New eight‐layer twinned hexagonal perovskite microwave dielectric ceramic Ba8NiNb6O24

A new eight‐layer hexagonal perovskite Ba₈NiNb₆O₂₄ was synthesized via the high‐temperature solid‐state reaction and its structure was characterized using selected area electron diffraction, high‐resolution transmission electron microscopy, and synchrotron X‐ray diffraction. Unlike the eight‐layer ordered shifted Ba₈CoNb₆O₂₄ and Ba₈ZnNb₆O₂₄, Ba₈NiNb₆O₂₄ adopts a twinned structure with stacking sequence (ccch)₂ for the BaO₃ layers and displays more disordered cation and vacancies over the face‐sharing octahedral (FSO) sites than the twinned tantalates Ba₈MTa₆O₂₄ (M=Zn, Ni, Co). The stabilization of twinned structure and cation/vacancy ordering in Ba₈NiNb₆O₂₄ composition is correlated with the smaller size difference between Ni²⁺ and Nb⁵⁺ in comparison with those between (Zn/Co)²⁺ and Nb⁵⁺ in the shifted Ba₈CoNb₆O₂₄ and Ba₈ZnNb₆O₂₄. The Ba₈NiNb₆O₂₄ pellet exhibits high dielectric permittivity ε_r ~ 40, modest Qf ~ 41 319 GHz, and large temperature coefficient of resonant frequency τ_f ~ 60 ppm/°C. The lower Qf value compared with the high‐Q Ba₈MTa₆O₂₄ is ascribed to the reduced short‐range B‐cationic ordering inside the FSO dimers in Ba₈NiNb₆O₂₄. These results contribute to understanding the interplay among chemical composition, structure, and dielectric properties of the eight‐layer twinned and shifted hexagonal perovskites.     

Influence of Ti4+ substitution for Ta5+ on the crystal structure,Raman spectra,and microwave dielectric properties of Ba3Ta4-4xTi4+5xO21 ceramics

This paper systematically investigated the influence of Ti⁴⁺ substitution for Ta⁵⁺ on the phase composition and microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1, 0.2, and 0.3) ceramics with hexagonal tungsten bronze-like structures. X-ray diffraction and Rietveld refinement results indicated that single-phase Ba₃Ta₄Ti₄O₂₁ could be obtained only with the x values of 0.1 and 0.2, and a secondary phase was detected at an x value of 0.3. The valence state of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.2) ceramics was analyzed through X-ray photoelectron spectroscopy. Increasing Ti⁴⁺/Ta⁵⁺ ratios could reduce sintering temperature and improve the microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ solid solutions. However, the dielectric properties, particularly the quality factor, of Ba₃Ta_4-4xTi_4+5xO₂₁ ceramics deteriorated severely as a result of oxygen vacancy defects caused by the transition of the valence state from Ti⁴⁺ to Ti³⁺ when x = 0.2 and the coexistence of the secondary phase when x = 0.3. Infrared reflectivity spectroscopy was performed to explore the intrinsic dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1) ceramics. The measured and extrapolated microwave dielectric properties of Ba₃Ta_4-4xTi_4+5xO₂₁ (x = 0.1) ceramics sintered at 1240 °C for 6 h were ε_r ~ 46.5, Q × f = 13,900 GHz, τ_f ~ +49.4 ppm/°C, and ε_r ~ 44, Q × f = 34,850 GHz.     

Products and microwave dielectric properties of ceramics with nominal composition (Ba0.9Ca0.1)(YxB′1/2)O(3x+4.5)/2 (B′=Nb5+, Ta5+)

The products and microwave dielectric properties of ceramics with nominal composition (Ba_0.9Ca_0.1)(Y_xB′_1/2)O_(3x+4.5)/2 (B′=Nb⁵⁺, Ta⁵⁺) are investigated. When x=0.5, i.e. (Ba_0.9Ca_0.1)(Y_1/2B′_1/2)O₃ (B′=Nb⁵⁺, Ta⁵⁺), the product contains a considerable amount of Y₂O₃ as well as the main perovskite phase. When x=0.3 the product is single phase, equivalent to Ba(Ca_1/9Y_3/9Nb_5/9)O₃ or Ba(Ca_1/9Y_3/9Ta_5/9)O₃. The lattice parameters of these new compounds are smaller than those of Ba(Y_1/2Nb_1/2)O₃ and Ba(Y_1/2Ta_1/2)O₃. The relative permittivities (ε_r) of these new compounds are larger than those of Ba(Y_1/2B′_1/2)O₃ (B′=Nb⁵⁺, Ta⁵⁺). The increase in ε_r of the Nb-system is about 4 times larger than that of the Ta-system. The Q f values of the present ceramics are larger than the Ca-containing perovskite in the (Ba_1−xCa_x)(Mg_1/3Ta_2/3)O₃ system. The sharp increase of ε_r in this study cannot be explained by the Ca²⁺ rattling ion model at the A-site, which applies to the case of the (Ba_1−xCa_x)(Mg_1/3Ta_2/3)O₃ system. A new method to explain the increase in ε_r is discussed.     

