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

Abstract

The invention 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 to form a mixed raw material; mixing the grinding balls, a process control agent and the mixed raw material, carrying out ball milling to obtain a mixed material, drying the mixed material, adding an adhesive, granulating, and pressing to form a green body; and carrying out four-stage heating sintering on the green body, and then carrying out furnace cooling to room temperature to obtain the high-entropy tungstate microwave dielectric ceramic material. Aiming at the condition of high sintering temperature of a tungstate-based ceramic dielectric material, the microwave dielectric ceramic material is prepared by a multi-element solid solution effect method, and the method has the advantages of simplicity and convenience in operation, accuracy in control and high stability, and can be applied to the field of preparation of high-frequency electronic elements such as microwave filters and resonators applied to LTCC (Low Temperature Co-Fired Ceramic).

Description

TECHNICAL FIELD

[0001] The present application relates to a high-entropy tungstate microwave dielectric ceramic material and a preparation method thereof, and belongs to the technical field of microwave dielectric ceramic materials. BACKGROUND

[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, antennas) to be embedded in a multilayer ceramic substrate, and to be co-sintered with metal conductors (usually silver, copper, low-melting-point high-conductivity metals) at low temperatures (usually < 900℃), forming a high-density, high-performance three-dimensional integrated module. The ideal LTCC material needs to meet the following stringent requirements: low-temperature sintering characteristics: the sintering temperature must be lower than the melting point of the internal electrode metal (such as the melting point of silver 961℃, the melting point of copper 1083℃), and needs to be controlled below 900℃, so that the electrode co-sintering does not occur melting, deformation or interface reaction. Excellent microwave dielectric properties: including moderate dielectric constant (ε ), extremely high quality factor (Q·f value, representing low dielectric loss) and near-zero temperature resonance coefficient (τf, representing frequency temperature stability). Low loss is crucial for high-frequency applications, which can reduce signal attenuation and heat generation; stable τf value can ensure the reliability of the device working in different environmental temperatures. Good chemical and mechanical compatibility: no chemical reaction with electrode materials during co-sintering, and the coefficient of thermal expansion is matched to avoid warping and cracking. Traditional tungstate ceramics (such as ZnWO4, NiWO4) have good dielectric properties, but their sintering temperature is generally higher (> 1000℃), and the τf value is often a large negative value, which is difficult to directly meet the LTCC application requirements.

[0003] To overcome the limitations of traditional materials, this study uses the design concept of high-entropy ceramics. High-entropy materials are known for their unique "high-entropy effect". Multiple main elements are solid-solved in the lattice, forming a stable single-phase structure, and can significantly regulate various properties of the material. Five elements (Li, Co, Ni, Cu, Zn) are introduced into the A site (metal cation site) of tungstate. This high-entropy configuration not only stabilizes the wolframite single-phase structure 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 to be the key to realize low-temperature sintering (850℃). These ions can usually form a low-melting-point liquid phase, promote particle rearrangement and densification process, thereby greatly reducing the sintering temperature without sacrificing performance, especially suitable for 5G / 6G millimeter wave filter, resonator or antenna substrate. Although traditional zinc tungstate (ZnWO4) ceramics have lower dielectric loss, their Q·f values (usually ≤40000 GHz) and sintering temperatures (>1000℃) cannot meet the requirements of high-frequency device miniaturization and low-temperature co-firing. High-entropy ceramics can optimize material performance through multi-principal element synergistic effect, but there are few high-entropy designs applied to tungstate systems at present. SUMMARY

[0004] One of the purposes of the present application is to provide a high-entropy tungstate microwave dielectric ceramic material, wherein the main crystal phase of the high-entropy tungstate microwave dielectric ceramic material is monoclinic wolframite structure ZnWO4; and 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 purpose of the present application is to provide a preparation method of the high-entropy tungstate microwave dielectric ceramic material, which specifically comprises the following steps: (1) weighing the raw materials in proportion and mixing them uniformly to form mixed raw materials.

[0006] (2) mixing the grinding balls (preferably zirconia grinding balls), the process control agent (preferably anhydrous ethanol) and the mixed raw materials, and then ball milling, and then sieving the mixture, and then adding a binder to the sieved mixture after drying, and then pressing to form a green body.

[0007] (3) four-stage temperature rising sintering of the green body, and then furnace cooling to room temperature to obtain the high-entropy tungstate microwave dielectric ceramic material.

