Microwave dielectric composite ceramic and method for manufacturing the same

Abstract

This invention provides a microwave dielectric composite ceramic and its preparation method. The microwave dielectric composite ceramic includes a main phase component and a second phase component. The main phase component includes Mg. 1.2 TiO 3.2 The second phase composition includes SiO2 or MgSiO4, wherein Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, is sintered with the main phase component to obtain a microwave dielectric ceramic. In the microwave dielectric composite ceramic provided by this invention, the main phase component is Mg, which has a high quality factor and low dielectric loss. 1.2 TiO 3.2 The second phase component has a lower dielectric constant and is compatible with Mg. 1.2 TiO 3.2 With similar capacitance temperature coefficients, they can be combined to form microwave dielectric composite ceramics, which reduce the dielectric constant without affecting the capacitance temperature coefficient.

Description

Technical Field

[0001] This invention belongs to the field of microwave ceramic materials technology, specifically relating to a microwave dielectric composite ceramic and its preparation method. Background Technology

[0002] Microwave dielectric ceramics are a new type of functional electronic ceramic. They refer to ceramics used as dielectric materials in microwave frequency band (mainly UHF and SHF bands) circuits to perform one or more functions. They have excellent microwave dielectric properties such as low microwave loss, moderate dielectric constant, and small frequency temperature coefficient. In microwave circuit systems, they play functions such as dielectric isolation, dielectric waveguide, and dielectric resonance. They are key materials for microwave components such as dielectric resonators (DR), dielectric filters (DF), dielectric oscillators (DRO), phase shifters, microwave capacitors, and microwave substrates, which are widely used in modern communication.

[0003] Magnesium titanate (MgTiO3) ceramics possess excellent dielectric properties, making them a promising candidate material for microwave applications. MgTiO3 ceramics prepared according to stoichiometric ratios typically contain the secondary phases Mg2TiO4 and MgTi2O5. MgTiO3 and Mg2TiO4 exhibit high quality factors, good microwave dielectric properties, and suitable capacitance temperature coefficients for microwave operating environments. However, MgTi2O5 has very high dielectric loss and is an undesirable phase during preparation, negatively impacting microwave dielectric efficiency. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a microwave dielectric composite ceramic, wherein the main phase is Mg, which has a high quality factor and low dielectric loss. 1.2 TiO 3.2 The second phase component has a lower dielectric constant and is compatible with Mg. 1.2 TiO 3.2 With similar capacitance temperature coefficients, they can be combined to form microwave dielectric composite ceramics, which reduce the dielectric constant without affecting the capacitance temperature coefficient.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component includes Mg. 1.2 TiO 3.2 The second phase composition includes SiO2 or MgSiO4, wherein Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain microwave dielectric ceramic.

[0007] The microwave dielectric composite ceramic provided by this invention has a main phase composition containing Mg. 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4 was prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1. By controlling the molar ratio of MgO to TiO2, the main crystalline phase MgTiO3 and the secondary crystalline phase Mg2TiO4 with high quality factor and low dielectric loss were formed, while the impurity phase MgTi2O5 with high dielectric loss was not generated. 1.2 TiO 3.2 It exhibits a high quality factor and low dielectric loss. The second phase composition includes SiO2 or MgSiO4, which has a low dielectric constant and a capacitance temperature coefficient similar to Mg. 1.2 TiO 3.2 Similar to Mg, therefore it can be used with Mg 1.2 TiO 3.2 Microwave dielectric composite ceramics are formed by combining materials, and the dielectric constant is adjusted without affecting the capacitance temperature coefficient, so as to adapt to the application of microwave dielectric composite ceramics in the microwave field.

[0008] Furthermore, the mass ratio of the main phase component to the second phase component ranges from 95:5 to 80:20. Adjusting the ratio of the main phase component to the second phase component allows for adjustment of the dielectric constant as needed while maintaining the capacity temperature coefficient.

