A microwave dielectric ceramic material, its preparation method and a microwave communication device

Abstract

This application relates to a microwave dielectric ceramic material, its preparation method, and a microwave communication device, belonging to the field of dielectric ceramics. A preparation method of a microwave dielectric ceramic material includes: mixing raw materials MgO and MoO3 in a molar ratio of 1:(1.5 - 2) to obtain a raw material; mixing the raw material with a grinding medium, and successively performing first ball milling, drying, and pre-sintering treatments to obtain a ceramic sample block; successively performing second ball milling, drying, pressing molding, and sintering treatments on the ceramic sample block to obtain the microwave dielectric ceramic material; wherein, the pre-sintering temperature is 500 - 650 °C, and the pre-sintering time is 2 - 4 h; the sintering temperature is 650 - 800 °C, and the sintering time is 4 - 6 h. The microwave dielectric ceramic material prepared by this preparation method can be sintered at a low temperature and simultaneously has a high quality factor and a low dielectric constant.

Description

Technical Field

[0001] The present application relates to the field of dielectric ceramic technology, and particularly to a microwave dielectric ceramic material, a preparation method thereof, and a microwave communication device. Background Art

[0002] Microwave dielectric ceramics are special ceramic materials used in microwave and radio frequency (RF) electronic devices, with excellent electrical and thermal properties. These ceramic materials are usually used to manufacture components such as antennas, filters, couplers, resonators, and dielectric substrates for transmitting, receiving, and processing microwave signals. They are widely used in many fields, including satellite communication, Internet of Things, software-defined radio, Global Positioning System (GPS), direct broadcast satellite television (DBS TV), and satellite environmental monitoring, etc.

[0003] Microwave dielectric ceramic materials play a crucial role in today's communication technology field. Especially with the popularization of 5G and 6G high-frequency applications, higher requirements are put forward for material properties. These materials not only need to have characteristics such as low dielectric constant, high quality factor, and temperature stability, but also need to perform well in miniaturization, high performance, and multifunctionality. Low-temperature co-fired ceramics (LTCC), as a very important technology in electronic communication, is mainly used in the technical aspects of high-integration and high-performance electronic packaging, and has great potential in terms of design flexibility, wiring density, and reliability. However, most traditional electronic ceramics cannot meet the requirements of LTCC technology for materials because the sintering temperature of the ceramics is still too high to co-fire with electrodes having a lower melting point. With the development of wearable wireless communication devices and the demand for device multifunctional integration development, the new trend of ceramic material development needs to co-fire with semiconductors, polymers, and metals, which requires the ceramic materials to have an ultra-low sintering temperature. Low-temperature sintering microwave dielectric ceramic materials can reduce energy consumption, inhibit the evaporation of volatile components, and can also reduce the reaction with other materials. Developing ultra-low temperature sintering microwave dielectric materials has become one of the research hotspots. Most dielectric materials with a high quality factor (Qf value) require a high sintering temperature, and usually sintering aids are added to reduce their sintering temperature, and the final densification of the sample is achieved through liquid-phase sintering, but this usually leads to the deterioration of the microwave dielectric properties of the material. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the objectives of the embodiments of the present application include providing a microwave dielectric ceramic material to achieve low-temperature sintering while having a high quality factor and a low dielectric constant.

