Molybdate-based microwave dielectric ceramic material with scheelite structure regulated and controlled through entropy and preparation method of molybdate-based microwave dielectric ceramic material

Abstract

The invention discloses a molybdate-based microwave dielectric ceramic material with a scheelite structure regulated and controlled through entropy and a preparation method of the molybdate-based microwave dielectric ceramic material, the temperature coefficient of resonance frequency is regulated and controlled through lattice distortion, and relatively low dielectric loss and dielectric constant are ensured through an entropy value. The molybdate-based microwave dielectric ceramic with the scheelite structure prepared by the invention has excellent microwave dielectric properties: epsilon r is equal to 9.74, Q * f is equal to 91273GHz, and tauf is equal to-48.34 ppm / DEG C. The molybdate-based microwave dielectric ceramic with the scheelite structure prepared by the invention is expected to be applied to the fields of microwave communication, smart phones, electronic equipment and the like, and provides a better choice for materials for preparing capacitors in the electronic industry.

Description

Technical Field

[0001] This invention belongs to the field of dielectric materials and their manufacturing, and relates to microwave dielectric ceramic materials. Specifically, it provides a molybdate-based microwave dielectric ceramic material with entropy-controlled scheelite structure and its preparation method. Background Technology

[0002] Communication technology is the cornerstone of global modern science and technology and the foundation for digital transformation. Microwave dielectric ceramics enable the miniaturization, chip-scale integration, and modularization of microwave devices, making them a key component of radio frequency units in communication base stations and holding an irreplaceable position in communication systems. However, with the widespread adoption of 5G networks globally, research and development for 6G communication has fully commenced, presenting both challenges and opportunities for microwave dielectric ceramics research. The development of 6G communication technology relies heavily on excellent microwave dielectric properties. A suitable dielectric constant allows for a reduction in resonator size while ensuring rapid signal transmission within the dielectric. The low dielectric loss of microwave dielectric ceramics at high frequencies satisfies the excellent frequency selectivity of devices. A near-zero temperature coefficient of resonant frequency ensures the temperature stability of the device during operation. However, during the ceramic fabrication process, uncontrollable factors such as polarization capability and intrinsic losses make it difficult to simultaneously achieve excellent microwave dielectric properties.

[0003] Molybdate-based (AMoO4) ceramics, exhibiting a scheelite structure, have attracted considerable attention due to their low dielectric constant and dielectric loss. However, the application of pure-phase molybdate-based ceramics is limited by their low temperature coefficient of resonant frequency. Doping can effectively address this issue. A-site substitution in molybdate-based ceramics effectively induces lattice distortion in [AO8], thereby increasing the temperature coefficient of resonant frequency. These properties promise to meet the requirements of next-generation wireless communication applications, and the material is environmentally friendly, complying with increasingly stringent environmental regulations, and possesses promising prospects for green applications.

[0004] However, molybdate-based ceramics also have some significant drawbacks, especially in wireless communication applications. Single-ion doping (such as Ba) 2+ or Ca 2+ Ion radius mismatch can also cause severe lattice distortion, leading to an irreversible increase in dielectric loss. Traditional "size compensation" schemes (such as co-doping with ions of similar radii) can alleviate the stress of single doping, but they are difficult to balance the requirements of wide temperature range stability and high-frequency low loss. A breakthrough doping design paradigm is urgently needed. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a molybdate-based microwave dielectric ceramic material with a scheelite structure and its preparation method. 2+ Ba with similar ionic radii 2+and Ca 2+ Microwave dielectric ceramics were prepared by ion substitution. The lattice distortion effectively increased the temperature coefficient of its resonant frequency. Secondly, by controlling the ionic radius of Ba... 2+ and Ca with smaller ionic radii 2+ The appropriate Ba / Ca ratio results in a lower lattice distortion rate, ensuring an increase in the temperature coefficient of the resonant frequency without increasing dielectric loss. It's worth noting that when the Ba / Ca ratio is 4:1 and 1:4, the ceramic is low-entropy, exhibiting larger lattice distortion. When the Ba / Ca ratio is 2:3 and 3:2, the ceramic is medium-entropy, exhibiting smaller lattice distortion. Furthermore, due to the unique ion diffusion hysteresis effect of ceramics, ion diffusion is suppressed, leading to a decrease in dielectric loss.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a molybdate-based microwave dielectric ceramic material with an entropy-controlled scheelite structure, the chemical formula of which is Sr 0.5 Ca x Ba y MoO4 (where x+y=0.5, x=0.1,0.2,0.3,0.4).