[0009] This invention also provides a method for preparing the above-mentioned microwave dielectric composite ceramic, comprising the following steps: mixing magnesium oxide and titanium dioxide according to Mg... 1.2 TiO 3.2 The chemical formula is used to formulate the ingredients, which are then mixed, ground, dried, and pre-fired to obtain a pre-fired product. The pre-fired product is mixed and ground with the second phase component, and then a binder is added. The mixture is then rolled and pressed into a sheet. The sheet is sintered at a high temperature of 1300-1400℃ and then cooled to obtain a microwave dielectric composite ceramic.

[0010] In the preparation method of the microwave dielectric composite ceramic of the present invention, magnesium oxide and titanium dioxide are pre-fired to guide the formation of MgTiO3 and Mg2TiO4 crystal nuclei, avoiding the formation of MgTi2O5 with high dielectric loss. The pre-fired product is then mixed with the second phase component and sintered at high temperature, forming MgTiO3 and Mg2TiO4 during high-temperature sintering. 1.2 TiO 3.2 It combines with the second phase component to form a microwave dielectric composite ceramic. The dielectric constant of the microwave dielectric ceramic is improved by the second phase component, which has a low dielectric constant and a capacity temperature coefficient similar to that of the main phase component. This allows the microwave dielectric composite ceramic to adjust its dielectric constant while maintaining a high quality factor and capacity temperature coefficient, thus adapting it to the application of microwave dielectric composite ceramics in the microwave field.

[0011] Furthermore, when magnesium oxide and titanium dioxide are mixed according to Mg... 1.2 TiO 3.2 In the step of preparing the ingredients according to the chemical formula, mixing and grinding, drying, and pre-calcining to obtain the pre-calcined product, magnesium oxide and titanium dioxide are mixed according to the main phase component Mg. 1.2 TiO 3.2 The chemical formulas were fed in a molar ratio of 1.2:1, ground, dried, and pre-calcined to obtain the pre-calcined product. By controlling the molar ratio of MgO to TiO2, the main crystalline phase MgTiO3 and the secondary crystalline phase Mg2TiO4 with high quality factor and low dielectric loss were formed, while avoiding the formation of the impurity phase MgTi2O5 with high dielectric loss.

[0012] Furthermore, when magnesium oxide and titanium dioxide are mixed according to Mg... 1.2 TiO 3.2 In the steps of preparing the chemical formula, mixing and grinding the ingredients, drying, and pre-calcining to obtain the pre-calcined product, the pre-calcination temperature is 1000-1200℃. The pre-calcination temperature is controlled below the high-temperature sintering temperature to induce the formation of crystal nuclei of the main crystalline phase MgTiO3 and the secondary crystalline phase Mg2TiO4.

[0013] Furthermore, in the step of mixing and grinding the pre-fired product with the second phase component, adding a binder, rolling, and then pressing into a sheet, the pre-fired product is mixed at a mass ratio of 95:5 to 80:20, ground, dried, and then the binder is added before pressing into a sheet. Controlling the ratio of the pre-fired product to the second phase component adjusts the Mg content in the resulting microwave dielectric composite ceramic. 1.2 TiO 3.2 The ratio of SiO2 to the dielectric constant can be adjusted according to requirements.

[0014] Further, in the step of mixing and grinding the pre-fired product with the second phase component, adding a binder, and then pressing it into a sheet, the pre-fired product and the second phase component are mixed, ball-milled, dried, and sieved. A binder is added at a ratio of 15 wt% to obtain ceramic powder agglomerates, wherein the binder includes polyvinyl alcohol with a solid content of 10%. The ceramic powder agglomerates are then rolled and pressed into sheets. Adding an appropriate proportion of binder helps to give the ceramic powder agglomerates formed by mixing the pre-fired product and the second phase component good plasticity and a certain strength, facilitating stamping processing.

[0015] Furthermore, in the step of sintering the pressed tablets at a high temperature of 1300-1400℃ and then cooling them down, the tablets are sintered at 1300-1400℃ and held at 1400℃ for 4 hours, followed by cooling. This high-temperature sintering process forms a microwave dielectric composite ceramic with good density and a certain strength.