[0005] In a first aspect, an embodiment of the present application provides a method for preparing a microwave dielectric ceramic material, including: mixing raw materials MgO and MoO3 in a molar ratio of 1:(1.5 - 2) to obtain a raw material; mixing the raw material with a grinding medium, and successively performing first ball milling, drying, and pre-sintering treatments to obtain a ceramic sample block; successively performing second ball milling, drying, pressing into shape, and sintering treatments on the ceramic sample block to obtain the microwave dielectric ceramic material; wherein, the temperature of the pre-sintering is 500 - 650 °C, and the time of the pre-sintering is 2 - 4 h; the temperature of the sintering is 650 - 800 °C, and the time of the sintering is 4 - 6 h. In the preparation method provided by the present application, by performing pre-sintering at 500 - 650 °C, organic substances and other volatile impurities that may exist in the raw material will volatilize at high temperature, purifying the raw material; thereby reducing the gases and odors generated during the subsequent sintering process, and thus improving the purity of the product. Moreover, the pre-sintering process can adjust and improve the crystal structure of the ceramic material, promote the particles to be more dense and uniform, and generate the required phases. This can improve the mechanical properties and microwave properties of the material, making it more stable under working conditions. At the same time, the pre-sintering process can eliminate the internal stress in the raw material, making the material less likely to crack or deform during the subsequent sintering process, thereby improving the overall stability of the microwave dielectric ceramic material. Further, sintering the ceramic sample block obtained after pre-sintering at 650 - 800 °C can make the material have a high density after sintering at a low temperature, thereby having a high quality factor and a low dielectric constant to meet the requirements of microwave communication devices. In addition, in the present application, since the synthesized molybdate powder has good fluidity, the powder in the present application does not need to be granulated and can be directly pressed into a tablet for subsequent sintering to obtain the required ceramic sample, so the preparation process steps are simple.

[0006] Second aspect, an embodiment of the present application provides a method for preparing a microwave dielectric ceramic material, including: mixing raw materials MgO and MoO3 in a molar ratio of 1:(1.5 - 2) to obtain a raw material; mixing the raw material with a grinding medium, and successively performing first ball milling, drying, and pre-sintering treatments to obtain a ceramic sample block; mixing the ceramic sample block with TiO2 according to the stoichiometric ratio of (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2, and then successively performing second ball milling, drying, pressing, and sintering treatments to obtain the microwave dielectric ceramic material; wherein, the pre-sintering temperature is 500 - 650 °C, and the pre-sintering time is 2 - 4 h; the sintering temperature is 650 - 800 °C, and the sintering time is 4 - 6 h. In the preparation method provided by the present application, by pre-sintering at 500 - 650 °C, organic substances and other volatile impurities that may exist in the raw material will volatilize at high temperature, purifying the raw material; thereby reducing the gases and odors generated during the subsequent sintering process, and thus improving the purity of the product. Moreover, the pre-sintering process can adjust and improve the crystal structure of the ceramic material, promote the particles to be more dense and uniform, and generate the required phases. This can improve the mechanical properties and microwave properties of the material, making it more stable under working conditions. At the same time, the pre-sintering process can eliminate the internal stress in the raw material, making the material less likely to crack or deform during the subsequent sintering process, thereby improving the overall stability of the microwave dielectric ceramic material. Further, the ceramic sample block obtained after pre-sintering is mixed with TiO2 according to the stoichiometric ratio of (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2 and sintered at 650 - 800 °C. By doping a small amount of TiO2 into the MgMo2O7 material, the obtained (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2 material can have a higher density and quality factor after sintering at low temperature, and its frequency temperature coefficient is closer to zero than that of the pure MgMo2O7 material, so as to meet the requirements of microwave communication devices. In addition, in the present application, since the synthesized molybdate powder has good fluidity, the powder in the present application does not need to be granulated and can be directly pressed into tablets for subsequent sintering to obtain the required ceramic sample. Therefore, the preparation process steps are simple.

[0007] In some embodiments of the present application, the first ball milling includes: adding the raw material, zirconium balls, and the grinding medium into a ball mill tank in a mass ratio of 1:(1.5 - 2):1 for the first ball milling.

[0008] In some embodiments of the present application, the grinding medium includes anhydrous ethanol. Anhydrous ethanol is selected as the ball milling medium because it has moderate viscosity and stability during the preparation of the microwave dielectric ceramic material, is easy to control, and does not introduce additional moisture or safety risks.

[0009] In some embodiments of the present application, the conditions for the first ball milling include: the ball milling speed is 200 - 300 r / min, and the ball milling time is 4 - 8 h. Within the above ranges of ball milling speed and ball milling time, the raw materials can be ground more fully and evenly.

[0010] In some embodiments of the present application, the conditions for the second ball milling include: the ball milling speed is 200 - 300 r / min, and the ball milling time is 4 - 8 h. The main purpose of the second ball milling is to grind the ceramic powder finer, which is more conducive to the subsequent sintering reaction.

