Structure and microwave dielectric properties of NaSr4V5O17 ceramics for LTCC applications

A new microwave dielectric ceramic, NaSr₄V₅O₁₇ with low firing temperature was fabricated via the traditional mixed oxide method. Rietveld refinement of XRD profiles and Raman spectrum analysis ascertained that the NaSr₄V₅O₁₇ compounds crystallized into Sr₂V₂O₇-like triclinic structure with space group P-1 (2) and Z = 1.6. The variation of Q × f value was explained by the combined effects of mean grain size and cell volume rather than packing fraction and bond valence. The change regulation of ε_r was similar to that of density. The |τ_f| value is mainly related to the cations bond valence. The NaSr₄V₅O₁₇ ceramics sintered at 725 °C showed good compatibility with Ag electrode and superior dielectric properties: ε_r = 8.6, Q × f = 45 900 GHz, τ_f = ?57.0 ppm/K, making it a potential application for LTCC.     

Improved dielectric properties in A′‐site nickel‐doped CaCu3Ti4O12 ceramics

The improved dielectric properties and voltage‐current nonlinearity of nickel‐doped CaCu₃Ti₄O₁₂ (CCNTO) ceramics prepared by solid‐state reaction were investigated. The approach of A′‐site Ni doping resulted in improved dielectric properties in the CaCu₃Ti₄O₁₂ (CCTO) system, with a dielectric constant ε′≈1.51×10⁵ and dielectric loss tanδ≈0.051 found for the sample with a Ni doping of 20% (CCNTO20) at room temperature and 1 kHz. The X‐ray photoelectron spectroscopy (XPS) analysis of the CCTO and the specimen with a Ni doping of 25% (CCNTO25) verified the co‐existence of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺. A steady increase in ε′(f) and a slight increase in α observed upon initial Ni doping were ascribed to a more Cu‐rich phase in the intergranular phase caused by the Ni substitution in the grains. The low‐frequency relaxation leading to a distinct enhancement in ε′(f) beginning with CCNTO25 was confirmed to be a Maxwell‐Wagner‐type relaxation strongly affected by the Ni‐related phase with the formation of a core‐shell structure. The decrease of the dielectric loss was associated with the promoted densification of CCNTO and the increase of Cu vacancies, due to Ni doping on the Cu sites. In addition, the Ni dopant had a certain effect on tuning the current‐voltage characteristics of the CCTO ceramics. The present A′‐site Ni doping experiments demonstrate the extrinsic effect underlying the giant dielectric constant and provides a promising approach for developing practical applications.     

Microwave dielectric properties of SnO‐SnF2‐P2O5 glass and its composite with alumina for ULTCC applications

Ultralow‐temperature sinterable alumina‐45SnF₂:25SnO:30P₂O₅ glass (Al₂O₃‐SSP glass) composite has been developed for microelectronic applications. The 45SnF₂:25SnO:30P₂O₅ glass prepared by melt quenching from 450°C has a low T_g of about 93°C. The SSP glass has ε_r and tanδ of 20 and 0.007, respectively, at 1 MHz. In the microwave frequency range, it has ε_r=16 and Q_u × f=990 GHz with τ_f=?290 ppm/°C at 6.2 GHz with coefficient of thermal expansion (CTE) value of 17.8 ppm/°C. A 30 wt.% Al₂O₃ ‐ 70 wt.% SSP composite was prepared by sintering at different temperatures from 150°C to 400°C. The crystalline phases and dielectric properties vary with sintering temperature. The alumina‐SSP composite sintered at 200°C has ε_r=5.41 with a tanδ of 0.01 (1 MHz) and at microwave frequencies it has ε_r=5.20 at 11 GHz with Q_u × f=5500 GHz with temperature coefficient of resonant frequency (τ_f)=?18 ppm/°C. The CTE and room‐temperature thermal conductivity of the composite sintered at 200°C are 8.7 ppm/°C and 0.47 W/m/K, respectively. The new composite has a low sintering temperature and is a possible candidate for ultralow‐temperature cofired ceramics applications.     