[0016] Furthermore, during the sintering of the pressed wafer at 1300-1400℃ and the subsequent cooling process, if the second phase is silicon dioxide, the cooling rate is controlled at a first rate within the 1000-1400℃ range, a second rate within the 280-1000℃ range, and a third rate within the 250-280℃ range. After cooling to below 250℃, the wafer is then cooled in the furnace. During the cooling process of SiO2, a phase transformation occurs, forming different crystal lattices and accompanied by volume changes. Therefore, different cooling rates are selected according to different temperature ranges to ensure that SiO2 passes through the phase transformation temperature range at an appropriate rate, avoiding the formation of microcracks due to volume changes that could affect the performance of the microwave dielectric composite ceramic.

[0017] Furthermore, during the cooling process of the tablets sintering at a high temperature of 1300-1400℃, if the second phase is composed of silicon dioxide, the cooling process is as follows: when the temperature range is 1000-1400℃, the cooling rate is controlled at a first cooling rate of 1.5-2.5℃ / min; when the temperature range is 280-1000℃, the cooling rate is controlled at a second cooling rate of 3-5℃ / min; when the temperature range is 250-280℃, the cooling rate is controlled at a third cooling rate of 0.2-0.7℃ / min; and when the temperature drops below 250℃, the tablets are cooled in the furnace.

[0018] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a flowchart of the preparation method of microwave dielectric composite ceramics.

[0020] Figure 2 This is a graph showing the relationship between SiO2 content and the dielectric constant of microwave dielectric composite ceramics.

[0021] Figure 3 This is a graph showing the relationship between SiO2 content and the capacitance temperature coefficient of microwave dielectric composite ceramics. Detailed Implementation

[0022] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit the scope of the invention. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the embodiments of the present invention, and not all structures.

[0023] Example 1

[0024] This embodiment provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component is Mg.1.2 TiO 3.2 The second phase composition includes SiO2, of which Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain a microwave dielectric ceramic. 1.2 TiO 3.2 The mass ratio of SiO2 to SiO2 ranges from 95:5 to 80:20.

[0025] In the microwave dielectric composite ceramic of this embodiment, Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4 was prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1. By controlling the molar ratio of MgO to TiO2, the main crystalline phase MgTiO3 and the secondary crystalline phase Mg2TiO4 with high quality factor and low dielectric loss were formed, while avoiding the formation of the impurity phase MgTi2O5 with high dielectric loss. 1.2 TiO 3.2 High quality factor, insulation resistance (@1MHz) 10 5 GΩ exhibits good performance, but its dielectric constant range is narrow. SiO2 has a low dielectric constant, and its capacitance temperature coefficient is similar to that of Mg. 1.2 TiO 3.2 Similar to Mg, therefore it can be used with Mg 1.2 TiO 3.2 Microwave dielectric composite ceramics are formed by combining materials, and the range of dielectric constants can be adjusted without affecting the capacitance temperature coefficient, so as to adapt to the application of microwave dielectric composite ceramics in the microwave field.

[0026] Example 2

[0027] This embodiment provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component is Mg. 1.2 TiO 3.2 The second phase composition includes SiO2, of which Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain a microwave dielectric ceramic. 1.2 TiO 3.2 The mass ratio of SiO2 to SiO2 is 95:5.

[0028] Example 3

[0029] This embodiment provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component is Mg. 1.2 TiO 3.2 The second phase composition includes SiO2, of which Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain a microwave dielectric ceramic. 1.2 TiO 3.2 The mass ratio of SiO2 to SiO2 is 90:10.

[0030] Example 4

[0031] This embodiment provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component is Mg. 1.2 TiO 3.2 The second phase composition includes SiO2, of which Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain a microwave dielectric ceramic. 1.2 TiO 3.2 The mass ratio of SiO2 to SiO2 is 85:15.

[0032] Example 5

[0033] This embodiment provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component is Mg. 1.2 TiO 3.2 The second phase composition includes SiO2, of which Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain a microwave dielectric ceramic. 1.2 TiO 3.2 The mass ratio of SiO2 to SiO2 ranges from 95:5 to 80:20.