[0011] By controlling the mass ratios of the raw materials, zirconium balls, and grinding medium, as well as the ball milling speed and time within the above ranges, it helps to obtain a uniform mixture, and can also achieve efficient material grinding, which is beneficial to improving the reactivity and compressibility of the raw materials and enhancing the quality of the ceramic materials.

[0012] In some embodiments of the present application, after the drying step, a sieving step is further included, and the mesh number of the sieve is 100 - 220. By sieving, larger or smaller particles can be removed, thereby obtaining a more uniform particle size distribution and making the prepared ceramic materials more stable and homogeneous.

[0013] In some embodiments of the present application, the drying temperature is 80 - 120 °C; and / or, the drying time is 15 - 18 h. Drying can effectively remove the moisture and humidity in the powder. By limiting the drying temperature and time within the above ranges, it helps to reduce the water content of the powder and improve the effect of subsequent processing steps.

[0014] In some embodiments of the present application, the conditions for pressing and forming include: the pressing pressure is 200 - 300 MPa.

[0015] In a third aspect, an embodiment of the present application provides a microwave dielectric ceramic material prepared by the above preparation method. This microwave dielectric ceramic material includes MgMo2O7. This material has both a high quality factor and a low dielectric constant.

[0016] In a fourth aspect, an embodiment of the present application provides a microwave dielectric ceramic material prepared by the above preparation method. This microwave dielectric ceramic material includes (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2. By doping TiO2 into the ceramic material in the present application, while the ceramic material has a high quality factor, its frequency temperature coefficient is closer to zero than that of a pure MgMo2O7 material.

[0017] In a fifth aspect, an embodiment of the present application provides a microwave communication device, including any of the above microwave dielectric ceramic materials. Description of the Drawings

[0018] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as a limitation of the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0019] Figure 1 The S 11 curve and the simulated S 11 curve of the antenna prepared from the ceramic material in Embodiment 1 of the present application;

[0020] Figure 2 The S 11 curve and the simulated S 11 curve of the antenna prepared from the ceramic material in Comparative Example 1 of the present application;

[0021] Figure 3 The simulated radiation pattern at the H-plane of the antenna fabricated based on β-MgMo2O7 in the present application;

[0022] Figure 4 The simulated radiation pattern at the E-plane of the antenna fabricated based on β-MgMo2O7 in the present application;

[0023] Figure 5 The simulated radiation pattern at the H-plane of the antenna fabricated based on MgMoO4 in the present application;

[0024] Figure 6 The simulated radiation pattern at the E-plane of the antenna fabricated based on MgMoO4 in the present application;

[0025] Figure 7 The simulated 3D far-field pattern at 5.8 GHz of the antenna fabricated based on β-MgMo2O7 in the present application;

[0026] Figure 8 The simulated 3D far-field radiation pattern at 5.8 GHz of the antenna fabricated based on MgMoO4 in the present application. Detailed implementation manners

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. For those not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchases.

[0028] With the development of high-frequency applications such as 5G and 6G, higher requirements are put forward for the performance of microwave dielectric ceramic materials, especially in terms of low dielectric constant, high quality factor, and frequency temperature coefficient. In high-frequency applications, substrate materials with low dielectric constant become particularly important because they can reduce the parasitic capacitance between traces and conductive structures and lower the communication signal transmission delay. At the same time, high-quality factor materials can reduce signal and electrical energy losses and are very suitable for high-power and high-performance applications. In addition, materials with a frequency temperature coefficient close to zero exhibit excellent temperature stability and are very suitable for electronic devices operating under extreme temperature conditions.

