A ltcc compatible high-entropy molybdate low-loss microwave dielectric ceramic material, a preparation method and application thereof

Abstract

The present application relates to a kind of LTCC compatible high-entropy molybdate low-loss microwave dielectric ceramic material and its preparation method and application, high-entropy molybdate low-loss microwave dielectric ceramic material provided by the present application is chemical formula for Mg x (NiZnCoMn) (1‑x) / 4 MoO4。The system selects the Mg 2+ 、Zn 2+ 、Co 2+ 、Ni 2+ 、Mn 2+ Five kinds of divalent metal ions with similar ionic radius but slightly different electronegativity, realize high-entropy solid solution in A site with different proportions, effectively control the microstructure and physical properties of the material, realize the synergistic optimization of low ε r, high Q×f and near zero τ f under the sintering temperature lower than 775 ℃, solve the technical problems of high sintering temperature, high loss and poor temperature stability in the prior art, and match with LTCC technology, provide high-performance dielectric materials for LTCC and 5G / 6G radio frequency devices.

Description

Technical Field

[0001] This invention relates to an LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material, its preparation method, and its application, belonging to the field of microwave dielectric ceramic material preparation technology. Background Technology

[0002] With the rapid development of 5G and millimeter-wave communication technologies, radio frequency (RF) front-end devices are placing more stringent requirements on microwave dielectric ceramics, primarily in terms of low loss, high frequency stability, and tunable dielectric constant. In dielectric resonators, filters, and integrated RF modules, materials not only need to have high Q×f values ​​to reduce signal attenuation, but also need to maintain a suitable dielectric constant ε. r To balance device miniaturization and signal transmission speed.

[0003] Low-temperature co-fired ceramic (LTCC) technology, as one of the important packaging technologies for realizing the miniaturization, high integration, and high frequency of electronic components, has shown promising application prospects. This technology typically involves co-firing multilayer ceramic substrates with high-conductivity metal pastes (such as silver or copper) under mild conditions below 900°C, thereby constructing a three-dimensional ceramic module that integrates integrated circuits and passive components.

[0004] While traditional molybdate ceramics possess advantages such as low dielectric constant and sintering temperature, single-component systems struggle to simultaneously achieve high Q×f values, excellent temperature stability, and ultra-low sintering temperatures, limiting their application in low-temperature co-fired ceramics (LTCC). In recent years, researchers have introduced high-entropy design concepts into molybdate systems. By introducing multiple equimolar divalent metal ions to randomly occupy A-sites, they increase configurational entropy, thereby stabilizing the single-phase wolframite structure and optimizing dielectric properties. For example, Li et al. prepared (Sr... 0.2 Ca 0.2 Ba 0.2 Bi 0.2 Na 0.2 MoO4 high-entropy ceramics, after sintering at 1050℃, achieved dielectric properties of εᵣ=10.29 and Q×f=42002 GHz, but their τf value remained at -37.74 ppm / °C. In contrast, the non-high-entropy Na... 0.48 La 0.52 MoO4 ceramics can achieve ε at 920℃ r The excellent performance of high-entropy molybdate ceramics, with a sintering temperature of 8.86 GHz, Q×f = 61378 GHz, and τf = -10.8 ppm / °C, indicates that adjusting the composition can effectively optimize temperature stability. However, existing high-entropy molybdate ceramics still suffer from bottlenecks such as high sintering temperatures (typically >1000°C) and difficulty in achieving τf values ​​close to zero, which cannot yet meet the stringent requirements of 5G / 6G communication for ultra-low loss and high-stability dielectric materials.

[0005] Therefore, existing high-entropy molybdate microwave dielectric ceramics mainly have the following problems:

[0006] 1) The sintering temperature is high, which leads to increased energy consumption and makes it difficult to be compatible with the LTCC process;

[0007] 2) At lower sintering temperatures, the Q×f value is lower and the intrinsic loss is higher, which cannot meet the low attenuation requirements of millimeter waves;

[0008] 3) The absolute value of τf is relatively large, resulting in poor temperature stability and making it difficult to achieve a near-zero temperature coefficient;

[0009] 4) Insufficient control of lattice distortion leads to uneven grain growth and high porosity, affecting density and dielectric properties.

[0010] The main root of these problems is that traditional solid solutions cannot simultaneously take into account configurational entropy, ionic polarizability and lattice rigidity, and existing high-entropy designs have not yet achieved optimal synergistic control of multiple A-site ions in molybdate-based systems.

