High-entropy tungstate microwave dielectric ceramic material and preparation method thereof

Abstract

The application discloses a high-entropy tungstate microwave dielectric ceramic material and a preparation method thereof, and relates to the technical field of microwave dielectric ceramic materials. The preparation method of the high-entropy tungstate microwave dielectric ceramic material comprises the following steps: weighing raw materials and uniformly mixing the raw materials to form mixed raw materials; mixing grinding balls, a process control agent and the mixed raw materials, and ball milling to obtain mixed materials; after the mixed materials are dried, an adhesive is added for granulation, and then a green body is formed by pressing; the green body is subjected to four-stage temperature rising sintering, and then is cooled to room temperature in a furnace, so that the high-entropy tungstate microwave dielectric ceramic material is obtained. According to the high sintering temperature of the tungstate-based ceramic dielectric material, the microwave dielectric ceramic material is prepared by the method of multi-element solid solution effect, and the method has the advantages of simple operation, accurate control and high stability, and can be applied to the preparation field of microwave filters, resonators and other high-frequency electronic components for LTCC applications.

Description

Technical Field

[0001] This invention relates to a high-entropy tungstate microwave dielectric ceramic material and its preparation method, belonging to the technical field of microwave dielectric ceramic materials. Background Technology

[0002] Low-Temperature Co-fired Ceramic (LTCC) technology is a key technology widely used in modern electronic packaging and microwave component manufacturing. It allows passive components (such as resistors, capacitors, inductors, filters, and antennas) to be embedded in multilayer ceramic substrates and co-sintered with metallic conductors (typically low-melting-point, high-conductivity metals like silver and copper) at low temperatures (usually <900°C) to form high-density, high-performance three-dimensional integrated modules. Ideal LTCC materials must meet the following stringent requirements: Low-temperature sintering characteristics: The sintering temperature must be lower than the melting point of the internal electrode metal (e.g., silver's melting point of 961°C, copper's melting point of 1083°C), and must be controlled below 900°C to prevent melting, deformation, or interfacial reactions during electrode co-firing. Excellent microwave dielectric properties: Including a suitable dielectric constant (ε). It features an extremely high quality factor (Q·f value, representing low dielectric loss) and a near-zero temperature resonance coefficient (τf, representing frequency temperature stability). Low loss is crucial for high-frequency applications, reducing signal attenuation and heat generation; a stable τf value ensures the reliability of the device operating under different ambient temperatures. It also exhibits good chemical and mechanical compatibility: it does not chemically react with electrode materials during co-firing, and its coefficient of thermal expansion is matched to avoid warping and cracking. While traditional tungstate ceramics (such as ZnWO4, NiWO4) possess good dielectric properties, their sintering temperatures are generally high (>1000℃), and their τf values ​​are often large and negative, making them difficult to directly meet the requirements of LTCC applications.

[0003] To overcome the limitations of traditional materials, this study adopts the design concept of high-entropy ceramics. High-entropy materials are known for their unique "high-entropy effect," where multiple principal elements are mutually dissolved in the crystal lattice to form a stable single-phase structure, which can significantly regulate various properties of the material. Five elements (Li, Co, Ni, Cu, Zn) were introduced into the A-site (metal cation site) of tungstate. This high-entropy configuration not only stabilizes the single-phase structure of ferrotungstate through entropy increase, but more importantly, the synergistic effect of multiple ions can effectively regulate sintering kinetics, microstructure, and final dielectric properties. Among them, Li... + and Cu 2+The introduction of these ions is considered key to achieving low-temperature sintering (850℃). These ions typically form a low-melting-point liquid phase, promoting particle rearrangement and densification processes, thereby significantly reducing the sintering temperature without sacrificing performance, making them particularly suitable for 5G / 6G millimeter-wave filters, resonators, or antenna substrates. While traditional zinc tungstate (ZnWO4) ceramics have low dielectric losses, their Q·f values ​​(typically ≤40000GHz) and sintering temperatures greater than >1000℃ make them unsuitable for the miniaturization and low-temperature co-firing requirements of high-frequency devices. High-entropy ceramics can optimize material properties through multi-principal element synergistic effects, but their application in high-entropy design of tungstate systems is currently rare. Summary of the Invention

[0004] One objective of this invention is to provide a high-entropy tungstate microwave dielectric ceramic material, wherein the main crystalline phase of the high-entropy tungstate microwave dielectric ceramic material is monoclinic wolframite structure ZnWO4; the high-entropy tungstate microwave dielectric ceramic material is composed of raw materials Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO, and WO3 in a molar ratio of 1:1:1:1:1:5.