[0034] Example 6

[0035] This embodiment provides a method for preparing the microwave dielectric composite ceramic described in any of Embodiments 1-5. Figure 1 Please refer to the flowchart for the preparation method of microwave dielectric composite ceramics. Figure 1 The preparation method of microwave dielectric composite ceramics includes the following steps:

[0036] Step S1: Mix magnesium oxide and titanium dioxide according to Mg 1.2 TiO 3.2 The chemical formula is used to formulate the ingredients, which are then mixed, ground, dried, and pre-calcined to obtain the pre-calcined product. The specific operation is as follows:

[0037] Magnesium oxide and titanium dioxide were mixed according to the main phase component Mg. 1.2 TiO 3.2 The chemical formula of the raw material is added to the ball mill jar in a molar ratio of 1.2:1. Zirconia balls and anhydrous ethanol are added to the ball mill jar in a ratio of total weight of raw material: weight of zirconia balls: weight of anhydrous ethanol = 1:5:3. The ball mill is then milled for 8-12 hours. After the ball milling is completed, the raw material is dried at a temperature of 70-90℃ for 12 hours.

[0038] The dried product was sieved through a 5 MPa sieve, pressed into blocks, and placed in a sintering furnace for pre-calcination at 1000-1200℃ for 4 hours to obtain the pre-calcined product. The purpose of pre-calcination is to achieve a temperature below Mg2+. 1.2 TiO 3.2 The two types of crystal nuclei, MgTiO3 and Mg2TiO4, were synthesized under the highest sintering temperature.

[0039] Step S2: After mixing and grinding the pre-calcined product with the second phase component, a binder is added, the mixture is processed by rolling, and then pressed into tablets. The specific operation is as follows:

[0040] The pre-calcined product and SiO2 are mixed in a mass ratio ranging from 95:5 to 80:20, ball-milled for 6-8 hours, dried, and sieved. The particle size is considered acceptable if it can pass through a 100-mesh sieve. A binder is added at a ratio of 15 wt%, wherein the binder includes 10% polyvinyl alcohol with a solid content. The mixture is stirred with a stirring rod until it forms a clump of powder that is not visible to the naked eye, thus obtaining ceramic powder clumps. The ceramic powder clumps are poured onto two counter-rotating rollers and repeatedly kneaded to allow the anhydrous ethanol to gradually evaporate until the ceramic powder clumps no longer stick to the rollers, thus obtaining a blank. The blank is folded, guided, and repeatedly rough-rolled to remove air bubbles and obtain a uniform film layer. Then, the gap between the rollers is gradually reduced for fine rolling to form a film with a thickness of 300±10 μm. The film is then stamped into 1.5-2.0 inch square sheets using a stamping machine.

[0041] Step S3: Sinter the pressed sheet at a high temperature of 1300-1400℃, then cool it down to obtain microwave dielectric composite ceramic. The specific operation is as follows:

[0042] The square wafers were sintered at 1300-1400℃ and held at 1400℃ for 4 hours before cooling. During the cooling process, a first cooling rate of 1.5-2.5℃ / min was used within the temperature range of 1000-1400℃; a second cooling rate of 3-5℃ / min was used within the temperature range of 280-1000℃; and a third cooling rate of 0.2-0.7℃ / min was used within the temperature range of 250-280℃. The wafers were then cooled in the furnace below 250℃. During the cooling process of SiO2, a phase transformation occurs, forming different crystal forms accompanied by volume changes. Therefore, different cooling rates were selected according to different temperature ranges to ensure that SiO2 passes through the phase transformation temperature range at an appropriate rate, avoiding microcracks caused by volume changes that could affect the performance of the microwave dielectric composite ceramic.