[0029] However, high performance and low sintering temperature are often contradictory in ceramic materials. A lower sintering temperature may lead to insufficient grain growth, resulting in poor ceramic densification and significantly deteriorating its performance. Therefore, low-temperature sintering microwave dielectric ceramics often require systems with low melting points. The currently reported low-temperature sintering microwave dielectric ceramic systems are mainly low-melting-point monovalent metal oxides (Na2O, K2O, Li2O, Ag2O, etc.) and low-melting-point oxide (V2O5, B2O3, MoO3, etc.) systems, such as vanadates, tellurates, borates, and molybdates. These system compounds have extremely low sintering temperatures, but their microwave properties are far inferior to those of high-temperature sintered ceramics. Among divalent metal oxides, compared with monovalent metal oxides, the cation radius is larger, it is more easily polarized, and it is arranged more closely and regularly in the crystal, and the chemical bond strength is high. Therefore, it will have better dielectric properties. For example, MgO ceramics have excellent dielectric properties (ε r = 9.1, tanδ < 1.6×10 -6 ), and are considered to be ideal substrate materials for microwave applications in 5G communication. However, the high sintering temperature of magnesium oxide limits its application in low-temperature co-fired ceramics (LTCC) and similar fields. Therefore, extensive research has focused on MgO-based materials to develop microwave dielectric ceramics with high performance and low sintering temperature.

[0030] An embodiment of this application provides a microwave dielectric ceramic material with the chemical formula MgMo2O7. The preparation method of this microwave dielectric ceramic material includes the following steps:

[0031] S101. Mix the raw materials MgO and MoO3 in a molar ratio of 1:2 to obtain the raw material; mix the raw material, zirconium balls, and grinding medium, such as absolute ethanol, and then add them together to a nylon jar for the first ball milling. Among them, the mass ratio of the raw material, zirconium balls, and grinding medium is 1:(1.5 - 2):1, the ball milling speed is 200 - 300 r / min, and the ball milling time is 4 - 8 h. The viscosity of absolute ethanol is moderate, which helps to maintain an appropriate adhesion between the raw material and zirconium balls. This helps to evenly mix the raw material and zirconium balls, enabling effective dispersion and grinding of the raw material particles during ball milling. Moreover, the molybdate in the ceramic material of this application is soluble in water, so it is more suitable to choose absolute ethanol as the grinding medium. By controlling the mass ratio of the raw material, zirconium balls, and grinding medium, as well as the ball milling speed and time within the above ranges, it helps to obtain a uniform mixture, and can also achieve efficient material grinding, which is beneficial to improving the reactivity and compressibility of the raw material and enhancing the quality of the ceramic material.

[0032] S102. Dry the powder obtained after the first ball milling at 80 - 120 °C for 15 - 18 h, and then pass it through a 120 - mesh sieve; put the sieved powder into a crucible and pre - sinter it in a muffle furnace at 500 - 650 °C for 2 - 4 h to obtain a ceramic sample block. By sieving, larger or smaller particles can be removed, thereby obtaining a more uniform particle size distribution and making the prepared ceramic material more stable and homogeneous. During the pre - sintering process, organic substances and other volatile impurities that may exist in the raw material will volatilize at high temperatures, purifying the raw material. This helps to reduce the gases and odors generated during the subsequent sintering process, thereby improving the purity of the product. The pre - sintering process helps to adjust and improve the crystal structure of the ceramic material, making the particles more dense and uniform, and generating the required phases. This can improve the mechanical properties and microwave properties of the material, making it more stable under working conditions. At the same time, the pre - sintering process helps to eliminate the internal stress in the raw material, making the material less likely to crack or deform during the subsequent sintering process, thereby improving the overall stability of the microwave dielectric ceramic material. In this application, the pre - sintering temperature includes but is not limited to 500 °C, 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C, 650 °C; the pre - sintering time includes but is not limited to 2 h, 2.5 h, 3 h, 3.5 h, 4 h.

[0033] S103. Perform a second ball milling treatment on the above - mentioned ceramic sample block to obtain the required ceramic powder. Among them, the ball milling speed of the second ball milling treatment is 200 - 300 r / min, and the ball milling time is 4 - 8 h.