[0005] The second objective of this invention is to provide a method for preparing high-entropy tungstate microwave dielectric ceramic materials, specifically including the following steps: (1) Weigh the raw materials according to the proportion and mix them evenly to form a mixed raw material.

[0006] (2) The grinding balls (preferably zirconia grinding balls), process control agent (preferably anhydrous ethanol) and mixed raw materials are mixed and ball-milled. The mixture is then sieved, dried, and granulated with binder. Finally, it is pressed to form a green embryo.

[0007] (3) The green embryo is sintered in four stages and then cooled to room temperature in the furnace to obtain high-entropy tungstate microwave dielectric ceramic material.

[0008] Preferably, in step (2), the grinding balls, process control agent and mixed raw materials are mixed in a mass ratio of (5~10):(5~10):(1~2); the ball milling conditions are: ball milling at 200~350 rpm for 14~16 hours.

[0009] Preferably, the size of the mixture after sieving in step (2) is 80-100 mesh; the adhesive is a polyvinyl alcohol aqueous solution with a mass percentage concentration of 5-10%; and the amount of adhesive added to the mixture after sieving is 5% by mass.

[0010] Preferably, the conditions for heating and sintering in step (3) are as follows: heating to 300-320℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours for the first stage of sintering; heating to 700-710℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours for the second stage of sintering; heating to 725-750℃ at a heating rate of 3-5℃ / min and holding for 13-15 hours for the third stage of sintering; and heating to 800-900℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours for the fourth stage of sintering.

[0011] Mechanism of the invention: This invention utilizes the synergistic effect of multiple ions and multi-stage sintering processes to form a low-melting-point liquid phase in the material, promoting particle rearrangement and densification. This significantly reduces the sintering temperature without sacrificing performance, resulting in a high-entropy tungstate microwave dielectric ceramic material, single-phase ZnWO4 (PDF#89-0447). The material exhibits a uniform elemental distribution forming a single wolframite structure, possessing excellent microwave dielectric properties and good chemical and mechanical compatibility.

[0012] The beneficial effects of this invention are: (1) Moderate dielectric constant: The ceramic material prepared in this invention contains Li + Co 2+ Ni 2+ Cu 2+ The average ionic radius is smaller than that of Zn. 2+ The ionic radius of [WO6] is reduced, the lattice of [WO6] is compressed, the lattice volume decreases, affecting the dielectric constant. The bond length of WO bonds decreases, the lattice energy increases, and the quality factor is improved. The high-entropy ceramics show small changes in half-peak width (FWHM) at different sintering temperatures, indicating a small change in the disorder of the sample structure. The FWHM values ​​of the ceramic materials prepared in this invention are all within 44 cm. -1 The fact that the cations are not arranged in a long-range ordered manner, but rather randomly distributed on lattice sites, results in a high degree of structural disorder, which gives the high-entropy tungstate microwave dielectric ceramic material prepared in this invention excellent microwave dielectric properties.

[0013] (2) Low dielectric loss: The high-entropy tungstate microwave dielectric ceramic material prepared by the present invention has a high quality factor and low dielectric loss performance.

[0014] (3) High frequency application: The high-entropy tungstate microwave dielectric ceramic material prepared by this invention has a low resonant frequency and high thermal stability.

[0015] (4) Low sintering temperature: Through the synergistic effect of multiple elements, the distorted lattice of this invention is in a metastable state and the atoms are in a high energy state. This makes it easier for atoms to escape from their original position and migrate under thermal activation, which is equivalent to reducing the energy required for atomic diffusion. Compared with traditional single-phase ceramics, the sintering temperature is reduced from more than 1000℃ to 850℃. At the same time, it is compatible with co-firing with silver electrodes, realizing efficient transmission of high-frequency signals with low loss. The compressed lattice compresses the WO bonds, increases the lattice energy and increases the quality factor. The slow diffusion effect hinders the generation of the second phase. Attached Figure Description

[0016] Figure 1 The image shows the XRD pattern of the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 of this invention.

[0017] Figure 2 This is a SEM image of the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 of the present invention.

