A microwave-tunable composite ceramic material and its preparation method

Abstract

This invention discloses a microwave-tunable composite ceramic material and its preparation method, belonging to the technical field of microwave ceramic materials. The material is composed of Ba... 1‑x Sr x It consists of three phases: TiO3, Li2Mg3TiO6, and Mg2SiO4, among which Ba 1‑x Sr x The mass percentage of TiO3 is 30%–95%, and the value of x ranges from 0.3 to 0.7; the mass percentage of Li2Mg3TiO6 is 3%–60%, with the remainder being Mg2SiO4. This material has a moderate dielectric constant, low dielectric loss, and high tuning efficiency, combining high performance with a low sintering temperature. It can be used in microwave devices such as phase shifters, tunable filters, delay lines, oscillators, resonators, and phased array antennas.

Description

Technical Field

[0001] This invention belongs to the field of microwave ceramic materials technology, and more specifically, relates to a microwave-tunable composite ceramic material and its preparation method. Background Technology

[0002] Microwave tuning materials are crucial for realizing microwave communication devices such as tunable filters, phase shifters, oscillators, and phased array antennas. Their dielectric constant can change with applied voltage, allowing for frequency tuning through voltage control, such as inducing frequency jumps in filters. This is significant for multi-user frequency resource sharing in future broadband communications. Such materials can significantly reduce the cost of phased array antennas, propelling their expansion from military to civilian applications and improving antenna performance in terms of speed, accuracy, and reliability. However, current technologies face serious challenges: commercially available phase shifters mainly use ferrite or semiconductor diodes. Ferrite offers low loss and high power capacity above 3GHz, but the entire tuning circuit is expensive, bulky, and consumes a lot of power, and it's difficult to achieve a planar structure, limiting its applications to military. PIN diodes, on the other hand, suffer from high loss, low power, require external logic circuitry for control, and cannot be continuously tuned at high frequencies.

[0003] At the materials level, barium strontium titanate (Ba 1-x Sr x TiO3 is considered an ideal microwave tuning material because its dielectric constant can be adjusted with an external electric field. However, its microwave dielectric loss is relatively high, and an excessively high dielectric constant can easily lead to increased insertion loss and difficulty in matching with circuits. To improve performance, Ba... 1-x Sr x TiO3-MgO composite ceramics have been developed, exhibiting relatively low dielectric constant and loss, but suffer from high sintering temperatures, typically exceeding 1400℃, and low tuning efficiency. Further composites using low-temperature sintering materials such as Li2Mg3TiO6 can lower the sintering temperature to around 1280℃, but the tuning efficiency remains unsatisfactory. Adding sintering aids such as oxides like B2O3, CuO, and Li2CO3 to reduce the sintering temperature can easily introduce impurity phases, leading to deterioration of dielectric properties.

[0004] Therefore, developing a microwave tunable ceramic material that can be sintered at low temperatures, has a high tunability, and is free of impurities has become an important direction for current technological breakthroughs. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a microwave-tunable composite ceramic material and its preparation method. This is achieved by constructing Ba... 1-x Sr xThe TiO3, Li2Mg3TiO6, and Mg2SiO4 three-phase composite system utilizes the low thermodynamic property of the ternary eutectic point temperature to achieve low-temperature sintering and high performance. According to the simple ternary eutectic phase diagram of immiscible solid systems, the temperature of the ternary eutectic point is lower than the temperatures of the three binary eutectic points. According to classical sintering theory, the sintering temperature (Ts) of a material satisfies the relationship Ts∝kTm (where k is a material constant). When the system composition is close to the ternary eutectic point, its liquidus temperature is significantly lower than that of any binary system, providing a thermodynamic basis for reducing the sintering temperature. Based on this thermodynamic property, this invention constructs a ternary composite system, utilizing the low ternary eutectic point temperature to achieve the goal of reducing the sintering temperature.

