Li3Mg2NbO6 Ceramics Research Articles

Effects of F− substitution on crystal structure, band characteristics and microwave dielectric properties of Li3Mg2NbO6 ceramics for high frequency applications

The structure–performance mechanism is essential to achieve comprehensive characteristics for advanced communication system. In the present work, F− ions were adopted to fabricated Li3Mg2NbO6-x/2Fx ceramics at a nitrogen atmosphere to modify dielectric characteristics. Correlation between bond characteristics, crystal structure and enhanced microwave dielectric characteristics was investigated through vibration analysis, P–V-L theory, Rietveld refinement, and First-principle calculations. Raman analysis and Rietveld refinement show that F− substitution led to a single phase. First-principle calculations indicates a high energy gap of 3.676 eV and p orbit contributed to Fermi energy. F− substitution led to the increase of Nb O bond ionicity and lattice energy, accounting for the variation in Q×f value and dielectric constant. The τf value was related to the expansion coefficient of the Li–O bond. Remarkably, the samples (x = 0.08) exhibited comprehensive dielectric characteristics with εr = 15.9, Q×f = 143,000 GHz and near-zero τf = −2.1 ppm/°C, proving an effective strategy for collaborative regulation. Based on structure simulation, 5G filter with ultra-low loss and high-suppression was designed through introducing transmission zeros from cross coupling. More specifically, a dielectric filter exhibited an interpolation loss of 0.2 dB at 3.3–3.6 GHz and high attenuations of 15 dB for 20 MHz outside the passband, verifying the feasibility for 5G applications.

Raman vibration, bond chemistry and enhanced microwave dielectric properties of Li3Mg2NbO6 ceramics under an oxygen atmosphere

An effective synthesis provides a significant influence on microwave dielectric ceramics for commercial production. In this work, single-phase Li3Mg2NbO6 ceramics were synthesized under an oxygen atmosphere to depress oxygen vacancies. Raman vibration, bond characteristics and crystal structure were analyzed to calculate the inherent features of the Li3Mg2NbO6 ceramics. The Raman spectra and group theory indicated that the mode at 772 cm−1 reflected the symmetric vibrations of Nb–O bonds in NbO6 octahedra and dominated the Raman vibrations. XRD patterns and Rietveld refinement indicated an orthorhombic rock-salt phase under an oxygen assisted sintering process. Well-distributed and homogeneous microstructures were obtained through SEM and grain distribution. From the chemical theory calculation, Nb–O bonds dominated the dielectric properties in consideration of their largest bond ionicity, lattice energy, and bond energy. The Li3Mg2NbO6 ceramics sintered at 1100 °C with an oxygen atmosphere exhibited remarkable performance: εr = 15.3, Q × f = 109,600 GHz and τf = −17.3 ppm/°C, providing enormous potential for communication applications.

B/C site modified Li3Mg2NbO6 dielectric properties for microwave application

The modified Li3+xMg2-xZnxNb1-xTixO6 ceramics were fabricated through a conventional solid-state reaction method. The charge compensation of Zn2+ ions substitution into Mg2+ site and Ti4+ ions substitution into Nb5+ site of Li3Mg2NbO6 ceramics were performed by introducing lithium ions. XRD patterns analysis and Rietveld refinements verified that Li3+xMg2-xZnxNb1-xTixO6 ceramics displayed an orthorhombic structure accompany with a little of impure phase. B/C site modification improved dielectric properties. An optimal dielectric properties of εr = 16.3, Q×f = 93,100 GHz, and τf = −34.1 ppm/°C were acquired for Li3.04Mg1.96Zn0.04Nb0.96Ti0.04O6 ceramics, which heralds their microwave application potential.

Microwave dielectric properties of Li3Mg2NbO6-based ceramics with (MxW1-x)5+ (M = Li+, Mg2+, Al3+, Ti4+) substitutions at Nb5+ sites

Li3Mg2Nb0.96 (MxW1-x)0.04O6 (M = Li+, Mg2+, Al3+, Ti4+) ceramics were prepared by the solid-state reaction method. The sintering characteristics, microstructure, phase composition and microwave dielectric properties of Li3Mg2NbO6 ceramics with equivalent substitution ((Li1/5W4/5)5+, (Mg1/4W3/4)5+, (Al1/3W2/3)5+ and (Ti1/2W1/2)5+) at the Nb-site were investigated firstly. After sintering at 1150 °C for 4 h, all samples were single-phase of orthogonal structure. Due to the difference in ion polarizability of the substituted ions, the dielectric constant changed. The substitution of (MxW1-x)5+ in Li3Mg2Nb0.96 (MxW1-x)0.04O6 ceramics significantly reduced dielectric loss. The quality factor showed a similar trend with the average bond valence. Moreover, the study found that the substitution of W-based composite ions has a small effect on the τf values of Li3Mg2NbO6 ceramics.

