Novel single-phase molybdate ceramic material and preparation method thereof

Abstract

The invention provides a novel single-phase molybdate ceramic material and a preparation method thereof, belongs to the field of electronic ceramics and manufacturing thereof, and particularly relates to the novel single-phase molybdate ceramic material and the preparation method thereof. The chemical formula of the material is Sr0. 5Ca0. 5MoO4. The material is prepared from the following raw materials: SrCO3, CaCO3 and MoO3 through a solid-phase sintering method: the material has a low dielectric constant (epsilon r = 10.15), a temperature coefficient of resonance frequency (-8.55 ppm / DEG C) close to 0 and a high quality factor (99928GHz). On the basis of traditional SrMoO4, A-site doping is carried out through Ca element, sintering is carried out at 950 DEG C, the low dielectric constant and low dielectric loss are guaranteed, meanwhile, the temperature coefficient of resonance frequency is increased, the SrMoO4 ceramic is suitable for electronic substrates and packaging materials, the preparation method is simple, and industrial production is easy.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic ceramics and their manufacturing technologies, and particularly relates to a novel single-phase molybdate ceramic material and a preparation method thereof. Background Art

[0002] The progress of communication technologies has greatly promoted the development of microwave dielectric ceramic materials, especially through the wide application of dielectric resonators in miniaturization, portability, high frequency, and low power consumption. Low-temperature co-fired ceramics (LTCC) have become the cornerstone of the field of electronic ceramics due to their ability to sinter at relatively low temperatures, achieve high integration, and provide superior performance in high-frequency communication systems. LTCC technology realizes miniaturization and high integration by co-firing active and passive components with low-melting-point electrodes (such as silver (Ag)), thus meeting the stringent requirements of high-frequency communication devices in terms of size, performance, and energy efficiency. Notably, when the sintering temperature does not exceed 950 °C, LTCC materials can be co-fired with Ag electrodes, which is crucial for ensuring the stability and reliability of the devices. In addition, a low dielectric constant is the key to reducing signal transmission delay, while a high quality factor (Q×f) effectively reduces energy dissipation, thereby enhancing signal integrity. A near-zero temperature coefficient of the resonance frequency ensures excellent stability and accuracy in high-frequency applications. Therefore, the development of LTCC materials with a low dielectric constant, high Q×f, and a resonance frequency close to zero temperature coefficient is crucial for advancing the next generation of high-performance electronic devices.

[0003] Among numerous electronic ceramics, molybdate-based ceramics have received extensive attention due to their low dielectric loss and low dielectric constant and have played an important role in the manufacture of electronic components. Among them, SrMoO4 has good microwave dielectric properties: ε r ≈9.49, Q×f≈61000 GHz, τ f =-67.17 ppm / °C. However, its relatively high sintering temperature and low temperature coefficient of the resonance frequency pose challenges to the application of LTCC. Summary of the Invention

[0004] Aiming at the above problems, the present invention aims to improve the dielectric properties of SrMoO4-based ceramics, develop a ceramic material with a low dielectric constant, high quality factor, and near-zero temperature coefficient of the resonance frequency, and provides a novel single-phase molybdate ceramic material and a preparation method thereof.

[0005] The present invention adopts the following technical solutions:

[0006] 1. A novel single-phase molybdate ceramic material, the chemical general formula of the material is Sr 0.5 Ca 0.5MoO4, with raw material composition of SrCO3, CaCO3 and MoO3, is synthesized by solid-phase method: when the sintering temperature is 950 °C, it has a low dielectric constant (ε r = 10.15), near-zero temperature coefficient of resonant frequency (-8.55 ppm / °C), and high quality factor (99928 GHz).

[0007] The specific preparation method is as follows:

[0008] Step 1: Weigh the raw powders of high-purity SrCO3, CaCO3 and MoO3 according to the chemical formula Sr 0.5 Ca 0.5 MoO4 for batching;

[0009] Step 2: Ball-mill the batching prepared in Step 1 for 8 hours according to the mass ratio of powder, zirconia balls and distilled water of 1:5:1. After taking it out, dry it at 110 °C and sieve it through a 200-mesh sieve. Place the sieved powder in a high-temperature muffle furnace and pre-sinter it at 650 °C for 4 hours. Ball-mill the pre-sintered powder for another 8 hours, dry it, then add 8% polyvinyl alcohol aqueous solution for granulation, and sieve it through a 200-mesh sieve to ensure that the particles are fine and uniform;

[0010] Step 3: Use a tablet press to press the granulated powder into a cylinder with dimensions of 12 mm × 6 mm at 20 MPa. Place the pressed cylinder in a muffle furnace and keep it at 650 °C for two hours to remove the binder. Subsequently, sinter it at 850 - 950 °C for 4 hours to obtain a single-phase molybdate ceramic material.

[0011] In the present invention, doping makes the ceramic have severe lattice distortion and microstrain. High lattice distortion and microstrain are beneficial to improving the temperature coefficient of resonant frequency. The lattice distortion of A-site cations can effectively reduce its sintering temperature to meet the requirements of LTCC. During doping, the ion diffusion path and the increased diffusion barrier inhibit ion diffusion, resulting in the phenomenon of retarded diffusion. Retarded diffusion can effectively reduce the migration loss to compensate for the increased loss caused by severe lattice distortion. When the ceramic sintering temperature reaches 950 °C, a new type of single-phase molybdate ceramic material is finally obtained.

