Excellent Microwave Dielectric Properties Research Articles

Processing strategy and composite regulation on dielectric performance in Li2O–Al2O3–B2O3 dielectric systems using SrTiO3

AbstractIn this paper, we investigated the effect of processing parameters and composite regulation on the structure and property relationship of lightweight low‐permittivity Li2O–Al2O3–B2O3 dielectric system. Li2BAlO4 ceramic and (1 − x)Li2BAlO4–xSrTiO3 ceramics were synthesized using a conventional solid‐state reaction method. Thermodynamic analysis, sintering temperature, phase formation, crystal structure, and microwave dielectric properties were investigated. Thermal analysis revealed a melting temperature of 847°C, suggesting a comparatively low temperature for the sintering of Li2BAlO4 ceramics. Li2BAlO4 crystalized into a monoclinic structure with P21/c space group, with [Al2B2O8] rings connected by [BO3] triangles and [AlO4] tetrahedra through Al–O–Al bridges. Dense Li2BAlO4 ceramics with a relative density of ∼97.7% were sintered at 750°C and had optimal microwave dielectric properties with relative permittivity (εr) of 5.13, quality factor (Q × f) of 22 610 GHz, and the temperature coefficient of resonance frequency (τf) of −112.5 ppm/°C. The 0.88Li2BAlO4–0.12SrTiO3 composite ceramic has excellent microwave dielectric properties with εr = 8.83, Q × f = 14 000 GHz, τf = 4.6 ppm/°C. The ceramics also demonstrated an inert behavior with silver electrodes proving its application in low‐temperature cofired ceramic (LTCC) technology.

Optimization mechanisms of density and quality factor of Ba(Mg1/3Ta2/3)O3 ceramics by adding CaO–B2O3–ZnO glass

In this study, Ba(Mg1/3Ta2/3)O3 (BMT) ceramics added with different amounts of CaO–B2O3–ZnO (CBZ) glass were prepared through the solid-state sintering route. The sintering behavior, microstructure, phase composition and dielectric properties of the BMT ceramics added with CBZ glass were investigated. The addition of CBZ glass decreased the sintering temperature of BMT ceramics by over 300 °C, resulting in a highly dense microstructure without interacting with the main BMT phase. The lower sintering temperature led to small ceramic grains and caused a decrease in the Q × f value. Prolonging the sintering time improved the ordering degree of cations on the B-site in BMT ceramic, leading to an enhancement in the Q × f value. The BMT ceramic added with 0.4 wt% CBZ glass exhibited excellent microwave dielectric properties: εr = 24.19, Q × f = 115,100 GHz, τf = 9.84 ppm/°C, after sintering at 1400 °C for 12 h.

Effects of Replacing Co2+ with Zn2+ on the Dielectric Properties of Ba [Zn1/3(Nb1/2Ta1/2)2/3]O3 Ceramics with High Dielectric Constant and High Quality Factor

In this study, we used solid-state synthesis to prepare Ba[(ZnxCo1−x)1/3(Nb0.5Ta0.5)2/3]O3 microwave ceramics for mobile communications. Compared with Ba[Zn1/3(Nb0.5Ta0.5)2/3]O3, in the prepared materials, Co2+ substitution with Zn2+ improved the Q × f value and enabled densification and sintering at a lower temperature. We used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the obtained microstructure. Ba[(ZnxCo1−x)1/3(Nb0.5Ta0.5)2/3]O3 was found to have a 1:2 ordered hexagonal structure, and its Q × f value increased with the increase in sintering temperature. In this work, excellent microwave dielectric properties—τf = −0.7 ppm/°C, εr = 34.5, and Q × f = 110,000 GHz—were obtained by sintering Ba[(Zn0.3Co0.7)1/3(Nb0.5Ta0.5)2/3]O3 at 1400 °C for 5 h.

