Temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material and preparation method thereof

Abstract

The invention discloses a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material and a preparation method thereof.The preparation method comprises the following steps that S1, Li2CO3, MgO, TiO2 and CaF2 are put into a ball milling tank according to the stoichiometric ratio, zirconium balls serve as grinding balls, absolute ethyl alcohol serves as a ball milling medium, full mixing and ball milling are conducted, and then pre-sintered powder is obtained after drying and pre-sintering; s2, putting the pre-sintered powder into a ball milling tank, fully mixing, drying, granulating and sieving by taking zirconium balls as grinding balls and absolute ethyl alcohol as a ball milling medium, preparing a cylindrical green body by using a powder tabletting machine, and sintering the green body to prepare the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material. According to the invention, the defect that the temperature coefficient of resonance frequency of a pure-phase Li3Mg3TiO6F ceramic material is relatively large is overcome, the temperature stability of the material is ensured, and the requirements of current high-frequency communication equipment on relatively good working environment temperature stability and a low-dielectric-constant material with a relatively high Q value are met.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic materials, and in particular to a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material and a preparation method thereof. Background Art

[0002] Microwave dielectric ceramics refer to ceramic materials used as dielectric materials in microwave frequency band (300MHz ~ 300GHz) circuits to perform one or more functions. Ideal microwave dielectric ceramics have a suitable dielectric constant ε r , high quality factor Q×f (good frequency selectivity) and resonant frequency temperature coefficient τ tending to zero f (High temperature stability). With the rapid development of contemporary microwave communication and wireless communication industries, especially the continuous expansion of the operating frequency of microwave devices as key components of communication systems to high frequency ends, such as 4G has begun to become popular and 5G technology is becoming more mature. This puts higher requirements on high-frequency microwave dielectric materials, requiring them to have low dielectric constants and good temperature stability. Generally, for a single-phase material system, it is difficult to meet the requirements of the above three performance parameter indicators at the same time, especially to have low εr, near-zero τf and high Q×f values ​​at the same time. Therefore, the development and research of microwave dielectric composite ceramics with good temperature stability and low dielectric constant for high frequency applications has received great attention.

[0003] Li3Mg3TiO6F microwave ceramics are rich in raw materials and low in cost, and are a promising low-ε r , high Q value high frequency microwave dielectric material. However, it has the disadvantage of poor temperature stability, (Li3Mg3TiO 6F τ f The frequency-temperature stability of Li3Mg3TiO6F microwave dielectric ceramics is -38.7ppm / ℃, which makes it unable to meet the actual application requirements. Therefore, improving the frequency-temperature stability of Li3Mg3TiO6F microwave dielectric ceramics and simplifying their preparation process are conducive to the commercialization of Li3Mg3TiO6F dielectric ceramics. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material and a preparation method thereof, which overcomes the disadvantage of a relatively large temperature coefficient of the resonant frequency of the pure phase Li3Mg3TiO6F ceramic material, ensures the temperature stability of the material, and meets the requirements of current high-frequency communication equipment for better working environment temperature stability and low dielectric constant materials with higher Q values.

[0005] The method for preparing the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material proposed by the present invention comprises the following steps:

[0006] S1: Preparation of calcined powder

[0007] Li2CO3, MgO, TiO2 and CaF2 are placed in a ball mill according to the stoichiometric ratio, zirconium balls are used as milling balls, anhydrous ethanol is used as the milling medium, and the mixture is fully mixed and milled, and then dried and pre-calcined to obtain pre-calcined powder;

[0008] S2: Preparation of Li3Mg3TiO6F-based microwave dielectric composite ceramic materials

[0009] The pre-sintered powder is put into a ball mill, fully mixed with zirconium balls as grinding balls and anhydrous ethanol as ball milling media, dried, granulated, sieved, and made into a cylindrical green body by a powder tabletting machine, and the green body is sintered to prepare a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material.

[0010] Preferably, the stoichiometric ratio of Li2CO3, MgO, TiO2 and CaF2 in S1 is 1:3:(1+3x):3x, where 0.04≤x≤0.07.