Microwave dielectric properties,microstructure, and bond energy of Zn3-xCoxB2O6 low temperature fired ceramics

Low temperature co-fired ceramics (LTCCs) technology plays an important role in modern wireless communication. Zn_3-xCo_xB₂O₆ (x = 0–0.25) low temperature fired ceramics were synthesized via traditional solid-state reaction method. Influences of Co²⁺ substitution on crystal phase composition, grain size, grain morphology, microwave dielectric properties, bond energy, and bond valence were investigated in detail. X-ray diffraction analysis indicated that the major phase of the ceramics was monoclinic Zn₃(BO₃)₂. Solid solution was formed with Co²⁺ substituted for Zn²⁺ because no individual phase that contained Co was observed. An increase in the amount of Co²⁺ substitution changed average grain sizes, and regrowth of grains were observed with Co²⁺ substitution. Appropriate amount of Co²⁺ substitution improved densification. With changes in Co²⁺ substitution, bond energy of major phase and average bond valence of B–O were positively correlated to temperature coefficient of resonant frequency. The Zn_2.927Co_0.075B₂O₆ ceramic sintered at 875 °C for 4 h exhibited excellent microwave properties with ε_r = 6.79, Q × f = 140,402 GHz, and τ_f = −87.42 ppm/°C. This ceramic is regarded as candidate for LTCC applications.     

Microwave dielectric properties of (1‐x)Ba3.75Nd9.5Cr0.25Nb0.25Ti17.5O54–xNdAlO3 ceramics

This study presents the microwave dielectric properties calculation of (1‐x)Ba_3.75Nd_9.5Cr_0.25Nb_0.25Ti_17.5O₅₄–xNdAlO₃ ceramics where x denotes the volume molar fraction. From X‐ray diffraction results, the solid solution limit is calculated to be about 0.76, where it forms a single BaNd₂Ti₄O₁₂ phase in Region I (0≤x<0.76), and both BaNd₂Ti₄O₁₂ and NdAlO₃ coexist in Region II (0.76≤x<1). The solid solution limit is confirmed by independently calculating it from the dielectric constant data. There is less than 4% deviation between the measured dielectric constant (ε_r) and the one calculated from the Maxwell‐Wagner formula. The total quality factor (Q) remains almost constant in Region I and increases rapidly with the volume molar fraction of NdAlO₃ in Region II. The measured Q×f, where f is the resonant frequency, is also consistent with the calculated value in both regions. The temperature coefficient at the resonant frequency is ?1.4 ppm/°C, which agrees well with the calculated value of 0 ppm/°C. In addition, we observed a close correlation between the bulk density and the phase evolution.     

Improved sintering behavior and microwave dielectric properties of SnO2-based ceramics and their LTCC materials with ultrawide temperature stability

Microwave dielectric ceramics with simple composition, a low permittivity (ε_r), high quality factor (Q × f) and temperature stability, specifically in the ultrawide temperature range, are vital for millimetre-wave communication. Hence, in this study, the improvements in sintering behavior and microwave dielectric properties of the SnO₂ ceramic with a porous microstructure were investigated. The relative density of the Sn_1-xTi_xO₂ ceramic (65.1%) was improved to 98.8%, and the optimal sintering temperature of Sn_1-xTi_xO₂ ceramics reduced from 1525 °C to 1325 °C when Sn⁴⁺ was substituted with Ti⁴⁺. Furthermore, the ε_r of Sn_1-xTi_xO₂ (0 ≤ x ≤ 1.0) ceramics increased gradually with the rise in x, which can be ascribed to the increase in ionic polarisability and rattling effects of (Sn_1-xTi_x)⁴⁺. The intrinsic dielectric loss was mainly controlled by r_c (Sn/Ti–O), and the negative τ_f of the SnO₂ ceramic was optimised to near zero (x = 0.1) by the Ti⁴⁺ substitution for Sn⁴⁺. This study also explored the ideal microwave dielectric properties (ε_r = 13.7, Q × f = 40,700 GHz at 9.9 GHz, and τ_f = ?7.2 ppm/°C) of the Sn_0.9Ti_0.1O₂ ceramic. Its optimal sintering temperature was decreased to 950 °C when the sintering aids (ZnO–B₂O₃ glass and LiF) were introduced. The Sn_0.9Ti_0.1O₂-5 wt% LiF ceramic also exhibited excellent microwave dielectric properties (ε_r = 12.8, Q × f = 23,000 GHz at 10.5 GHz, and τ_f = ?17.1 ppm/°C). At the ultrawide temperature range (?150 °C to +125 °C), the τ_ε of the Sn_0.9Ti_0.1O₂-5 wt% LiF ceramic was +13.3 ppm/°C, indicating excellent temperature stability. The good chemical compatibility of the Sn_0.9Ti_0.1O₂-5 wt% LiF ceramic and the Ag electrode demonstrates their potential application for millimetre-wave communication.     