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

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

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

[0011] Mechanism of the present application: The present application forms a low melting point liquid phase by the synergistic effect of multiple ions and multiple sintering processes, promotes the particle rearrangement and densification process, thereby greatly reduces the sintering temperature without sacrificing the performance, and the prepared high-entropy tungstate microwave dielectric ceramic material single-phase ZnWO4 (PDF#89-0447) has uniform element distribution, forms a single wolframite structure, and has excellent microwave dielectric performance and good chemical and mechanical compatibility.

[0012] Advantages of the present application: (1) Moderate dielectric constant: the average ion radius of Li + , Co 2+ , Ni 2+ , Cu 2+ in the ceramic material prepared by the present application is smaller than the ion radius of Zn 2+ , the [WO6] lattice is compressed, the volume of the lattice is smaller, the dielectric constant is affected, the W-O bond length is shorter, the lattice energy is increased, and the quality factor is improved; the high-entropy ceramic half-peak width changes little at different sintering temperatures, which indicates that the degree of disorder of the sample structure changes little. The half-peak width of the ceramic material prepared by the present application is about 44 cm -1 , which indicates that the cations are not long-range ordered arrangement, but are randomly distributed on the lattice sites, forming a high degree of structural disorder, so that the high-entropy tungstate microwave dielectric ceramic material prepared by the present application has excellent microwave dielectric performance.

[0013] (2) Low dielectric loss: the high-entropy tungstate microwave dielectric ceramic material prepared by the present application 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 the present application has a low resonance frequency and high material thermal stability.

[0015] (4) Low sintering temperature: the distorted crystal lattice is in a metastable state and the atoms are in a high energy state through the synergistic effect of multiple elements; this makes the atoms more easily migrate from the original position under thermal activation, which is equivalent to reducing the energy required for atomic diffusion, compared with the traditional single-phase ceramic, the sintering temperature is reduced from more than 1000 DEG C of the traditional tungstate to 850 DEG C, and the silver electrode is compatible with co-sintering, realizing efficient transmission of high-frequency signals with small loss; the compressed lattice makes the W-O bond compressed, increases the lattice energy and increases the quality factor; the slow diffusion effect hinders the generation of the second phase. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The XRD graph of the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 of the present application is shown.

[0017] Figure 2 The SEM graph of the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 of the present application is shown.

[0018] Figure 3 The sintering temperature comparison graph (a) of the ceramic material of Example 1 and Comparative Example 1 and the differential scanning calorimetry (DSC) analysis graph (b) of the high-entropy tungstate microwave dielectric ceramic material of Example 1 are shown. DETAILED DESCRIPTION

[0019] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples.

[0020] In the examples and comparative examples of the present application, the chemical reagents not specifically mentioned are all commercially available analytical pure reagents used for experiments; the Li2CO3, NiCO3·2Ni(OH)2·XH2O, ZnO, CuO and WO3 raw materials used in the examples and comparative examples of the present application have a purity of 99%, and the CoCO3 has a purity of 99.5%.

[0021] Example 1 A preparation method of a high-entropy tungstate microwave dielectric ceramic material, specifically comprising the following steps: (1) Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO and WO3 raw materials are weighed according to a molar ratio of 1:1:1:1:1:5 and mixed uniformly to form a mixed raw material.

[0022] (2) The zirconium oxide grinding ball, anhydrous ethanol and mixed raw materials are mixed in a mass ratio of 5:5:1, and ball milling is performed at 300 rpm for 16 h at room temperature to obtain a mixture, and then the mixture is sieved to obtain a mixture of 80-100 mesh, and then the sieved mixture is dried at 80℃ for 12 h, and then a PVA aqueous solution with a mass percentage of 5% is added as a binder, and the amount of the binder in the sieved mixture is 5% by mass percentage, and then a green body with a diameter of 12 mm and a height of 2.5 mm is formed by pressing.

[0023] (3) The green body is placed in a crucible and sintered in a muffle furnace at a heating rate of 3℃ / min to 310℃ for 2 h for the first stage sintering, at a heating rate of 3℃ / min to 707℃ for 2 h for the second stage sintering, at a heating rate of 3℃ / min to 725℃ for 14 h for the third stage sintering, and at a heating rate of 3℃ / min to 850℃ for 4 h for the fourth stage sintering, and then cooled to room temperature in the furnace to obtain a high-entropy tungstate microwave dielectric ceramic material.