Influence of Li2O–MgO–ZnO–B2O3–SiO2 glass doping on the microwave dielectric properties and sintering temperature of Li3Mg2NbO6 ceramics

Li3Mg2NbO6 + x wt% Li2O–MgO–ZnO–B2O3–SiO2 (LMZBS, x = 2, 4, 6, 8, 10) microwave dielectric ceramics with the rock-salt structure were primarily investigated by the traditional solid-state method. The microstructures, microwave dielectric properties, and sintering characteristics were studied systematically according to the doping concentration and sintering temperature. It could be seen that the LMZBS glass effectively lower the sintering temperature of Li3Mg2NbO6 ceramics from 1250 to 925 °C with microwave dielectric properties changing as a function of the amounts of the LMZBS glass. The experimental results showed that 4 wt% LMZBS glass enabled Li3Mg2NbO6 ceramics sintered at 925 °C for 4 h to have excellent microwave dielectric properties: er = 16.02, Q × f = 56,455 GHz, τf = − 18.81 ppm/°C. Therefore, Li3Mg2NbO6 ceramics doped with LMZBS glass meet the requirements of low-temperature co-fired ceramics.

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

Li3Mg2(Nb1-xWx)O6+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(Nb1-xWx)O6+x/2 ceramics. The relationship between the crystal structure and dielectric properties of Li3Mg2(Nb1-xWx)O6+x/2 ceramics was researched through polarizability, average bond valence, and bond energy. The substitution of W6+ for Nb5+ in Li3Mg2(Nb1-xWx)O6+x/2 ceramics significantly promoted the Q × f values. In addition, the increase of W6+ content improved the thermal stability of the Li3Mg2(Nb1-xWx)O6+x/2 ceramics. The Li3Mg2(Nb0.94W0.06)O6.03 ceramics sintered at 1175 °C for 6h possessed excellent properties: εr ~ 15.82, Q × f ~ 124,187 GHz, τf ~ −18.28 ppm/°C.

Low-loss and temperature-stable (1−x)Li2TiO3–xLi3Mg2NbO6 microwave dielectric ceramics

Low-loss (1−x)Li2TiO3–xLi3Mg2NbO6 (LT-LMN, 0.02 ≤ x ≤ 0.08) microwave dielectric ceramics (MDCs) with rock salt structures were fabricated via a traditional solid-state reaction route. Li3Mg2NbO6 was used as a Li2TiO3 compensator to improve temperature stability. Scanning electron microscope observations and X-ray diffraction analyses were used to investigate the microstructures and crystalline structures of the ceramics, respectively. We demonstrated a correlation between macroscopic “dark hole” phenomena and the microwave dielectric properties (MDPs) of LT-LMN ceramics by analysing the valence states of Ti ions and the content of oxygen vacancies using X-ray photoelectron spectra. We continuously added Li3Mg2NbO6 to pure Li2TiO3 to form MDCs, and found that at x = 0.04, (1−x)Li2TiO3–xLi3Mg2NbO6 ceramics achieved a near-zero resonance-frequency temperature coefficient (τf). 0.96Li2TiO3–0.04Li3Mg2NbO6 ceramics sintered at 1250 °C had excellent MDP values: appropriate permittivity (ϵr) = 19.12, high quality factors (Q × ƒ) = 70814 GHz (at 6.105 GHz), and τf = 2.6 ppm/°C. This indicates that LT-LMN ceramics are promising materials for high-selectivity microwave ceramic dielectric substrates.