Raman spectroscopy, chemical bonding, and microwave dielectric properties of Li4AlSbO6 ceramics

A novel Li4AlSbO6 (LASO) microwave dielectric ceramic with a monoclinic structure and space group C12/c1 was successfully prepared using traditional solid-state methods. When the sintering temperature was 1200 °C, it had excellent microwave dielectric properties, with εr = 8.2, Q × f = 22,098 GHz, and τf = −15.53 ppm/°C. Raman spectroscopy analysis showed that the FWHM of the strong peak at 691 cm−1 reflected the variation trend of Q × f value and was opposite to the variation trend of Q × f value. Additionally, the augmentation in the Q × f value can be attributed to a higher relative density. As per the bond valence analysis, εr is closely connected to the rattling and compressing effects of A-site cations, and the higher εtheo than εr in Li4AlSbO6 can be attributed to the strong compression effect induced by Li+. Additionally, τf may be influenced by both the Sb–O bond and relative density.

The ultralow loss Li2Mg3Ti1−xAl4x/3O6 microwave dielectric ceramics and its design of dielectric resonator antenna

The Li2Mg3Ti1−xAl4x/3O6 (0 ≤ x ≤ 0.1) ceramics are synthesized using the solid phase method, showing excellent microwave dielectric properties with εr = 14.05, Q × f = 144 500 GHz, and τf = −43 ppm/°C at x = 0.04. Rietveld refinements, based on the XRD data, reveal that the Li2Mg3Ti1−xAl4x/3O6 ceramics crystallize in the rock salt structure with Fm-3m space group. The relationship between the crystal structure and intrinsic microwave dielectric properties is studied in detail. The variation in the dielectric constant is related to ionic polarization and relative density. The quality factor (Q × f) demonstrates a strong correlation with lattice energy, relative density, and concentration of Ti3+. The variation of τf is influenced by the bond thermal expansion coefficient and bond valence. The dielectric resonant antenna, manufactured from Li2Mg3Ti0.96Al0.0533O6-0.09TiO2 ceramic with near-zero τf, shows a bandwidth of 230 MHz at 7.40 GHz and a high radiant efficiency, which indicates that high-quality factor Li2Mg3Ti0.96Al0.0533O6 ceramic has significant potential in relevant fields such as 5G and smart driving.

A novel dielectric ceramic Na0·48La0·52MoO4 with excellent thermal stability for LTCC applications

This article reports the fabrication of a novel molybdate compound, Na0·48La0·52MoO4 (NLM), through the solid-state reaction method. The structural characterization and dielectric properties of NLM were conducted via powder X-ray diffraction, SEM, laser Raman spectroscopy, and vector network analysis. The research results indicate that the sintering temperature directly affects the firing process and microwave dielectric properties. NLM ceramics sintered at 920 °C demonstrate excellent microwave dielectric properties of εr = 8.86, Q × f = 61,378 GHz (at 13.5 GHz) and τf = −10.8 ppm/°C. Furthermore, NLM ceramics exhibit favorable chemical compatibility with Ag. These findings underscore the significant potential of NLM ceramics for utilization in LTCC applications.

Preparation of Sol-Gel-Derived CaO-B2O3-SiO2 Glass/Al2O3 Composites with High Flexural Strength and Low Dielectric Constant for LTCC Application.

Low-temperature co-fired ceramic (LTCC) substrate materials are widely applied in electronic components due to their excellent microwave dielectric properties. However, the absence of LTCC materials with a lower dielectric constant and higher mechanical strength restricts the creation of integrated and minified electronic devices. In this work, sol-gel-derived CaO-B2O3-SiO2 (CBS) glass/Al2O3 composites with high flexural strength and low dielectric constant were successfully prepared using the LTCC technique. Among the composites sintered at different temperatures, the composites sintered at 870 °C for 2 hours possess a dielectric constant of 6.3 (10 GHz), a dielectric loss of 0.2%, a flexural strength of 245 MPa, and a CTE of 5.3 × 10-6 K-1, demonstrating its great potential for applications in the electronic package field. By analyzing the CBS glass' physical characteristics, it was found that the sol-gel-derived glass has an extremely low dielectric constant of 3.6 and does not crystallize or react with Al2O3 at the sintering temperature, which is conducive to improving the flexural strength and reducing the dielectric constant of CBS glass/Al2O3 composites.

Influence of sintering characteristics and structural properties on the microwave dielectric properties of non-stoichiometric Ca3Mn2+xGe3O12+δ (x = 0–0.2) ceramics

The structural characteristics of Ca3Mn2+xGe3O12+δ (x = 0.1) ceramics correspond to their excellent microwave dielectric properties: εr = 8.88, Q × f = 50 793 GHz, τf = −39.35 ppm °C−1.

