Germanium-doped uvarovite microwave dielectric ceramic as well as preparation method and application thereof

Abstract

The invention provides germanium-doped uvarovite microwave dielectric ceramic as well as a preparation method and application thereof, and relates to the technical field of microwave dielectric ceramic materials. The invention provides germanium-doped uvarovite microwave dielectric ceramic. The chemical general formula of the germanium-doped uvarovite microwave dielectric ceramic is Ca3Cr2 (Si < 1-x > Ge < x >) 3O12, wherein x is the mole fraction of the Ge element, and x is larger than or equal to 0.025 and smaller than or equal to 0.4. The normal-pressure solid-phase reaction is combined with the gradient cold isostatic pressing process, the method is simple in process and non-toxic (dichromate is not used), a sintering aid does not need to be introduced, and the single-phase compact microwave dielectric ceramic with the high quality factor can be prepared at the normal pressure. The prepared germanium-doped uvarovite microwave dielectric ceramic realizes component regulation and control by partially replacing Si < 4 + > with Ge < 4 + >, so that the stability of the material is improved, and meanwhile, the germanium-doped uvarovite microwave dielectric ceramic has a relatively low dielectric constant (epsilon r = 7.67-8.66), a high quality factor (Q * f = 13871-39146 GHz) and a good temperature coefficient of resonance frequency (tau f =-41-36ppm / DEG C), and meets the strict requirements of 5G / 6G high-frequency communication devices on low loss and high stability.

Description

Technical Field

[0001] This invention relates to the field of microwave dielectric ceramic materials technology, and in particular to a germanium-doped calcium chromium garnet microwave dielectric ceramic, its preparation method, and its application. Background Technology

[0002] With the rapid development of 5G / 6G mobile communication technologies, communication frequency bands are expanding into millimeter waves, placing stringent demands on the signal transmission efficiency of passive devices (such as dielectric antennas and filters). Microwave dielectric ceramics, as core materials, urgently require the development of materials with lower losses, better temperature stability, and higher quality factors. In silicate systems, calcium chromate (Ca3Cr2Si3O4) is a suitable candidate for this purpose. 12 Garnet has attracted much attention due to its unique crystal structure. However, because chromium is highly volatile above 1200℃ and exhibits multiple valence states, and because Ca3Cr2Si3O2 is produced during traditional solid-state sintering... 12 It is prone to thermal decomposition, making it difficult to obtain a pure, dense ceramic body, which severely restricts its practical application in microwave devices.

[0003] To address the challenges of synthesizing chromium-containing garnet, existing technologies have explored various approaches, but all have significant limitations. In physical synthesis routes, for example, Chinese patent CN114318489A, published on April 12, 2022, discloses a method for preparing grossular garnet single crystals. While this method can synthesize chromium-containing garnet crystals, it relies on ultra-high pressure equipment (10 GPa). This method is extremely expensive, has very low yield per batch, and is only suitable for geological simulations, failing to meet the needs of large-scale industrial production of electronic ceramics. In wet chemical synthesis routes, for example, Chinese patent CN110182818A, published on August 30, 2019, discloses a method for preparing a green pigment of grossular garnet using a liquid-phase co-precipitation method. This process involves complex solution titration, precise pH control (8.5-9.5), and multi-step washing and drying processes. Although this method can obtain powder at relatively low temperatures (900℃), its target product is a pigment powder (Victoria Green) for ceramic decoration, focusing on chromaticity (Lab* value) rather than density and dielectric properties. Furthermore, this method introduces lithium fluoride (LiF) as a mineralizing agent to lower the synthesis temperature. For microwave dielectric ceramics, alkali metal ions (Li...) + ) and fluoride ions (F - Residues of these pigments can become harmful impurities, significantly increasing dielectric loss and leading to a substantial decrease in the quality factor. Therefore, this type of pigment preparation process cannot be directly used to manufacture high-performance microwave dielectric dense ceramics.

[0004] Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a germanium-doped calcium chromium garnet microwave dielectric ceramic, its preparation method, and its applications. (The invention relates to Ge...) 4+ Partially replaces Si 4+ By achieving compositional control, the stability of the material is improved, and the instability of Cr in existing technologies is solved. In the traditional solid-state sintering process, Ca3Cr2Si3O... 12 It is prone to thermal decomposition, making it difficult to obtain a pure, dense ceramic body, which seriously restricts its practical application in microwave devices.

[0006] In a first aspect, the present invention provides a germanium-doped calcium chromium garnet microwave dielectric ceramic with the general chemical formula Ca3Cr2(Si 1-x Ge x )3O 12 Where x is the mole fraction of Ge, and 0.025 ≤ x ≤ 0.4.