Enhanced electrical properties and strong red light‐emitting in Eu3+‐doped Sr1.90Ca0.15Na0.9Nb5O15 ceramics

The luminescent‐ferroelectic materials based on Sr_1.90Ca_0.15Na_0.9Nb₅O₁₅ (SCNN) matrix doping with Eu³⁺ were synthesized by the conventional solid‐state reaction method. The crystal structure, photoluminescence, thermal stability, dielectric, ferroelectric, and piezoelectric behaviors were systematically investigated. XRD results revealed that Eu³⁺ introduction could induce the tungsten bronze phase transition from orthorhombic to tetragonal structures. The dielectric spectra of all specimens showed two broad dielectric anomalies: a high‐temperature ferroelectric phase transition (T_c) and a low‐temperature ferroelastic phase transition (T_s), both of which were suppressed at higher Eu³⁺ concentrations. The enhanced electrical properties were obtained in a proper Eu³⁺ concentration range of 0.03‐0.05. For all SCNN:xEu³⁺ samples, the strong red emission peak at 617 nm originating from the electric dipole transition of ⁵D₀ →⁷F₂ was excited by different light excitations of 395 or 463 nm. Our results demonstrated that Eu³⁺‐doped SCNN materials might have promising potential in advanced multifunctional optoelectronic applications.     

Microwave dielectric properties and thermally stimulated depolarization of Al-doped Ba4(Sm,Nd)9.33Ti18O54 ceramics

Ba₄(Sm_0.15Nd_0.85)_9.33Ti_18-zAl_3z/4O₅₄ (BSNT-zAl, 0.0 ≤ z ≤ 2.5) ceramics were prepared via a solid-state reaction, and the effects of Al doping on the microwave dielectric properties and defect behavior of the title compound were studied. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) photographs suggested that Al ions successfully entered the lattice to form tungsten-bronze-like solid solutions. With a small amount of Al substitution, the relative dielectric constant (ε_r), and the temperature coefficient of resonant frequency (τ_f) values decreased, whereas the quality factor (Q × f) substantially increased by approximately 50%. The defect-related extrinsic dielectric loss was clarified via the thermally stimulated depolarization current (TSDC) technique. With Al doping, the TSDC relaxation of across-grain-boundary oxygen vacancies () vanished, whereas that of defect dipoles () appeared at relatively low temperatures. Therefore, in the BSNT-zAl ceramics, oxygen vacancies were more inclined to interconnect with to form defect dipoles. This could reduce the activity of and account for the notable improvement in the Q × f values. In particular, the excellent characteristics of ε_r = 67.33, Q × f = 16 530 GHz, and τ_f = +0.87 ppm/°C were achieved in the specimens with z = 1.5 sintered at 1350°C for 4 hours.     

Low temperature fired CaF2-based microwave dielectric ceramics with enhanced microwave properties

Low-temperature-fired microwave ceramics are key to realizing the integration and miniaturization of microwave devices. In this study, a facile wet chemical method was applied to synthesize homogenous nano-sized CaF₂ powders for simultaneously achieving low-temperature sintering and superior microwave dielectric properties. Pure CaF₂ ceramics sintered at 950 °C for 6 h with good microwave dielectric properties (ε_r = 6.22, Q×f = 36,655 GHz, and τ_f = ?102 ppm/°C) was achieved. The microwave dielectric properties of the CaF₂ ceramics were further improved by introducing LiF as a sintering aid. The sintering temperature of CaF₂-based ceramics was effectively lowered from 950 °C to 750 °C with 10 wt% LiF doping, and excellent microwave dielectric properties (ε_r = 6.37, Q×f = 65,455 GHz, and τ_f = ?71 ppm/°C) were obtained.     