[0011] In summary, existing high-entropy molybdate ceramics still suffer from high dielectric loss and exhibit poor sintering adaptability and low quality factor, making it difficult to meet the application requirements of high-frequency communication and LTCC scenarios. Therefore, developing novel microwave dielectric ceramic materials that are compatible with LTCC technology and possess low εr, high Q×f, and near-zero τf is a key path to meeting the requirements of 5G / 6G high-frequency communication technologies, and has significant theoretical and engineering application value. Summary of the Invention

[0012] To address the shortcomings of existing technologies, this invention provides an LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material, its preparation method, and its applications.

[0013] The high-entropy molybdate low-loss microwave dielectric ceramic material provided by this invention has the chemical formula Mg. x (NiZnCoMn) (1-x) / 4MoO4. This system selects Mg with similar ionic radii but slightly different electronegativity. 2+ Zn 2+ Co 2+ Ni 2+ Mn 2+ Five divalent metal ions are used to achieve high-entropy solid solution at the A site in different proportions, which effectively controls the microstructure and physical properties of the material. The synergistic optimization of low εr, high Q×f and near-zero τf is achieved at a sintering temperature below 775℃, which solves the technical problems of high sintering temperature, high loss and poor temperature stability in the existing technology. It is also compatible with LTCC technology and provides high-performance dielectric materials for LTCC and 5G / 6G RF devices.

[0014] This invention is achieved through the following technical solution:

[0015] An LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material, the general chemical formula of which is Mg x (NiZnCoMn) (1-x) / 4 MoO4, where 0.1≤x≤1.

[0016] According to a preferred embodiment of the present invention, x = 0.2-0.8.

[0017] The optimal value is x=0.6.

[0018] According to a preferred embodiment of the present invention, the dielectric constant ε of the LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material is... r Within the range of 7.0 to 8.0, with a quality factor Q×f value of 30,000 to 50,000 GHz, τ f The value is -27 to -10 ppm / ℃.

[0019] According to a preferred embodiment of the present invention, the LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material is selected from one of the following:

[0020] Mg 0.2 (NiZnCoMn) 0.2 MoO4, Mg 0.4 (NiZnCoMn) 0.15 MoO4, Mg 0.6 (NiZnCMn) 0.1 MoO4, Mg 0.8 (NiZnCoMn) 0.05 MoO4.

[0021] The second aspect of this invention provides a method for preparing the above-mentioned LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material.

[0022] The preparation method of the above-mentioned LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material is characterized by the following steps:

[0023] 1) Using MgO, NiO, ZnO, CoO, MnO, and MoO3 as raw materials, according to the chemical formula Mg x (NiZnCoMn) (1-x) / 4 Weigh each raw material according to the stoichiometric ratio of MoO4, then mix the mixed raw materials with ZrO2 grinding balls and anhydrous ethanol, place them in a ball mill jar for ball milling, dry, pulverize, and sieve to obtain the mixture;

[0024] 2) The mixture is mixed with binder until homogeneous, then pressed into shape to obtain a green body;

[0025] 3) The green body is first debinded, and then heated for sintering to obtain LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material.

[0026] According to a preferred embodiment of the present invention, in step 1), Mg x (NiZnCoMn) (1-x) / 4 MoO4, x=0.2-0.8, with x=0.6 being the most preferred, where x represents the molar ratio.

[0027] According to a preferred embodiment of the present invention, in step 1), the mass ratio of the mixed raw materials, ZrO2 grinding balls and anhydrous ethanol is 1:(2-5):(1-3).

[0028] According to a preferred embodiment of the present invention, in step 1), ball milling is performed at a rotation speed of 300-500 r / min for 4-8 hours.

[0029] According to a preferred embodiment of the present invention, in step 1), the ball-milled slurry is transferred to an evaporation vessel and dried to constant weight in an electric heating forced-air drying oven at 60°C.

[0030] According to a preferred embodiment of the present invention, in step 1), the dried powder is ground through an 80-mesh sieve.

[0031] According to a preferred embodiment of the present invention, in step 2), the binder is a 4-8 wt.% aqueous solution of polyvinyl alcohol (PVA), and the amount of binder used is 6-12 wt% of the weight of the mixture.

[0032] According to a preferred embodiment of the present invention, in step 2), the obtained green blank is a cylindrical blank with a diameter of 10-15 mm and a height of 4-7 mm.