[0034] S104. After drying the ceramic powder, it is compacted at 200 - 300 Mpa. Generally, a cylindrical shape with a diameter of 10 mm and a height of 5 mm is pressed. According to needs, it can also be pressed into other shapes, which can be determined according to specific requirements, and this application does not make any limitations in this regard. Since the molybdate powder synthesized in this application has good powder fluidity and is relatively easy to form, applying a relatively low compaction pressure (200 - 300 Mpa) can also make the ceramic green body have a high density. Moreover, precisely because the synthesized molybdate powder has good fluidity, the powder in this application does not need to be granulated and can be directly pressed into tablets for subsequent sintering to obtain the required ceramic samples.

[0035] S105. The ceramic block after compaction is sintered at 650 - 800 °C for 4 - 6 h to obtain a microwave dielectric ceramic material. Limiting the sintering temperature and time within the above ranges can control the microstructure of the microwave dielectric ceramic material, including grain size and distribution, which helps the material to have the required performance characteristics. Moreover, within the above sintering temperature and time ranges, the material can reach a sufficient density to meet the requirements of microwave communication devices. In this application, the sintering temperature includes but is not limited to 650 °C, 685 °C, 690 °C, 695 °C, 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C, 800 °C; the sintering time includes but is not limited to 4 h, 4.5 h, 5 h, 5.5 h, 6 h.

[0036] The embodiment of this application also provides a microwave dielectric ceramic material, and its chemical formula is (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2. The preparation method of this microwave dielectric ceramic material includes the following steps:

[0037] S201. Mix the raw materials MgO and MoO3 in a molar ratio of 1:2 to obtain a raw material; after mixing the raw material, zirconium balls, and a grinding medium, such as anhydrous ethanol, add them together to a nylon jar for the first ball milling. Among them, the mass ratio of the raw material, zirconium balls, and the grinding medium is 1:(1.5 - 2):1, the ball milling speed is 200 - 300 r / min, and the ball milling time is 4 - 8 h.

[0038] S202. Dry the powder obtained after the first ball milling at 80 - 120 °C for 15 - 18 h, and then pass it through a 120 - mesh sieve; put the sieved powder into a crucible and pre - sinter it in a muffle furnace at 500 - 650 °C for 2 - 4 h to obtain a ceramic sample block.

[0039] S203. Mash and grind the above ceramic sample blocks in a mortar to obtain the pre-fired ceramic powder. Mix the pre-fired ceramic powder with TiO2 and conduct the second ball milling treatment to obtain the required ceramic powder. Among them, the conditions of the second ball milling treatment are the same as those of the first ball milling treatment. Among them, the pre-fired ceramic powder and TiO2 are proportioned according to the chemical formula (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2.

[0040] S204. After drying the ceramic powder, press it into shape at 200 - 300 Mpa. Generally, a cylindrical shape with a diameter of 10 mm and a height of 5 mm is pressed. According to needs, it can also be pressed into other shapes, which can be determined according to specific requirements, and this application does not make any limitations in this regard.

[0041] S205. Sinter the pressed ceramic blocks at 650 - 800 °C for 4 - 6 h to obtain the microwave dielectric ceramic material.

[0042] The embodiment of the present application also provides a microwave dielectric ceramic material, whose chemical formula is MgMo2O7 - MgMoO4. The preparation method of this microwave dielectric ceramic material is basically the same as that of the preparation method with the chemical formula MgMo2O7, the difference being that in the above step S101, MgO and MoO3 are mixed according to a molar ratio of 2:3. The characteristics and properties of the present application will be further described in detail below in combination with the embodiments.

[0043] Example 1

[0044] This embodiment provides a microwave dielectric ceramic material, whose chemical formula is MgMo2O7, and its preparation method is as follows:

[0045] (1) Mix the raw materials MgO and MoO3 according to a molar ratio of 1:2 to obtain the raw material; after mixing the raw material, zirconium balls, and a grinding medium, such as anhydrous ethanol, add them together to a nylon tank for the first ball milling. Among them, the mass ratio of the raw material, zirconium balls, and the grinding medium is 1:2:1, the ball milling speed is 300 r / min, and the ball milling time is 4 h.

[0046] (2) Dry the powder obtained after the first ball milling at 90 °C for 16 h, and then pass it through a 120-mesh sieve; put the sieved powder into a crucible and pre-fire it in a muffle furnace at 600 °C for 4 h to obtain the ceramic sample blocks.