[0018] Figure 3 The image shows a comparison of the sintering temperatures of ceramic materials in Example 1 and Comparative Example 1 (a) and a differential scanning calorimetry (DSC) analysis image of the high-entropy tungstate microwave dielectric ceramic material in Example 1 (b). Detailed Implementation

[0019] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0020] Unless otherwise specified, all chemical reagents used in the embodiments and comparative examples of this invention were commercially available analytical grade reagents. The purity of the raw materials Li2CO3, NiCO3·2Ni(OH)2·XH2O, ZnO, CuO, and WO3 used in the embodiments and comparative examples of this invention was 99%, and the purity of CoCO3 was 99.5%.

[0021] Example 1 A method for preparing a high-entropy tungstate microwave dielectric ceramic material specifically includes the following steps: (1) Weigh out Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO and WO3 raw materials in a molar ratio of 1:1:1:1:1:5 and mix them evenly to form a mixed raw material.

[0022] (2) The zirconia grinding balls, anhydrous ethanol and mixed raw materials are mixed in a mass ratio of 5:5:1 and ball-milled at 300 rpm for 16 h at room temperature to obtain a mixture. The mixture is then sieved to obtain a mixture of 80-100 mesh. The sieved mixture is dried at 80°C for 12 h. Then, 5% PVA aqueous solution is added as a binder for granulation. The amount of binder added to the sieved mixture is 5% by mass. Then, it is pressed to form a green embryo of Φ12mm×2.5mm.

[0023] (3) The green blank is placed in a crucible and heated to 310°C at a heating rate of 3°C / min and held for 2 hours for the first stage of sintering; heated to 707°C at a heating rate of 3°C / min and held for 2 hours for the second stage of sintering; heated to 725°C at a heating rate of 3°C / min and held for 14 hours for the third stage of sintering; heated to 850°C at a heating rate of 3°C / min and held for 4 hours for the fourth stage of sintering; and then cooled to room temperature with the furnace to obtain high-entropy tungstate microwave dielectric ceramic material.

[0024] XRD phase analysis was performed on the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1. The test results are as follows: Figure 1 As shown, analysis revealed that the main peak matches ZnWO4 (PDF#89-0447); Figure 2 The SEM image of the high-entropy tungstate microwave dielectric ceramic material shows that the sintered ceramic microstructure in this embodiment is relatively dense, with small gaps between grains, and the sintering density is relatively high at this temperature.

[0025] Microwave performance testing: The high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 was tested using the Hakki-Coleman method. The ε value was obtained from the test. r =13.9, Q·f=23714GHz, τƒ=21.6ppm / ℃.

[0026] The ceramic material prepared in this embodiment achieves a low-melting-point liquid phase through the synergistic effect of multiple ions and a multi-stage sintering process, promoting particle rearrangement and densification. The addition of multiple elements with varying ionic radii in this embodiment induces lattice distortion, thereby lowering the sintering temperature. Figure 3 (a) shows the DSC diagram of the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1. Figure 3 As shown in (b), the high-entropy tungstate microwave dielectric ceramic material begins to dehydrate at 310°C, undergoes a phase transition at 707°C, and ends the phase transition at 721°C. The ceramic material prepared in this embodiment has extremely low dielectric loss, excellent microwave dielectric properties, good chemical and mechanical compatibility, a small temperature coefficient of resonant frequency, and high thermal stability.

[0027] Example 2 A method for preparing a high-entropy tungstate microwave dielectric ceramic material specifically includes the following steps: (1) Weigh out Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO and WO3 raw materials in a molar ratio of 1:1:1:1:1:5 and mix them evenly to form a mixed raw material.

[0028] (2) The zirconia grinding balls, anhydrous ethanol and mixed raw materials are mixed in a mass ratio of 10:10:1 and ball-milled at room temperature at 200 rpm for 15 h to obtain a mixture. The mixture is then sieved to obtain a mixture of 80~100 mesh. The sieved mixture is dried at 80℃ for 12 h. Then, 8% PVA aqueous solution is added as a binder for granulation. The amount of binder added to the sieved mixture is 5% by mass. Then, it is pressed to form a green embryo of Φ12mm×2.5mm.

[0029] (3) The green blank is placed in a crucible and heated to 320°C at a heating rate of 5°C / min and held for 3 hours for the first stage of sintering; heated to 710°C at a heating rate of 5°C / min and held for 3 hours for the second stage of sintering; heated to 750°C at a heating rate of 5°C / min and held for 13 hours for the third stage of sintering; heated to 900°C at a heating rate of 5°C / min and held for 2 hours for the fourth stage of sintering; and then cooled to room temperature with the furnace to obtain high-entropy tungstate microwave dielectric ceramic material.