[0007] Secondly, the present invention also provides a method for preparing the above-mentioned germanium-doped calcium chromium garnet microwave dielectric ceramic, comprising the following steps: S1. Batching and primary ball milling: Weigh the raw materials CaCO3, Cr2O3, SiO2 and GeO2, mix them and perform the first wet ball milling treatment to obtain a mixed slurry; S2. Drying and pre-calcination: The mixed slurry is dried and then pre-calcined to obtain pre-calcined powder; S3. Secondary ball milling and granulation: The pre-fired powder is subjected to a second wet ball milling process, and after drying, ceramic powder is obtained; a binder is added to the ceramic powder for granulation to obtain granulated powder; S4. Molding and cold isostatic pressing: The granulated powder is pressed into a green body, and the green body is vacuum sealed and then subjected to cold isostatic pressing. S5. Sintering: The green body after cold isostatic pressing is sintered to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic; its general chemical formula is Ca3Cr2(Si 1-x Ge x )3O 12 Where x is the mole fraction of Ge, and 0.025 ≤ x ≤ 0.4.

[0008] Optionally, in S1, the CaCO3, Cr2O3, SiO2 and GeO2 are mixed in stoichiometric proportions according to the general chemical formula.

[0009] Optionally, in S1, the conditions for the first wet ball milling treatment are as follows: using zirconia balls as the ball milling medium; using anhydrous ethanol as the ball milling aid; ball milling at a speed of 500 r / min for 8 hours; and the mass ratio of the raw material, the ball milling medium and the ball milling aid is 1:3:3.

[0010] Optionally, in S2, the drying is performed at a temperature of 65°C-75°C for 8-12 hours.

[0011] Optionally, in S2, the pre-firing temperature is 1300℃-1400℃, the holding time is 2h-6h, and the heating rate is 5℃ / min.

[0012] Optionally, in S3, the conditions for the second wet ball milling treatment are as follows: using zirconia balls as the ball milling medium; using anhydrous ethanol as the ball milling aid; ball milling at a speed of 500 r / min for 8 h; and the mass ratio of the pre-calcined powder, the ball milling medium, and the ball milling aid is 1:3:3.

[0013] Optionally, in S3, the drying is performed at a temperature of 65°C-75°C for 8-12 hours.

[0014] Optionally, in S3, the granulation includes: mixing ceramic powder with an adhesive and then grinding the mixture, passing it through 40-mesh and 80-mesh sieves, and collecting particles with a particle size between 40 and 80 mesh; the adhesive is a 7% (w / w) aqueous solution of polyvinyl alcohol.

[0015] Optionally, in S4, the granulated powder is pressed into shape under a pressure of 10 MPa.

[0016] Optionally, in S4, the cold isostatic pressing process is carried out using a gradient pressurization method; the gradient pressurization method includes at least two pressure stages, and the pressure value of the later stage is higher than that of the earlier stage.

[0017] Optionally, in S4, the pressure medium used in the cold isostatic pressing is deionized water.

[0018] Optionally, the pressures applied sequentially by the gradient pressurization include 20 MPa, 40 MPa, 80 MPa, 160 MPa, 200 MPa and 220 MPa.

[0019] Optionally, the sintering temperature is 1400℃-1550℃, and the holding time is 2h-6h.

[0020] Optionally, the sintering process includes: first heating to 600°C at a heating rate of 5°C / min, holding at that temperature for 4 hours to remove the adhesive, then heating to 1430°C-1510°C at a heating rate of 5°C / min, holding at that temperature for 4 hours; and finally, cooling down in the furnace.

[0021] Thirdly, the present invention also provides an application of the above-mentioned germanium-doped calcium chromium garnet microwave dielectric ceramic in the fabrication of microwave devices, wherein the microwave devices include dielectric resonators, filters, dielectric antennas, or microwave substrates.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The germanium-doped calcium chromium garnet microwave dielectric ceramic material provided by the present invention, through Ge 4+ Partially replaces Si 4+ The composition control strategy effectively stabilized the garnet crystal structure, significantly suppressed the volatilization of Cr and material decomposition during high-temperature sintering, and successfully solved the problem of traditional Ca3Cr2Si3O4. 12 The fundamental problem of obtaining pure-phase dense bodies in ceramics; (2) The preparation method provided by the present invention adopts atmospheric pressure solid-phase reaction combined with gradient cold isostatic pressing process, which does not rely on ultra-high pressure equipment or introduce mineralizers such as LiF. The process is simple, low cost and environmentally friendly, avoids the damage of harmful impurities to dielectric properties, and has the potential for large-scale industrial production. (3) The ceramic material prepared by this invention exhibits excellent comprehensive microwave dielectric properties: it also has a low dielectric constant ( ε r =7.67~8.66), significantly improved quality factor ( Q × f Up to 39146 GHz) and good temperature stability of resonant frequency ( τ f =-41~-36ppm / ℃), meeting the stringent requirements of 5G / 6G high-frequency communication devices for low loss and high stability; (4) Through the aforementioned composition and process, a high-purity single-phase, high-density (relative density up to 98.54%) ceramic body was obtained, with stable material structure and reliable performance; (5) The materials and preparation method of this invention provide a new solution for high-performance, low-cost microwave dielectric ceramics. The provided calcium chromium garnet microwave dielectric ceramic material has a low dielectric constant, a high quality factor, and good temperature stability of the resonant frequency, exhibiting outstanding comprehensive dielectric properties. These characteristics make it very suitable for fabricating microwave devices for high-speed signal transmission, such as dielectric antennas, microwave substrates, and dielectric resonators, and it has broad application potential. Attached Figure Description