Crystal structures and high microwave dielectric properties in Li+/Ti4+ ions co-doped Li3Mg2NbO6 ceramics

A series of novel Li3+xMg2Nb1-xTixO6 (0.02 ≤ x ≤ 0.08) ceramics with excellent microwave dielectric properties and relatively low sintering temperatures were synthesized via the solid-phase method. The correlations between sintering characteristics and microwave dielectric properties of the novel system were analyzed in detail. By (Li+/Ti4+) ions co-doped Li3Mg2NbO6 ceramics, all compounds possessed a single phase with orthorhombic structure, pertaining to the space group Fddd (70). The change regulation of dielectric constant and Q*f values was similar to density, which ascended to the maximum value first and then declined as the sintering temperature increased. Furthermore, the τf values constantly shifted to 0 ppm/°C with the content of complex ions (Li+/Ti4+) increasing. The best properties of Li3.06Mg2Nb0.94Ti0.06O6 ceramics sintered at 1025 °C were εr = 14.34, Q*f = 154,113 GHz, and τf = −2.17 ppm/°C.

Effects of Li2O–B2O3–SiO2–CaO–Al2O3 glass addition on the sintering behavior and microwave dielectric properties of Li3Mg2NbO6 ceramics

Li3Mg2NbO6 ceramics modified with Li2O–B2O3–SiO2–CaO–Al2O3 (LBSCA) glass additives were densified below 950 °C via a solid-state route. Single orthorhombic phase and dense morphology were obtained with the LBSCA glass introduction. Promising microwave dielectric properties, especially with an improved Q × f value, were obtained in the Li3Mg2NbO6 ceramics with 0.5 wt% of the LBSCA glass addition sintered at 925 °C for 4 h: er = 15.16, Q × f = 90,557 GHz, τf = − 16.22 ppm/°C. It is suggested that the microwave dielectric performance was highly related to the densification, the polarizability, and the effects of the packing fraction. All experimental facts indicate that the LBSCA modified Li3Mg2NbO6 ceramics are potential candidates for Low-Temperature Co-fired Ceramic (LTCC) applications.

Synthesis, crystal structure and low loss of Li3Mg2NbO6 ceramics by reaction sintering process

Abstract An investigation into an effective and simple process for the production of a low-cost material with high production efficiency has resulted in a significant impact on commercial production. In the present work, we synthesized the low loss Li 3 Mg 2 NbO 6 ceramic using an effective and simple reaction sintering process. A single orthorhombic phase was corroborated by XRD and Rietveld refinement. The packing fraction and Nb-O bond valence were determined according to the Rietveld refinement results to explore the relationship between the structure and microwave dielectric performance. The Raman analysis indicated that the shift of the band near 772 cm -1 assigned to the Mg-O bond vibration was consistent with the diversification of the cell volume. Furthermore, dense and homogeneous microstructures with large grain sizes (∼130 μm) were obtained when sintered at 1350 °C. The relative density exerted an influence on the dielectric constant, while the packing fraction and grain size influenced the Q × f value of the Li 3 Mg 2 NbO 6 ceramics. Moreover, the Nb-O bond valence dominated the τ f value of the Li 3 Mg 2 NbO 6 ceramics. Excellent microwave dielectric characteristics for the samples sintered at 1350 °C: e r = 14.5, Q × f = 116,000 (9.76 GHz) GHz and τ f = −24.5 ppm/°C were achieved by the reaction sintering process, exhibiting a potential for industrial production.

Low loss and low temperature sintering of Li3Mg2NbO6 ceramics for LTCC applications

We fabricated the low loss Li3Mg2NbO6-xV2O5 (x = 0.25–1.25 wt%)ceramics by the solid-state reaction procedure and discussed the impacts of V2O5 addition on the phase structure, sintering characteristics, microstructure, grain growth, grain size and microwave dielectric characterizations of Li3Mg2NbO6-xV2O5 ceramics. Single-phase Li3Mg2NbO6 orthorhombic structure was obtained for all compositions and substitution of V5+ ions for Nb5+ ions occurred. Homogeneous and dense microstructures with grain size of ∼11.2 μm could be observed when sintered at 925 °C, indicating that suitable V2O5 addition content promoted the grain growth. The relative permittivity was associated with the relative density and the Q × f value was correlated to the grain size and relative density. The τf value was relevant to the porosity corrected relative permittivity. Remarkable microwave dielectric properties: εr = 15.1, Q × f = 91,000 GHz (9.76 GHz) and τf = −24 ppm °C−1 were acquired for the samples with x = 1 wt%, indicating a potential for LTCC applications.