Remarkable piezoelectricity and stable high‐temperature dielectric properties of quenched BiFeO3–BaTiO3 ceramics

Effects of quenching process on dielectric, ferroelectric, and piezoelectric properties of 0.71BiFeO₃?0.29BaTiO₃ ceramics with Mn modification (BF–BT?xmol%Mn) were investigated. The dielectric, ferroelectric, and piezoelectric properties of BF–BT?xmol%Mn were improved by quenching, especially to the BF–BT?0.3 mol%Mn ceramics. The dielectric loss tanδ of quenched BF–BT?0.3 mol%Mn ceramics was only 0.28 at 500°C, which was half of the slow cooling one. Meanwhile, the remnant polarization P_r of quenched BF–BT?0.3 mol%Mn ceramics increased to 21 μC/cm². It was notable that the piezoelectric constant d₃₃ of quenched BF–BT?0.3 mol%Mn ceramics reached up to 191 pC/N, while the T_C was 530°C, showing excellent compatible properties. The BF–BT?xmol%Mn system ceramics showed to obey the Rayleigh law within suitable field regions. The Rayleigh law results indicated that the extrinsic contributions to the dielectric and piezoelectric responses of quenched BF–BT?xmol%Mn ceramics were larger than the unquenched ceramics. These results presented that the quenched BF–BT?xmol%Mn ceramics were promising candidates for high‐temperature piezoelectric devices.     

A low-sintering temperature microwave dielectric ceramic for 5G LTCC applications with ultralow loss

In next-generation mobile and wireless communication systems, low sintering temperature and excellent dielectric properties are synergistic objectives in the application of dielectric resonators/filters. In this work, Li₂Ti_0·98Mg_0·02O_2·96F_0.04–1 wt% Nb₂O₅ (LTMN) ceramics were fabricated, and their sintering temperature was successfully lowered from 1120 °C to 750 °C by adjusting the mass ratio of B₂O₃–CuO (BC) additive. The optimum dielectric properties (ԑ_r ~ 24.44, Q × f ~ 60,574 GHz and τ_f ~ 22.8 ppm/°C) were obtained in BC-modified LTMN ceramics sintered at 790 °C. Even if their sintering temperature was lowered to 750 °C, the lowest temperature among the Li₂TiO₃-based dielectric ceramics currently used for LTCC technology, excellent dielectric properties (ԑ_r ~ 23.77, Q × f ~ 51,636 GHz) were still maintained. Additionally, no extra impurity phase was detected in BC-modified LTMN ceramics co-fired with Ag at 790 °C, indicating that BC-modified LTMN ceramics have a bright prospect in high-performance LTCC devices for 5G applications.     

Effect of milling on the anisotropic grain growth in a sintered Ba5Nb4O15 specimen and its effect on microwave dielectric properties

In this study, relationships between the processing, microstructure, and properties of barium niobate (Ba₅Nb₄O₁₅) are investigated. The milling of a Ba₅Nb₄O₁₅ powder in water is effective with respect to size reduction. However, after milling in water, BaCO₃ is formed within the slurry. With the increase in the amount of BaCO₃ formed, the aspect ratio of the elongated Ba₅Nb₄O₁₅ grains increases. The formation of the elongated Ba₅Nb₄O₁₅ grains prohibits the densification. Hence, the microwave dielectric properties, including permittivity and quality factor, are poor because of the low density. In addition, milling in ethanol is carried out for comparison: A lower amount of BaCO₃ is formed after milling in ethanol; the extent of anisotropic grain growth is thus reduced.     

Microwave dielectric properties of low firing temperature stable scheelite structured (Ca,Bi)(Mo,V)O4 solid solution ceramics for LTCC applications

In the present work, a systematic study on microwave properties of Ca_1-xBi_xMo_1-xV_xO₄ (0.2 ≤ x ≤ 0.5) solid solution ceramics synthesized by using the traditional solid-state reaction method was conducted. A scheelite structured solid solution was formed in the composition range 0.2 ≤ x ≤ 0.5. We successfully prepared a microwave dielectric ceramic Ca_0.66Bi_0.34Mo_0.66V_0.34O₄ with a temperature coefficient of resonant frequency (TCF) near to zero and a low sintering temperature by using (Bi, V) substituted (Ca, Mo) in CaMoO₄ to form a solid solution. The Ca_0.66Bi_0.34Mo_0.66V_0.34O₄ ceramic can be well sintered at only 870 °C and exhibits good microwave dielectric properties with a permittivity (ε_r) ?21.9, a Qf ?18,150 GHz (at 7.2 GHz) (Q = quality factor = 1/dielectric loss; f = resonant frequency), a TCF ? + 0.1 ppm/°C. The chemical compatibility with silver indicated that the Ca_0.66Bi_0.34Mo_0.66V_0.34O₄ ceramic might be a good candidate for the LTCC applications.     