[0023] Figure 1 The Ca3Cr2(Si) prepared in Example 1 of this invention 0.975 Ge 0.025 )3O 12 XRD and SEM images of ceramics, where Figure a is the XRD image and Figure b is the SEM image; Figure 2 The Ca3Cr2(Si) prepared in Example 2 of this invention 0.95 Ge 0.05 )3O12 XRD and SEM images of ceramics, where Figure a is the XRD image and Figure b is the SEM image; Figure 3 The Ca3Cr2(Si) prepared in Example 3 of this invention 0.9 Ge 0.1 )3O 12 XRD and SEM images of ceramics, where Figure a is the XRD image and Figure b is the SEM image; Figure 4 The Ca3Cr2(Si) prepared in Example 4 of this invention 0.8 Ge 0.2 )3O 12 XRD and SEM images of ceramics, where Figure a is the XRD image and Figure b is the SEM image; Figure 5 The Ca3Cr2(Si) prepared in Example 5 of this invention 0.6 Ge 0.4 )3O 12 XRD and SEM images of ceramics, where Figure a is the XRD image and Figure b is the SEM image; Figure 6 Ca3Cr2Si3O prepared for Comparative Example 1 of this invention 12 XRD and SEM images of ceramics, where Figure a is the XRD image and Figure b is the SEM image. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0025] This invention provides a germanium-doped calcium chromium garnet microwave dielectric ceramic with the chemical formula Ca3Cr2(Si). 1- x Ge x )3O 12 Where x is the mole fraction of Ge, and 0.025 ≤ x ≤ 0.4. In fact, through Ge... 4+ Partially replaces Si 4+The composition control strategy, combined with atmospheric pressure solid-state reaction and gradient cold isostatic pressing, effectively stabilized the garnet crystal structure and significantly suppressed the volatilization and material decomposition of Cr during high-temperature sintering, successfully solving the problem of traditional Ca3Cr2Si3O4. 12 The fundamental problem of obtaining pure-phase dense ceramics; while possessing a low dielectric constant ( ε r =7.67~8.66), high quality factor ( Q × f =13871~39146GHz) and a good temperature coefficient of resonant frequency ( τ f =-41~-36ppm / ℃), meeting the stringent requirements of 5G / 6G high-frequency communication devices for low loss and high stability.

[0026] The present invention also provides a method for preparing the above-mentioned germanium-doped calcium chromium garnet microwave dielectric ceramic, comprising the following steps: S1. Batching and primary ball milling: Weigh the raw materials CaCO3, Cr2O3, SiO2 and GeO2, mix them and perform the first wet ball milling treatment to obtain a mixed slurry; S2. Drying and pre-calcination: The mixed slurry is dried and then pre-calcined to obtain pre-calcined powder; S3. Secondary ball milling and granulation: The pre-fired powder is subjected to a second wet ball milling process, and after drying, ceramic powder is obtained; a binder is added to the ceramic powder for granulation to obtain granulated powder; S4. Molding and cold isostatic pressing: The granulated powder is pressed into a green body, and the green body is vacuum sealed and then subjected to cold isostatic pressing. S5. Sintering: The green body after cold isostatic pressing is sintered to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic; its general chemical formula is Ca3Cr2(Si 1-x Ge x )3O 12 Where x is the mole fraction of Ge, and 0.025 ≤ x ≤ 0.4.

[0027] In some embodiments, during step S1, CaCO3, Cr2O3, SiO2, and GeO2 are mixed according to the general chemical formula Ca3Cr2(SiO2). 1-x Ge x )3O 12 The materials were mixed in stoichiometric proportions. Specifically, the purity of CaCO3, SiO2, and GeO2 used was 99.99%, and the purity of Cr2O3 used was 99.95%.

[0028] In fact, by using water-insoluble Cr2O3 as the chromium source, the use of Cr-containing compounds is avoided.6+ The potential environmental pollution and safety risks posed by compounds (such as K2Cr2O7), while utilizing Ge 4+ Replace Si 4+ By precisely controlling the stoichiometric ratio, the thermodynamic stability of ceramic samples can be improved, thereby obtaining high-purity Ca3Cr2(Si) 1-x Ge x )3O 12 Ceramics. Utilizing Ge 4+ Replace Si 4+ It can effectively inhibit its high-temperature decomposition, while making Ca3Cr2Si3O 12 The quality factor of ceramics has been significantly improved.