Effects of Sb content on electrical properties of lead-free piezoelectric (K0.4425Na0.52Li0.0375) (Nb0.9625−xSbxTa0.0375)O3 ceramics

Lead-free (K_0.4425Na_0.52Li_0.0375) (Nb_0.9625−xSb_xTa_0.0375)O₃ piezoelectric ceramics were prepared by the conventional sintering method. The effects of the Sb content on the phase structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the (K_0.4425Na_0.52Li_0.0375) (Nb_0.9625−xSb_xTa_0.0375)O₃ ceramics were investigated. The much higher Pauling electronegativity of Sb compared with Nb makes the ceramics more covalent. By increasing x from 0.05 to 0.09, all samples exhibit a single perovskite structure with an orthorhombic phase over the whole compositional range, and the bands in the Raman scattering spectra shifted to lower frequency numbers. The grain growth of the ceramics was improved by substituting Sb⁵⁺ for Nb⁵⁺. Significantly, the (K_0.4425Na_0.52Li_0.0375) (Nb_0.8925Sb_0.07Ta_0.0375)O₃ ceramics show the peak values of the piezoelectric coefficient (d₃₃), electromechanical coupling coefficient (k_p), and dielectric constant (?), which are 304 pC/N, 48% and 1909, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Besides, the underlying mechanism for variations of the electrical properties due to Sb⁵⁺ substitution was explained in this work.     

Relaxor behavior and energy storage density induced by B-sites substitutions in (Ca0.28Ba0.72)2.1Na0.8Nb5O15 Tungsten bronze ceramics

Lead-free relaxor ferroelectrics (Ca_0.28Ba_0.72)_2.1Na_0.8Nb_5-xSb_xO₁₅ (CBNNS) and (Ca_0.28Ba_0.72)_2.1Na_0.8Nb_5-yTa_yO₁₅ (CBNNT) with tungsten bronze structure were fabricated via solid-state reactions. The obtained CBNNS and CBNNT ceramics showed different dielectric behaviors. Only the CBNNS ceramics revealed an intensified diffusion and relaxor-like characteristics, which could be verified by the modified Curie–Weiss law. The relaxor behaviors in CBNNS were attributed to the radii difference between Sb⁵⁺ and Nb⁵⁺ ions co-occupying in B-sites. For the substitution of Nb⁵⁺ by Sb⁵⁺ in CBNNS ceramics, the change from macroscopic polarization to local polarization could also give rise to the obvious relaxor behavior. The Raman spectra verified a larger off-centering of the cation and a higher distortion degree for BO₆ octahedron in the ab plane for CBNNS ceramics when compared with those of CBNNT. In addition, the ferroelectric properties of CBNNS ceramics further indicated the relaxor ferroelectric nature, and also confirmed that the relaxor behavior helped to improve the energy-storage performance.     

High permittivity and low loss dielectric ceramics in the BaO–La2O3–TiO2–Ta2O5 system

Dielectric ceramics were synthesized and characterized in the BaO–La₂O₃–TiO₂–Ta₂O₅ quaternary system for the three typical compositions: Ba₃La₃Ti₅Ta₅O₃₀, Ba₄La₂Ti₄Ta₆O₃₀ and Ba₅LaTi₃Ta₇O₃₀, which formed the filled tungsten-bronze structures. The present ceramics indicated high dielectric constant ε (127.7–148.1) and low dielectric loss tanδ (in the order of 10⁻⁴–10⁻³ at 1 MHz). Meanwhile, the temperature coefficient of dielectric constant τ_ε varied from −728 to −1347 ppm/°C with increasing Ba and Ta and decreasing La and Ti concentration in the temperature range of 20–85 °C. The present ceramics are promising candidates for high-ε and low loss dielectric ceramics, and the suppression of τ_ε should be the primary issue in the future work.     