[0011] Preferably, the drying temperature in S1 is 80-100° C. and the drying time is 12-24 h.

[0012] Preferably, the pre-burning temperature in S1 is 900-1000° C. and the time is 4-6 hours.

[0013] Preferably, the sintering temperature in S2 is 1150-1275° C. and the sintering time is 6-10 h.

[0014] The invention provides a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material prepared by the method mentioned above.

[0015] Preferably, the composite ceramic material comprises cubic structured Li3Mg3TiO6F phase, CaTiO3 phase and Mg2TiO4 phase, wherein the content of Li3Mg3TiO6F is 79.6wt% to 85.8wt%, the content of CaTiO3 is 8.9wt% to 14.2wt%, and the rest is Mg2TiO4.

[0016] Preferably, the composite ceramic material has a resonant frequency temperature coefficient of -7.86 to +5.10 ppm / °C, a quality factor of 43220 to 48245 GHz, and a dielectric constant of 13.1 to 13.6.

[0017] Mechanism of action

[0018] Frequency Temperature Stability of Li3Mg3TiO6F Microwave Dielectric Ceramics (τ f~-38.7ppm / ℃) is poor. The existing method of improving its frequency temperature stability mainly improves its frequency temperature stability by adding compounds with opposite frequency temperature stability coefficients as additives. However, its preparation process is complicated and the added composite materials often have large losses, which greatly increases the loss while regulating its temperature stability, seriously damaging its quality factor.

[0019] The present invention uses CaF to replace LiF in the raw materials, and promotes the reaction between Li2CO3, MgO, TiO2 and CaF2 in the raw materials by adjusting the raw material ratio between Li2O-MgO-TiO2-CaF2 and the selection of the later sintering process, so as to generate CaTiO3 and Li3Mg3TiO6F and Mg2TiO4 phases with opposite frequency temperature coefficients. The frequency temperature stability of Li3Mg3TiO6F-based ceramics is significantly improved, and a new composite material with good microwave dielectric properties is obtained.

[0020] Beneficial technical effects of the present invention

[0021] The temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic of the present invention has good microwave performance (resonance frequency temperature coefficient is -7.86 to +5.10ppm / ℃, quality factor is 43220 to 48245GHz, dielectric constant is 13.1 to 13.6), overcomes the shortcoming of pure phase Li3Mg3TiO6F ceramic material with large resonant frequency temperature coefficient, ensures the temperature stability of the material, and meets the requirements of current high-frequency communication equipment for better working environment temperature stability and low dielectric constant materials with high Q value. The preparation method of the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material of the present invention is simple, the raw materials used are abundant in source, the cost is low, and it is suitable for large-scale production. The prepared temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic can be widely used in the communication field where microwave ceramic components are needed, such as satellite high-precision positioning, mobile communication filters, resonators, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the X-ray powder diffraction pattern of the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material proposed in the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further explained below in conjunction with specific embodiments.

[0024] Example 1

[0025] The method for preparing the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material proposed by the present invention comprises the following steps:

[0026] (1) Preparation of Li3Mg3TiO6F-based microwave dielectric composite ceramic pre-sintered powder

[0027] According to the stoichiometric ratio of Li2O:MgO:TiO2:CaF2=1:3:(1+3x):3x(x=0.06), 3.1498 g Li2CO3, 5.1537 g MgO, 4.0176 g TiO2 and 0.5990 g CaF2 were weighed and put into a ball mill, with zirconium balls as grinding balls and anhydrous ethanol as ball milling media. After fully mixing and ball milling for 10 hours, the mixture was dried at 100°C for 24 hours and pre-calcined at 950°C for 6 hours to obtain pre-calcined powder.

[0028] (2) Preparation of Li3Mg3TiO6F-based microwave dielectric composite ceramics

[0029] The pre-sintered powder is put into a ball mill, zirconium balls are used as grinding balls, anhydrous ethanol is used as ball milling media, and the mixture is fully mixed for 8 to 10 hours. After drying, 0.6 g of a 5% by mass polyvinyl alcohol solution is added for granulation, and the mixture is passed through a 120-mesh sieve. A cylindrical green body with a diameter of 13 mm and a thickness of 5.5 to 6.5 mm is formed by a powder tablet press under a pressure of 98 MPa. The green body is sintered at 1250° C. for 6 hours to prepare a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic.

