ZnO-TiO2-based microwave dielectric ceramic material and preparation method thereof

Abstract

The invention belongs to the field of electronic ceramics and manufacturing thereof, and relates to a ZnO-TiO2-based microwave dielectric ceramic material and a preparation method thereof, the chemical general formula of the ceramic material is (Zn < 0.98-x > Mg < x >) < 1-y > (Mn < 1 / 2 > Ni < 1 / 2 >) < y > Ti < 1 + z > O < 3 >, y is equal to 0.01 to 0.03; z is equal to 0.06 to 0.1; the material is prepared by a sol-gel method, the principal crystalline phase of the phase is ZnTiO3, and the sintering temperature is 825-900 DEG C. By adopting a sol-gel preparation process, synthesis of a ZnTiO3 phase in a low temperature range (825-900 DEG C) is realized, and the problem that the ZnTiO3 phase is easily decomposed into a Zn2TiO4 phase and a TiO2 phase during high-temperature sintering (gt, 900 DEG C) is solved. The ceramic forming performance of the microwave dielectric ceramic material is improved, and a high quality factor and a near-zero temperature coefficient are obtained.

Description

Technical Field

[0001] The present invention belongs to the field of electronic ceramics and their manufacturing, and relates to a ZnO-TiO2-based microwave dielectric ceramic material and a preparation method thereof. Background Art

[0002] With the rapid development of mobile communication technology, high-performance microwave dielectric materials have become an indispensable key component in electronic communication, radar systems, and various microwave devices. These materials need to possess excellent electromagnetic properties, such as high dielectric constant, high quality factor, and good thermal stability, etc., to meet the increasing technological requirements.

[0003] Zn-TiO2 is a very important microwave dielectric ceramic material. In the ZnO-TiO2 system, there are three stable phases, namely zinc orthotitanate (Zn2TiO4), zinc metatitanate (ZnTiO3), and zinc dititanium trioxide (Zn2Ti3O8) phase. Among them, the Zn2Ti3O8 phase structure is a defective distorted spinel structure. Research has shown that the stable temperature range of the Zn2Ti3O8 phase is relatively narrow (750 °C to 800 °C). When the temperature exceeds 800 °C, it will transform into the ZnTiO3 phase, and then further transform into Zn2TiO4. Therefore, the existence temperature range of the Zn2Ti3O8 phase is relatively low (≤820 °C), and the reaction process is difficult to control. Zinc orthotitanate Zn2TiO4 is a high-temperature phase with good stability, but its quality factor in the microwave frequency band is very small and cannot meet the application requirements of microwave and millimeter-wave devices. Zinc metatitanate ZnTiO3 belongs to the ABO3-type hexagonal ilmenite phase. In the Zn-TiO2 system, only the ZnTiO3 phase has relatively excellent microwave dielectric properties: dielectric constant 19, quality factor greater than 30000 GHz, and frequency temperature coefficient -55 ppm / o °C. However, the synthesis temperature range of ZnTiO3 ceramics is narrow, and it is easy to decompose into the Zn2TiO4 phase during high-temperature sintering (>900 o °C), which is not conducive to the preparation of microwave dielectric ceramic materials with relatively excellent dielectric properties. Therefore, the optimal preparation temperature of ZnTiO3 microwave ceramic materials is 820 - 900 °C.

[0004] Microwave dielectric ceramic materials are generally prepared by the solid-phase method. However, a large number of research reports show that it is very difficult to prepare single-phase ZnTiO3 ceramic materials using the traditional solid-phase sintering method, and the resonance frequency temperature coefficient of ZnTiO3 ceramic materials is relatively large, which does not meet the actual application requirements (generally, the closer the frequency temperature coefficient is to 0 ppm / oC), for microwave dielectric ceramic materials, the smaller the absolute value of the frequency temperature coefficient, the better the temperature stability of the materials. There have been many studies on Zn-TiO2-based microwave dielectric ceramic materials, but it is a difficult problem that needs to be overcome urgently to obtain dielectric properties with high quality factors and achieve near-zero frequency temperature coefficients in the material system.