Correlation between crystal structure and modified microwave dielectric characteristics of Cu2+ substituted Li3Mg2NbO6 ceramics

Structural characteristics exert significant influences on microwave dielectric properties, and ion substitution is widely adopted to modify material performances by adjusting the crystal structure. In this work, low loss Li3Mg2-xCuxNbO6 (x = 0–0.04) ceramics were prepared by Cu2+ substitution. The impacts of Cu2+ substitution for Mg2+ sites on the microwave dielectric characteristics and crystal structure were discussed in detail. Rietveld refinement results implied that a single Li3Mg2NbO6 phase was formed. Additionally, a dense and homogeneous microstructure with grain sizes of 7–9 μm could be achieved, and moderate Cu2+ substitution could significantly promote the grain growth. The correlation between microwave dielectric characteristics and crystal structure was discussed by calculating some structural parameters. The εr was determined by the polarizability. The Q × f was influenced by the packing fraction. The τf value was dependent on the NbO6 octahedron distortion, and the τf value could be adjusted to near zero for x = 0.02. Typically, the Li3Mg2-xCuxNbO6 (x = 0.02) composition exhibited remarkable microwave dielectric performances: εr = 15.75, Q × f = 92,134 GHz (9.86 GHz) and τf = −2 ppm/°C, making it a promising candidate for temperature-stable millimeter-wave applications.

Ultralow loss and temperature stability of Li3Mg2NbO6-xLiF ceramics with low sintering temperature

Novel temperature stable Li3Mg2NbO6-xLiF (x = 0.5–8 wt %) ceramics with ultralow loss were fabricated by the solid-state reaction process. The influence of LiF addition on the sintering, grain growth and morphology, and improved microwave dielectric characteristics was investigated. A single orthorhombic Li3Mg2NbO6 structure could be confirmed by Raman spectra and XRD patterns. Dense and homogeneous microstructure could be obtained with ∼10 μm average grain size. Results demonstrated that the εr values were relevant to bulk density and the high Q×f values were influenced by the large grain sizes. The τf values depend on porosity corrected dielectric constant. Notably, the remarkably desirable microwave dielectric characteristics: εr = 15.4, Q×f = 100,000 GHz, τf = −3.1 ppm/°C were achieved for the Li3Mg2NbO6 ceramics with x = 6 wt% sintered at 925 °C, which could be applied for ultra-low loss LTCC applications.

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

Novel low-temperature fired Li3Mg2Nb1-xVxO6 (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 ɛr 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 τf values was attributed to NbO6 octahedron distortion. Notably, the Li3Mg2Nb1-xVxO6 (x = 0.02) ceramics sintered at 900 °C had outstanding microwave dielectric properties: εr= 16, Q×f= 131,000 GHz (9.63 GHz), and τf= − 26 ppm/°C, making these ceramics promising ultralow loss candidates for low temperature co-fired ceramics (LTCC) applications.

Low temperature sintering and microwave dielectric properties of Li3Mg2NbO6 ceramics

The Li3Mg2NbO6 (LMN) ceramics were synthesized through the traditional solid-state process. The sintering characteristics, microwave dielectric properties and the morphology of LMN ceramics with various BaCu(B2O5) (BCB) addition were investigated. No secondary phase was found in the BCB added ceramics. Low-level doping of BCB (≤ 2 wt%) could significantly improve the densification of LMN ceramics due to the liquid phase sintering mechanism. The dielectric constant and the quality factor value had the same variation trend with bulk density. The temperature coefficient of resonant frequency (τf) value presented descending tendency as the BCB content increased. Besides, the X-ray diffraction result and the back scattered electron image of the sample confirmed the chemical compatibility silver electrodes. The optimum microwave dielectric of er = 14.27, Q × f = 55521 GHz and τf = − 18.2 ppm/°C was obtained, when the LMN ceramics with 0.1 wt% BCB sintered at 950 °C for 4 h, which could be a promising candidate material for low temperature co-fired ceramics applications.

Nanopowders preparation and dielectric properties of low-fired Li3Mg2NbO6 ceramics

The pure phase of Li3Mg2NbO6 powders was fabricated with an average grain size of 222 nm at 800 °C derived from high energy ball-milling method. By using the nanopowders as a precursor, well-densified Li3Mg2NbO6 ceramics were obtained with a relative density of 95.9% at 950 °C, which is 300 °C lower than that required by the conventional ball-milling method. Low-fired Li3Mg2NbO6 ceramics exhibited good microwave dielectric properties of er = 18.0, Q × f = 51,870 GHz, τf = − 23.01 ppm/°C, which suggests the developed materials are suitable for low-temperature co-fired ceramic applications.