[0024] The high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 is subjected to XRD phase analysis, and the test results are shown in Figure 1 , and analysis shows that the main peak matches ZnWO4 (PDF #89-0447); the SEM image of the high-entropy tungstate microwave dielectric ceramic material shows that the sintered ceramic microstructure of this example is relatively dense, and the gap between the grains is small, and the density is large at this temperature. Figure 2

[0025] Microwave performance test: The high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 is subjected to microwave performance test by Hakki-Coleman method, and the test results show that ε r = 13.9, Q·f = 23714 GHz, τf = 21.6 ppm / ℃.

[0026] The ceramic material prepared in this example is subjected to the synergistic effect of multiple ion and multiple stage sintering process, which forms a low melting point liquid phase, promotes the grain rearrangement and densification process; this example adds elements with different ionic radii, which produces lattice distortion and reduces the sintering temperature, as shown in Figure 3 (a); the DSC graph of the high-entropy tungstate microwave dielectric ceramic material prepared in Example 1 is shown in Figure 3 (b), which starts to dehydrate at 310℃, undergoes phase transition at 707℃, and the phase transition ends at 721℃; the ceramic material prepared in this example has very small dielectric loss, excellent microwave dielectric performance and good chemical and mechanical compatibility, and small resonant frequency temperature coefficient and high thermal stability. ​

[0027] Example 2 A preparation method of a high-entropy tungstate microwave dielectric ceramic material, specifically comprising the following steps: (1) Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO, and WO3 raw materials are weighed according to a molar ratio of 1:1:1:1:1:5 and mixed uniformly to form mixed raw materials.

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

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

[0030] The high-entropy tungstate microwave dielectric ceramic material prepared in Example 2 is subjected to XRD phase analysis, and the analysis shows that the main peak matches ZnWO4 (PDF #89-0447); the SEM image of the high-entropy tungstate microwave dielectric ceramic material shows that the sintered ceramic microstructure of this example is relatively dense, and the gap between the grains is small, and the sintering density is large at this temperature.

[0031] Microwave performance test: The high-entropy tungstate microwave dielectric ceramic material prepared in Example 2 is subjected to microwave performance test by Hakki-Coleman method, and the test shows that ε r =9.676, Q·f=12637GHz, τƒ=23.659ppm / ℃.

[0032] The ceramic material prepared in the embodiment is sintered through a multi-ion and multi-stage sintering process, so that a low-melting-point liquid phase is formed, and the particle rearrangement and densification process is promoted; the embodiment adds elements with different ionic radii, so that lattice distortion is generated, and the sintering temperature is reduced; the ceramic material prepared in the embodiment has small dielectric loss, excellent microwave dielectric properties, good chemical and mechanical compatibility, small resonant frequency temperature coefficient, and high thermal stability.

[0033] Embodiment 3 The application discloses a preparation method of a high-entropy tungstate microwave dielectric ceramic material. (1) Li2CO3, NiCO3·2Ni(OH)2·XH2O, CoCO3, ZnO, CuO and WO3 raw materials are weighed according to a molar ratio of 1:1:1:1:1:5 and uniformly mixed to form mixed raw materials.

[0034] (2) Zirconium oxide grinding balls, anhydrous ethanol and the mixed raw materials are mixed according to a mass ratio of 5:5:2, and then ball-milled at 350 rpm at room temperature for 14 hours to obtain a mixture, and then the mixture is sieved to obtain a mixture with a particle size of 80-100 mesh; the sieved mixture is dried at 80 DEG C for 12 hours, and then a PVA aqueous solution with a mass percentage of 10% is added as a binder to granulate, wherein the amount of the binder in the sieved mixture is 5% by mass percentage; and then a green body with a diameter of 12 mm and a thickness of 2.5 mm is formed by pressing.

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

[0036] The high-entropy tungstate microwave dielectric ceramic material prepared in Embodiment 3 is subjected to XRD phase analysis, and the analysis shows that the main peak matches ZnWO4 (PDF #89-0447); the SEM image of the high-entropy tungstate microwave dielectric ceramic material shows that the sintered ceramic microstructure in the embodiment is relatively dense, and the gap between the grains is small, and the sintering density is large at this temperature.

[0037] The high-entropy tungstate microwave dielectric ceramic material prepared in Embodiment 3 is subjected to microwave performance testing by using the Hakki-Coleman method, and the test shows that the high-entropy tungstate microwave dielectric ceramic material has a dielectric constant εr of 18.5, a dielectric loss tan δ of 0.0002, a temperature coefficient of resonant frequency of -30.5 ppm / DEG C, and a thermal conductivity of 2.5 W / m·K. r= 10.265, Q?f = 8714 GHz, t = 34.261 ppm / ℃.