[0033] According to a preferred embodiment of the present invention, in step 3), the glue removal is performed by holding the product at 550°C for 3 hours.

[0034] According to a preferred embodiment of the present invention, in step 3), sintering is performed by holding at 675~775°C for 4-8 hours.

[0035] According to a preferred embodiment of the present invention, in step 3), the heating rate is 2-4 °C / min.

[0036] This invention achieves ε by controlling the Mg content (x = 0.2~0.8). r In the range of 7.0 to 8.0, Q×f value is greater than 30000 GHz, τ f Excellent performance in the range of -27 to -10 ppm / ℃ (optimal at x=0.6).

[0037] LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic materials are used in resonators, filters, and antennas in 5G / 6G communications, satellite internet, and millimeter-wave radar systems.

[0038] The high-entropy molybdate microwave dielectric ceramic material of the present invention has the following advantages:

[0039] 1. The sintering temperature is significantly reduced (675~775℃), which is 150~200℃ lower than that of traditional molybdate ceramics, resulting in significant energy savings and compatibility with LTCC process (co-firing temperature <900℃).

[0040] 2. Excellent dielectric properties: ε r In the range of 7.0 to 8.0, Q×f values ​​are greater than 30,000 GHz (typical values ​​reach 35,000 to 40,000 GHz), τ f The value is in the range of -27 to -10 ppm / ℃, achieving synergistic optimization of low dielectric constant, quality factor and near-zero temperature coefficient;

[0041] 3. Through the Mg-Ni-Zn-Co-Mn pentagonal A-site variable molar high-entropy design, the configuration entropy is significantly improved, effectively suppressing abnormal grain growth and elemental segregation (e.g., SEM shows uniform grain size of 2~5 μm), and enhancing lattice stiffness (Raman Ag). (4) Peak blue shift 5~10 cm -1 (This reduces the half-width at half-maximum and thermal stability.)

[0042] 4. The preparation process adopts the conventional solid-state method (ball milling-pre-firing-forming-air atmosphere sintering), which does not require special atmosphere or precious metal additives, has low raw material cost (MoO3 as the main component), good process repeatability, and is suitable for large-scale industrial production.

[0043] 5. For the first time, the Mg-Ni-Zn-Co-Mn pentagonal high-entropy design system was applied to monoclinic wolframite MoO4-based microwave dielectric ceramic materials, realizing variable-proportional random occupancy of A sites;

[0044] 6. Achieve optimal overall performance with low dielectric constant, quality factor and near-zero temperature coefficient at a low sintering temperature of 675~775℃.

[0045] 7. Through Raman Ag (4) Peak blue shift and FWHM minimization reveal the high-entropy-induced lattice stiffness enhancement and anharmonic scattering suppression mechanism. Attached Figure Description

[0046] Figure 1 Mg prepared in Examples 1-4 x (NiZnCoMn) (1-x) / 4XRD pattern of MoO4 ceramics;

[0047] Figure 2 Mg prepared in Examples 1-4 x (NiZnCoMn) (1-x) / 4 Variations in the unit cell parameters of MoO4 ceramics;

[0048] Figure 3 Mg prepared in Examples 1-4 x (NiZnCoMn) (1-x) / 4 SEM images and particle size analysis of MoO4 ceramics;

[0049] Figure 4 Mg plotted for VESTA x (NiZnCoMn) (1-x) / 4 Model diagram of MoO4 ceramic crystal structure;

[0050] Figure 5 For different Mg contents Mg x (NiZnCoMn) (1-x) / 4 ε of MoO4 r The variation of Q×f and relative density with sintering temperature;

[0051] Figure 6 Examples 1-4 show different Mg contents. x (NiZnCoMn) (1-x) / 4 τ of MoO4 f The variation pattern with composition;

[0052] Figure 7 Mg prepared in Examples 1-4 x (NiZnCoMn) (1-x) / 4 Raman spectra of MoO4 ceramics;

[0053] Figure 8 Mg prepared in Example 1 0.6 (NiZnCMn) 0.1 Raman fitting curve of MoO4 ceramic (x=0.6).