[0030] XRD phase analysis was performed on the high-entropy tungstate microwave dielectric ceramic material prepared in Example 2. The analysis showed that the main peak matched ZnWO4 (PDF#89-0447). The SEM image of the high-entropy tungstate microwave dielectric ceramic material showed that the ceramic microstructure of this example was relatively dense, with small gaps between grains, and the sintering density was relatively high at this temperature.

[0031] Microwave performance testing: The high-entropy tungstate microwave dielectric ceramic material prepared in Example 2 was tested using the Hakki-Coleman method. The results showed that ε... r =9.676, Q·f=12637GHz, τƒ=23.659ppm / ℃.

[0032] The ceramic material prepared in this embodiment achieves a low-melting-point liquid phase through the synergistic effect of multiple ions and multi-stage sintering processes, promoting particle rearrangement and densification. The addition of multiple elements with varying ionic radii in this embodiment generates lattice distortion, lowering the sintering temperature. The ceramic material prepared in this embodiment exhibits low dielectric loss, excellent microwave dielectric properties, good chemical and mechanical compatibility, a small temperature coefficient of resonant frequency, and high thermal stability.

[0033] Example 3 A method for preparing a high-entropy tungstate microwave dielectric ceramic material specifically includes the following steps: (1) Weigh out Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO and WO3 raw materials in a molar ratio of 1:1:1:1:1:5 and mix them evenly to form a mixed raw material.

[0034] (2) The zirconia grinding balls, anhydrous ethanol and mixed raw materials are mixed in a mass ratio of 5:5:2 and ball-milled at 350 rpm at room temperature for 14 h to obtain a mixture. The mixture is then sieved to obtain a mixture of 80~100 mesh. The sieved mixture is dried at 80℃ for 12 h. Then, 10% PVA aqueous solution is added as a binder for granulation. The amount of binder added to the sieved mixture is 5% by mass. Then, it is pressed to form a green embryo of Φ12mm×2.5mm.

[0035] (3) The green blank is placed in a crucible and heated to 300°C at a heating rate of 4°C / min and held for 6 hours for the first stage of sintering; heated to 700°C at a heating rate of 4°C / min and held for 6 hours for the second stage of sintering; heated to 740°C at a heating rate of 4°C / min and held for 15 hours for the third stage of sintering; heated to 800°C at a heating rate of 4°C / min and held for 6 hours for the fourth stage of sintering; and then cooled to room temperature with the furnace to obtain high-entropy tungstate microwave dielectric ceramic material.

[0036] XRD phase analysis was performed on the high-entropy tungstate microwave dielectric ceramic material prepared in Example 3. The analysis showed that the main peak matched ZnWO4 (PDF#89-0447). The SEM image of the high-entropy tungstate microwave dielectric ceramic material showed that the ceramic microstructure sintered in this example was relatively dense with small gaps between grains and a high sintering density at this temperature.

[0037] Microwave performance testing: The high-entropy tungstate microwave dielectric ceramic material prepared in Example 3 was tested using the Hakki-Coleman method. The results showed that ε... r=10.265, Q·f=8714GHz, τƒ=34.261ppm / ℃.

[0038] The ceramic material prepared in this embodiment achieves a low-melting-point liquid phase through the synergistic effect of multiple ions and multi-stage sintering processes, promoting particle rearrangement and densification. The addition of multiple elements with different ionic radii in this embodiment generates lattice distortion, which lowers the sintering temperature. The ceramic material prepared in this embodiment has excellent microwave dielectric properties and good chemical and mechanical compatibility, as well as a small temperature coefficient of resonant frequency and high thermal stability.

[0039] Comparative Example 1 A traditional method for preparing zinc tungstate ceramic powder specifically includes the following steps: (1) Weigh out ZnO and WO3 raw materials in a molar ratio of 1:1 and mix them evenly to form a mixed raw material.

[0040] (2) The zirconia grinding balls, anhydrous ethanol and mixed raw materials are mixed in a mass ratio of 5:5:1 and ball-milled at 300 rpm for 16 h at room temperature to obtain a mixture. The mixture is then sieved to obtain a mixture of 80-100 mesh. The sieved mixture is dried at 80°C for 12 h. Then, 5% PVA aqueous solution is added as a binder for granulation. The amount of binder added to the sieved mixture is 5% by mass. Then, it is pressed to form a green embryo of Φ12mm×2.5mm.