[0029] In some embodiments, when performing step S1, the conditions used for the first wet ball milling process are as follows: using zirconia balls as the ball milling media; using anhydrous ethanol as the ball milling aid; ball milling at a speed of 500 r / min for 8 hours; and the mass ratio of the raw materials, ball milling media and ball milling aid used is 1:3:3.

[0030] In some embodiments, during step S2, drying is performed at a temperature of 65°C-75°C for 8-12 hours.

[0031] In some embodiments, during step S2, the pre-firing temperature is 1300℃-1400℃, the holding time is 2h-6h, and the heating rate is 5℃ / min. Specifically, the preferred pre-firing conditions are: temperature 1350℃, holding time 4h, and heating rate 5℃ / min.

[0032] In some embodiments, when performing step S3, the conditions used for the second wet ball milling process are as follows: using zirconia balls as the ball milling media; using anhydrous ethanol as the ball milling aid; ball milling at a speed of 500 r / min for 8 hours; and the mass ratio of the pre-calcined powder, the ball milling media, and the ball milling aid is 1:3:3.

[0033] Specifically, during step S1 or step S3, the zirconia balls used in the first and second wet ball milling processes are independently composed of zirconia balls with diameters of 1 mm, 3 mm, 5 mm, and 7 mm. In practice, using zirconia balls of different diameters allows for more thorough grinding of agglomerated samples.

[0034] In fact, the first wet ball milling process is to ensure that the raw materials CaCO3, Cr2O3, SiO2 and GeO2 are mixed evenly, so that the subsequent pre-firing reaction is more complete; the second wet ball milling process is to make the powder of the sample that has agglomerated after pre-firing finer, so that the ceramic sample after subsequent sintering is more dense; the drying process after ball milling is to make the anhydrous ethanol mixed during ball milling evaporate and obtain a dry powder sample.

[0035] In some embodiments, during step S3, drying is performed at a temperature of 65°C-75°C for 8-12 hours. Specifically, the preferred drying conditions are: a drying temperature of 70°C and a drying time of 8-12 hours.

[0036] In some embodiments, when performing step S3, granulation includes: mixing ceramic powder with an adhesive and then grinding it, passing it through 40-mesh and 80-mesh sieves, and collecting particles with a particle size between 40 and 80 mesh; the adhesive used is a 7% by mass aqueous solution of polyvinyl alcohol (PVA).

[0037] In some embodiments, during step S4, the granulated powder is pressed into shape under a pressure of 10 MPa. In reality, although the granulated powder has good flowability, direct cold isostatic pressing may not result in uniform stress distribution. Therefore, pressing can serve as a pre-forming process. Low pressure is used to initially transform the loose granulated powder into a green body with a basic shape, certain mechanical strength, and a relatively uniform internal structure, providing a prerequisite for subsequent advanced densification processes (such as cold isostatic pressing).

[0038] Specifically, a vacuum sealing process occurs between pressing the granulated powder into shape and cold isostatic pressing the green body. This involves placing the green body obtained after pressing into shape into a plastic bag, removing the air from the bag, and sealing it. In effect, vacuum sealing isolates the green body from the medium during subsequent processing, preventing sample contamination. It also eliminates a large number of voids and residual air inside and on the surface of the green body, eliminating the "air cushion" effect and ensuring that the pressure is applied directly and evenly to the green body during the subsequent cold isostatic pressing process.

[0039] In some embodiments, when performing step S4, the cold isostatic pressing process is performed using a gradient pressurization method; the gradient pressurization method includes at least two pressure stages, and the pressure value of the later stage is higher than that of the earlier stage.

[0040] In some embodiments, deionized water is used as the pressure medium for cold isostatic pressing when performing step S4.

[0041] In some embodiments, the pressures applied sequentially during gradient pressurization include 20 MPa, 40 MPa, 80 MPa, 160 MPa, 200 MPa, and 220 MPa.

[0042] In fact, cold isostatic pressing (CIP) can densify the green body, significantly shorten sintering time, lower the required sintering temperature, better promote densification, and reduce the risk of chromium-containing garnet decomposition at high temperatures. Secondly, the losses in microwave dielectric ceramics mainly originate from intrinsic lattice vibrations and intrinsic factors (such as porosity, impurities, and grain boundary defects). CIP, by maximizing the reduction of porosity and creating a uniform microstructure starting point, makes it possible to obtain an ideal microstructure with clear grain boundaries, minimal porosity, and low defect density after sintering. Q × f The physical basis of the energy value up to 39146GHz is the guarantee for ultimately achieving the material's "high purity, high uniformity, and low loss".