[0047] (3) Conduct the second ball milling treatment on the above ceramic sample blocks to obtain the required ceramic powder. Among them, the conditions of the second ball milling treatment are the same as those of the first ball milling treatment.

[0048] (4) After drying the ceramic powder, press it into a cylindrical sample block with a diameter of 10 mm and a height of 5 mm at 300 Mpa.

[0049] (5) Sinter the cylindrical sample after pressing and forming at 685 °C for 4 h to obtain the microwave dielectric ceramic material.

[0050] Unless otherwise specified, the preparation processes of the remaining examples are basically the same as that of Example 1, except for the addition amounts of the reagents or different preparation parameters, etc. For some parameters, please refer to Table 1 for details.

[0051] Table 1

[0052] Group Pre-sintering Temperature (°C) Pre-sintering Time (h) Sintering Temperature (°C) Sintering Time (h) Example 1 600 4 685 4 Comparative Example 1 450 4 685 4 Comparative Example 2 700 4 685 4 Comparative Example 3 600 4 620 4 Comparative Example 4 600 4 850 4

[0053] Example 2

[0054] This example provides a microwave dielectric ceramic material with the chemical formula MgMo2O7 - MgMoO4, and its preparation method is basically the same as that of Example 1, except that in step (1), MgO and MoO3 are mixed according to a molar ratio of 2:3.

[0055] Example 3

[0056] This example provides a microwave dielectric ceramic material with the chemical formula 0.91MgMo2O7 - 0.09TiO2, and its preparation method is as follows:

[0057] (1) Mix the raw materials MgO and MoO3 according to a molar ratio of 1:2 to obtain the raw material; mix the raw material, zirconium balls, and grinding medium, such as anhydrous ethanol, and then add them together into a nylon jar for the first ball milling. Among them, the mass ratio of the raw material, zirconium balls, and grinding medium is 1:2:1, the ball milling speed is 300 r / min, and the ball milling time is 4 h.

[0058] (2) Dry the powder obtained after the first ball milling at 90 °C for 16 h, and then pass it through a 120 - mesh sieve; put the sieved powder into a crucible and pre - sinter it in a muffle furnace at 600 °C for 4 h to obtain a ceramic sample.

[0059] (3) Mash and grind the above - mentioned ceramic sample in a mortar to obtain the pre - sintered ceramic powder, mix the pre - sintered ceramic powder and TiO2 for the second ball milling treatment to obtain the required ceramic powder. Among them, the conditions of the second ball milling treatment are the same as those of the first ball milling treatment. Among them, the pre - sintered ceramic powder and TiO2 are formulated according to the chemical formula 0.91MgMo2O7 - 0.09TiO2.

[0060] (4) Dry the ceramic powder and then press it into a cylindrical sample with a diameter of 10 mm and a height of 5 mm under 300 Mpa.

[0061] (5) Sinter the cylindrical sample after pressing and forming at 685 °C for 4 h to obtain the microwave dielectric ceramic material.

[0062] Comparative Example 5

[0063] This example provides a microwave dielectric ceramic material with the chemical formula MgMoO4. Its preparation method is basically the same as that of Example 1, except that in step (1), MgO and MoO3 are mixed in a molar ratio of 1:1.

[0064] Test Example 1

[0065] In this test example, the microwave dielectric ceramic materials provided in Examples 1 - 3 and Comparative Examples 1 - 5 were respectively subjected to performance measurements, including dielectric constant, quality factor, and frequency temperature coefficient. The specific test methods are as follows:

[0066] Measurement of dielectric constant: According to the TE 01δ mode closed - cavity resonance method for measurement.

[0067] Measurement of quality factor: According to the TE 01δ mode closed - cavity resonance method for measurement.