[0030] Example 2

[0031] In step (2) of this embodiment, the cylindrical sample is sintered at 1150° C. for 6 hours. The other steps are the same as those in embodiment 1. A temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic is prepared according to the same steps.

[0032] Example 3

[0033] In step (2) of this embodiment, the cylindrical sample is sintered at 1275° C. for 6 hours. The other steps are the same as those in embodiment 1. A temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic is prepared according to the same steps.

[0034] Example 4

[0035] In step (1) of this embodiment, Li2CO33.1676 g, MgO 5.1829 g, TiO23.8348 g and CaF20.4016 g are weighed according to the stoichiometric ratio of Li2O:MgO:TiO2:CaF2=1:3:(1+3x):3x(x=0.04), and the other steps are the same as those in Example 1. A temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic is prepared according to the same steps.

[0036] Example 5

[0037] In step (1) of this embodiment, Li2CO33.1587 g, MgO 5.1683 g, TiO23.9264 g and CaF20.5006 g are weighed according to the stoichiometric ratio of Li2O:MgO:TiO2:CaF2=1:3:(1+3x):3x(x=0.05), and the other steps are the same as those in Example 1. A temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic is prepared according to the same steps.

[0038] Example 6

[0039] In step (1) of this embodiment, 3.1409 g of Li2CO3, 5.1393 g of MgO, 4.1081 g of TiO2 and 0.6969 g of CaF2 were weighed according to the stoichiometric ratio of Li2O:MgO:TiO2:CaF2=1:3:(1+3x):3x(x=0.07). The other steps were the same as those in Example 1. A temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic was prepared according to the same steps.

[0040] Comparative Example 1

[0041] According to the stoichiometric ratio of Li2O:MgO:TiO2:LiF=1:3:1:1, 2.8796 g of Li2CO3, 4.7129 g of MgO, 3.1127 g of TiO2 and 1.0109 g of LiF were weighed and put into a ball mill, with zirconium balls as grinding balls and anhydrous ethanol as ball milling media. After fully mixing and ball milling for 10 hours, the mixture was dried at 100°C for 24 hours and pre-calcined at 750°C for 4 hours to obtain pre-calcined powder. The pre-sintered powder was put into a ball mill, with zirconium balls as grinding balls and anhydrous ethanol as ball milling media, and fully mixed for 8 to 10 hours. After drying, 0.6 g of a 5% polyvinyl alcohol solution was added for granulation, and the powder was sieved through a 120-mesh sieve. A cylindrical green body with a diameter of 13 mm and a thickness of 5.5 to 6.5 mm was formed by a powder tablet press at a pressure of 98 MPa. The green body was sintered at 850° C. for 5 hours to prepare Li3Mg3TiO6F dielectric ceramics.

[0042] Comparative Example 2

[0043] In step (1) of this comparative example, 3.1856 g of Li2CO3, 5.2124 g of MgO, 3.6500 g of TiO2 and 0.2019 g of CaF2 were weighed according to the stoichiometric ratio of Li2O:MgO:TiO2:CaF2=1:3:(1+3x):3x(x=0.02). The other steps were the same as those in Example 1. Li3Mg3TiO6F-based microwave dielectric composite ceramics were prepared according to the same steps.

[0044] Comparative Example 3

[0045] In step (1) of this comparative example, 3.1322 g of Li2CO3, 5.1249 g of MgO, 4.1982 g of TiO2 and 0.7942 g of CaF2 were weighed according to the stoichiometric ratio of Li2O:MgO:TiO2:CaF2=1:3:(1+3x):3x(x=0.08), and the other steps were the same as those in Example 1. Li3Mg3TiO6F-based microwave dielectric composite ceramics were prepared according to the same steps.