Temperature‐stable unfilled tungsten bronze dielectric ceramics: Ba3.5Sm1.5Fe0.75Nb9.25O30

Unfilled tungsten bronze ceramic Ba_3.5Sm_1.5Fe_0.75Nb_9.25O₃₀ was prepared by a conventional solid‐state reaction method. Its structure, microstructure, and dielectric properties were investigated. Dielectric behaviors indicate that the ceramics are ferroelectric at room temperature with a remnant polarization ~1.61 μC/cm² and a coercive field ~13.91 kV/cm. Ba_3.5Sm_1.5Fe_0.75Nb_9.25O₃₀ ceramics have temperature stability with a high dielectric constant (ε_r) varying from 172 to 202 at the temperature range ?55 to 200°C (at 1 MHz). Capacitance change rate of the sample is less than 15%. These results indicate that Ba_3.5Sm_1.5Fe_0.75Nb_9.25O₃₀ ceramics might be promising in temperature‐stable multi‐layer ceramic capacitors.     

Study of the microwave dielectric properties of (La1−xSmx)NbO4 (x=0‐0.10) ceramics via bond valence and packing fraction

The (La_1?xSm_x)NbO₄ (x=0‐0.10) ceramics were prepared by the conventional solid‐state reaction method. The microstructure and the microwave dielectric properties were discussed in detail. The X‐ray diffraction patterns of (La_1?xSm_x)NbO₄ (x=0‐0.10) showed that only a single monoclinic fergusonite structure of LaNbO₄ could be found. The dielectric constant (ε_r) was affected by the dielectric polarizabilities and the B‐site bond valence. The variation trend of Q×f₀ was in accordance with packing fraction. The temperature coefficient of resonant frequency (τ_f) had a close relationship with the B‐site bond valence, which was determined by the bond strength and bond length. When sintered at 1325°C for 4 hours, the (La_1?xSm_x)NbO₄ ceramics with x=0.08 exhibited enhanced microwave dielectric properties: ε_r=19.37, Q×f₀=62203 GHz and τ_f=2.57 ppm/°C. In addition, we made an overview about the ceramics that possess the same packing fraction and bond valence relationships, the results show that this structure‐property relationship has a wide applicability.     

Effect of Microwave Processing on the Crystallization and Energy Density of BaO‐Na2O‐Nb2O5‐SiO2‐B2O3 Glass‐Ceramics

Barium sodium niobate (BNN) glass‐ceramics were successfully synthesized through a controlled crystallization method, using both a conventional and a microwave hybrid heating process. The dielectric properties of glass‐ceramics devitrified at different temperatures and conditions were measured. It was found that the dielectric constant increased with higher crystallization temperature, from 750°C to 1000°C, and that growth of the crystalline phase above 900°C was essential to enhancing the relative permittivity and overall energy storage properties of the material. The highest energy storage was found for materials crystallized conventionally at 1000°C with a discharge energy density of 0.13 J/cm³ at a maximum field of 100 kV/cm. Rapid microwave heating was found to not give significant enhancement in dielectric properties, and coarsening of the ferroelectric crystals was found to be critical for higher energy storage.     

Deficient or excessive CuO-TiO2 phase influence on dielectric properties of CaCu3Ti4O12 ceramics

The influence of the CuO–TiO₂ phase (CT) on dielectric properties of the CCTO ceramic was investigated. CaCu_XTi_YO₁₂ (CC_XT_YO) powders were prepared based on the coprecipitated method, where 2.70 ≤ x ≤ 3.30 and 3.25 ≤ y ≤ 4.75. XRD patterns confirmed the presence of CCTO and also the secondary phases as CuO, TiO₂, and CaTiO₃ for each sample and aided in its quantification. Scanning Electron Microscopy (SEM) shows secondary phases evolution in the grain boundaries, and its influence on size and morphology of the grains. Impedance spectroscopy measurements showed that the ceramics with lower amount of CuO and TiO₂ phases (CT/deficient ceramics) exhibited the highest ε′ values (2.1 × 10⁴ at 1 kHz for CC_2.9T_3.75O ceramic). Also, CT/deficient ceramics showed lower tanδ values (0.090 at 1 kHz for CC_2.9T_3.75O ceramic) than ceramics prepared with excessive CuO–TiO₂ phase (0.241 at 1 kHz for CC_3.1T_4.25O ceramics). The deficiency of CuO and TiO₂ phases associated with high percentage of CCTO and CaTiO₃ phases resulted in ceramics with the higher ε′ values.     