[0068] Measurement of frequency temperature coefficient: According to the test method of microwave dielectric properties, the resonant cavity was placed in an incubator (Delta9023, Delta Design, Poway, CA), the incubator was started, and the test temperature range, heating rate, frequency, and bandwidth of the resonant peak were set on the computer software. After clicking start, the data was automatically recorded every 10 s and saved on the computer. The frequency temperature coefficient TCF (τ f ) of the ceramic sample was calculated according to the following formula:

[0069]

[0070] In the formula: f 25 , f 85 are the resonant frequencies at 25 °C and 85 °C in the TE 01δ mode respectively.

[0071] The measurement results of dielectric constant, quality factor, and frequency temperature coefficient are shown in Table 2.

[0072] Table 2

[0073]

[0074] As can be seen from Table 2, the microwave dielectric ceramic material with the chemical formula MgMo2O7 provided in the examples of this application can be sintered at a low temperature (685 °C), and at the same time has a low dielectric constant (6.09), a high quality factor (125200 GHz), and a near - zero frequency temperature coefficient (-42 ppm / °C). The inventors found through experiments that doping a small amount of TiO2 in the preparation of this material can make the frequency temperature coefficient of the ceramic material closer to zero.

[0075] In Comparative Example 1, the pre-sintering temperature was lower than 500 °C, and the phase synthesis reaction could not occur. In Comparative Example 2, since the pre-sintering temperature was relatively high (higher than 650 °C), molybdenum volatilization would occur, resulting in a phase change reaction, and finally the phase was transformed into MgMoO4, thereby leading to a decrease in the quality factor.

[0076] In Comparative Example 3, the sintering temperature was lower than 650 °C, which would result in a relatively low density of the synthesized ceramic material, thereby affecting the dielectric properties of the material and leading to a decrease in the quality factor. In Comparative Example 4, the sintering temperature was relatively high (higher than 800 °C), which would result in over-sintering, thereby affecting the dielectric properties of the material and leading to a decrease in the quality factor.

[0077] Test Example 2

[0078] In this test example, the microwave dielectric ceramic materials provided in Example 1 and Comparative Example 1 were used as substrates to prepare corresponding microstrip patch antennas, and the following tests were respectively carried out on them:

[0079] (1) Measurement of S 11 Value

[0080] The S 11 value was measured according to the waveguide method.

[0081] The S 11 parameter represents the matching degree between the signal input to the antenna and the signal reflected from the antenna, and is also called the echo loss or reflection loss. The lower the value of S 11 , the better the matching degree and the smaller the reflection loss.

[0082] Figure 1 is the S 11 curve and the simulated S 11 curve of the antenna prepared from the ceramic material in Example 1 of this application; Figure 2 is the S 11 curve and the simulated S 11 curve of the antenna prepared from the ceramic material in Comparative Example 1 of this application. As can be seen from Figure 1 and Figure 2 , for the antennas of β-MgMo2O7 and MgMoO4 at the resonance frequency of 5.8 GHz, the best values of S 11 are both less than -30 dB, indicating that both antennas have good emission efficiency.

[0083] The -10dB bandwidth of an antenna refers to the operating frequency range of the antenna. Within the -10dB bandwidth of the antenna, the performance of the antenna is generally relatively good, and it can effectively receive or transmit signals. This value is generally used to evaluate the frequency response characteristics of the antenna. In this work, the antenna based on β-MgMo2O7 exhibits an simulated -10dB bandwidth of 410MHz and a measured bandwidth of 351MHz; the antenna based on MgMoO4 exhibits an simulated -10dB bandwidth of 380MHz and a measured bandwidth of 330MHz, indicating that the antenna prepared from the ceramic material provided in Embodiment 1 of the present application has a wider application frequency band.