Enhanced quality factor (∼336,800 GHz) of MgTiO3 ceramic by Hf substitution for Ti-site

Mg(Ti1–xHfx)O3 (0 ≤ x ≤ 0.1) microwave dielectric ceramics were synthesized by solid-state reaction method. The effects of Hf substitution for the Ti-site on the phase composition, structure, and microwave dielectric properties of MgTiO3 ceramic were systematically investigated. The study demonstrated that Hf substitution significantly improved the quality factor of MgTiO3 ceramic. A single phase was confirmed at x = 0.002 and 0.005 by XRD and SEM, while secondary phases were observed at x ≥ 0.02. The Rietveld refinement of XRD data implied that the distortion of [Ti(Hf)O6] octahedron started with alleviation and then gradually deteriorated with an increase in Hf content. Raman spectra displayed that the frequencies of the vibrational modes were high when there was low distortion in [Ti(Hf)O6] octahedron, manifesting that the low distortion weakened the effect of non-harmonic vibration. The quality factor of the samples with x ≤ 0.05 was far higher than that of undoped MgTiO3, which may be related to low distortion in [Ti(Hf)O6] octahedron and high relative density. Notably, the excellent microwave dielectric properties of Q × f ∼336,829 GHz, εr ∼17.2 and τf ∼ -49.7 ppm/°C were achieved for the Mg(Ti0.995Hf0.005)O3 ceramic. The greatly improved quality factor of MgTiO3-based microwave ceramics through Hf substitution makes it a suitable candidate material for ceramic filters.

Crystal structures and microwave dielectric properties of (1-x)Ba(Zn1/3Nb2/3)O3 − xBaWO4 (0 ≤ x ≤ 0.25) ceramics

The (1-x)Ba(Zn1/3Nb2/3)O3 − xBaWO4 (0 ≤ x ≤ 0.25) ceramics were manufactured by the conventional solid-phase reaction process, and the effects of BaWO4 addition on the phase composition, crystal structures, microstructure, and microwave dielectric properties were investigated. X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy were implemented to explore the phase composition, crystal structure and chemical states of the samples, respectively. According to XRD analysis, the main phase of the samples was assigned as Ba(Zn1/3Nb2/3)O3 (BZN), while the secondary phases contained Ba5Nb4O15 and BaWO4. Scanning electron microscopy photographs suggested the average grain size firstly increased and then decreased with the replacement of W6+ ions to Nb5+ ions in BZN. Due to the proper substitution amount of W6+, the apparent density increased accordingly. The microwave dielectric properties were closely associated with the secondary phases and apparent density. Finally, (1-x)Ba(Zn1/3Nb2/3)O3 − xBaWO4 (x = 0.15) ceramics sintered at 1325 °C for 4 h had excellent microwave dielectric properties with ε r = 33.11, Q × f = 90,479 GHz, and τ f = +0.86 ppm °C−1.

Re2TiO5: Special dielectric titanates exhibiting abnormally low permittivity and a positive coefficient of resonance frequency

AbstractIn this study, a series of rare‐earth titanates with the general formula Re2TiO5 (Re = Er, Tm, Yb, and Lu) were synthesized and their microwave dielectric properties were reported. The impact of differences in rare‐earth cation radii on the structure and dielectric properties was systematically analyzed. The findings indicated that ceramics of Re2TiO5 (Re = Er, Tm, Yb, and Lu) were crystallized into a cubic structure with space group Fd‐3m, as confirmed by Rietveld refinement and selected‐area electron diffraction patterns. The rare‐earth elements were analyzed for their impact on microwave dielectric properties, considering factors such as ionic polarizability, packing fraction, and bond valence theory. The resulting materials exhibited excellent microwave dielectric properties with a low permittivity (6.95–7.21), high‐quality factors (19 451–20 115 GHz), and low positive temperature coefficient of resonance frequency (19.34–20.90 ppm/°C). The origin of low permittivity was elucidated through the analysis of bond length, X‐ray photoelectron spectroscopy, and impedance spectroscopy. This series of titanates exhibited unusually low permittivity characteristics in the microwave frequency range, which could meet the low signal transmission delay requirements in wireless communication.