Microwave dielectric properties of multi-ions Ba(Zn,Ta)O3-based perovskite ceramics

In this study, Ba(Zn_1/3Ta_2/3)O₃-based complex perovskite compounds, including Ba(Zn_1/3Ta_2/3)O₃, Ba(Zn_1/3Ta_1/3Nb_1/3)O₃, Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃, and Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃, were prepared and characterized. There was no second phase formation shown in the XRD patterns. Though it has been suggested that substitutions of multiple ions over A-site or B-site of the Ba(Zn_1/3Ta_2/3)O₃ ceramics may not be beneficial to their microwave dielectric properties, the Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ and Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramics in this study were found to perform in a fairly acceptable manner. The Ba(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramic (sintered at 1575 °C for 6 h) and the Ba_1/2Sr_1/2(Zn_1/6Co_1/6Ta_2/9Nb_2/9Sb_2/9)O₃ ceramic (sintered at 1550 °C for 6 h) reported the following characteristics after annealing at 1400 °C for 10 h: 24.9 and 27.0 for dielectric constants (?_r), 83,000 and 32,100 GHz for quality factors (Q × f) values and −12.8 and −22.6 ppm/°C for temperature coefficients of resonance frequency (τ_f).     

Microwave dielectric characteristics of 0.75(Al1/2Ta1/2)O2–0.25(Ti1−xSnx)O2 ceramics

The microwave dielectric characteristics of 0.75(Al_1/2Ta_1/2)O₂–0.25(Ti_1−xSn_x)O₂ ceramics were investigated. The microwave dielectric properties of 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂ sintered at 1450 °C exhibited a dielectric constant (ϵ_r) of 31.2, a Q·f₀ of 54,590 GHz, and the temperature coefficient of resonant frequency (τ_f) of +12.8 ppm/°C. To control of the τ_f and enhance the Q·f₀ for 0.75(Al_1/2Ta_1/2)O₂–0.25TiO₂, Sn⁴⁺ was substituted for Ti⁴⁺. With an increase of Sn content from 5 to 50 mol%, the ε_r slightly decreased, the Q·f₀ increased and the τ_f shifted from positive to negative value. The τ_f within ±10 ppm/°C of zero was realized for the Sn content below 30 mol% and the microwave dielectric properties had the ε_r value of 31.2–26.3, the Q·f₀ of 54,600–70,700 GHz, and τ_f of +12.8–−9.3 ppm/°C for this compositions. The relationship between microstructure and microwave dielectric characteristics was investigated.     

Correlations between the structural characteristics and enhanced microwave dielectric properties of V–modified Li3Mg2NbO6 ceramics

Novel low-temperature fired Li₃Mg₂Nb_1-xV_xO₆ (x?=?0.02??0.08) microwave dielectric ceramics were synthetized by the partial substitution of V⁵⁺ ions on the Nb⁵⁺ sites. The effects of V⁵⁺ substitution on structure and microwave dielectric properties were investigated in detail. XRD patterns and Rietveld refinement demonstrated that all of the samples exhibited a single orthorhombic structure. The structural characteristics such as the polarizability, packing fraction and NbO₆ octahedron distortion were determined to establish the correlations between the structure and the microwave dielectric characteristics. The ?_r values presented a tendency similar to that of the polarizability. The high Q×f values were mainly attributed to the effects of the grain sizes and density rather than the packing fraction. The variation in the τ_f values was attributed to NbO₆ octahedron distortion. Notably, the Li₃Mg₂Nb_1-xV_xO₆ (x?=?0.02) ceramics sintered at 900?°C had outstanding microwave dielectric properties: ε_r=?16, Q×f=?131,000?GHz (9.63?GHz), and τ_f=???26?ppm/°C, making these ceramics promising ultralow loss candidates for low temperature co-fired ceramics (LTCC) applications.     