[0006] The technical solution of this invention is implemented as follows:

[0007] On one hand, the present invention provides a microwave-tunable composite ceramic material, the material being composed of Ba... 1-x Sr x The system consists of three phases: TiO3, Li2Mg3TiO6, and Mg2SiO4. This system is designed based on a ternary eutectic strategy, where the three phases are immiscible, forming a stable composite structure. This ternary eutectic characteristic stems from the thermodynamic principle of immiscible solid systems, where the ternary eutectic point temperature is lower than that of any binary system, providing a basis for reducing the sintering temperature; specifically, Ba... 1-x Sr x The sintering temperature of the TiO3-Li2Mg3TiO6 binary composite has increased from Ba... 1-x Sr x The temperature of TiO3-MgO was reduced from 1400°C to 1280°C, while the introduction of Mg2SiO4 further optimized the eutectic behavior.

[0008] Based on the above technical solutions, preferably, the microwave-tunable composite ceramic material is characterized by Ba 1-x Sr x The mass percentage of TiO3 is 30%-95%, and the value of x ranges from 0.3 to 0.7. If x < 0.3, Ba 1-x Sr x TiO3 has a high Curie temperature and relatively high dielectric loss; if x > 0.7, Ba 1-x Sr x TiO3 has a low tuning rate.

[0009] More preferably, the Ba 1-x Sr x The value of x in TiO3 ranges from 0.4 to 0.6.

[0010] More preferably, the mass percentage of Li2Mg3TiO6 is 3%-60%.

[0011] More preferably, the mass percentage of Mg2SiO4 is 2%-50%; in the mixture of Li2Mg3TiO6 and Mg2SiO4, the mass percentage of Mg2SiO4 is 20%-90%. If the mass percentage of Mg2SiO4 is less than 20%, the tuning rate of the composite ceramic is low; if the mass percentage of Mg2SiO4 is greater than 90%, the sintering temperature will increase.

[0012] On the other hand, the present invention also provides a method for preparing microwave-tunable composite ceramic materials:

[0013] S1, Preparation of Ba 1-x Sr x TiO3, Li2Mg3TiO6 and Mg2SiO4 powders were mixed, ball-milled and then dried.

[0014] S2. Press the dried material into a green body, sinter it and keep it warm to obtain a microwave-tuned composite ceramic material.

[0015] Based on the above technical solutions, preferably, in step S1, Ba 1-x Sr x TiO3 powder is obtained by ball milling and pre-calcining a mixture of BaCO3, SrCO3 and TiO3; Li2Mg3TiO6 powder is obtained by ball milling and pre-calcining a mixture of Li2CO3, TiO2 and MgO; Mg2SiO4 powder is obtained by ball milling and pre-calcining a mixture of SiO2 and MgO.

[0016] More preferably, in step S1, the pre-firing temperature range is 1000℃-1200℃, and the pre-firing time is 2-6 hours.

[0017] Further preferably, in step S1, according to the ratio in Ba 1-x Sr x Powdered Li2Mg3TiO6 and Mg2SiO4 are added to TiO3 powder, which is then wet-milled for 6-24 hours before being discharged and dried.

[0018] In a further preferred embodiment, in step S2, 3-8 wt% of polyvinyl alcohol is added to the dried material to granulate it, and then it is pressed into a green compact. The green compact is heated to 400℃-800℃ at a heating rate of less than or equal to 30℃ / minute, and then held at that temperature for 2-4 hours to remove organic matter from the green compact.

[0019] More preferably, in step S2, the sintering temperature range is 1150℃-1250℃; the holding time is 2-4 hours.

[0020] The technical solutions conceived in this invention have the following advantages over the prior art:

[0021] (11) The composite ceramic material of the present invention utilizes Ba 1-x Sr x The ternary eutectic properties of TiO3, Li2Mg3TiO6, and Mg2SiO4 significantly reduce the sintering temperature and can improve the Ba content. 1-x Sr x The tuning efficiency of TiO3-Li2Mg3TiO6 was achieved. This composite ceramic material can be sintered in the range of 1150℃-1250℃ and has excellent properties such as moderate dielectric constant, low dielectric loss, and high tuning efficiency, achieving a combination of high performance and low sintering temperature.