[0054] Figure 9 Mg prepared in Examples 1-4 x (NiZnCoMn) (1-x) / 4 Diothermal and loss temperature spectra of MoO4 ceramics at different frequencies;

[0055] Figure 10 Mg x (NiZnCoMn) (1-x) / 4XPS spectra of MoO4 ceramics: (a) Full spectrum scan of each component; (b) Mo 3d high-resolution energy spectrum at x=0.6; (cf) O 1s high-resolution energy spectrum of samples at x=0.2, 0.4, 0.6, and 0.8 respectively. Detailed Implementation

[0056] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0057] All raw materials used in the examples are conventional raw materials and commercially available products.

[0058] Example 1

[0059] The preparation method of LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material includes the following steps:

[0060] (1) Raw material preparation

[0061] According to the chemical formula Mg 0.6 (NiZnCMn) 0.1 The stoichiometric ratio of MoO4 is obtained by taking high-purity MgO, NiO, ZnO, CoO, MnO and MoO3 raw materials (all with a purity ≥ 99.9%).

[0062] (2) Ball milling mixing

[0063] The weighed raw materials were placed in a ball mill jar, and ZrO2 grinding balls and anhydrous ethanol were added as the ball milling media. The raw materials, ZrO2 grinding balls and ethanol were mixed at a mass ratio of 1:3:1.2. The mixture was then subjected to planetary ball milling at a speed of 400 r / min for 6 h to ensure that the raw materials were fully mixed and uniform and to reduce the particle size.

[0064] (3) Drying and granulation

[0065] The ball-milled slurry was transferred to an evaporation container and dried to constant weight in a 60°C electric hot air drying oven. The dried powder was then ground through an 80-mesh sieve, and 5 wt.% polyvinyl alcohol (PVA) aqueous solution was added as a binder. After thorough stirring and granulation, the granules were sieved again for later use.

[0066] (4) Press molding

[0067] The granulated powder is loaded into a metal mold and pressed into a circular blank with a diameter of 10 mm and a thickness of about 5 mm under a pressure of 10 MPa.

[0068] (5) Sintering

[0069] The pressed green body was placed in an alumina crucible and placed in a high-temperature furnace under an air atmosphere. It was heated to 725°C at a heating rate of 3°C / min and held at that temperature for 5 hours. Then it was naturally cooled to room temperature with the furnace to obtain a high-entropy molybdate microwave dielectric ceramic material sample.

[0070] Example 2

[0071] The preparation method is the same as that described in Example 1, except that:

[0072] In step 1), according to the chemical formula Mg 0.2 (NiZnCoMn) 0.2 The stoichiometric ratio of MoO4 was calculated to determine the proportions of each raw material, and the corresponding masses were weighed. Other procedures were carried out according to Example 1.

[0073] Example 3

[0074] The preparation method is the same as that described in Example 1, except that:

[0075] In step 1), according to the chemical formula Mg 0.4 (NiZnCoMn) 0.15 The stoichiometric ratio of MoO4 was calculated to determine the proportions of each raw material, and the corresponding masses were weighed. Other procedures were carried out according to Example 1.

[0076] Example 4

[0077] The preparation method is the same as that described in Example 1, except that:

[0078] In step 1), according to the chemical formula Mg 0.8 (NiZnCoMn) 0.05 The stoichiometric ratio of MoO4 was calculated to determine the proportions of each raw material, and the corresponding masses were weighed. Other procedures were carried out according to Example 1.

[0079] Experimental Example

[0080] Phase analysis: The sintered samples were identified using X-ray diffractometer (Rigaku MiniFlex 600, Cu target, λ=1.5406 Å), with a scanning range of 10°~80° and a step size of 0.02°. The samples were confirmed to have a monoclinic wolframite structure with no obvious second phase.

[0081] Microscopic morphology observation: Scanning electron microscopy was used to observe the cross-sectional morphology of the sample and analyze the grain size distribution and porosity.

[0082] Raman spectroscopy analysis: Room temperature Raman spectra of the samples were measured using a Raman spectrometer, with a focus on the 350–370 cm⁻¹ region. -1 Nearby Ag (4) The shift and full width at half maximum (FWHM) of characteristic peaks are used to assess lattice order and distortion.

[0083] Dielectric property testing: The dielectric constant ε of the sample was tested in the microwave band using a vector network analyzer combined with the resonant cavity method. r Quality factor Q×f and temperature coefficient of resonant frequency τ f .

[0084] Experimental Example 1:

[0085] The XRD patterns of the high-entropy molybdate low-loss microwave dielectric ceramic materials prepared in Examples 1-4 are shown below. Figure 1 All samples were prepared by sintering at 725℃. Diffraction analysis showed that all samples synthesized a monoclinic wolframite structure, and the characteristic peak positions were in good agreement with the standard card PDF#97-002-0418. No obvious second-phase impurities were found.