[0084] Figure 3 Simulated radiation pattern at the H-plane of the antenna fabricated based on β-MgMo2O7; Figure 4 Simulated radiation pattern at the E-plane of the antenna fabricated based on β-MgMo2O7; Figure 5 Simulated radiation pattern at the H-plane of the antenna fabricated based on MgMoO4; Figure 6 Simulated radiation pattern at the E-plane of the antenna fabricated based on MgMoO4; Figure 7 Simulated 3D far-field radiation pattern of the antenna fabricated based on β-MgMo2O7 at 5.8GHz; Figure 8 Simulated 3D far-field radiation pattern of the antenna fabricated based on MgMoO4 at 5.8GHz. The above two antennas are directional antennas, and one of the main lobes radiates outward from the patch side. The maximum gains of the antennas fabricated based on β-MgMo2O7 and MgMoO4 are 6.49dB and 6.05dB respectively (as shown in Figure 8 ). By making two slices through the 3D pattern (xoz and yoz planes), the radiation patterns of the two main planes (E-plane and H-plane) can be obtained, as shown in Figures 3 - 6 . Among them, the E-plane is the plane where the maximum radiation electric field is located. From the above results and from Figures 3 - 6 , it can be found that compared with the antenna fabricated from MgMoO4, the antenna fabricated from β-MgMo2O7 provided in Embodiment 1 of the present application has a higher gain, indicating that the antenna has good directivity and concentrated energy, and the antenna meets the expected performance and is compatible with 5.8GHz WLAN applications.

[0085] The embodiments described above are some embodiments of the present application, rather than all embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

Claims

1. A preparation method of a microwave dielectric ceramic material, characterized in that, Comprising: Mix raw materials MgO and MoO3 in a molar ratio of 1:(1.5 - 2) to obtain a raw material; mix the raw material with a grinding medium, and successively perform first ball milling, drying, and pre-sintering treatments to obtain a ceramic sample block; successively perform second ball milling, drying, pressing, and sintering treatments on the ceramic sample block to obtain the microwave dielectric ceramic material; Wherein, the temperature of the pre-sintering is 500 - 650 °C, and the time of the pre-sintering is 2 - 4 h; the temperature of the sintering is 650 - 800 °C, and the time of the sintering is 4 - 6 h.

2. A preparation method of a microwave dielectric ceramic material, characterized in that Comprising: Mix raw materials MgO and MoO3 in a molar ratio of 1:(1.5 - 2) to obtain a raw material; mix the raw material with a grinding medium, and successively perform first ball milling, drying, and pre-sintering treatments to obtain a ceramic sample block; mix the ceramic sample block with TiO2 according to the stoichiometric ratio of (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2, and then successively perform second ball milling, drying, pressing, and sintering treatments to obtain the microwave dielectric ceramic material; Wherein, the temperature of the pre-sintering is 500 - 650 °C, and the time of the pre-sintering is 2 - 4 h; the temperature of the sintering is 650 - 800 °C, and the time of the sintering is 4 - 6 h.

3. The preparation method according to claim 1 or 2, characterized in that, The first ball milling includes: Add the raw material, zirconium balls, and the grinding medium into a ball milling tank in a mass ratio of 1:(1.5 - 2):1 to perform the first ball milling.

4. The preparation method according to claim 3, characterized in that, The grinding medium includes absolute ethanol.

5. The preparation method according to claim 1 or 2, characterized in that, The conditions of the first ball milling include: the ball milling speed is 200 - 300 r / min, and the ball milling time is 4 - 8 h.

6. The preparation method according to claim 5, characterized in that, The conditions of the second ball milling include: the ball milling speed is 200 - 300 r / min, and the ball milling time is 4 - 8 h.

7. The preparation method according to claim 1 or 2, characterized in that, After the drying step, a sieving step is further included, and the mesh number of the sieve is 100 - 220.

8. The preparation method according to claim 1 or 2, characterized in that, The temperature of the drying is 80 - 120 °C; and / or, the time of the drying is 15 - 18 h.

9. The preparation method according to claim 1 or 2, characterized in that, The conditions of the pressing include: the pressing pressure is 200 - 300 MPa.

10. A microwave dielectric ceramic material prepared by the preparation method according to claim 1, characterized in that, The microwave dielectric ceramic material includes MgMo2O7.

11. A microwave dielectric ceramic material prepared by the preparation method according to claim 2, characterized in that, The microwave dielectric ceramic material includes (0.75 - 0.99)MgMo2O7-(0.01 - 0.25)TiO2.

12. A microwave communication device, characterized in that, Comprising the microwave dielectric ceramic material according to claim 10 or 11.

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