Crystal structure and enhanced microwave dielectric properties of Ta5+ substituted Li3Mg2NbO6 ceramics

Composition and structure play dominant roles in realizing the microwave dielectric properties that are necessary for the ever-increasing demands of the Internet of Things and related communication technologies. In the present study, the substitution of Ta⁵⁺ in Li₃Mg₂Nb_1−xTa_xO₆ ceramics and its effect on the structural characteristics and microwave dielectric performances is systematically studied. All the substituted compositions were determined to be pure phase orthorhombic Li3Mg2NbO6 structure of space group Fddd. Furthermore, a NbO₆ octahedral distortion, Nb-O bond valence, packing fraction and polarizability were calculated to explore the structure-property-performance paradigm in the context of microwave dielectric performance. Scanning electron microscopy revealed homogeneous microstructures, with the introduction of Ta⁵⁺ promoting grain growth. Raman spectra indicated that the variation of the band (blue shift and red shift) at 771 cm⁻¹ was highly correlated with the variation in unit cell volume. The polarizability significantly impacted ɛ_r values. The Q × f values were strongly influenced by the packing fraction and grain size. The changes in the NbO₆ octahedral distortion and Nb–O bond valence impacted the τ_f values. The Li₃Mg₂Nb_0.98Ta_0.02O₆ composition displayed the most dramatic improvements in microwave dielectric properties: ε_r = 15.58, Q × f = 113 000 GHz and τ_f  = −4.5 ppm/°C, providing a potential candidate for next generation microwave and millimeter-wave applications.     

Effects of W6+ substitution on crystal structure and microwave dielectric properties of Li3Mg2NbO6 ceramics

Li₃Mg₂(Nb_1-xW_x)O_6+x/2 (0 ≤ x ≤ 0.08) ceramics were synthesized by the solid-state reaction route. The effects of W⁶⁺ substitution on the phase composition, microstructure and microwave dielectric properties of Li₃Mg₂NbO₆ ceramics were investigated systematically. The XRD results showed that all the samples formed a pure solid solution in the whole doping range. The SEM iamges and relative density revealed the dense structure of Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics. The relationship between the crystal structure and dielectric properties of Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics was researched through polarizability, average bond valence, and bond energy. The substitution of W⁶⁺ for Nb⁵⁺ in Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics significantly promoted the Q × f values. In addition, the increase of W⁶⁺ content improved the thermal stability of the Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics. The Li₃Mg₂(Nb_0.94W_0.06)O_6.03 ceramics sintered at 1175 °C for 6h possessed excellent properties: ε_r ~ 15.82, Q × f ~ 124,187 GHz, τ_f ~ −18.28 ppm/°C.     

Low-temperature sintering and microwave dielectric properties of Ba5Nb4O15–BaNb2O6 mixtures for LTCC applications

The addition of B₂O₃ to Ba₅Nb₄O₁₅–BaNb₂O₆ significantly lowered the sintering temperature to ∼900 °C in comparison to ∼1250 °C for samples without B₂O₃. The presence of a B₂O₃-rich intergranular phase in the sample was observed, which was attributed to the presence of a liquid phase during sintering. The barium metaniobate, BaNb₂O₆ has two polymorphs, with orthorhombic and hexagonal forms. A major contributor to microwave dielectric properties of low-fired samples is the low temperature phase, hexagonal BaNb₂O₆. The small amount of hexagonal BaNb₂O₆ could tune τ_f of Ba₅Nb₄O₁₅. Therefore, Ba₅Nb₄O₁₅–BaNb₂O₆ with B₂O₃ can be a suitable for low-temperature cofired ceramic (LTCC), due to its reduced sintering temperature and good microwave dielectric properties: Q×f=28 000 GHz, ε_r and τ_f are 42 and 0 ppm/°C, respectively. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Effects of (Mg1/3Ta2/3)-substitution for Ti-site on the microwave dielectric properties of Li2MgTiO4 ceramics

Novel high quality factor microwave dielectric ceramics Li₂MgTi_1?x(Mg_1/3Ta_2/3)_xO₄ (0 ≤ x ≤ 0.5) were successfully prepared via a conventional solid-state ceramic route. The effects of isovalent substitutions (Mg_1/3Ta_2/3)⁴⁺ at the Ti-site on the sintering behaviors, microstructures, and microwave dielectric properties of Li₂MgTiO₄ ceramics were investigated in this paper. The sintered samples exhibited the single phase with cubic rock-salt structure belonging to Fm-3m space group in the whole composition range. Rietveld refinement which could be performed by the Fullprof program was taken to explain the effects of (Mg_1/3Ta_2/3)⁴⁺ ion substitution on the crystal structures of Li₂MgTiO₄ ceramics. With the (Mg_1/3Ta_2/3)⁴⁺ content increasing from 0 to 0.5, the quality factor Q·f firstly increased and decreased thereafter, while the dielectric constant ε_r almost linearly decreased. In addition, the τ_f values shifted to positive value with the amount of (Mg_1/3Ta_2/3)⁴⁺ increasing. The best composition appeared to be Li₂MgTi_0.6(Mg_1/3Ta_2/3)_0.4O₄, which showed excellent microwave dielectric properties of ε_r = 15.73, Q·f = 184,000 GHz and τ_f = ? 12.54 ppm/°C. This made the Li₂MgTi_0.6(Mg_1/3Ta_2/3)_0.4O₄ ceramic a very promising candidate for use as a low-loss microwave material.     