[0086] The diffraction peak shifts with x: when x = 0.2 → 0.4, the (220) peak shifts to a lower angle, indicating lattice expansion; when x = 0.4 → 0.8, it shifts to a higher angle, indicating lattice contraction. This is related to the difference in ionic radii. Due to Mg 2+ The lattice size (0.72 Å) is smaller than the average radius of the doped transition metal (~0.75 Å), and the lattice tends to become denser with increasing Mg content. The diffraction peak intensity decreases at x=0.8, which is due to lattice distortion and a decrease in long-range order caused by high entropy. The composition-dependent lattice evolution demonstrates the fine control of the monoclinic structure by high entropy. The disordered distribution of multi-component cations, while increasing configurational entropy and suppressing phase separation, introduces local strain, providing a structural basis for controlling material polarization and microwave loss.

[0087] Figure 2 Showing Mg x (NiZnCoMn) (1-x) / 4 The cell parameters of MoO4 ceramics changed. XRD analysis showed that with increasing Mg content, the main diffraction peaks shifted towards higher angles, corresponding to a gradual decrease in interplanar spacing. Rietveld refinement results further confirmed that lattice parameters a, b, c, and cell volume V all decreased linearly with increasing Mg content, reaching a minimum at x=0.8. This lattice shrinkage effect mainly stems from the radius difference of the substituted ions. The average radius (approximately 0.75 Å) of the substituted transition metal ions (Ni, Zn, Co, Mn) is greater than that of Mg. 2+ (0.72Å), with the small radius Mg 2+ As the content increases, the crystal lattice structure becomes more compact, leading to overall cell shrinkage. This variation, consistent with Vegard's law, indicates that Mg... 2+The Mg element successfully dissolved into the crystal lattice and replaced some transition metal sites. The diffraction peak intensity decreased at x=0.8, mainly due to the significantly lower atomic scattering factor of Mg compared to the replaced transition metal, rather than a decrease in lattice order. Refinement results showed that axes a, b, and c all decreased synchronously, reflecting the overall shrinkage of the monoclinic structure. Simultaneously, the low refinement residuals indicated a high degree of agreement between the experimental data and the computational model; regardless of compositional variations, the sample consistently maintained good crystallinity and long-range lattice order. These refinement analyses, at the atomic scale, verified the regulatory mechanism of Mg content variation on lattice structure.

[0088] from Figure 3 It can be seen that with the increase of Mg content, the average particle size of the ceramic gradually decreases from 4.95 μm at x=0.2 to 4.29 μm at x=0.6. This grain refinement phenomenon is mainly attributed to the solute dragging effect and the increase of diffusion resistance in the multi-component solid solution, which effectively inhibits grain boundary migration and thus limits excessive grain growth.

[0089] Figure 4 For drawing Mg x (NiZnCoMn) (1-x) / 4 A crystal structure model of MoO4 ceramics. This system maintains a monoclinic structure of the α-MgMoO4 type with space group C2 / m. Within the crystal framework, Mo... 6+ With four O 2- They combine to form isolated MoO4 tetrahedral units, while divalent cations (Mg) 2+ Ni 2+ Zn 2+ Co 2+ Mn 2+ Occupying the center of the oxygen octahedron, it forms a six-coordinate MO6 octahedron. These polyhedra are interconnected through shared vertices, forming a three-dimensional spatial framework.

[0090] In this multi-component system, cations of different radii are randomly distributed at the same lattice sites, and this compositional disorder inevitably leads to local lattice distortion. The microstructural distortion and the synergistic effect of multiple cations are key factors in regulating the microwave dielectric properties of this system. Specifically, the polyhedral twisting caused by lattice distortion alters the effective bonding strength of the Mo-O bonds, thereby regulating the anharmonic phonon scattering of the system and significantly affecting the quality factor. Furthermore, the random distribution of A-site cations effectively changes the intrinsic polarization response of the system in the microwave band. These microstructural features constitute the physical basis for achieving synergistic optimization of low dielectric constant (εr) and high quality factor (Q×f) in this ceramic.

[0091] Figure 5The density variation, Q×f value variation trend, and dielectric constant εr variation with sintering temperature of ceramics with different Mg contents were compared.