[0046] The temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic materials obtained in the above examples 1-6 were characterized by a Smartlab X-ray diffractometer. Figure 1 .Depend on Figure 1 It can be seen that the prepared ceramic material is composed of cubic Li3Mg3TiO6F phase, CaTiO3 phase and Mg2TiO4 phase. The mass percentage of each phase of each substance is shown in Table 1.

[0047] Table 1 Phase composition of microwave dielectric composite ceramic material of the present invention

[0048] Group <![CDATA[Li3Mg3TiO6F(wt%)]]> <![CDATA[CaTiO3]]> <![CDATA[Mg2TiO4(wt%)]]> Example 1 82.4 13.5 4.1 Example 2 82.8 12.9 4.3 Example 3 82.2 13.6 4.2 Example 4 79.6 8.9 11.5 Example 5 83.7 12.2 4.1 Example 6 85.8 14.2 0

[0049] The temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramics prepared in Examples 1-6 and the Li3Mg3TiO6F-based microwave dielectric ceramics prepared in Comparative Examples 1-3 were fully ground and processed into cylindrical samples with a diameter of 13 mm and a height of 5.5-6.5 mm. The microwave dielectric properties of the ceramic materials were tested using a closed cavity resonance method and a ZVB20 vector network analyzer (Rohde & Schwarz, Germany). The test results are shown in Table 2.

[0050] Table 2 Comparison of microwave dielectric properties of different materials

[0051]

[0052]

[0053] As can be seen from Table 2, the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material of the present invention has good microwave performance (resonance frequency temperature coefficient is -7.86~+5.10ppm / ℃, quality factor is 43220~48245GHz, and dielectric constant is 13.1~13.6). While maintaining the high quality factor value of Li3Mg3TiO6F-based microwave dielectric ceramics, it overcomes the shortcomings of its large resonant frequency temperature coefficient and insufficient stability, and fully meets the requirements of microwave dielectric equipment in mobile communication equipment for temperature stability and ultra-low dielectric loss.

Claims

1. A method for preparing a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material, characterized in that: The steps are as follows: S1: Preparation of calcined powder Li2CO3, MgO, TiO2 and CaF2 are placed in a ball mill according to the stoichiometric ratio, zirconium balls are used as milling balls, anhydrous ethanol is used as the milling medium, and the mixture is fully mixed and milled, and then dried and pre-calcined to obtain pre-calcined powder; S2: Preparation of Li3Mg3TiO6F-based microwave dielectric composite ceramic materials The pre-sintered powder is put into a ball mill, fully mixed with zirconium balls as grinding balls and anhydrous ethanol as ball milling media, dried, granulated, sieved, and made into a cylindrical green body by a powder tabletting machine, and the green body is sintered to prepare a temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material.

2. The method for preparing the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material according to claim 1, characterized in that: The stoichiometric ratio of Li2CO3, MgO, TiO2 and CaF2 in S1 is 1:3:(1+3x):3x, where 0.04≤x≤0.

07.

3. The method for preparing the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material according to claim 1, characterized in that: The drying temperature in S1 is 80-100°C and the drying time is 12-24h.

4. The method for preparing the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material according to claim 1, characterized in that: The pre-burning temperature in S1 is 900-1000°C and the time is 4-6h.

5. The method for preparing the temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material according to claim 1, characterized in that: The sintering temperature in S2 is 1150-1275°C and the sintering time is 6-10h.

6. A temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material prepared by the method according to any one of claims 1 to 5.

7. The temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material according to claim 6, characterized in that: The composite ceramic material comprises a cubic structure of Li3Mg3TiO6F phase, CaTiO3 phase and Mg2TiO4 phase, wherein the content of Li3Mg3TiO6F is 79.6wt% to 85.8wt%, the content of CaTiO3 is 8.9wt% to 14.2wt%, and the rest is Mg2TiO4.

8. The temperature-stable Li3Mg3TiO6F-based microwave dielectric composite ceramic material according to claim 6, characterized in that: The resonant frequency temperature coefficient of the composite ceramic material is -7.86 to +5.10 ppm / °C, the quality factor is 43220 to 48245 GHz, and the dielectric constant is 13.1 to 13.6.

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