Structure evolution of wolframite-type ZnZrC2O8 (C = Nb,Ta) ceramics in relation to microwave dielectric properties

The relationship among the sintering behavior, crystal structure, chemical bonding properties, and dielectric properties of wolframite-type ZnZr(Nb_1−xTa_x)₂O₈ (0.0 ≤ x ≤ 1.0) ceramics was investigated with the progressive replacement of Nb⁵⁺ by Ta⁵⁺. The optimum sintering temperature increases from 1225 to 1375°C with increasing Ta⁵⁺ content. The ε_r value falls from 27.34 to 22.34 due to a gradual decrease in bond ionicity and a shift in the Raman vibration modes toward higher wave numbers. The Q × f increases from 63 604 GHz (@6.71 GHz) to 115 631 GHz (@7.89 GHz), which is since the increase in the total lattice of chemical bonds. Moreover, the reduction in grain boundary area and the gradual lowering of the full width at half maximum of the Raman vibration modes contribute to the reduction in dielectric losses. First-principles calculations illustrate that the growth in bandgap and electron cloud density in the internal space of the [Zn/ZrO₆] octahedron leads to a reduction in dielectric loss. Furthermore, the reduced degree of oxygen octahedral distortion causes a change in τ_f from −46.56 to −37.40 ppm/°C.     

Phase structure,band gap and microwave dielectric properties of Ba8Ti3Nb4−xSbxO24 ceramics

High dielectric constant and low loss ceramics in the Ba₈Ti₃Nb_4?xSb_xO₂₄ (x=0–2) system were prepared by conventional solid-state ceramic route. As x increased from 0 to 1.5, a single phase with hexagonal 8H perovskite structure was formed and the band gap values increased from 3.38 to 3.47 eV. However, the Sb₂O₃ secondary phase was detected as the x reached 2. The optimum sintering temperature was reduced from 1460 to 1380 °C, the quality factors (Q×f) were effectively enhanced from 22,900 to 38,000 GHz and τ_f was significantly lowered from 110 ppm/°C to 2 ppm/°C, whereas the dielectric constant decreased from 49 to 35. A good combined microwave dielectric properties with ε_r=37.5, Q×f=38,000 GHz, τ_f=15 ppm/°C were obtained for x=1.5.     

Structural dependence of microwave dielectric performance of wolframite structured Mg1-xCaxZrNb2O8 ceramics: Crystal structure,microstructure evolution,Raman analysis and chemical bond theory

Wolframite-structured Mg_1-xCa_xZrNb₂O₈ (0?0.1) ceramics were synthesized through a solid-state procedure. Crystal refinement indicates a pure Mg_1-xCa_xZrNb₂O₈ ceramic with a wolframite structure. Ca²⁺ substitution led to the redshift of the Ag mode at approximately 896 cm^?1. Additionally, Ca²⁺ substitution could promote grain growth and contribute to microstructure evolution from a polyhedral shape to a rod shape. According to chemical bond theory, an appropriate Ca²⁺ concentration can increase NbO bond iconicity and NbO bond lattice energy, which contributed to the great improvement in the dielectric constant and Q × f value. Additionally, the τ_f value was affected by the bond valence and thermal expansion coefficient of the MgO bond. The Mg_1-xCa_xZrNb₂O₈ (x = 0.04) ceramics exhibited great improvement in the Q × f value: ε_r = 25.21, Q × f = 116,000 GHz (@7.17 GHz) and τ_f = ?24.4 ppm/°C, which provides enormous potential for future millimeter-wave applications.     