Cracking behavior of Sm2O3 ceramics and enhanced microwave dielectric properties with MgO addition: Insights from chemical bond characteristics and microstructure

Monoclinic Sm2O3 ceramics were prepared using the conventional solid-state sintering method. The influences of sintering temperature on structure, morphology, and performance of Sm2O3 ceramics were studied systematically. The excellent microwave dielectric properties (εr = 21.95, Q × f = 47,000 GHz, and τf = +30.15 ppm/°C) were achieved in Sm2O3 ceramic sintered at 1550 °C for 4 h. Interestingly, varying degrees of cracking were observed after the sintered samples were placed for a short time, with the extent depending on the sintering temperatures. The reasons for cracking were analyzed through chemical bond characteristics and microstructure. The analysis of bond valence and microstructure revealed that Sm2O3 ceramics sintered at higher temperatures exhibited larger bond strain index, global instability index, and interplanar spacings. These results suggest that the cracking of Sm2O3 ceramics originates from inner stress resulting from structural variations caused by variations in sintering temperatures. The effect of MgO addition on microwave dielectric properties and stability of Sm2O3 ceramics was also investigated. Phase identification and elemental distribution indicated that MgO existed as a secondary phase. The Sm2O3 ceramic with 20 wt% MgO addition exhibited optimal microwave dielectric properties: εr = 17.72, Q × f = 61,100 GHz, and τf = +2.4 ppm/°C. Importantly, cracking was not observed when MgO addition amounts were 5 wt% or higher. The attractive microwave dielectric properties and favorable stability confirm the possibility of the 5G applications for Sm2O3/MgO composite ceramics.

Structure, composition, microwave dielectric properties and improved ultra-low temperature sintering characteristics of Lyonsite structural Li2Mg2Mo3O12 ceramic

(1-x)Li2Mg2Mo3O12-xTiO2 (x = 0.1–0.5) composite ceramics are prepared by solid-state sintering process. And the structure, composition, microwave dielectric properties and ultra-low temperature sintering characteristics are studied. The result of two-phase (Li2Mg2Mo3O12 and TiO2) coexistence is definitely identified through XRD, mapping and Raman analysis along different regions. Furthermore, as the sintering temperature increases, the enhanced degree of densification plays a positive role in determining microwave dielectric properties. Sintering additives are used to lower sintering temperature of 0.6Li2Mg2Mo3O12-0.4TiO2 composite ceramics, where 1 wt% H3BO3 is applied to reduce the temperature from 750 °C to 700 °C and maintain excellent microwave dielectric characteristics. The cooling mechanism of sintering aids are also thoroughly studied. In all, 0.6Li2Mg2Mo3O12-0.4TiO2 composite ceramic with 1 wt% H3BO3 sintered at 700 °C displays excellent microwave dielectric properties (εr∼11.27, Q × f ∼43056 GHz, τf ∼ -3 ppm/°C). It can be served as a pioneering candidate in applications of ULTCC (ultra-low temperature co-fired ceramic).

Sintering behavior of 0.95MgTiO3-0.05CaTiO3 ceramics with high densification, high Q and enhanced mechanical properties for 5G massive MIMO technology: Effect of particle gradation

An increase in the requirements for microwave dielectric materials was brought on by the quick growth of communication technologies. In this study, the sintering problems including the narrow sintering densification range and high sintering temperature of 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics with high densification and high Q, as one of the candidate materials for 5G filters, were discussed and overcome through the particle gradation with sub-micrometric and micrometric powders according to closest packing models. It was found that sub-micrometric (0.7–1 μm) 95MCT powder particles agreed well with the Andreasen model, while micrometric (1–3 μm) particles agreed better with the Dinger-Funk model. With increasing of sub-micrometric powders, the activation energy decreased from 926.01 ± 75.49 to 569.49 ± 31.57 kJ/mol, and the relative density of samples which contained 20–60% fine powders were increased to 98%. The average grain size and grain homogeneity decreased from 7.36 μm to 2.54 μm and 3.36 to 1.79, respectively, to improve the mechanical properties. The results show that the powder grading further improved the comprehensive performance of 95MCT, and the best performance point was J1 which exhibited excellent microwave dielectric properties with εr = 21.1, Qf = 82000 GHz, τf = −0.9 ppm/°C, RD = 98.2%, σf = 178.7 MPa and HV = 8.78 GPa after sintering at 1225 °C for 3h.