Microwave dielectric properties and crystal structures of Mg0.7Al2.2O4 and Mg0.4Al2.4O4 ceramics with defect structures

Mg_0.7Al_2.2O₄ and Mg_0.4Al_2.4O₄ ceramics with cation vacancies were synthesized using the molten salt method, and the relationships between the microwave dielectric properties and crystal structures of these materials were investigated. The ²⁷Al NMR spectra of these ceramics indicate that the preferential occupation of tetrahedral sites by Al³⁺ cations was enhanced by the introduction of cation vacancies. The λ values of Mg_0.7Al_2.2O₄ and Mg_0.4Al_2.4O₄ ceramics fired at 1600°C, which correspond to the fraction of Al³⁺ cations in tetrahedral sites, were 0.37 and 0.60, respectively. Crystal structure refinements using the Rietveld method suggest that cation vacancies are preferentially located at octahedral sites in both ceramics. The ε_r and Q·f values of a Mg_0.7Al_2.2O₄ ceramic fired at 1600°C were 7.7 and 201 111 GHz, respectively, while those of a Mg_0.4Al_2.4O₄ ceramic fired at 1600°C were 7.5 and 232 301 GHz, respectively. These data demonstrate that the preferential occupation of tetrahedral sites by Al³⁺ cations following the introduction of cation vacancies enhances the Q·f value.     

SrLa(R0.5Ti0.5)O4 (R=Mg,Zn) microwave dielectric ceramics with complex K2NiF4‐type layered perovskite structure

Dense SrLa(R_0.5Ti_0.5)O₄ (R=Mg, Zn) ceramics were prepared by a standard solid‐state reaction method. The single phase with complex K₂NiF₄‐type layered perovskite structure and I4/mmm space group was revealed by XRD, and the refined structure was analyzed by Rietveld analysis. Significantly improved dielectric constant was obtained in SrLa(R_0.5Ti_0.5)O₄ ceramics compared to the analogues SrLaAlO₄ and SrLaGaO₄, which is attributed to the increasing normalized bond lengths of Sr/La‐O(1) and Sr/La‐O(2a) bonds and the higher polarizability of (R_0.5Ti_0.5)³⁺ than Al³⁺ and Ga³⁺. In addition, τ_f converts to a positive value with the increase in dielectric constant. The following microwave dielectric properties were obtained in the dense ceramics: ε_r=25.5, Qf=72 000 GHz, τ_f=29 ppm/°C for SrLa(Mg_0.5Ti_0.5)O₄, and ε_r=29.4, Qf=34 000 GHz, τ_f=38 ppm/°C for SrLa(Zn_0.5Ti_0.5)O_4. Furthermore, the stability of K₂NiF₄‐type structure in MLnBO₄ [M=Ca, Sr, Ba; Ln=Y, Sm, Nd, La; B=Al, Ga, (Mg_0.5Ti_0.5), (Zn_0.5Ti_0.5)] compounds was discussed in relation to the tolerance factor of perovskite layer and the radius ratio of M²⁺ and Ln³⁺, based on which near‐zero τ_f values are expected to be obtained in SrLa(R_0.5Ti_0.5)O₄‐SrLaAlO₄ and SrLa(R_0.5Ti_0.5)O₄–SrLaGaO₄ unlimited solid solutions.     

Microwave dielectric properties of low loss microwave dielectric ceramics: A0.5Ti0.5NbO4 (A = Zn,Co)

The microwave dielectric properties of low-loss A_0.5Ti_0.5NbO₄ (A = Zn, Co) ceramics prepared by the solid-state route had been investigated. The influence of various sintering conditions on microwave dielectric properties and the structure for A_0.5Ti_0.5NbO₄ (A = Zn, Co) ceramics were discussed systematically. The Zn_0.5Ti_0.5NbO₄ ceramic (hereafter referred to as ZTN) showed the excellent dielectric properties, with ɛ_r = 37.4, Q × f = 194,000 (GHz), and τ_f = −58 ppm/°C and Co_0.5Ti_0.5NbO₄ ceramic (hereafter referred to as CTN) had ɛ_r = 64, Q × f = 65,300 (GHz), and τ_f = 223.2 ppm/°C as sintered individually at 1100 and 1120 °C for 6 h. The dielectric constant was dependent on the ionic polarizability. The Q × f and τ_f are related to the packing fraction and oxygen bond valence of the compounds. Considering the extremely low dielectric loss, A_0.5Ti_0.5NbO₄ (A = Zn and Co) ceramics could be good candidates for microwave or millimeter wave device application.