[0043] In some embodiments, the sintering temperature is 1400℃-1550℃, and the holding time is 2h-6h. Specifically, the preferred sintering conditions are: a sintering temperature of 1430℃-1510℃ and a holding time of 4h.

[0044] In some embodiments, the sintering process includes: first heating to 600°C at a rate of 5°C / min and holding for 4 hours to remove the adhesive; then heating to 1430°C-1510°C at a rate of 5°C / min and holding for 4 hours; finally, cooling in the furnace. In practice, heating to 600°C at a gradual rate of 5°C / min and holding for a long time (4 hours) ensures that the organic adhesive has sufficient time to slowly and completely oxidize and decompose into CO2 and H2O gases and be slowly discharged, avoiding damage to the green body structure; subsequently, holding at 1430°C-1510°C for 4 hours achieves high-temperature densification and crystallization. Specifically, the resulting germanium-doped calcium chromium garnet microwave dielectric ceramic has a relative density of over 98.54% and exhibits excellent microwave dielectric properties.

[0045] The present invention also provides an application of germanium-doped calcium chromium garnet microwave dielectric ceramic prepared using any of the above embodiments in the fabrication of microwave devices, wherein the microwave devices include dielectric resonators, filters, dielectric antennas, or microwave substrates.

[0046] In the following embodiments and comparative examples of the present invention, the zirconia balls used as the milling media are composed of zirconia balls with a diameter of 1 mm, zirconia balls with a diameter of 3 mm, zirconia balls with a diameter of 5 mm, and zirconia balls with a diameter of 7 mm. Example 1

[0047] This embodiment 1 provides a germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(Si) 0.975 Ge 0.025 )3O 12 The preparation method of ) includes the following steps: S1, according to Ca3Cr2(Si 0.975Ge 0.025 )3O 12 The stoichiometric ratio (molar ratio) of CaCO3 (purity 99.99%), Cr2O3 (purity 99.95%), SiO2 (purity 99.99%) and GeO2 (purity 99.99%) was determined, and the weights were weighed to an accuracy of 0.0001 g. After mixing, a raw material mixture was obtained. The raw material mixture, zirconia balls, and anhydrous ethanol were loaded into a polyethylene ball mill jar at a mass ratio of 1:3:3 and ball milled thoroughly at 500 r / min for 8 h to obtain a mixed slurry. S2. The mixed slurry obtained in step S1 is dried at 70°C for 8-12 hours, then placed in an alumina crucible and heated to 1350°C at a heating rate of 5°C / min, and pre-calcined at 1350°C for 4 hours to obtain pre-calcined powder. S3. Add the pre-fired powder, zirconia balls, and anhydrous ethanol to a polyethylene ball mill jar in a mass ratio of 1:3:3. Mill the powder thoroughly at 500 r / min for 8 hours. Dry the powder at 70℃ for 8 to 12 hours to obtain ceramic powder. Granulate the ceramic powder in an agate mortar using a 7wt% PVA aqueous solution as a binder. Pass the granules through 40-mesh and 80-mesh sieves to obtain particles with a particle size between 40 and 80 mesh.

[0048] S4. The sample particles prepared in step S3 are pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder tablet press (pressure 10 MPa). The cylindrical green bodies are then neatly arranged and placed into a plastic sealing bag. The air in the plastic sealing bag is expelled using a vacuum pump, and the bag is sealed by heating. Then, deionized water is used as the pressure medium and gradient pressure is applied in a warm water isostatic press at pressures of 20, 40, 80, 160, 200, and 220 MPa, with processing times of 1 min, 1 min, 1 min, 1 min, 1 min, and 30 min, respectively. S5. After removing the plastic seal, the cylindrical green body is debonded at 600℃, and then sintered at 1460℃ for 4 hours (heating rate of 5℃ / min) to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(Si 0.975 Ge 0.025 )3O 12 ceramics).

[0049] The Ca3Cr2(Si) prepared in Example 1 0.975 Ge 0.025 )3O 12 XRD and SEM images of the ceramics are shown below. Figure 1 ;in, Figure 1 Figure a in the diagram is an XRD pattern. Figure 1 Image b in the image is an SEM image.

[0050] from Figure 1 As can be seen from Ca3Cr2Si3O 12 (PDF#01-076-2981) Calibrates the Ca3Cr2(Si) prepared in this embodiment. 0.975 Ge 0.025 )3O 12 The X-ray diffraction peaks observed in the ceramic sintered at 1460℃, along with the absence of a second phase, indicate that a single phase can be formed at this temperature, further proving the existence of Ge. 4+ Entering Ca3Cr2Si3O 12 Crystal lattice. Combined with SEM images, it can be found that when the doping amount is 0.075 mol (accounting for 2.5 mol% of the total amount of Ge and Si) and the sintering temperature is 1460℃, the ceramic grain size is uniform, the grains are spherical, and the result is relatively low density. Example 2