[0043] The performance of the microwave dielectric composite ceramics described in Examples 2-5 was tested respectively. Figure 2 This is a graph showing the relationship between SiO2 content and dielectric constant. Figure 3 This is a graph showing the relationship between SiO2 content and capacity temperature coefficient. Please refer to it. Figure 2-3 The decrease in dielectric constant of microwave dielectric composite ceramics is positively correlated with the increase in SiO2 content; the higher the SiO2 content, the lower the dielectric constant of the microwave dielectric composite ceramic, making it suitable for microwave applications. This is because the capacitance temperature coefficient of SiO2 is related to that of Mg. 1.2 TiO 3.2 Similarly, with the increase of SiO2 content, the capacitance temperature coefficient of the microwave dielectric composite ceramic does not change significantly in different temperature environments. That is, the microwave dielectric composite ceramic prepared by the preparation method described in Example 6 can utilize SiO2 to regulate the dielectric constant without changing the capacitance temperature coefficient.

[0044] Example 7

[0045] This embodiment provides a microwave dielectric composite ceramic, comprising a main phase component and a second phase component, wherein the main phase component is Mg. 1.2 TiO 3.2 The second phase composition includes MgSiO4, wherein Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4, prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, was sintered with the main phase component to obtain a microwave dielectric ceramic. 1.2 TiO 3.2 The mass ratio of Mg to MgSiO4 ranges from 95:5 to 80:20. In one specific embodiment, Mg... 1.2 TiO 3.2The mass ratio of the MgSiO4 to MgSiO4 is one of 95:5, 90:10, 85:15, or 80:20.

[0046] In the microwave dielectric composite ceramic of this embodiment, Mg 1.2 TiO 3.2 A mixture of MgTiO3 and Mg2TiO4 was prepared by mixing MgO and MgSiO4 in a molar ratio of 1.2:1. By controlling the molar ratio of MgO to MgSiO4, a main crystalline phase MgTiO3 and a secondary crystalline phase Mg2TiO4 with high quality factor and low dielectric loss were formed, while the impurity phase MgTi2O5 with high dielectric loss was not generated. 1.2 TiO 3.2 High quality factor, insulation resistance (@1MHz) 10 5 GΩ exhibits good performance but has a narrow dielectric constant range, while MgSiO4 has a low dielectric constant and a similar capacitance temperature coefficient to Mg. 1.2 TiO 3.2 Similar to Mg, therefore it can be used with Mg 1.2 TiO 3.2 Microwave dielectric composite ceramics are formed by combining materials to adjust the range of dielectric constants without affecting the capacitance temperature coefficient, thereby reducing the dielectric constant to suit the application of microwave dielectric composite ceramics in the microwave field.

[0047] The preparation method of the microwave dielectric composite ceramic in this embodiment is similar to the preparation method of the microwave dielectric composite ceramic described in Example 6, with the main difference being:

[0048] Step S2: After mixing and grinding the pre-calcined product with the second phase component, add the binder and then press it into a tablet. The specific operation is as follows:

[0049] The pre-calcined product and MgSiO4 are mixed in a mass ratio ranging from 95:5 to 80:20, ball-milled for 6-8 hours, dried, and sieved. The particle size is considered acceptable if it can pass through a 100-mesh sieve. A binder is added at a ratio of 15 wt%, wherein the binder includes 10% polyvinyl alcohol with a solid content. The mixture is stirred with a stirring rod until it forms a clump of powder that is not visible to the naked eye, thus obtaining ceramic powder clumps. The ceramic powder clumps are poured onto two counter-rotating rollers and repeatedly kneaded to allow the anhydrous ethanol to gradually evaporate until the ceramic powder clumps no longer stick to the rollers, thus obtaining a blank. The blank is folded, guided, and repeatedly rough-rolled to remove air bubbles and obtain a uniform film layer. Then, the gap between the rollers is gradually reduced for fine rolling to form a film with a thickness of 300±10 μm. The film is then stamped into 1.5-2.0 inch square sheets using a stamping machine.

[0050] This invention is not limited to the above-described embodiments. If any modifications or variations to this invention do not depart from the spirit and scope of this invention, and if such modifications and variations fall within the scope of the claims and equivalent technologies of this invention, then this invention also intends to include such modifications and variations.

