The relationship between crystal structure and modified microwave dielectric properties of Ca3SnSi2-xGexO9 ceramics

Ca₃SnSi_2-xGe_xO₉ (0 ≤ x ≤ 0.8) and (1–y) Ca₃SnSi_1.6Ge_0.4O₉ – y CaSnSiO₅ – 2 wt% LiF (y = 0.4 and 0.5) microwave dielectric ceramics were prepared by traditional solid-state reaction through sintering at 1250°C–1425°C for 5 h and at 875°C for 2 h, respectively. Ge⁴⁺ replaced Si⁴⁺, and Ca₃SnSi_2-xGe_xO₉ (0 ≤ x ≤ 0.4) solid solutions were obtained. At 0.1 ≤ x ≤ 0.4, the Ge⁴⁺ substitution for Si⁴⁺ decreased the sintering temperature of Ca₃SnSi_2-xGe_xO₉ from 1425 to 1300°C, the SnO₆ octahedral distortions, and the average CaO₇ decahedral distortions, which affected the τ_f value. The large average decahedral distortions corresponded with nearer-zero τ_f values at Ca₃SnSi_2-xGe_xO₉ (0.1 ≤ x ≤ 0.4) ceramics. The τ_f value and sintering temperature of Ca₃SnSi_2-xGe_xO₉ (x = 0.4) ceramic were adjusted to near-zero by CaSnSiO₅ and decreased to 875°C upon the addition of 2 wt% LiF. The (1 – y) Ca₃SnSi_1.6Ge_0.4O₉ – y CaSnSiO₅ – 2 wt% LiF (y = 0.5) ceramic sintered at 875°C for 2 h exhibited good microwave dielectric properties: ε_r = 10.3, Q × f = 14 300 GHz (at 12.2 GHz), and τ_f = ‒5.8 ppm/°C.     

Low-temperature sintering and microwave dielectric properties of CaSnxSiO(3+2x)-based positive τf compensator

The sinterability, phase compositions, and microwave dielectric properties of LiF-doped nonstoichiometric CaSn_xSiO_(3+2x) ceramics prepared by the solid-state reaction were investigated. LiF addition effectively reduced the sintering temperature of CaSn_xSiO_(3+2x) ceramics and inhibited the volatilization of Sn. A pure monoclinic CaSnSiO₅ phase was achieved in the 1.0?wt% LiF-doped CaSn_0.94SiO_4.88 ceramics sintered at 1175?°C, which exhibited good microwave dielectric properties of ε_r =?11.6, Q?×?f?=?34000?GHz, and τ_f =?+73.2?ppm/°C. The positive τ_f value was an atypical and important phenomenon for low-permittivity microwave dielectric ceramics, which could be a promising τ_f compensator.     

Optimized sintering behavior and microwave dielectric properties of Ca1+2xSnSi2x+yO3+6x+2y by composition modulation

Ca_1+2xSnSi_2x+yO_3+6x+2y (0.1 ≤ x ≤ 0.9; 0.1 ≤ y ≤ 0.9) microwave dielectric ceramics were prepared through traditional solid-state reaction sintered at 1450°C–1500°C for 5 hours. The Ca₃SnSi₂O₉ second phase replaced the SnO₂ second phase of the Ca_1+2xSnSi_2xO_3+6x (x = 0, y = 0) ceramics by controlling the ratio of Ca:Sn:Si. The cracks of CaSnO₃ (x = 0, y = 0) ceramic were inhibited, the microwave dielectric properties were optimized by introducing the Ca₃SnSi₂O₉ second phase, and the CaSnO₃-Ca₃SnSi₂O₉ mixture system existed at (0.1 ≤ x ≤ 0.9, y = 0). The CaSnSiO₅ phase with positive τ_f value was related to the Si-rich in CaSnSi_yO_3+2y (x = 0; 0.1 ≤ y ≤ 0.9), and the coexistence of three and four phases was obtained at CaSnSi_yO_3+2y (0.1 ≤ y ≤ 0.9) ceramics. The CaSnSiO₅ phase appeared at CaSnSi_yO_3+2y (0.3 ≤ y ≤ 0.9) ceramics. The CaSnSi_yO_3+2y (y = 0.8) ceramic with 49.2 wt% CaSnSiO₅ phase exhibited excellent microwave dielectric properties: ε_r = 11.06, Q × f = 57,500 GHz (at 11.5 GHz), and τ_f = +8.1 ppm/°C.     

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.     