[0051] This embodiment 2 provides a germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(Si) 0.95 Ge 0.05 )3O 12 The preparation method of Ca3Cr2(Si) differs from that of Example 1 in that, in step S1, the method follows the steps described in Example 1. 0.95 Ge 0.05 )3O 12 The stoichiometric ratio (molar ratio) of CaCO3 (99.99% purity), Cr2O3 (99.95% purity), SiO2 (99.99% purity), and GeO2 (99.99% purity) was determined, and the amounts were weighed to an accuracy of 0.0001 g. After mixing, a raw material mixture was obtained. In step S5, after removing the plastic seal, the cylindrical green body was debonded at 600℃, and then sintered at 1430℃ for 4 hours (heating rate of 5℃ / min) to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(SiO2)O3, Cr2 ... 0.95 Ge 0.05 )3O 12 ceramics).

[0052] The Ca3Cr2(Si) prepared in Example 2 0.95 Ge 0.05 )3O 12 XRD and SEM images of the ceramics are shown below. Figure 2 ;in, Figure 2 Figure a in the diagram is an XRD pattern. Figure 2 Image b in the image is an SEM image.

[0053] from Figure 2 As can be seen from Ca3Cr2Si3O 12 (PDF#01-076-2981) Calibrates the Ca3Cr2(Si) prepared in this embodiment.0.95 Ge 0.05 )3O 12 The X-ray diffraction peaks observed in the ceramic sintered at 1430℃, along with the absence of a second phase, indicate that a single phase can be formed at this temperature, further proving the existence of Ge. 4+ Entering Ca3Cr2Si3O 12 Crystal lattice. Combined with SEM images, it can be found that when the doping amount is 0.15 mol (accounting for 2.5 mol% of the total amount of Ge and Si) and the sintering temperature is 1430℃, the lower sintering temperature results in smaller ceramic grain size, with the grains being spherical and exhibiting a more dense structure. Example 3

[0054] This embodiment 3 provides a germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(Si) 0.9 Ge 0.1 )3O 12 The preparation method of Ca3Cr2(Si) differs from that of Example 1 in that, in step S1, the method follows the steps described in Example 1. 0.9 Ge 0.1 )3O 12 The stoichiometric ratio (molar ratio) of CaCO3 (99.99% purity), Cr2O3 (99.95% purity), SiO2 (99.99% purity), and GeO2 (99.99% purity) was determined, and the amounts were weighed to an accuracy of 0.0001 g. After mixing, a raw material mixture was obtained. In step S5, after removing the plastic seal, the cylindrical green body was debonded at 600℃, and then sintered at 1490℃ for 4 hours (heating rate of 5℃ / min) to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(SiO2)O3, Cr2 ... 0.9 Ge 0.1 )3O 12 ceramics).

[0055] The Ca3Cr2(Si) prepared in Example 3 0.9 Ge 0.1 )3O 12 XRD and SEM images of the ceramics are shown below. Figure 3 ;in, Figure 3 Figure a in the diagram is an XRD pattern. Figure 3 Image b in the image is an SEM image.

[0056] from Figure 3 As can be seen from Ca3Cr2Si3O 12 (PDF#01-076-2981) Calibrates the Ca3Cr2(Si) prepared in this embodiment. 0.9 Ge 0.1 )3O 12The X-ray diffraction peaks observed in the ceramic sintered at 1490℃, along with the absence of a second phase, indicate that a single phase can be formed at this temperature, further proving the existence of Ge. 4+ Entering Ca3Cr2Si3O 12 Crystal lattice. Combined with SEM images, it can be found that when the doping amount is 0.3 mol (accounting for 10 mol% of the total amount of Ge and Si) and the sintering temperature is 1490℃, the ceramic grain size is relatively large, resulting in a relatively dense structure. Example 4

[0057] This embodiment 4 provides a germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(Si) 0.8 Ge 0.2 )3O 12 The preparation method of Ca3Cr2(Si) differs from that of Example 1 in that, in step S1, the method follows the steps described in Example 1. 0.8 Ge 0.2 )3O 12 The stoichiometric ratio (molar ratio) of CaCO3 (99.99% purity), Cr2O3 (99.95% purity), SiO2 (99.99% purity), and GeO2 (99.99% purity) was determined, and the amounts were weighed to an accuracy of 0.0001 g. After mixing, a raw material mixture was obtained. In step S5, after removing the plastic seal, the cylindrical green body was debonded at 600℃, and then sintered at 1510℃ for 4 hours (heating rate of 5℃ / min) to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(SiO2)O3, Cr2 ... 0.8 Ge 0.2 )3O 12 ceramics).

[0058] The Ca3Cr2(Si) prepared in Example 4 0.8 Ge 0.2 )3O 12 XRD and SEM images of the ceramics are shown below. Figure 4 ;in, Figure 4 Figure a in the diagram is an XRD pattern. Figure 4 Image b in the image is an SEM image.