A novel temperature stable and high Q microwave dielectric ceramic in Li3(Mg1−xMnx)2NbO6 system

The compositions of Li3(Mg1−xMnx)2NbO6 ceramics were prepared by the conventional solid state reaction method. The effects of Mn2+ substitution on the microstructure, sintering behavior and microwave dielectric properties of Li3(Mg1−xMnx)2NbO6 ceramics were investigated systematically. The XRD patterns revealed that all the specimens sintered at 1075–1200 °C remained a single phase with orthorhombic structure. The obtained microwave dielectric properties indicated that appropriate amount of Mn2+ substitution for Mg2+ could significantly promote the grain growth and densify Li3Mg2NbO6 ceramics. The permittivity and Q × f values were strongly dependent on the bulk density and grain size, respectively. And near zero τ f values could be realized in the Li3(Mg1−xMnx)2NbO6 (0.02 ≦ x ≦ 0.08) compounds sintered at 1125 °C. To sum up, the x = 0.02 sample sintered at 1125 °C for 4 h exhibited excellent microwave dielectric properties of er ~ 15.22, Q × f ~110,582 GHz, τ f ~−4.57 ppm/°C which demonstrated that the Li3(Mg0.98Mn0.02)2NbO6 ceramic would be a novel temperature stable and high Q material for microwave device.

Low temperature sintering and microwave dielectric properties of Li3Mg2NbO6 ceramics for LTCC application

The Li3Mg2NbO6 ceramics doped with ZnO-B2O3-SiO2 (ZBS) additives were synthesized via the conventional solid-state reaction process. The influence of ZBS additives on phase composition, sintering behavior, microstructure and microwave dielectric properties of Li3Mg2NbO6 ceramics were investigated in detail. The XRD patterns showed that the sintered specimen presented a single phase and no secondary phase appeared. We found that proper amount of ZBS additives could significantly reduce the sintering temperature from 1250 to 925 °C and promote the densification of Li3Mg2NbO6 ceramics. The er and Q × f value were strongly affected by bulk density and grain size, respectively. As ZBS content increased, the τf value shifted toward negative direction. In summary, excellent microwave dielectric properties of er ~ 14.84, Q × f ~ 73,987 GHz, τf ~ −16.05 ppm/°C could be obtained in 0.5 wt.% ZBS modified sample when sintered at 925 °C for 4 h. Furthermore, the material was compatible with Ag electrode, demonstrating that it would be a promising candidate material for LTCC application.

Effects of B2O3 addition on the sintering behavior and microwave dielectric properties of Li3Mg2NbO6 ceramics

Li3Mg2NbO6 + x wt% B2O3 compounds were prepared through conventional solid-state reaction route. The effect of B2O3 additives on the sintering characteristics, microstructures and microwave dielectric properties of Li3Mg2NbO6 ceramics have been investigated. We found that doping with the B2O3 reduced the sintering temperature and improved the grain growth. The dielectric constant er and the quality factor value Q × f had same variation trend with bulk density. The τf values toward the negative direction with the increasing the amount of B2O3. Typically, excellent microwave dielectric properties with er = 14.0, Q × f = 67,451 GHz, τf = −16.82 ppm/°C were obtained for Li3Mg2NbO6 + 0.1 wt% B2O3 ceramics sintered at 925 °C.

Effects of MBS addition on the low temperature sintering and microwave dielectric properties of Li3Mg2NbO6 ceramics

MBS (0.1–2.0 wt%) composed of MgO–B2O3–SiO2 were added into the Li3Mg2NbO6 ceramics to achieve low temperature sintering. The effects of MBS on the sintering temperature, phase compositions, microstructure and microwave dielectric properties of Li3Mg2NbO6 ceramics were investigated systematically. The XRD results indicated that the sintered sample presented a single-phase without extra secondary phase. The microwave dielectric properties of Li3Mg2NbO6 ceramics were mainly dependent on the MBS additives. In the case of 0.5 wt% MBS additives, Li3Mg2NbO6 ceramics exhibited satisfying microwave dielectric properties with e r = 14.5, Q × f = 80,759 GHz, τ f = −20.7 ppm/°C sintered at 925 °C for 4 h.