[0022] (12) By adjusting the doping ratio of Li2Mg3TiO6 and Mg2SiO4 in the composition, the content ratio of the two and the Sr / Ba ratio, the Curie temperature of the material can be effectively controlled, thereby accurately designing key parameters such as dielectric constant, dielectric loss and tuning rate, and broadening its application adaptability.

[0023] (13) The composite ceramic material of the present invention is composed of Ba 1-x Sr x A three-phase complex of TiO3, Li2Mg3TiO6 and Mg2SiO4 exists, and no impurity phase is formed.

[0024] (14) This composite ceramic material can be widely used in microwave tuning components such as variable capacitors, tunable filters, phase shifters, tunable delay lines, voltage-controlled oscillators, tunable dielectric resonators, and tunable impedance matching devices. As the core component of phased array antennas, the cost and performance of phase shifters are directly affected by the materials used. This material can replace expensive ferrites, enabling phased array antennas to be miniaturized, lightweight, and cost-effective, thus promoting their expansion from military to civilian applications.

[0025] (15) The preparation method adopts the traditional electronic ceramic process, including powder preparation, ball milling, granulation, debinding and sintering. The process is simple, the cost is low, and the material system is environmentally friendly and non-toxic, which is suitable for large-scale production. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 Ba obtained in Examples 1-8 1-x Sr xXRD spectrum of TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramic material;

[0028] Figure 2 Here are SEM images of the surface morphology of the composite ceramic obtained in Example 3;

[0029] Figure 3 Ba obtained in Examples 1-8 1-x Sr x The changes in dielectric constant and dielectric loss of TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics at 10kHz frequency;

[0030] Figure 4 Ba obtained in Examples 1-8 1-x Sr x Tuning rate of TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics at 10kHz frequency and under different DC electric field strengths. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Table 1: Material Source Description Table

[0033]

[0034] Examples 1-8:

[0035] S1. Prepare Ba according to stoichiometric ratios. 1-x Sr x TiO3 (x=0.5), Li2Mg3TiO6, and Mg2SiO4. Specifically, powdered BaCO3, SrCO3, and TiO2 were mixed in a certain proportion as a set of raw materials and pre-calcined at 1100°C for 2 hours to obtain Ba. 0.5 Sr 0.5 TiO3; Li2CO3, TiO2, and MgO were mixed in a certain proportion as another set of raw materials and pre-calcined at 1000°C for 4 hours to obtain Li2Mg3TiO6 powder; SiO2 and MgO were mixed in a certain proportion as a third set of raw materials and pre-calcined at 1200°C for 3 hours to obtain Mg2SiO4 powder. Deionized water was added to the raw materials, and zirconium dioxide was used as the ball milling medium. The mass ratio of powder, solvent, and ball milling medium was 1:2 to 5:10. After wet ball milling for 6 hours, the material was discharged and dried.

[0036] S2. Granulation was performed using 5 wt% polyvinyl alcohol as a binder, and the powder was pressed into shape under a pressure of 150 MPa. After debinding at 600°C, it was sintered at 1200°C for 3 hours in air to obtain Mn-doped Ba. 0.5 Sr 0.5 TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics. After firing, the samples are finely ground, ultrasonically cleaned, and then fitted with silver electrodes, making them suitable for dielectric property testing.

[0037] FixedBa 0.5 Sr 0.5 The mass percentage of TiO3 is 50%, and the mass percentages of Li2Mg3TiO6 are 40%, 35%, 30%, 25%, 20%, 15%, 10% and 5%, respectively. The remaining component is Mg2SiO4, corresponding to Examples 1 to 8, as shown in Table 2.