[0092] The density changes show that the sample density gradually decreases with increasing x value. This is mainly due to the combined effects of the relatively light atomic weight of Mg and the decreased sintering activity of the system caused by high Mg content. All samples reached their peak density at 725 °C, confirming that this temperature is the optimal densification temperature for the system.

[0093] The trend of Q×f values ​​shows that before 725 °C, thanks to the increased densification of the ceramic and the optimization of its microstructure, the Q×f value increases with increasing temperature. When x=0.6 and the sintering temperature is 725 °C, Q×f reaches its maximum value (35,080 GHz). At this point, the lattice distortion within the ceramic is effectively balanced, and intrinsic losses are minimized. However, above 725 °C, excessively high sintering energy induces abnormal grain growth and increased porosity, leading to a significant increase in extrinsic losses due to interface defects, resulting in a marked decrease in the Q×f value.

[0094] The results of the dielectric constant εr variation with sintering temperature show that, at all temperatures, εr gradually decreases with increasing Mg content. This is mainly attributed to the substitution of transition metal ions by the lighter element Mg, which has lower polarizability, thus weakening the overall polarizability of the system. Furthermore, all components reach a minimum εr value at 725 °C (especially at x=0.6, εr=7.12). This is primarily because the lattice contraction effect is most significant at this temperature, enhancing the confinement of ion displacement; subsequent lattice thermal expansion caused by further heating weakens this confinement effect, allowing ion polarization to partially recover, thus slightly increasing εr.

[0095] Based on the above analysis, 725 ℃ is the key equilibrium point for controlling the performance of this system. Experimental results confirm that the x=0.6 composition exhibits the most ideal microstructure and the best overall microwave dielectric properties when sintered at 725 ℃.

[0096] Figure 6 The variation of τf in ceramics with Mg content (x) is shown. As x increases from 0.2 to 0.8, τf first increases and then decreases, reaching its optimal state (-19.5 ppm / ℃) closest to zero at x=0.6.

[0097] The temperature coefficient of thermal expansion (τf) of ceramics is jointly regulated by the lattice thermal expansion coefficient (αL) and the temperature coefficient of dielectric constant (τε), and the relationship is as follows: In this context, a positive αL represents the frequency shift caused by lattice thermal expansion, and τε reflects the trend of dielectric constant change with temperature.

[0098] With changes in Mg content, the internal distortion and bond strength of the monoclinic lattice change, leading to alterations in αL and τε. At x=0.6, the frequency drift caused by thermal expansion and the temperature change in dielectric constant reach optimal compensation, canceling each other out and causing τf to significantly approach zero. This indicates that the random distribution of multi-component cations in the lattice effectively alters the lattice's thermal stability, and precise control of the system's temperature stability can be achieved by rationally optimizing the component x value.

[0099] Figure 7 The images show the Raman spectra of the ceramics from Examples 1-4 at room temperature. The characteristic vibrational peaks of all samples are in high agreement with the structure of monoclinic wolframite, indicating that the A-site multi-ion substitution did not change the single-phase structure of the matrix.

[0100] In the spectrum, 800-1000 cm -1 The high-frequency region mainly corresponds to the Mo-O stretching vibration mode of the [MoO4] tetrahedron; while the low-frequency region mainly reflects the vibration of the A-site oxygen octahedron. From the magnified view, it can be seen that as the Mg content (x) increases, the vibration at 361 cm⁻¹... -1 The nearby Ag(4) characteristic peaks showed a significant blue shift (moving towards higher wavenumbers).

[0101] According to the harmonic oscillator model, the relationship between the vibration frequency ν and the force constant k and the reduced mass μ satisfies:

[0102] With Mg having a smaller radius and atomic weight 2+ The introduction of Mg reduces the reduced mass (μ) of the system; simultaneously, lattice contraction increases the effective force constant (k). Under the synergistic effect of decreased mass and increased force constant, the vibrational frequency rises significantly, leading to a blue shift in the Raman spectrum peak. This blue shift objectively reflects the enhanced lattice stiffness within the system. Since stronger lattice stiffness suppresses ionic polarization response under an external electric field, this also explains, at the atomic scale, the underlying microscopic mechanism by which the dielectric constant εr gradually decreases with increasing Mg content.