[0012] The preparation method is traditional pressureless sintering. On the premise of low cost and simple process, it can greatly improve the microwave dielectric properties of SrMoO4 and is suitable for mass production.

[0013] In summary, the novel single-phase molybdate ceramic provided by the present invention has a dense microstructure, high quality factor, low dielectric constant and near-zero temperature coefficient of resonant frequency, and has great prospects in the application materials of electronic substrates. Brief Description of the Drawings

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description only relate to some embodiments of the present invention and do not limit the present invention.

[0015] Figure 1 X-ray diffraction patterns for Examples 1-5;

[0016] Figure 2 Microscopic morphology diagrams for Examples 1-5;

[0017] Figure 3 Densities and relative densities for Examples 1-5;

[0018] Figure 4 Microwave dielectric properties for Examples 1-5; Detailed implementation manners

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0020] As Figures 1 to 2 shown, the present invention will be described in detail below with reference to the accompanying drawings and examples.

[0021] The chemical formula of the material of the present invention is Sr 0.5 Ca 0.5 MoO4. This material is prepared by the solid-phase method, and the specific steps are the same as the above steps.

[0022] The xrd patterns ( Figure 1 ) of ceramic samples of different examples were analyzed, and it was found that a single-phase tetragonal structure with the I41 / a space group was shown at different sintering temperatures, with the characteristics of the scheelite-type structure. As the sintering temperature increased, the XRD peaks gradually shifted to lower angles, indicating lattice expansion. As the sintering temperature increased, the ionic activity was activated, making it easier for ions to diffuse. Considering that the ionic radius of Ca 2+ is less than Ca 2+ shows a stronger diffusivity than Sr 2+ , resulting in an expansion of the lattice parameters and the unit cell volume. To further study the structural transformation caused by different sintering temperatures, all samples were subjected to Rietveld refinement. The detailed results and phase compositions are shown in Figure 1 (c-h). In addition, the crystal structure of (Ca 0.5 Sr 0.5 )MoO4 is as shown in Figure 1 (i).

[0023] Figure 2 (a - e) of [sample name] show the SEM micrographs of Samples 1 to 5 respectively. All samples exhibit a dense microstructure. As the sintering temperature increases, the number of pores gradually decreases and the densification is significantly improved. This is because the increase in temperature promotes grain growth, which is beneficial for pore filling. It is worth noting that at a sintering temperature of 950 °C, there are almost no pores on the surface of the sample, reaching the peak density, thus confirming the optimality of this sintering condition.

[0024] Figure 3 shows the density and relative density of Samples 1 to 5. Both the density and relative density gradually increase with the increase in sintering temperature, which is due to the improvement of pore filling at high temperatures, thus increasing these two parameters. When the sintering temperature is 950 °C, both the density and relative density reach their peaks. Ceramics with high relative density usually exhibit low dielectric loss. Sample 5 shows the highest density and relative density, indicating that Sample 5 has a denser microstructure.

[0025] Figure 4 shows the microwave dielectric properties of Samples 1 to 5. As the sintering temperature increases, the dielectric constant of the samples gradually decreases, the dielectric loss gradually decreases, and the temperature coefficient of resonant frequency gradually increases. The decrease in the dielectric constant is closely related to the reduction of grain boundaries. The decrease in dielectric loss is attributed to the increase in density and relative density. The increase in the temperature coefficient of resonant frequency is closely related to microstrain and lattice distortion rate. Overall, when the sintering temperature reaches 950 °C, the best microwave dielectric properties are obtained: ε r = 10.15, τ f = -8.55 ppm / °C, Q×f = 99928 GHz.

[0026] In summary, the present invention uses the solid-phase method to prepare a new type of single-phase molybdate ceramic. By adjusting the sintering temperature and testing the properties to obtain the best performance (Sample 5), the density, relative density, and temperature coefficient of resonant frequency can be significantly improved. It is suitable for electronic packaging substrate materials, has low requirements for production conditions, and is easy to industrialize and mass-produce.

[0027] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A novel single-phase molybdate ceramic material, characterized in that, The base formulation is SrCO3, CaCO3 and MoO3, prepared by the solid-phase method: having a low dielectric constant (ε r = 10.15), a near-zero temperature coefficient of resonant frequency (-8.55 ppm / °C), and a high quality factor (99928 GHz).

2. The preparation method of the novel single-phase molybdate ceramic material according to claim 1, characterized in that, The details are as follows: Step 1: Prepare the raw powders of high-purity SrCO3, CaCO3 and MoO3 according to the chemical formula Sr 0.5 Ca 0.5 MoO4 is used for batching; Step 2: Ball mill the ingredients prepared in Step 1 for 8 hours according to the mass ratio of powder material, zirconia balls, and distilled water of 1:5:

1. After taking out, dry it at 110 °C and sieve it through a 200-mesh sieve. Place the sieved powder in a high-temperature muffle furnace and pre-burn it at 650 °C for 4 hours. The pre-burned powder is ball milled for another 8 hours, dried, and then 8% polyvinyl alcohol aqueous solution is added for granulation, and sieved through a 200-mesh sieve to ensure that the particles are fine and uniform; Step 3: Use a tablet press to press the granulated powder material into a cylinder with a size of 12 mm × 6 mm under a pressure of 20 MPa. Place the pressed cylinder in a muffle furnace and keep it at 650 °C for two hours for debinding, and then sinter it at 850 - 950 °C for 4 hours to obtain a single-phase molybdate ceramic material.

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