[0005] Many researchers at home and abroad have made various attempts to obtain pure-phase materials and good porcelain-forming properties. Lei Shenhui et al. prepared pure ZnTiO3 ceramics through pre-sintering, cold isostatic pressing, sintering, and then introducing nano-ZnO into the ZnO-TiO2 precursor, followed by re-forming and sintering. Its sintering temperature is above the phase transition temperature, and the preparation process is complex and difficult to control. Hou Yudong, H.T. Kim, etc. found that adding MgO can stabilize the hexagonal phase of ilmenite within a wide sintering range through the traditional solid-state reaction method of oxides. However, when the sintering temperature exceeds the appropriate temperature (>900 °C), phase decomposition will occur, the density of the ceramic will decrease, and the porcelain-forming dielectric properties will be poor. More scholars synthesized ZnO-TiO2-based powders by solid-phase method and then added glass, low-temperature compounds, low-temperature oxides, etc. to reduce the porcelain-forming temperature of the ceramics in order to obtain better microwave dielectric properties. For example, Wang Jing et al. added ZnO-B2O3-SiO2 glass to reduce the sintering temperature of solid-phase synthesized (Zn 0.9 Mg 0.1 )TiO3. With the addition of glass, although the sintering temperature reaches below the phase transition temperature of ZnO-TiO2, the quality factor (Qf) of the material decreases significantly. Hu Yunyuan et al. added low-melting-point oxides and glass to modify ZnO-TiO2-based microwave dielectric ceramics. Finally, the quality factor and frequency temperature characteristics of the prepared materials are not good. Sintered at 900 °C, the quality factor is 21700, and the frequency temperature coefficient is -13 ppm / °C. Zhang Wu et al. adjusted the frequency temperature coefficient of the ceramic material by Zn, Mg compounding, adding 5wt.% zinc borate glass, and adding 15wt.% TiO2. Sintered at 925 °C, the dielectric constant is 27.2, the quality factor is 49772, and the frequency temperature coefficient is 5.4 ppm / °C. The addition of a large amount of TiO2 leads to a decrease in the quality factor, and the temperature coefficient does not achieve near zero. Zhao Qizhi et al. synthesized (Zn / Mg)TiO3 by solid-phase method with different ratios of Zn, Mg, and Ti, and reduced the sintering temperature by adding different low-temperature compounds. The temperature coefficient of ZnO-TiO2-based ceramics was adjusted by adding CaTiO3. Finally, the dielectric constant was 25, the quality factor was 10391, and the temperature coefficient of the dielectric constant was 6×10 -6 ppm / °C. The addition of a large amount of CaTiO3 deteriorated the porcelain-forming properties (quality factor) of the ceramics. Through the above means such as high-temperature solid-phase synthesis and adding low-temperature additives, it is impossible to obtain ZnO-TiO2-based microwave dielectric ceramic materials with high quality factors and good temperature stability due to reasons such as phase transition, deterioration of porcelain-forming properties, and increased loss.

[0006] The sol-gel method is an advanced material preparation technology that can precisely control the chemical composition and microstructure. Salavati-Niasari M et al. used Zn(CH3COO)2·2H2O and Ti(OC4H9)4 as raw materials to prepare single-phase ZnTiO3 powder by the sol-gel method. However, they explored the photocatalytic degradation performance of ZnTiO3 and did not conduct research on its microwave dielectric properties. Li Junsheng et al. prepared zinc titanate nanoparticles by the hydrothermal-assisted sol-gel method and mainly studied their photocatalytic performance. Yu Lifang, Yu Youhua et al. used tetrabutyl titanate and zinc nitrate hexahydrate as raw materials to prepare ZnTiO3 powder by the sol-gel method. When Zn:Ti was 1:1 and the synthesis temperature was 800 °C, hexagonal ilmenite-type ZnTiO3 powder could be obtained, but the microwave dielectric properties of ZnTiO3 and how to obtain ceramic materials with high quality factors and good temperature stability were not studied. Summary of the Invention

[0007] The object of the present invention is to address the problem that the synthesis temperature range of ZnTiO3 ceramics is narrow and it is easily decomposed into Zn2TiO4 phase and TiO2 phase during high-temperature sintering (>900 °C), which is not conducive to the preparation of microwave dielectric ceramic materials with excellent dielectric properties. The present invention proposes a ZnO-TiO2-based microwave dielectric ceramic material and its preparation method to meet the application requirements of electronic devices.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A ZnO-TiO2-based microwave dielectric ceramic material with the chemical general formula: (Zn 0.98-x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3, where x = 0.02~0.05; y = 0.01~0.03; z = 0.06~0.1; Prepared by the sol-gel method, the main crystal phase of its phase is ZnTiO3, and the sintering temperature is 825 o °C ~900 o °C.

[0009] Furthermore, when x = 0.04, y = 0.02 and z = 0.1, at the sintering temperature of 875 o °C, the dielectric constant of the material is 26.5@10GHz, and the dielectric loss is 1.21×10 -4@10GHz, Q×f value 77998 GHz, frequency temperature coefficient is 3.5 ppm / o C (-40~85℃).