[0103] Figure 8 The Raman spectrum of the sample from Example 1 and its Lorentz fitting results are shown. The peak at 361 cm⁻¹ was analyzed in detail by precisely separating the overlapping peaks. -1 Nearby A g(4)The vibrational mode is highly sensitive to the local coordination environment of A-site ions and lattice distortion. Table 1 shows that the intensity and full width at half maximum (FWHM) of the characteristic peaks evolve systematically with increasing Mg content (x), indicating that changes in A-site composition have a significant modulating effect on lattice order. According to microwave dielectric theory, the degree of distortion and spatial order of polyhedra within the lattice are key factors determining the intrinsic loss of the material. Reducing lattice distortion helps suppress phonon scattering, thereby increasing the Q×f value of the material. g(4) The peak frequency exhibits a significant blue shift with increasing x. This evolution trend closely matches the decreasing trend of the dielectric constant εr, indicating that Mg... 2+ The introduction of enhances the chemical bonding energy of the A-site octahedron; the increase in lattice stiffness effectively restricts the mobility of the polar dipole, thereby reducing the dielectric response.

[0104] In addition, A g(4) The full width at half maximum (FWHM) of the peak reaches a minimum at x = 0.6, and this change shows a strong negative correlation with the increase in the Q×f value. According to phonon vibration theory, the narrowing of the Raman peak directly reflects the reduction in lattice disorder. This indicates that in the x = 0.6 composition, the local lattice distortion caused by multi-aspect A-site substitution is optimally compensated. This structural ordering significantly suppresses the anharmonic phonon scattering process, thereby greatly improving the Q×f value of the material. g(4) The vibrational characteristics of the mode directly reveal the mechanism by which the A-site structural evolution regulates the dielectric properties of ceramics at the microscale.

[0105] Table 1 Mg x (NiZnCoMn) (1-x) / 4 Raman Shift and FWHM of MoO4 ceramics (x=0.6)

[0106]

[0107] Figure 9 The dielectric temperature spectra of ceramics with different compositions are presented in the range of 1 kHz to 200 kHz. Below 300 ℃, the dielectric constant curves of each composition are highly coincident and flat, exhibiting excellent frequency independence and temperature stability. However, as the temperature increases above 300 ℃, the dielectric constants show obvious frequency dispersion characteristics, with values ​​distributed according to the pattern of 1 kHz > 10 kHz > 100 kHz > 200 kHz.

[0108] This high-temperature polarization response is primarily related to the Maxwell-Wagner effect. Under high-temperature thermal excitation, charged defects such as oxygen vacancies in the crystal lattice undergo long-range migration and accumulate at non-uniform interfaces such as grain boundaries, thereby inducing space charge polarization. Comparison of the various compositions shows that the x=0.2 composition exhibits the most intense polarization response in the high-temperature region, which perfectly matches the XPS findings previously revealed that this composition has the highest concentration of oxygen vacancy defects.

[0109] With increasing Mg content, the x=0.4 and x=0.6 components exhibit wide polarization fluctuations in the 400-500 °C range under low-frequency conditions; while the absolute value of the dielectric constant of the x=0.8 component is lower, its temperature-dependent fluctuation trend remains significant. This phenomenon indicates that although A-site compositional modulation can effectively suppress oxygen vacancies and optimize room-temperature dielectric properties, at high temperatures, interfacial space charge polarization induced by thermally excited defect carriers remains the key factor restricting the dielectric temperature stability of this system.

[0110] In order to analyze the variation law of dielectric loss from the perspective of chemical valence state and microscopic defects, XPS was used to characterize the ceramics of Examples 1-4.

[0111] Figure 10 The full-spectrum scan of a showed clear characteristic peaks for each element and no impurity signals, confirming the extremely high chemical purity of this multi-component solid solution. Regarding the reduction loss problem that easily occurs in molybdate systems, Figure 10 b shows the high-resolution energy spectrum of Mo3d at x=0.6. The symmetrical doublets at 232.36 eV and 235.51 eV (split energy 3.15 eV) correspond to Mo3d, respectively. 5 / 2 and Mo 3d 3 / 2 Orbit. This confirms that molybdenum in the system exists entirely in the stable form of Mo. 6+ The existence of this form effectively eliminates the adverse effects of free electrons generated by the reduction of low-valence Mo ions on dielectric loss, laying the chemical state basis for a high Q×f value.