[0041] (3) The green blank is placed in a crucible and heated to 310°C in a muffle furnace at a heating rate of 3°C / min and held for 2 hours for the first stage of sintering; heated to 900°C at a heating rate of 3°C / min and held for 2 hours for the second stage of sintering; heated to 925°C at a heating rate of 3°C / min and held for 14 hours for the third stage of sintering; heated to 1150°C at a heating rate of 3°C / min and held for 4 hours for the fourth stage of sintering; and then cooled to room temperature with the furnace to obtain conventional zinc tungstate ceramic powder.

[0042] Microwave performance testing: The microwave performance of the conventional zinc tungstate ceramic powder prepared in Comparative Example 1 was tested using the Hakki-Coleman method. The results showed that ε r =13.57, Q·f=19312GHz, τƒ=44.3ppm / ℃; For example Figure 3 As shown in (a), the traditional zinc tungstate ceramic prepared in this comparative example has no lattice distortion in a single component, has a high sintering temperature, and cannot change its thermal stability by controlling the composition through high entropy.

[0043] Comparative Example 2 A method for preparing a high-entropy tungstate microwave dielectric ceramic material specifically includes the following steps: (1) Weigh out Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO, and WO3 raw materials in a molar ratio of 1:1:1:1:1:5 and mix them evenly to form a mixed raw material.

[0044] (2) The zirconia grinding balls, anhydrous ethanol and mixed raw materials are mixed in a mass ratio of 5:5:1 and ball-milled at 300 rpm for 16 h at room temperature to obtain a mixture. The mixture is then sieved to obtain a mixture of 80-100 mesh. The sieved mixture is dried at 80°C for 12 h. Then, 5% PVA aqueous solution is added as a binder for granulation. The amount of binder added to the sieved mixture is 5% by mass. Then, it is pressed to form a green embryo of Φ12mm×2.5mm.

[0045] (3) The green blank is placed in a crucible and heated to 1150°C in a muffle furnace at a heating rate of 3°C / min and held for 14 hours for sintering. Then it is cooled to room temperature with the furnace to obtain high-entropy tungstate microwave dielectric ceramic material.

[0046] Microwave performance testing: The high-entropy tungstate microwave dielectric ceramic material prepared in Comparative Example 2 was tested using the Hakki-Coleman method. The results showed that ε r =8.656, Q·f=5314GHz, τƒ=51.261ppm / ℃; In this comparative example, sintering at 1150℃ resulted in excessive grain growth, producing a secondary phase, which led to a decrease in the relative density of the ceramic, affecting the quality factor and causing poor low-loss characteristics of the material.

[0047] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A high-entropy tungstate microwave dielectric ceramic material, characterized in that, The main crystalline phase of the high-entropy tungstate microwave dielectric ceramic material is monoclinic wolframite structure ZnWO4; the high-entropy tungstate microwave dielectric ceramic material is obtained by mixing, pressing, and sintering Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO, and WO3 raw materials in a molar ratio of 1:1:1:1:1:5, followed by four-stage heating and sintering reaction. The conditions for the four-stage heating and sintering are as follows: the first stage of sintering is carried out by heating to 300-320℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours; the second stage of sintering is carried out by heating to 700-710℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours. The third stage of sintering is carried out by heating to 725-750℃ at a heating rate of 3-5℃ / min and holding for 13-15 hours; the fourth stage of sintering is carried out by heating to 800-900℃ at a heating rate of 3-5℃ / min and holding for 2-6 hours.

2. The method for preparing the high-entropy tungstate microwave dielectric ceramic material according to claim 1, characterized in that, Specifically, the following steps are included: (1) Weigh the raw materials according to the proportion and mix them evenly to form a mixed raw material; (2) Mix the grinding balls, process control agent and raw materials, and ball mill to obtain a mixture. Then, sieve the mixture, dry the sieved mixture, add binder to granulate, and then press to form a green embryo. (3) The green embryo is sintered in four stages and then cooled to room temperature in the furnace to obtain high-entropy tungstate microwave dielectric ceramic material.

3. The method for preparing the high-entropy tungstate microwave dielectric ceramic material according to claim 2, characterized in that, In step (2), the grinding balls, process control agent and mixed raw materials are mixed in a mass ratio of (5~10):(5~10):(1~2); the ball milling conditions are: ball milling at 200~350 rpm for 14~16 hours.

4. The method for preparing the high-entropy tungstate microwave dielectric ceramic material according to claim 2, characterized in that, The size of the mixture after sieving in step (2) is 80-100 mesh; the adhesive is a polyvinyl alcohol aqueous solution with a mass percentage concentration of 5-10%; the amount of adhesive added to the mixture after sieving is 5% by mass.

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