[0038] The ceramic material prepared in the embodiment is formed into a low-melting-point liquid phase by the synergistic effect of the multi-ion and multi-stage sintering process, which promotes the particle rearrangement and densification process; the embodiment adds elements with different ionic radii, which produces lattice distortion and reduces the sintering temperature; the ceramic material prepared in the embodiment has excellent microwave dielectric properties and good chemical and mechanical compatibility, and has a small resonant frequency temperature coefficient and high thermal stability.

[0039] Comparative Example 1 A preparation method of a traditional zinc tungstate ceramic powder specifically includes the following steps: (1) ZnO and WO3 raw materials are weighed according to a molar ratio of 1:1 and uniformly mixed to form mixed raw materials.

[0040] (2) Zirconia grinding balls, anhydrous ethanol and the mixed raw materials are mixed according to a mass ratio of 5:5:1, and ball-milled at 300 rpm at room temperature for 16 h to obtain a mixture, which is then sieved to obtain a mixture of 80-100 mesh. The sieved mixture is dried at 80℃ for 12 h, and then a PVA aqueous solution with a mass fraction of 5% is added as a binder. The amount of the binder added in the sieved mixture is 5% by mass fraction, and then a green body with a diameter of 12 mm and a height of 2.5 mm is formed by pressing.

[0041] (3) The green body is placed in a crucible and heated in a muffle furnace at a heating rate of 3℃ / min to 310℃ for 2h for first-stage sintering, at a heating rate of 3℃ / min to 900℃ for 2h for second-stage sintering, at a heating rate of 3℃ / min to 925℃ for 14h for third-stage sintering, and at a heating rate of 3℃ / min to 1150℃ for 4h for fourth-stage sintering, and then cooled to room temperature in the furnace to obtain the traditional zinc tungstate ceramic powder.

[0042] Microwave performance test: the traditional zinc tungstate ceramic powder prepared in Comparative Example 1 is tested for microwave performance by the Hakki-Coleman method, and the test results are as follows: ε r = 13.57, Q?f = 19312 GHz, t = 44.3 ppm / ℃; as Figure 3 (a) shows that 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 be adjusted by high-entropy components to change the thermal stability.

[0043] Comparative Example 2 A preparation method of a high-entropy tungstate microwave dielectric ceramic material, specifically comprising the following steps: (1) Li2CO3, NiCO3.2Ni(OH)2.XH2O, CoCO3, ZnO, CuO, and WO3 raw materials are weighed according to a molar ratio of 1:1:1:1:1:5 and mixed uniformly to form mixed raw materials.

[0044] (2) Zirconium oxide grinding balls, anhydrous ethanol, and the mixed raw materials are mixed according to a mass ratio of 5:5:1, and then ball-milled at 300 rpm at room temperature for 16 h to obtain a mixture, and then the mixture is sieved to obtain a mixture of 80-100 mesh, and then the sieved mixture is dried at 80 DEG C for 12 h, and then a PVA aqueous solution with a mass fraction of 5% is added as a binder, wherein the addition amount of the binder in the sieved mixture is 5% by mass, and then a green body with a diameter of 12 mm and a height of 2.5 mm is formed by pressing.

[0045] (3) The green body is placed in a crucible and sintered in a muffle furnace at a heating rate of 3 DEG C / min to 1150 DEG C for 14 h, and then cooled to room temperature in the furnace to obtain a high-entropy tungstate microwave dielectric ceramic material.

[0046] Microwave performance test: the high-entropy tungstate microwave dielectric ceramic material prepared in Comparative Example 2 is tested for microwave performance by using the Hakki-Coleman method, and the test results are as follows: ε r = 8.656, Q·f = 5314 GHz, and τf = 51.261 ppm / ℃; the sintering temperature of this comparative example is 1150 DEG C, the grain grows excessively, a secondary phase is generated, the relative density of the ceramic is reduced, the quality factor is affected, and the material has poor low-loss characteristics.

[0047] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications, or improvements to the technology in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A high-entropy tungstate microwave dielectric ceramic material, characterized in that, The main crystal 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.

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.

5. The method for preparing the high-entropy tungstate microwave dielectric ceramic material according to claim 2, characterized in that, 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. 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.

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