Crystal structures, Raman spectra, chemical bonds, and microwave dielectric properties of novel low-εr CaASbWO8 (A = Gd, La) ceramics with opposite temperature coefficients

In this work, two novel CaASbWO8 (A = Gd, La; named CGSWO and CLSWO) microwave dielectric ceramics were synthesized by a classical solid-state method. Remarkably, the outstanding microwave dielectric properties (εr = 12.97, Q×f = 45,034 GHz, and τf = −16.29 ppm/°C) were achieved for CGSWO ceramics sintered at 1440 °C, and CLSWO ceramics sintered at 1300 °C possessed the excellent microwave dielectric properties of εr = 9.89, Q×f = 61,326 GHz, and τf = 0.55 ppm/°C. Bond valence, ionic polarizability, Raman spectroscopy and Phillips–Vechten–Levine (P-V-L) theory were used to study the internal lattice vibration and chemical bonds in detail, and the dielectric properties were explored from the internal factors. In comparison to the εr, the εtheo of CGSWO was found to be consistently underestimated, whereas CLSWO exhibited a contrasting pattern. This discrepancy was primarily attributed to the rattling and compressed effects of A-site cation. According to the analysis of P-V-L theory, W-O bond played an important role in regulating the Q×f value. Moreover, the τf values of CGSWO and CLSWO ceramics were opposite, which provided an opportunity to manufacture microwave ceramic devices with good temperature stability.

Rattling and compressed cations resulting in distinct microwave dielectric characteristics of SrPrBO4 (B = Ga, Al) with K2NiF4 structure

In this work, tetragonal K2NiF4 structured SrPrBO4 (B = Ga, Al) ceramics with I4/mmm space group were synthesized via the conventional solid-phase method. High relative density (>95 %) and excellent microwave dielectric properties of εr = 18.15, Q×f = 36,643 GHz, τf = −20.20 ppm/°C for SrPrAlO4, and εr = 22.02, Q×f = 27,475 GHz, τf = +19.11 ppm/°C for SrPrGaO4 were obtained when sintered at 1500 °C and 1375 °C, respectively. Analyses of the bond valences show that the εr and τf values are closely related to the rattling and compressing effects of the A-site cation. The strong compressed effect of Sr2+ in SrPrAlO4 leads to its εr value less than the εr(C-M); while, the strong rattling effect of Pr3+ in SrPrGaO4 leads to its εr value higher than the εr(C-M), and thus to a positive τf. The Al/Ga–O bonds play a crucial role in the influence of the dielectric loss according to the P–V–L chemical bonding theory analysis. The Edc of SrPrAlO4 (0.99 eV) and SrPrGaO4 (0.52 eV) indicates that the formation mechanisms of oxygen vacancies in both ceramics are different.

Crystal structure of barium manganese vanadate BaMnV2O7

Relevance. The development of materials with excellent dielectric properties is crucial for modern telecommunications. The value of this study lies in the importance of examining these properties in the context of expanding possibilities for high-frequency applications in modern telecommunication technologies, including 4G and 5G communication. Purpose. The purpose of this study is to investigate the crystal structure of the compound BaMnV2O7 and its dielectric properties. Methodology. To achieve the set purpose, methods of analysis, experimentation, comparison, and computer modelling were used. Within this study, the material of low-temperature co-fired ceramics (LTCC) was thoroughly examined, known for its high efficiency as moisture protection. Results. A structural model for the compound BaMnV2O7 was proposed and investigated. In particular, it was found that the radius of Mn2+ (0.75 Å) is almost identical to the radius of Zn2+ (0.68 Å), confirming the similarity of the crystal structures of BaMnV2O7 and BaZnV2O7. The main results showed that pyrovanadate has a monoclinic symmetry and has a spatial symmetry group P121/c1 (14), characterised by lattice parameters: a=5.6221(5) Å, b=15.271(1) Å, c=9.7109(8) Å, β=123.702(3)°. The divergence factor was 9.05, indicating the model’s correspondence to experimental data. Additionally, the density of the compound was calculated, amounting to 4.2699 g/cm3. Conclusions. Experimental data confirmed the presence of interatomic distances within 1.33-3.47 Å. The minimum interatomic distance in the compound structure is 1.33 Å between oxygen (O5) and vanadium (V2) atoms. The maximum interatomic distance is 3.47 Å observed between oxygen (O1) and (O2) atoms. With characteristics such as low dielectric permittivity (εr~8.9) and a high quality factor coefficient (Qu×f 31362 GHz), the compound BaMnV2O7 exhibits excellent microwave dielectric properties. The practical value of the obtained results lies in the potential development and improvement of materials with high dielectric properties, such as BaMnV2O7, for their application in telecommunication technologies, contributing to the development of more compact and reliable components for electronics