Weak ferroelectricity and low-permittivity microwave dielectric properties of Ba2Zn(1+x)Si2O(7+x) ceramics

Ba₂Zn_(1+x)Si₂O_(7+x) ceramics were prepared using the conventional solid-state method at 1200 °C for 3 h in air. Apart from the previously reported Ba₂Zn_(1+x)Si₂O_(7+x) (x = 0) with a monoclinic structure (C 2/c), the end-member compositions at x = −1 and 1 exhibit single-phase β-BaSiO₃ with an orthorhombic structure (P2₁2₁2₁) and BaZnSiO₄ with a hexagonal structure (P6₃), and possess a coexistence of weak ferroelectricity and low-permittivity microwave dielectric properties. A reduction in Zn²⁺ content mainly decreases the intensity of the ε_r anomaly peak at lower temperature and increases the ε_r (or frequency) stability against temperature. The Zn²⁺-rich BaZnSiO₄ phase has a τ_f value of −181 ppm/°C, whereas the τ_f value of Zn²⁺-free BaSiO₃ phase decreases to −35.4 ppm/°C. The Zn²⁺ deficiency in Ba₂ZnSi₂O₇ composition could inhibit the presence of BaZnSiO₄ phase and improve the τ_f value, whereas excessive Zn²⁺ cations prompt the formation of the BaZnSiO₄ phase to deteriorate significantly the τ_f value.     

Microwave dielectric properties of SnO2-doped CaSiO3 ceramics

SnO₂-doped CaSiO₃ ceramics were successfully synthesized by a solid-state method. Effects of different SnO₂ additions on the sintering behavior, microstructure and dielectric properties of Ca(Sn_1−xSi_x)O₃ (x=0.5–1.0) ceramics have been investigated. SnO₂ improved the densification process and expanded the sintering temperature range effectively. Moreover, Sn⁴⁺ substituting for Si⁴⁺ sites leads to the emergence of Ca₃SnSi₂O₉ phase, which has a positive effect on the dielectric properties of CaO–SiO₂–SnO₂ materials, especially the Qf value. The Ca(Sn_0.1Si_0.9)O₃ ceramics sintered at 1375 °C possessed good microwave dielectric properties: ε_r =7.92, Qf =58,000 GHz and τ_f=−42 ppm/°C. The Ca(Sn_0.4Si_0.6)O₃ ceramics sintered at 1450 °C also exhibited good microwave dielectric properties of ε_r=9.27, Qf=63,000 GHz, and τ_f=−52 ppm/°C. Thus, they are promising candidate materials for millimeter-wave devices.     

High-Qf value and temperature stable Zn2+-Mn4+ cooperated modified cordierite-based microwave and millimeter-wave dielectric ceramics

Cordierite-based dielectric ceramics with a lower dielectric constant would have significant application potential as dielectric resonator and filter materials for future ultra-low-latency 5G/6G millimeter-wave and terahertz communication. In this article, the phase structure, microstructure and microwave dielectric properties of Mg₂Al_4–2x(Mn_0.5Zn_0.5)_2xSi₅O₁₈ (0 ≤ x ≤ 0.3) ceramics are studied by crystal structure refinement, scanning electron microscope (SEM), the theory of complex chemical bonds and infrared reflectance spectrum. Meanwhile, complex double-ions coordinated substitution and two-phase complex methods were used to improve its Q×f value and adjust its temperature coefficient. The Q×f values of Mg₂Al_4–2x(Mn_0.5Zn_0.5)_2xSi₅O₁₈ single-phase ceramics are increased from 45,000 GHz@14.7 GHz (x = 0) to 150,500 GHz@14.5 GHz (x = 0.15) by replacing Al³⁺ with Zn²⁺-Mn⁴⁺. The positive frequency temperature coefficient additive TiO₂ is used to prepare the temperature stable Mg₂Al_3.7(Mn_0.5Zn_0.5)_0.3Si₅O₁₈-ywt%TiO₂ composite ceramic. The composite ceramic of Mg₂Al_3.7(Mn_0.5Zn_0.5)_0.3Si₅O₁₈-ywt%TiO₂ (8.7 wt% ≤ y ≤ 10.6 wt%) presents the near-zero frequency temperature coefficient at 1225 °C sintering temperature: ε_r = 5.68, Q×f = 58,040 GHz, τ_f = ?3.1 ppm/°C (y = 8.7 wt%) and ε_r = 5.82, Q×f = 47,020 GHz, τ_f = +2.4 ppm/°C (y = 10.6 wt%). These findings demonstrate promising application prospects for 5 G and future microwave and millimeter-wave wireless communication technologies.     