[0112] The core loss suppression mechanism of the system can be revealed through the evolution of the O 1s energy spectrum. For example... Figure 10 As shown in cf, the O 1s spectrum is decomposed into a lattice oxygen peak at approximately 530.0 eV (O I ) and the defect / adsorbed oxygen peak at approximately 531.6 eV (O II In an initial equimolar composition with x=0.2, O represents the defect state. IIThe peak proportions are relatively large. This is mainly attributed to the drastic local lattice distortion caused by the equal and random occupancy of the five A-site cations, resulting in highly disordered oxygen sublattices and inducing a high concentration of oxygen vacancies. With increasing Mg content, the proportion of the OI peak, representing structural integrity, significantly increases. At x=0.6, the lattice oxygen proportion reaches 59.47%, indicating that Mg... 2+ The dominant position of the component effectively alleviates the local strain field caused by random occupancy of multiple components and significantly suppresses the generation of charged defects such as oxygen vacancies.

[0113] The evolution of this defect is highly consistent with the aforementioned experimental results: the decrease in oxygen vacancy concentration effectively weakens the extrinsic losses caused by defect polarization and charge transitions, explaining the significant increase in Q×f value as x increases from 0.2 to 0.6 at the microscopic level. This also corroborates the increased lattice order (decreased full width at half maximum) shown in Raman spectroscopy, jointly confirming that the excellent microwave dielectric properties of the x=0.6 composition originate from the synergistic effect of intrinsic lattice ordering and extrinsic defect suppression. Furthermore, the reduction in oxygen vacancies also weakens the interfacial polarization effect at high temperatures, further revealing the physical mechanism by which this ceramic system can operate stably over a wide temperature range.

Claims

1. An LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material, wherein the general chemical formula of the LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material is Mg. x (NiZnCoMn) (1-x) / 4 MoO4, where 0.1≤x≤1.

2. The LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material according to claim 1, characterized in that, x = 0.2-0.8, preferably x = 0.

6.

3. The LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material according to claim 1, characterized in that, LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material with dielectric constant ε r Within the range of 7.0 to 8.0, the quality factor Q×f is 30000 to 50000 GHz, τ f The value is -27 to -10 ppm / ℃.

4. The LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material according to claim 1, characterized in that, LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material, selected from one of the following: Mg 0.2 (NiZnCoMn) 0.2 MoO4、Mg 0.4 (NiZnCoMn) 0.15 MoO4、Mg 0.6 (NiZnCMn) 0.1 MoO4、Mg 0.8 (NiZnCoMn) 0.05 MoO4。 5. The preparation method of the LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material according to claim 1, characterized in that, The steps include the following: 1) Using MgO, NiO, ZnO, CoO, MnO, and MoO3 as raw materials, according to the chemical formula Mg x (NiZnCoMn) (1-x) / 4 Weigh each raw material according to the stoichiometric ratio of MoO4, then mix the mixed raw materials with ZrO2 grinding balls and anhydrous ethanol, place them in a ball mill jar for ball milling, dry, pulverize, and sieve to obtain the mixture; 2) The mixture is mixed with binder until homogeneous, then pressed into shape to obtain a green body; 3) The green body is first debinded, and then heated for sintering to obtain LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material.

6. The preparation method according to claim 5, characterized in that, In step 1), Mg x (NiZnCoMn) (1-x) / 4 MoO4, x=0.2-0.8, the mass ratio of mixed raw materials, ZrO2 grinding balls and anhydrous ethanol is 1:(2-5):(1-3).

7. The preparation method according to claim 5, characterized in that, In step 1), the ball milling is carried out at a speed of 300-500 r / min for 4-8 hours. The slurry after ball milling is transferred to an evaporation container and dried in an electric heating forced-air drying oven at 60℃ until constant weight. The dried powder is then ground through an 80-mesh sieve.

8. The preparation method according to claim 5, characterized in that, In step 2), the binder is a 4-8 wt.% aqueous solution of polyvinyl alcohol (PVA), and the amount of binder is 6-12 wt% of the weight of the mixture. The resulting green body is a cylindrical green body with a diameter of 10-15 mm and a height of 4-7 mm.

9. The preparation method according to claim 5, characterized in that, In step 3), the glue removal is carried out at 550℃ for 3 hours, and the sintering is carried out at 675~775℃ for 4-8 hours, with a heating rate of 2-4℃ / min.

10. The LTCC-compatible high-entropy molybdate low-loss microwave dielectric ceramic material of claim 1 is used in resonators, filters and antennas in 5G / 6G communication, satellite internet and millimeter-wave radar systems.

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