[0059] from Figure 4 As can be seen from Ca3Cr2Si3O 12 (PDF#01-076-2981) Calibrates the Ca3Cr2(Si) prepared in this embodiment. 0.8 Ge 0.2 )3O 12 The X-ray diffraction peaks observed in the ceramic sintered at 1510℃, along with the absence of a second phase, indicate that a single phase can be formed at this temperature, further proving the existence of Ge. 4+ Entering Ca3Cr2Si3O 12Crystal lattice. Combined with SEM images, it can be found that when the doping amount is 0.6 mol (accounting for 20 mol% of the total amount of Ge and Si) and the sintering temperature is 1510℃, the ceramic grain size is relatively large, the grain boundaries are obvious, and the result is dense. Example 5

[0060] This embodiment 5 provides a germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(Si) 0.6 Ge 0.4 )3O 12 The preparation method of Ca3Cr2(Si) differs from that of Example 1 in that, in step S1, the method follows the steps described in Example 1. 0.6 Ge 0.4 )3O 12 The stoichiometric ratio (molar ratio) is determined by weighing CaCO3 (99.99% purity) and Cr2O3 (99.95% purity). SiO2 (99.99% purity) and GeO2 (99.99% purity), accurate to 0.0001g, are mixed to obtain a raw material mixture; after removing the plastic seal in step S5, the cylindrical green body is debonded at 600℃, and then sintered at 1510℃ for 4h (heating rate of 5℃ / min) to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2(SiO2)O2) 0.6 Ge 0.4 )3O 12 ceramics).

[0061] The Ca3Cr2(Si) prepared in Example 5 0.6 Ge 0.4 )3O 12 XRD and SEM images of the ceramics are shown below. Figure 5 ;in, Figure 5 Figure a in the diagram is an XRD pattern. Figure 5 Image b in the image is an SEM image.

[0062] from Figure 5 As can be seen from Ca3Cr2Si3O 12 (PDF#01-076-2981) Calibrates the Ca3Cr2(Si) prepared in this embodiment. 0.6 Ge 0.4 )3O 12 The X-ray diffraction peaks observed in the ceramic sintered at 1510℃, along with the absence of a second phase, indicate that a single phase can be formed at this temperature, further proving the existence of Ge. 4+ Entering Ca3Cr2Si3O 12Crystal lattice. Combined with SEM images, it can be found that when the doping amount is 1.2 mol (accounting for 10 mol% of the total amount of Ge and Si) and the sintering temperature is 1510℃, the grain growth is rapid, the ceramic grain size is large, the grain boundaries are obvious, and the result is relatively dense.

[0063] Comparative Example 1 Comparative Example 1 provides a calcium chromium garnet microwave dielectric ceramic (Ca3Cr2Si3O4). 12 The preparation method of Ca3Cr2Si3O differs from that of Example 1 in that, in step S1, Ca3Cr2Si3O 12 The stoichiometric ratio (molar ratio) of CaCO3 (99.99% purity), Cr2O3 (99.95% purity), and SiO2 (99.99% purity) was determined, and the weights were weighed to an accuracy of 0.0001 g. The mixture was then obtained. In step S2, the temperature was increased to 1370℃ at a rate of 5℃ / min, and pre-fired at 1370℃ for 4 hours to obtain pre-fired powder. In step S5, after removing the plastic seal, the cylindrical green body was debonded at 600℃, and then sintered at 1420℃ for 4 hours (heating rate of 5℃ / min) to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic (Ca3Cr2Si3O3). 12 ceramics).

[0064] The Ca3Cr2Si3O prepared in Comparative Example 1 12 XRD and SEM images of the ceramics are shown below. Figure 6 ;in, Figure 6 Figure a in the diagram is an XRD pattern. Figure 6 Image b in the image is an SEM image.

[0065] from Figure 6 As can be seen from Ca3Cr2Si3O 12 (PDF#01-076-2981) Calibration of Ca3Cr2Si3O prepared in this embodiment 12 X-ray diffraction peaks of the ceramic sintered at 1420℃ revealed the presence of a small amount of a second phase, with impurities mainly consisting of CaSiO3 and Cr2O3. Combined with SEM images, it was found that at a sintering temperature of 1420℃, the ceramic grain size was smaller, the grains were more compact, and the grain boundaries were more distinct, resulting in a relatively dense structure.

[0066] The density, sintering temperature, and microwave dielectric properties of the calcium chromium garnet microwave dielectric ceramic materials prepared in Examples 1 to 5 and Comparative Example 1 were measured (the microwave dielectric properties were evaluated using the resonant cavity method), and the results are shown in Table 1.