[0007] This invention also provides a method for preparing the above-mentioned scheelite-structured molybdate-based microwave dielectric ceramic material, comprising the following steps: (1) According to Sr 0.5 Ca x Ba y The raw materials, including SrCO3, BaCO3, MoO3, and CaCO3, were weighed according to the stoichiometric ratio of MoO4. The raw materials were placed in a ball mill jar with distilled water and ball milled. Then, they were dried and ground in sequence to obtain powder. (2) Pre-fire the powder obtained in (1); (3) The powder obtained in (2) is subjected to secondary ball milling, drying, grinding and adding binder. After grinding and granulation, it is pressed into sheets and then placed in a muffle furnace for debinding and sintering in sequence to obtain the molybdate-based ceramic.

[0008] Specifically, in step (1), the ball milling time is 8 hours and the rotation speed is 280 r / min.

[0009] Specifically, in step (2), the preheating temperature is 650°C and the time is 4 hours.

[0010] Specifically, in step (3), the secondary ball milling time is 8 hours, the rotation speed is 280 r / min, the binder is 8% PVA aqueous solution, and the tableting pressure is 20 MPa.

[0011] Specifically, in step (3), the glue removal temperature is 650℃ and the glue removal time is 2h; the sintering temperature is 900-1050℃ and the sintering time is 4h.

[0012] Compared with the prior art, the technical effects of the present invention are reflected in: (1) It has excellent microwave dielectric properties: ε r =9.74, Q×f=91273GHz, τ f = -48.34ppm / ℃. (2) The inhibition of A-site cation diffusion in ceramics can effectively reduce its migration loss. (3) Due to the small lattice distortion of medium-entropy ceramics, the temperature coefficient of its resonant frequency can be increased without increasing the dielectric loss.

[0013] Some of the additional advantages, objectives and features of the present invention will be described in detail below, which will enable those skilled in the art to clearly understand the essence of the invention and guide related research or practice.

[0014] Please note that the scope of application of this invention is not limited to the specific description above, and the various objectives and advantages that this invention can achieve can be more fully understood based on the detailed description below, including but not limited to the above content. Attached Figure Description

[0015] Figure 1 These are X-ray diffraction (XRD) patterns of various embodiments of the present invention.

[0016] Figure 2 These are scanning electron microscope (SEM) images of various embodiments of the present invention.

[0017] Figure 3 The density and relative density are for each embodiment of the present invention.

[0018] Figure 4 The figures show the dielectric constant and Q×f variation curves of various embodiments of the present invention.

[0019] Figure 5 The curves showing the variation of the temperature coefficient of the resonant frequency in various embodiments of the present invention are shown. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0021] Example 1: This embodiment describes an entropy-controlled scheelite-structured molybdate-based microwave dielectric ceramic material and its preparation method. The chemical composition of the ceramic material in this embodiment is (Sr... 0.5 Ca0.1 Ba 0.4 MoO4, a low-entropy ceramic with an entropy value of approximately 0.94, is prepared as follows: SrCO3, BaCO3, MoO3, and CaCO3 were selected as raw materials. The required mass of raw materials was calculated based on their chemical composition and weighed. Then, distilled water and zirconia balls were mixed in a ratio of 1:3:5 and ball-milled at 280 r / min for 8 hours to obtain a slurry. The slurry was dried to obtain powder, which was then placed in a muffle furnace and pre-fired at 650℃ for 4 hours. The pre-fired powder was ball-milled again under the same conditions as the previous ball milling and dried. The dried powder was mixed with an 8% PVA aqueous solution and granulated, and then passed through a 200-mesh sieve. 2.5 g of the granulated powder was placed into a cylindrical mold with a diameter of 12 mm and pressed into a sheet at 20 MPa for 60 s to obtain a ceramic green body. The ceramic green body was placed in a muffle furnace at 650℃ for 2 hours to remove the binder, then sintered at 900℃ for 4 hours, and then naturally cooled to room temperature before being removed.

[0022] Example 2: This embodiment describes an entropy-controlled scheelite-structured molybdate-based microwave dielectric ceramic material and its preparation method. The chemical composition of the ceramic material in this embodiment is (Sr... 0.5 Ca 0.2 Ba 0.3 MoO4, prepared using the same steps as in Example 1, is a medium-entropy ceramic with an entropy value of approximately 1.02.

[0023] Example 3: This embodiment describes an entropy-controlled scheelite-structured molybdate-based microwave dielectric ceramic material and its preparation method. The chemical composition of the ceramic material in this embodiment is (Sr... 0.5 Ca 0.3 Ba 0.2 MoO4, prepared using the same steps as in Example 1, is a medium-entropy ceramic with an entropy value of approximately 1.02.