[0038] Table 2. Mass percentage of each component in the prepared microwave-tunable composite ceramic material

[0039]

[0040] The XRD spectra of the composite ceramic materials prepared in Examples 1-8 are as follows: Figure 1 As shown, the composite ceramic material is made of Ba 0.5 Sr 0.5 The three phases of TiO3, Li2Mg3TiO6 and Mg2SiO4 are present without any impurity phases, indicating that the three phases do not undergo chemical reactions and can exist independently.

[0041] The SEM image of the surface morphology of the composite ceramic obtained in Example 1 is shown below. Figure 2 As shown, it is clear that there are three types of grains, and the density is high.

[0042] Ba prepared in Examples 1-8 0.5 Sr 0.5 The tuning rate of TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics at 10kHz is as follows: Figure 3 As shown, decreasing the mass percentage of Li₂Mg₃TiO₆ and increasing the mass percentage of Mg₂SiO₄ increases the dielectric constant of the composite ceramic. The dielectric constants of Examples 1, 4, and 7 are 171.9, 196.5, and 241.9, respectively. The dielectric losses of Examples 1 to 8 are all very low, with the highest not exceeding 0.0015, and the dielectric loss of Example 2 is only 0.00074.

[0043] Ba prepared in Examples 1-8 0.5 Sr 0.5The tuning rate of TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics at 10kHz frequency and under different DC electric field strengths is as follows: Figure 4 As shown. Therefore, decreasing the mass percentage of Li₂Mg₃TiO₆ and increasing the mass percentage of Li₂Mg₃TiO₆ can improve the performance of Ba. 0.5 Sr 0.5 The tuning rate of TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics increases monotonically. For example, when the mass percentage of Mg2SiO4 in the composite ceramic increases from 10% (Example 1) to 35% (Example 6), the tuning rate at 10 kHz and 3 kV / mm increases from 9.4% to 19.2%, more than doubling, while the corresponding dielectric constant only increases from 171.9 to 203.3. In contrast, the binary 50Ba sintered at 1280°C... 0.5 Sr 0.5 The TiO3-50Li2Mg3TiO6 composite ceramic exhibits a dielectric constant of 131.7 and a dielectric loss of 0.0017 at 10 kHz, with a tuning efficiency of only 5.7% at 3 kV / mm. Ba2O3 composite ceramics constructed based on a eutectic strategy... 0.5 Sr 0.5 The TiO3-Li2Mg3TiO6-Mg2SiO4 composite ceramics reduced the sintering temperature and significantly improved the tuning efficiency. When the sintering temperature increased to 1230°C, the composite ceramic of Example 1 with a high Li2Mg3TiO6 content exhibited melting, indicating that the three-phase eutectic point was around 1230°C, much lower than that of Ba. 0.5 Sr 0.5 The melting points of TiO3, Li2Mg3TiO6 and Mg2SiO4 are due to Ba 0.5 Sr 0.5 TiO3, Li2Mg3TiO6 and Mg2SiO4 are mutually insoluble, enabling liquid-phase sintering, which greatly reduces the sintering temperature.

[0044] In existing technologies, microwave-tunable ceramic materials suffer from problems such as high sintering temperatures and low tuning rates. This invention reduces the sintering temperature of microwave-tunable composite ceramics and improves their tuning rate, thus solving these problems. By adjusting the Sr / Ba ratio, the mass percentage of Li₂Mg₃TiO₆-Mg₂SiO₄, and the Li₂Mg₃TiO₆ / Mg₂SiO₄ ratio, a series of materials with different dielectric constants and tuning rates can be obtained.

[0045] Example 9

[0046] Unlike Example 1: Ba 1-x Sr xThe mass percentage of TiO3 (x=0.3) is 30%, the mass percentage of Li2Mg3TiO6 is 60%, and the mass percentage of Mg2SiO4 is 10%.