[0067] Table 1: Properties of Calcium Chromium Garnet Microwave Dielectric Ceramic Materials

[0068] As shown in Table 1, the density of the stable calcium chromium garnet microwave dielectric ceramic material achieved by the present invention through germanium doping control is 3.559 g / cm³. 3 ~4.082 g / cm 3 Its relative density is 92.296%~98.543%, and its dielectric constant is... ε r The quality factor is 7.67~8.66. Q × f The resonant frequency temperature coefficient ranges from 13871 to 39146 GHz. τ f The dielectric constant is -41.4 to -36.2 ppm / ℃. From the above data, it can be seen that the germanium-doped calcium chromium garnet microwave dielectric ceramic prepared by this invention has excellent microwave dielectric properties. Therefore, it can be widely used in the manufacture of microwave communication components such as dielectric antennas, microwave substrates, and dielectric resonators, meeting the technical needs of mobile communication and satellite communication systems.

[0069] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A germanium-doped calcium chromium garnet microwave dielectric ceramic, characterized in that, Its general chemical formula is Ca3Cr2(Si) 1-x Ge x )3O 12 Where x is the mole fraction of Ge, and 0.025 ≤ x ≤ 0.

4.

2. A method for preparing germanium-doped calcium chromium garnet microwave dielectric ceramic as described in claim 1, characterized in that, Includes the following steps: S1. Batching and primary ball milling: Weigh the raw materials CaCO3, Cr2O3, SiO2 and GeO2, mix them and perform the first wet ball milling treatment to obtain a mixed slurry; S2. Drying and pre-calcination: The mixed slurry is dried and then pre-calcined to obtain pre-calcined powder; S3. Secondary ball milling and granulation: The pre-fired powder is subjected to a second wet ball milling process, and after drying, ceramic powder is obtained; a binder is added to the ceramic powder for granulation to obtain granulated powder; S4. Molding and cold isostatic pressing: The granulated powder is pressed into a green body, and the green body is vacuum sealed and then subjected to cold isostatic pressing. S5. Sintering: The green body after cold isostatic pressing is sintered to obtain germanium-doped calcium chromium garnet microwave dielectric ceramic; its general chemical formula is Ca3Cr2(Si 1-x Ge x )3O 12 Where x is the mole fraction of Ge, and 0.025 ≤ x ≤ 0.

4.

3. The method according to claim 2, characterized in that, In S1, the CaCO3, Cr2O3, SiO2, and GeO2 are mixed in stoichiometric proportions according to the general chemical formula; and / or, the conditions for the first wet ball milling treatment are: using zirconia balls as the ball milling media; using anhydrous ethanol as the ball milling aid; ball milling at 500 r / min for 8 h; and the mass ratio of the raw material, the ball milling media, and the ball milling aid is 1:3:

3.

4. The method according to claim 2, characterized in that, In S2, the drying is performed at a temperature of 65℃-75℃ for 8-12 hours; and / or, the pre-firing temperature is 1300℃-1400℃, followed by heat preservation. The time is 2h-6h, and the heating rate is 5℃ / min.

5. The method according to claim 2, characterized in that, In S3, the conditions for the second wet ball milling treatment are as follows: using zirconia balls as the ball milling medium; using anhydrous ethanol as the ball milling aid; ball milling at a speed of 500 r / min for 8 h; the mass ratio of the pre-calcined powder, the ball milling medium, and the ball milling aid is 1:3:3; and / or, the drying is performed at a temperature of 65℃-75℃ for 8 h-12 h; and / or, the granulation includes: mixing the ceramic powder with an adhesive and then grinding it, passing it through 40 mesh and 80 mesh sieves, and collecting particles with a particle size between 40 and 80 mesh; the adhesive is a 7% (w / w) polyvinyl alcohol aqueous solution.

6. The method according to claim 2, characterized in that, In S4, the granulated powder is pressed into shape under a pressure of 10 MPa; and / or, the cold isostatic pressing process is carried out using a gradient pressurization method; the gradient pressurization method includes at least two pressure stages, and the pressure value of the later stage is higher than that of the previous stage; and / or, the pressure medium used in the cold isostatic pressing is deionized water.

7. The method according to claim 6, characterized in that, The pressures applied sequentially by the gradient pressurization include 20 MPa, 40 MPa, 80 MPa, 160 MPa, 200 MPa and 220 MPa.

8. The method according to claim 2, characterized in that, The sintering temperature is 1400℃-1550℃, and the holding time is 2h-6h.

9. The method according to claim 2, characterized in that, The sintering process includes: first, heating to 600°C at a heating rate of 5°C / min and holding for 4 hours to remove the adhesive; then heating to 1430°C-1510°C at a heating rate of 5°C / min and holding for 4 hours; finally, cooling down with the furnace.

10. The application of the germanium-doped calcium chromium garnet microwave dielectric ceramic as described in claim 1 in the fabrication of microwave devices, characterized in that, The microwave device includes a dielectric resonator, a filter, a dielectric antenna, or a microwave substrate.

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