Crystal structure, chemical bonding and infrared reflectivity of microwave dielectric SrIn2O4 ceramics

In this work, the orthorhombic structured SrIn2O4 ceramics with a space group Pnam were synthesized by a solid-state reaction method. A high relative density (96.5%) coupled with excellent microwave dielectric properties (εr ~ 12.3, Q × f = 96,900 GHz, τf ~ -61.6 ppm/°C) were obtained as sintered 1300 °C for 4 h. The bond valence analysis demonstrates that the large sized cation Sr2+ exhibits a compressed state, while the In3+ exhibits a weaken rattling effect. The P-V-L chemical bond theory analysis indicates that the In-O bonds play a key role in affecting the dielectric loss. The thermally conductivity activation energy Edc (0.94 eV) of SrIn2O4 was obtained by the dielectric spectroscopy, indicating that the Edc was contributed to the double ionized oxygen vacancies. Furthermore, the intrinsic dielectric properties (εr ~ 11.2, Q × f = 148,900 GHz) of SrIn2O4 were obtained by infrared reflectivity spectroscopy.

Optimized crystal structure and microwave dielectric properties of BaZnSi3O8‐based ceramics

AbstractIn this study, we synthesized BaZnSi3O8‐based compounds with monoclinic structures (P21/a) using a solid‐state method. The crystal structure, phase composition, and microwave dielectric properties of BaZnSi3O8‐based ceramics were systematically investigated systematically. X‐ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images proved that the maximum solubility of BaZn1‐xMgxSi3O8 ranged between 0.3 and 0.4. Rietveld refinement and Phillips–Van Vechten–Levine complex chemical bond theory were used to illustrate the relationship between the microwave dielectric performance and lattice parameters. To further improve the properties, we substituted Ba2+ with Sr2+ in BaZn0.8Mg0.2Si3O8. Ba1‐ySryZn0.8Mg0.2Si3O8 remained in a single‐phase as y increased from 0 to 1.0. We achieved thermal stability of the resonance frequency of the BaZnSi3O8‐based ceramics by adjusting TiO2 to form composite ceramics. After sintering at 1020°C for 5 h, excellent microwave dielectric properties with εr = 7.44, Q×f = 57,400 GHz, and τf = − 0.2 ppm/°C were realized in the SrZn0.8Mg0.2Si3O8+8 wt %TiO2 system.

The structural characteristics and microwave dielectric properties of (Mg0.5Ti0.5)3+ substituted Sr0.6Ca0.4LaAlO4 ceramics

Achieving both high Qf and near-zero τf values for microwave dielectric ceramics in the microwave frequency band is challenging. In this work, the effect of (Mg0.5Ti0.5)3+ substitution on the structural characteristics and microwave dielectric properties of Sr0.6Ca0.4LaAlO4 ceramics was systematically investigated. The Sr0.6Ca0.4LaAl1-x(Mg0.5Ti0.5)xO4 (x = 0–0.5) ceramics were successfully synthesized. The average bond length of Sr/Ca/La–O for Sr0.6Ca0.4LaAl1-x(Mg0.5Ti0.5)xO4 ceramics is related to the dielectric constant (εr). The relative density of the ceramics and FWHM of the Raman peak have strong effects on the Qf values. There is a dependence of the [AlO6] octahedral distortion on the τf values, which provides new possibilities for tuning the temperature coefficient of the K2NiF4-type ceramics. When x is 0.4, the excellent microwave dielectric properties are obtained as following: εr = 20.52, Qf = 103,600 GHz (at 7.79 GHz), and τf = −3.77 ppm/°C. The above work provides a deeper insight into the relationship between the crystal structure characteristics and the microwave dielectric properties of the K2NiF4-type ceramics.