[0047] Example 10

[0048] Unlike Example 1: Ba 1-x Sr x The mass percentage of TiO3 (x=0.45) is 40%, the mass percentage of Li2Mg3TiO6 is 10%, and the mass percentage of Mg2SiO4 is 50%.

[0049] Example 11

[0050] Unlike Example 1: Ba 1-x Sr x The mass percentage of TiO3 (x=0.6) is 60%, the mass percentage of Li2Mg3TiO6 is 25%, and the mass percentage of Mg2SiO4 is 15%.

[0051] Example 12

[0052] Unlike Example 1: Ba 1-x Sr x The mass percentage of TiO3 (x=0.7) is 95%, the mass percentage of Li2Mg3TiO6 is 3%, and the mass percentage of Mg2SiO4 is 2%.

[0053] Comparative Example 13

[0054] Unlike Example 1: Ba 1-x Sr x The mass percentage of TiO3 (x=0.8) is 97%, the mass percentage of Li2Mg3TiO6 is 2%, and the mass percentage of Mg2SiO4 is 1%.

[0055] Comparative Example 14

[0056] Unlike Example 1: Ba 1-x Sr x The mass percentage of TiO3 (x=0.2) is 20%, the mass percentage of Li2Mg3TiO6 is 65%, and the mass percentage of Mg2SiO4 is 15%.

[0057] Comparative Example 15

[0058] Unlike Example 1: Ba 1-x Sr xThe mass percentage of TiO3 (x=0.2) is 20%, the mass percentage of Li2Mg3TiO6 is 25%, and the mass percentage of Mg2SiO4 is 55%.

[0059] The materials prepared using the materials and chemical ratios described in Examples 9-12 above, and following the preparation process described in Examples 1-8, all achieve the technical effects described in this invention.

[0060] Examples 13-15 are comparative examples outside the scope of this invention. A comparison with Example 1 shows that Example 13 cannot operate at 1150-1250 degrees Celsius. o The dense sintering of C is due to the low content of Li2Mg3TiO6 and Mg2SiO4, resulting in a high dielectric constant and dielectric loss in the densely sintered sample. The loss of tuning performance in Examples 14 and 15 is attributed to Ba. 1-x Sr x The TiO3 content is too low.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A microwave-tunable composite ceramic material, characterized in that, The material is made of Ba 1-x Sr x It consists of three phases: TiO3, Li2Mg3TiO6 and Mg2SiO4; Among them, Ba 1-x Sr x The mass percentage of TiO3 is 30%-95%, and x is 0.5; The mass percentage of Li2Mg3TiO6 is 3%-60%; the mass percentage of Mg2SiO4 is 2%-50%; and in the mixture of Li2Mg3TiO6 and Mg2SiO4, the mass percentage of Mg2SiO4 is 20%-90%.

2. A method for preparing the microwave-tuned composite ceramic material as described in claim 1, characterized in that, Includes the following steps: S1, Preparation of Ba 1-x Sr x TiO3, Li2Mg3TiO6 and Mg2SiO4 powders were mixed, ball-milled and then dried. S2. Press the dried material into a green body, sinter it and keep it warm to obtain a microwave-tuned composite ceramic material.

3. The preparation method according to claim 2, characterized in that, In step S1, Ba 1-x Sr x TiO3 powder is obtained by ball milling and pre-calcining a mixture of BaCO3, SrCO3 and TiO3; Li2Mg3TiO6 powder is obtained by ball milling and pre-calcining a mixture of Li2CO3, TiO2 and MgO; Mg2SiO4 powder is obtained by ball milling and pre-calcining a mixture of SiO2 and MgO.

4. The preparation method according to claim 3, characterized in that, The pre-firing temperature range is 1000℃-1200℃, and the pre-firing time is 2-6 hours.

5. The preparation method according to claim 2, characterized in that, In step S2, the sintering temperature range is 1150℃-1250℃; the holding time is 2-4 hours.

6. A microwave device, characterized in that, It includes the microwave-tunable composite ceramic material as described in claim 1.

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