Enhancing the microwave dielectric performance of SrSm2Al2O7 ceramic by Sr2+ nonstoichiometry and sintering aid addition

Sr_1+xSm₂Al₂O_7+x (0 ≤ x ≤ 0.05) ceramics were prepared by a conventional solid-state reaction method. Slight Sr²⁺ nonstoichiometry dramatically enhanced the microwave dielectric performance of the ceramics. Compared with the stoichiometric material, Sr-deficient ceramics show greatly enhanced microwave dielectric properties. For x = 0.03, the ceramics exhibited good microwave dielectric properties of ε_r = 18.31, Q × f = 78,000 GHz and τ_f = 2.28 ppm/°C. ZnO and LiF sintering aids were added to the ceramic to reduce the presintering temperature and enhance the microwave dielectric properties of the ceramics. After 0.25 wt% ZnO and 0.25 wt% LiF were added, the ceramics exhibited microwave dielectric properties of ε_r = 19.40, Q × f = 81,400 GHz and τ_f = 3.27 ppm/°C.     

Lattice structure analysis and optimised microwave dielectric properties of LiAl1-x(Zn0.5Si0.5)xO2 solid solutions

Low-permittivity LiAl_1-x(Zn_0.5Si_0.5)_xO₂ microwave dielectric ceramics were prepared by the solid-state reaction method. Single-phase LiAlO₂ solid solutions with a tetragonal structure were achieved at x ≤ 0.12. Partial substitution of [Zn_0.5Si_0.5]³⁺ for Al³⁺ could improve the microstructure and prevent from absorbing moisture of pure LiAlO₂ ceramics, which slightly increases their relative permittivity (ε_r). The quality factor (Q × f) and temperature coefficient of resonant frequency (τ_f) were closely related to the crystallinity and cation disorder of the B-site characterized by the full width at half-maximum of B₁⁽¹⁾ –mode assigned to Li–O–Al stretching. The optimum microwave dielectric properties (ε_r = 6.12, Q × f = 56986 GHz and τ_f = -122 ppm/°C) were obtained in the sample with x = 0.02 sintered at 1300 °C.     

Correlation between crystal structure and microwave dielectric properties of two garnet-type ceramics in rare-earth-free gallates

Two garnet-type rare-earth-free ceramics, Ca₃M₂SiGa₂O₁₂ (M = Sn and Zr), were prepared through a solid-state reaction method. The relationship between crystal structure and microwave dielectric properties was investigated. The larger deviation of ε_r from ε_theo in Ca₃Zr₂SiGa₂O₁₂ could be ascribed to the rattling Zr⁴⁺. The increase in packing fraction and the decrease in FWHM enhance the Q × f value by substituting Zr⁴⁺ with Sn⁴⁺. The smaller oxygen bond valence in Ca₃Zr₂SiGa₂O₁₂ indicates a smaller τ_f value. Good microwave dielectric properties are obtained with ε_r = 9.14 ± 0.02, Q × f = 106,800 ± 1700 GHz and τ_f = -45.8 ± 1.8 ppm/°C for Ca₃Sn₂SiGa₂O₁₂ and ε_r = 11.98 ± 0.03, Q × f = 84,200 ± 1500 GHz, and τ_f = -32.8 ± 1.4 ppm/°C for Ca₃Zr₂SiGa₂O₁₂. Furthermore, near-zero τ_f values of +5.7 ± 1.9 ppm/°C and +4.5 ± 1.6 ppm/°C appear in 0.95Ca₃Sn₂SiGa₂O₁₂-0.05CaTiO₃ and 0.96Ca₃Zr₂SiGa₂O₁₂-0.04CaTiO₃, respectively.     

A novel low-fired,temperature-stable,and low-cost (1−x)BaCu(B2O5)−xTiO2 microwave dielectric ceramic

BaCu(B₂O₅) is a typical microwave dielectric ceramic (MDC) with a low sintering temperature, but it exhibits a large negative temperature coefficient of resonant-frequency (τ_f) which makes it difficult to use in wireless communications. We employ TiO₂ to improve its temperature-stability of resonant-frequency, and reveal the effects of TiO₂ on the densification and the microwave dielectric properties of BaCu(B₂O₅). Here we show that BaCu(B₂O₅) can be well-sintered at 825 °C with proper TiO₂ additions; we find that the TiO₂ grains homogeneously distribute in the boundaries of BaCu(B₂O₅) grains, resulting in the τ_f compensation of BaCu(B₂O₅). Enhanced temperature-stability of resonant-frequency can be achieved by increasing the content of TiO₂ properly. A novel temperature-stable (1-x)BaCu(B₂O₅)–xTiO₂ (x = 0.20) MDC (τ_f =?0.8 ± 3.0 ppm/°C, ε_r = 8.8 ± 0.36, Q×f = 28,612 ± 1170 GHz) is obtained using some low-cost raw materials. Our results provide the underlying insights needed to guide the design of temperature-stable MDCs for wireless communication applications.     