Claims

1. A microwave dielectric composite ceramic, characterized in that: consisting of a main phase component and a second phase component, the main phase component being Mg 1.2 TiO 3.2 , the second phase component being SiO2, wherein Mg 1.2 TiO 3.2 is a mixture of MgTiO3 and Mg2TiO4 prepared by mixing MgO and TiO2 in a molar ratio of 1.2:1, and the main phase component and the second phase component are mixed and sintered to obtain the microwave dielectric ceramic; the mass ratio of the main phase component to the second phase component ranges from 95:5 to 80:

20.

2. A method of making the microwave dielectric composite ceramic of claim 1, characterized in that, comprising the following steps: Magnesium oxide and titanium dioxide are dosed according to the chemical formula of Mg 1.2 TiO 3.2 , mixed, ground, dried, pre-fired to obtain a pre-fired product; mixing and grinding the pre-sintered product with the second phase component, adding a binder, roll processing, and then stamping into a pressed piece; sintering the pressed piece at a high temperature of 1300-1400℃, and then cooling to obtain the microwave dielectric composite ceramic.

3. The preparation method of the microwave dielectric composite ceramic according to claim 2, characterized in that: MgO and TiO2 are dosed according to the chemical formula of Mg 1.2 TiO 3.2 After mixing and grinding, MgO and TiO2 are dosed according to the chemical formula of Mg 1.2 TiO 3.2 After mixing and grinding, MgO and TiO2 are dosed according to the chemical formula of Mg 4. The preparation method of the microwave dielectric composite ceramic according to claim 3, characterized in that: The magnesium oxide and titanium dioxide are mixed according to the formula Mg 1.2 TiO 3.2 The pre-sintering temperature is 1000-1200°C in the step of mixing, grinding, drying, pre-sintering the magnesium oxide and titanium dioxide according to the formula Mg 5. The preparation method of the microwave dielectric composite ceramic according to claim 2, characterized in that: in the step of mixing and grinding the pre-sintered product with the second phase component, adding a binder, roll processing, and then stamping into a pressed piece, the pre-sintered product and the second phase component are mixed in a mass ratio of 95:5 to 80:20, and then dried after grinding, a binder is added, and a pressed piece is stamped.

6. The preparation method of the microwave dielectric composite ceramic according to claim 5, characterized in that: in the step of mixing and grinding the pre-sintered product with the second phase component, adding a binder, roll processing, and then stamping into a pressed piece, the pre-sintered product and the second phase component are mixed and then ball milled, dried, sieved, and a binder is added in a proportion of 15wt% to obtain a ceramic powder mass, wherein the binder comprises 10% solid content polyvinyl alcohol; the ceramic powder mass is roll processed and then stamped into a pressed piece.

7. The preparation method of the microwave dielectric composite ceramic according to claim 2, characterized in that: in the step of sintering the pressed piece at a high temperature of 1300-1400℃, and then cooling, the pressed piece is sintered at a temperature of 1300-1400℃, and then held at 1400℃ for 4 hours, and then cooled after the holding is completed.

8. The preparation method of the microwave dielectric composite ceramic according to any one of claims 2-7, characterized in that: in the step of sintering the pressed piece at a high temperature of 1300-1400℃, and then cooling, during the cooling process, the temperature is controlled to decrease at a first cooling rate in a temperature range of 1000-1400℃, at a second cooling rate in a temperature range of 280-1000℃, at a third cooling rate in a temperature range of 250-280℃, and then cooled with the furnace after the temperature is decreased to below 250℃.

9. The preparation method of the microwave dielectric composite ceramic according to claim 8, characterized in that: in the step of sintering the pressed piece at a high temperature of 1300-1400℃, and then cooling, during the cooling process, the temperature is controlled to decrease at a first cooling rate in a temperature range of 1000-1400℃, the first cooling rate being 1.5-2.5℃ / min; at a second cooling rate in a temperature range of 280-1000℃, the second cooling rate being 3-5℃ / min; at a third cooling rate in a temperature range of 250-280℃, the third cooling rate being 0.2-0.7℃ / min; and then cooled with the furnace after the temperature is decreased to below 250℃.

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