[0024] Example 4: This embodiment describes an entropy-controlled scheelite-structured molybdate-based microwave dielectric ceramic material and its preparation method. The chemical composition of the ceramic material in this embodiment is (Sr... 0.5 Ca 0.4 Ba 0.1 MoO4, prepared using the same steps as in Example 1, is a low-entropy ceramic with an entropy value of approximately 0.94.

[0025] Figure 1The XRD patterns of each embodiment are shown. Data analysis shows that all embodiments and comparative examples exhibit a tetragonal scheelite structure without the formation of other impurity phases. When Ba / Ca = 2:3, its lattice parameter is closest to that of SrMoO4, indicating that its lattice distortion is relatively small. Reduced lattice distortion can decrease the generation of defects and vacancies, which is beneficial for reducing dielectric loss.

[0026] Figure 2 The images shown are SEM images of each embodiment. The average grain size of low-entropy ceramics is larger than that of medium-entropy ceramics. This is because the significant lattice distortion caused by the large difference in ionic radii in low-entropy ceramics results in a high concentration of oxygen vacancies, which enhances diffusion. This enhanced diffusion leads to accelerated grain boundary migration, promoting excessive grain growth.

[0027] Figure 3 The values ​​represent the density and relative density of each embodiment. The density and relative density of low-entropy ceramics are lower than those of medium-entropy ceramics. This is because the greater number of defects and vacancies in low-entropy ceramics promotes abnormal grain growth, resulting in numerous pores at grain boundaries.

[0028] Figure 4 Here, εr and Q×f represent the dielectric constants of each embodiment. The dielectric constant gradually increases as the Ba / Ca ratio decreases. This increase in dielectric constant may be due to the shrinkage of the unit cell volume, enhanced Coulomb interactions between ions, and thus increased polarizability of the material. Severe distortion in the low-entropy ceramic samples leads to a large number of defects and vacancies, increased lattice anharmonicity, and increased energy loss.

[0029] Figure 5 The resonant frequency temperature coefficients for each embodiment are shown. The larger lattice distortion in low-entropy ceramics results in a higher resonant frequency temperature coefficient than that in medium-entropy ceramics. The resonant frequency temperature coefficient of medium-entropy ceramics is closely related to lattice distortion and microstrain.

[0030] In summary, the molybdate-based microwave dielectric ceramic described above can effectively increase the temperature coefficient of the resonant frequency without increasing the dielectric loss, and possesses excellent microwave dielectric properties: ε r =9.74, Q×f=91273GHz, τ f = -48.34ppm / ℃.

[0031] While specific embodiments have been described, it should be understood that the present invention is more flexible and adaptable. Any modifications, equivalent changes, or improvements made based on the core technology of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A molybdate-based microwave dielectric ceramic material with an entropy-controlled scheelite structure, characterized in that, The chemical formula of the ceramic is: Sr 0.5 Ca x Ba y MoO4 (where x+y=0.5, x=0.1,0.2,0.3,0.4).

2. The method for preparing molybdate-based microwave dielectric ceramic material with entropy-controlled scheelite structure according to claim 1, characterized in that, Includes the following steps: (1) According to Sr 0.5 Ca x Ba y The raw materials, including SrCO3, BaCO3, MoO3, and CaCO3, were weighed according to the stoichiometric ratio of MoO4. The raw materials were placed in a ball mill jar with water and ball milled. Then, they were dried and ground in sequence to obtain powder. (2) Pre-fire the powder obtained in (1); (3) The powder obtained in (2) is subjected to secondary ball milling, drying, grinding and adding binder. After grinding and granulation, it is pressed into sheets and then placed in a muffle furnace for debinding and sintering in sequence to obtain the molybdate-based ceramic.

3. The preparation method according to claim 2, characterized in that, In step (1), the ball milling time is 8 hours and the rotation speed is 280 r / min.

4. The preparation method according to claim 2, characterized in that, In step (2), the preheating temperature is 650℃ and the time is 4h.

5. The preparation method according to claim 2, characterized in that, In step (3), the secondary ball milling time is 8 hours, the rotation speed is 280 r / min, the binder is 8% PVA aqueous solution, and the tableting pressure is 20 MPa.

6. The preparation method according to claim 2, characterized in that, In step (3), the glue removal temperature is 650℃ and the glue removal time is 2h; the sintering temperature is 950-1150℃ and the sintering time is 4h.

Images