Microwave dielectric characterization of Ca0.6(La1-xYx)0.2667TiO3 perovskite ceramics with high positive temperature coefficient

Solid solution Ca_0.6(La_1-xY_x)_0.2667TiO₃ dielectric ceramic systems with various x values were studied, which were prepared using a solid-state reaction method. X-ray diffraction and X-ray spectroscopy analyses showed that the crystal structure of these samples was orthorhombic perovskite. The microstructures with the substitution amount of Y³⁺ and the dielectric performances of the Ca_0.6(La_1-xY_x)_0.2667TiO₃ ceramics were also explored. With x = 0.1, the Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃ ceramic could be sintered at 1350 °C, and the microwave dielectric performance was found to be strongly correlated with the sintering temperature. A maximum Qf value of 23,100 (GHz), dielectric constant (ε_r) of 111, and temperature coefficient (τ_f) of 374.6 ppm/°C were achieved for samples sintered at 1350 °C for 4 h. This dielectric ceramic possessed good potential as a τ_f compensator to obtain a near-zero τ_f mixture for high-quality substrates for use in wireless communication systems.     

Influence of Cr3+ substitution for Mg2+ on the crystal structure and microwave dielectric properties of CaMg1-xCr2x/3Si2O6 ceramics

The CaMg_1-xCr_2x/3Si₂O₆ (0?≤?x?≤?0.1) microwave dielectric ceramics were synthesized via conventional solid state reaction. In this study, the effects of Cr³⁺ substituting for Mg²⁺ on morphology, crystal structure and microwave dielectric properties of CaMg_1-xCr_2x/3Si₂O₆ ceramics were explored. XRD diffraction patterns exhibited that the CaMg_1-xCr_2x/3Si₂O₆ ceramics possessed the pure phase of CaMgSi₂O₆ when x?≤?0.06 and a small amount of secondary phase Ca₃Cr₂(SiO₄)₃ for 0.08?≤?x?≤?0.1. SEM micrographs revealed that the substitution of Mg²⁺ with Cr³⁺ could decrease the grain size. The apparent density was affected by the concentration of Mg vacancies. The correlation between crystal structure and microwave dielectric properties was investigated through the Rietveld refinement and Raman analysis. The microwave dielectric properties were mainly dependent on relative density, ionic polarizabilities, internal strain ?, disordered structure and MgO₆ octahedron distortions. Finally, CaMg_1-xCr_2x/3Si₂O₆ (x?=?0.02) ceramics sintered at 1270?°C for 3?h exhibited excellent microwave dielectric properties of ε_r?=?8.06, Q?×?f?=?89054?GHz, τ_f?=??44.92182?ppm/ºC.     

Microstructure and microwave dielectric properties of (1 − x)Ca0.6La0.267TiO3–xCa(Mg1/3Nb2/3)O3 ceramics

(1 ? x)Ca_0.6La_0.267TiO₃–xCa(Mg_1/3Nb_2/3)O₃ ceramics were prepared by a conventional solid-state ceramic route. The microstructure and microwave dielectric properties were investigated as a function of composition and sintering temperature. As the content of Ca(Mg_1/3Nb_2/3)O₃ increased, the temperature coefficient of resonant frequency (τ_f) value decreased gradually. By appropriately adjusting the x value in the present ceramic system, a near-zero τ_f value could be achieved. The appropriate increase of sintering temperature could significantly improve Q·f value by influencing the grain growth. The optimal microwave dielectric properties with a dielectric constant (?_r) of 52.4, Q·f of 36,428 GHz (at 5.8 GHz), and τ_f of 3.4 ppm/°C were obtained for the specimen 0.5Ca_0.6La_0.267TiO₃–0.5Ca(Mg_1/3Nb_2/3)O₃ sintered at 1490 °C for 4 h.     

Microwave dielectric properties of Bi2O3-doped Ca[(Li1/3Nb2/3)1−xTix]O3−δ ceramics

The effect of the additive on the densification, low temperature sintering, and microwave dielectric properties of the Ca[(Li_1/3Nb_2/3)_1−xTi_x]O_3−δ(CLNT) was investigated. Bi₂O₃ addition improved the densification and reduced the sintering temperature from 1150 to 900 °C of CLNT microwave dielectric ceramics. As the Bi₂O₃ content increased, the dielectric constant (ε_r) and bulk density increased. The quality factor (Q·f₀), however, was decreased slightly. The temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Bi₂O₃ content. The dielectric properties (ε_r, Q·f_0, τ_f) of Ca[(Li_1/3Nb_2/3)_0.95Ti_0.05]O_3−δ and Ca[(Li_1/3Nb_2/3)_0.8 Ti_0.2]O_3−δ with 5 wt.% Bi₂O₃ sintered at 900 °C for 3 were 20, 6500 GHz, −4 ppm/°C, and 35, 11,000 GHz, 13 ppm/°, respectively. The relationship between the microstructure and dielectric properties was studied by X-ray diffraction (XRD), and SEM.     

