrO₂. By use of submicrometer BaCO₃ the intermediate formation of Ba₂TiO₄ second phase can be widely suppressed. Monophase perovskites of BaTiO₃ were already formed at 900°C and Ba(Ti,Zr)O₃ at 1050°C. Aggregates of very small subgrains could be easily disintegrated to particle sizes <0.5 μm.     

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.     

Effect of BaWO4 on the Microwave Dielectric Properties of Ba(Mg1/3Ta2/3)O3 Ceramics

Physical and microwave dielectric properties of complex perovskite Ba(Mg_1/3Ta_2/3)O₃ ceramics have been investigated as a function of the amount of BaWO₄ in the temperature range from 20° to 80°C at 10.5 GHz. Up to 0.05 mol BaWO₄ addition, the lattice constant ratio ( c/a ), ordering parameter, apparent density, and unloaded Q all increase, due to the increase in the substitution of Ta⁵⁺ ions of Ba(Mg_1/3Ta_2/3)O₃ by W⁶⁺ ions from the melted BaWO₄ at above 1430°C. With further addition of BaWO_4, the unloaded Q decreases, due to an increase of the BaWO₄ phase. The temperature coefficient of resonant frequency (TCF) can be controlled by the volume mixture rule of Ba(Mg_1/3Ta_2/3)O₃ and BaWO₄. When 0.09 mol BaWO₄ is added, TCF becomes 0 ppm/°C.     

Effects of Stacking Scheme on Microwave Dielectric Characteristics of Ca(Mg1/3Nb2/3)O3–Ba(Zn1/3Nb2/3)O3 Layered Dielectric Resonators

Ca(Mg_1/3Nb_2/3)O₃ (CMN) and Ba(Zn_1/3Nb_2/3)O₃ (BZN) ceramic disks were stacked with three stacking schemes, designated as CMN/BZN, CMN/BZN/CMN, and BZN/CMN/BZN, to yield layered dielectric resonators, and the microwave dielectric characteristics were evaluated with the TE_01δ mode. Both experiments and finite element analysis showed that the microwave dielectric characteristics of the layered resonator were determined not only by the volume fraction of BZN but also by the stacking scheme. For each stacking scheme, a good combination of microwave dielectric characteristics with an effective dielectric constant of 34.33–34.52, a Q × f value of 58 800–62 080 GHz, and a near-zero temperature coefficient of resonant frequency could be achieved by adjusting the volume fraction of BZN. The effects of the stacking scheme on the microwave dielectric characteristics of the temperature-stable layered resonator were discussed by combining finite element analysis and dielectric composite models.     

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.     

Microwave Dielectric Properties of A6B5O18-Type Perovskites

Cation-deficient perovskites with the general formula A₆B₅O₁₈ (A=Ba, Sr, La; B=Nb, Ta, Ti, Zr, Mg, and Zn) have been synthesized and their microwave dielectric properties have been investigated. X-ray diffraction studies indicate the formation of monophase materials. The structures of Ba₆Ta₄TiO₁₈ and Ba₅SrTa₄TiO₁₈ are different from that of Sr₆Ta₄TiO₁₈. The A₆B₅O₁₈ have Q × f in the range 5600–51 000 GHz, dielectric constants 26–48, and the temperature coefficient of resonant frequency varies from −39 to +83 ppm/°C, depending on the composition. Scanning electron microscopy studies show that the grain size decreases with an increase in the Sr content.     

Piezoelectric Properties and Phase Relations of Pb(Mg1/3Nb2/3)O3-PbTiO3−PbZrO3 Ceramics with Barium or Strontium Substitutions

When a small amount of Ba or Sr is substituted for Pb in Pb(Mg_1/3 Nb_2/3)O₃-PbTiO₃-Pb2rO 3 , the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing PbTiO₃ content. The tetragonality of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ and Pb(Mg_1/2 Nb_2/3)-O₃-PbTiO₃-PbZrO₃ ceramics decreased with increasing Ba or Sr content. The lattice parameter (α axis) in the rhombohedral or pseudocubic phase increased with the increase of Ba but decreased with the increase of Sr substitution. Although the Curie temperature was lowered with the increase of Ba or Sr, the dielectric constants of the ceramics were increased. The dielectric and piezoelectric properties of the ternary compositions near the morphotropic boundary were improved through selection of sub-stituent and base composition. A planar coupling coefficient of 0.66 and a low Young's modulus were obtained with substitution of 5 mole % Ba. A dielectric constant greater than 3500 and a planar coupling of 0.63 can be obtained by substituting 5 mole % Sr.     

Doped Ca(Ca1/4A2/4Ti1/4)O3 (A=Nb, Ta) Dielectrics for Microwave Telecommunication Applications

Ca(Ca_1/4A_2/4Ti_1/4)O₃ (A=Nb, Ta) dielectric resonator materials have been prepared by the solid-state ceramic route. The effects of various amounts of di-, tri-, tetra-, penta-, and hexavalent impurities on the structure, microstructure, density, and microwave dielectric properties of the complex perovskites have been investigated. The structure of the parent materials remained unchanged while slight increase in density was observed with a small amount of certain dopants. An improvement in dielectric constant, quality factor, and temperature coefficient of resonant frequency was observed with the doping of small amounts of MgO, ZnO, NiO, CuO, Co₃O₄, Cr₂O₃, SnO₂, and Sb₂O₅. A correlation between the microwave dielectric properties of Ca(Ca_1/4A_2/4Ti_1/4)O₃ (A=Nb, Ta) ceramics and ionic radius of the dopant has been observed. The reported ceramics are potential candidates for dielectric resonator applications in wireless communication devices operating in the S and C bands.