Low temperature sintered Li6MgTiNb1-xVxO8F microwave dielectric ceramics with high-quality factor

Li₆MgTiNb_1?xV_xO₈F (0 ≤ x ≤ 0.08) ceramics were prepared using a solid-state reaction. The correlations between their sintering characteristics and the microwave dielectric performance as functions of V⁵⁺ substitution and sintering temperature were investigated systematically. Rietveld refinements of the X-ray diffraction data showed that all the samples had a cubic rock-salt structure. The Li₆MgTiNbO₈F ceramic sintered at 1175 °C exhibited an attractive Q × f value of 105,700 ± 1600 GHz. The substitution of V⁵⁺ for Nb⁵⁺ decreased the sintering temperature while improving the relative density and relative permittivity. The V-beared Li₆MgTiNb_0.98V_0.02O₈F ceramic sintered at 850 °C showed outstanding dielectric properties of ε_r = 18.14 ± 0.05, Q × f = 58,300 ± 1300 GHz, and τ_f = ?42.66 ± 0.33 ppm/°C. Good chemical compatibility with Ag electrodes highlighted the potential of the ceramic in low-temperature co-fired ceramic applications.     

Effects of Ni2+ substitution on the crystal structure,bond valence,and microwave dielectric properties of BaAl2–2xNi2xSi2O8–x ceramics

BaAl_2?2xNi_2xSi₂O_8?x (x = 0, 0.005, 0.01, 0.02, 0.03) ceramics were prepared using traditional solid phase reaction method. The microwave dielectric properties, including permittivity (ε_r), quality factor (Q × f), and temperature coefficient of resonant frequency (τ_f), were discussed based on the bond valence theory. The first-principle calculation was adopted to determine the site (Ba, Al, and Si) where doping element (Ni²⁺) would be inclined to occupy. The substitution of Ni²⁺ for Al³⁺ contributed to the breaking of Al-O and Si-O bonds and then facilitated the BaAl₂Si₂O₈ (BAS) hexacelsian-celsian transformation. Moreover, this substitution could change the bond strength between cation and oxygen anion due to the variation of the bond valence, which reasonably explained the variation of ε_r, Q × f, and τ_f values. Well-sintered and completely transformed celsian ceramics can be obtained after doping with Ni²⁺. When x = 0.01, compact BaAl_1.98Ni_0.02Si₂O_7.99 ceramic exhibited highly promising microwave dielectric properties: ε_r = 6.89, Q × f = 53, 287 GHz and τ_f = -25.31 × 10^?6 /°C.     

Effects of structural characteristics on microwave dielectric properties of low-loss (Zn1-xNix)ZrNbTaO8 ceramics

Low-loss (Zn_1-xNi_x)ZrNbTaO₈ (0.02?≤?x?≤?0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni²⁺ (x?=?0.06) in A-site with the fixed substitution of Ta⁵⁺ in B-site can effectually raise the Q?×?f value of ZnZrNb₂O₈ ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ_f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn_0.94Ni_0.06)ZrNbTaO₈ ceramic sample sintered at 1150?°C for 3?h exhibits an outstanding combination of microwave dielectric properties: ε_r =?27.88, Q?×?f?=?128,951?GHz, τ_f =?–39.9?ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency.     

Investigation of crystal characteristics,Raman spectra,and microwave dielectric properties of Mg1-xZnxTa2O6 ceramics

Mg_(1-x)Zn_xTa₂O₆ (x = 0.00?0.08) dielectric ceramics were synthesized via the traditional solid-state reaction method. We used XRD and Rietveld refinement to demonstrate that a pure Mg_(1-x)Zn_xTa₂O₆ phase with trirutile structure was formed. Zn²⁺ substitution helped to decrease the Raman full width at half width of the A_1g mode at 703 cm^?1, which resulted in an increase in the order and rigidity of the TaO₆ octahedron, this in turn contributed to improving the Q×f values. Additionally, the introduction of Zn²⁺ significantly promoted grain growth and increased the dense, and the molecular polarizability, these factors lead to a higher permittivity. Moreover, enhanced Ta-O bond energy resulted in a more stable TaO₆ octahedron in the Mg_(1?x)Zn_xTa₂O₆ system, which contributed to enhanced τ_f values via substitution of Zn²⁺ doped on the A-site. Correspondingly, the microwave dielectric properties were significantly improved for 0.04-doped samples, obtaining: ε_r = 27, Q × f = 185,000 GHz (at 7.47 GHz), τ_f =32 ppm/°C.