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.     

Microstructures and microwave dielectric properties of (1 − y)La1−xSmx(Mg0.5Sn0.5)O3–yCa0.8Sm0.4/3TiO3 ceramics

The (1 ? y)La_1?xSm_x(Mg_0.5Sn_0.5)O₃–yCa_0.8Sm_0.4/3TiO₃ ceramics were prepared by the conventional solid-state method. The X-ray diffraction patterns of the La_1?xSm_x(Mg_0.5Sn_0.5)O₃ ceramics revealed that La_1?xSm_x(Mg_0.5Sn_0.5)O₃ is the main crystalline phase, which is accompanied by a little La₂Sn₂O₇ as the second phase. An apparent density of 6.59 g/cm³, a dielectric constant (?_r) of 19.9, a quality factor (Q × f) of 70,200 GHz, and a temperature coefficient of resonant frequency (τ_f) of ?77 ppm/°C were obtained when the La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics were sintered at 1500 °C for 4 h. The temperature coefficient of resonant frequency (τ_f) increased from ?77 to +6 ppm/°C as y increased from 0 to 0.6 when the (1 ? y)La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sm_0.4/3TiO₃ ceramics were sintered at 1500 °C for 4 h. 0.425La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–0.575Ca_0.8Sm_0.4/3TiO₃ ceramic that was sintered at 1500 °C for 4 h had a τ_f of ?3 ppm/ °C.     

Effects of Sr2+ substitution on the crystal structure,Raman spectra,bond valence and microwave dielectric properties of Ba3-xSrx(VO4)2 solid solutions

The effects of Sr²⁺ substitution for Ba²⁺ on microwave dielectric properties and crystal structure of Ba_3-xSr_x(VO₄)₂ (0 ≤ x ≤ 3, BSVO) solid solution were investigated. Such Sr²⁺ substitution contributes to significant reduction in sintering temperature from 1400 °C to 1150 °C. Both permittivity (∑_r) and quality factor (Q × f) values decreased with increasing x value, which was determined to be related with the descending values of average polarizability and packing fraction, whereas the increase in τ_f value was explained by the decreased average VO bond length, A-site bond valence. BSVO ceramics possessed encouraging dielectric performances with ∑_r = 12.2–15.6 ± 0.1, Q × f = 44,340 - 62,000 ± 800 GHz, and τ_f = 24.5–64.5 ± 0.2 ppm/°C. Low-temperature sintering was manipulated by adding B₂O₃ as sintering additive for the representative Sr₃V₂O₈ (SVO) ceramic and only 1 wt.% B₂O₃ addition successfully contributed to a 21.7% decrease in sintering temperature to 900 °C, showing good chemical compatibility with silver electrodes, which render BSVO series and SVO ceramics potential candidates in multilayer electronic devices fabrication.     

Cation distribution of high-performance Mn-substituted ZnGa2O4 microwave dielectric ceramics

In current study, only 5?mol% Mn²⁺ was applied to fabricate high performance microwave dielectric ZnGa₂O₄ ceramics, via a traditional solid state method. The crystal structure, cation distribution and microwave dielectric properties of as-fabricated Mn-substituted ZnGa₂O₄ ceramics were systematically investigated. Mn²⁺-substitution led to a continuous lattice expansion. Raman, EPR and crystal structure refinement analysis suggest that Mn²⁺ preferentially occupies the tetrahedral site and the compounds stay normal-spinel structure. The experimental and theoretical dielectric constant of Zn_1-xMn_xGa₂O₄ ceramics fit well. In all, this magnetic ion, Mn²⁺, could effectively adjust the τ_f value to near zero and double the quality factor from 85,824?GHz to 181,000?GHz of Zn_1-xMn_xGa₂O₄ ceramics at the meantime. Zn_1-xMn_xGa₂O₄ (x?=?0.05) ceramics sintered at 1400?°C for 2?h exhibited excellent microwave dielectric properties, with ε_r =?9.7(@9.85?GHz), Q?×?f?=?181,000?GHz, tanδ?=?5.44?×?10^?5,and τ_f =???12?ppm/°C.     

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.