[0010] Furthermore, the method for preparing the above-mentioned low-temperature sintered microwave dielectric ceramic material comprises the following steps: Step 1: Prepare the raw materials of Zn, Mg, Ti, Mn and Ni according to the chemical formula (Zn 0.98-x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3 is used for batching, x = 0.02~0.05; y = 0.01~0.03; z = 0.06~0.1; Step 2: Add weighed ZnO and MgO powders to deionized water and stir to form a suspension; dilute concentrated nitric acid and deionized water in a volume ratio of 1:1; add the diluted nitric acid to the suspension and stir thoroughly until it is completely dissolved and becomes clear, thereby forming an inorganic solution; Step 3: Measure tetrabutyl titanate (C 16 H 36 Place the O4Ti) solution in a beaker, add anhydrous ethanol at a volume ratio of 1:1, and stir for 10-30 minutes for pre-hydrolysis to form an organic solution; Step 4: Slowly add the inorganic solution prepared in step 2 to the organic solution prepared in step 3, stir for 10 to 30 minutes, then add weighed Mn(NO3)2 and Ni(NO3)2, and continue stirring for 1 to 3 hours to form a gel; Step 5: The gel prepared in step 4 is sealed and placed in a 60°C oven for aging for 4 to 10 hours, then placed in an 80 to 100°C oven for drying, and then pre-calcined in an air atmosphere at 500 to 700°C for 2 to 5 hours; Step 6: The powder pre-calcined in step 5 is ball-milled in a mass ratio of powder: zirconium balls: deionized water of 1:5:1 to a ball-milled particle size D50 of 0.5-2 μm. The powder is dried at 80°C-100°C and granulated with 10-20 wt.% of an acrylic emulsion binder to obtain a ceramic raw material. Step 7: Press the ceramic raw material obtained in step 6 into shape, heat it to 450℃ in a muffle furnace at 0.5~2℃ / min and keep it for 2 hours to remove the binder, heat it to 825~900℃ at 2~8℃ / min and keep it for 1~2 hours to sinter, and then (Zn 0.78 Mg 0.2 ) 1-x (Mn0.02 Ni y ) x Ti 1+z O3 microwave dielectric ceramic material.

[0011] Furthermore, in step 7, the ceramic raw material obtained in step 6 is pressed into a cylinder with a F15 mm diameter and a height of 7 mm, and then heated to 450° C. at 1° C. / min in a muffle furnace for 2 hours to remove the binder, and then heated to 825-900° C. at 4° C. / min for 1 hour to sinter, thereby obtaining (Zn 0.98-x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3 microwave dielectric ceramic material.

[0012] In summary, the present invention provides a modified ZnO-TiO2 based ceramic material, the chemical formula of which is (Zn 0.98- x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3, by adopting the sol-gel preparation process, the ZnTiO3 phase is synthesized in the low temperature range (825~900℃), which solves the problem of easy decomposition into Zn2TiO4 phase and TiO2 phase during high temperature sintering (>900℃); it adopts non-stoichiometric chemical ratio, by adjusting the molar content of each doping ion, especially controlling the molar content of Zn to be lower than Ti, on the one hand, suppressing the generation of Zn2TiO4 and Zn2Ti3O8, on the other hand, 2+ This ratio is beneficial to make Mn with smaller ionic radius 2+ 、Ni 2+ Replace Zn 2+ , reduce the generation of oxygen vacancies, enhance the stability of ionic crystals, and improve the order of cations, thereby improving the quality factor and temperature stability of ZnO-TiO2 based microwave dielectric ceramics, and the resonant frequency temperature coefficient is 3.5 ppm / o C. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 XRD diffraction patterns of the corresponding embodiments; Figure 2 Corresponding SEM morphology image of Example 9. DETAILED DESCRIPTION

[0014] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0015] A method for preparing a low-temperature sintered microwave dielectric ceramic material, comprising the following steps: Step 1: Prepare the raw materials of Zn, Mg, Ti, Mn and Ni according to the chemical formula (Zn 0.98-x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3 ( x = 0.02~0.05; y = 0.01~0.03; z = 0.06~0.1) for accurate calculation and weighing; Step 2: Add weighed ZnO and MgO powders to deionized water and stir to form a suspension. Dilute concentrated nitric acid with deionized water at a ratio of 1:1. Slowly add the diluted nitric acid to the suspension and stir thoroughly until it is completely dissolved and clear, forming an inorganic solution. Step 3: Accurately measure analytically pure tetrabutyl titanate (C 16 H 36 O4Ti) solution was placed in a beaker, and anhydrous ethanol was added at a volume ratio of 1:1. Stir for 10-30 minutes for pre-hydrolysis to form an organic solution. Step 4: Add the inorganic solution prepared in step 2 to the organic solution prepared in step 3, stir for 10 to 30 minutes, then add weighed Mn(NO3)2 and Ni(NO3)2, and continue stirring for 2 hours to form a gel; Step 5: The gel prepared in step 4 is sealed and placed in a 60°C oven for aging for 4 to 10 hours, then placed in an 80 to 100°C oven for drying, and then pre-calcined in an air atmosphere at 500 to 700°C for 2 to 5 hours; Step 6: The powder pre-calcined in step 5 is ball-milled in a mass ratio of powder: zirconium balls: deionized water of 1:5:1 to a ball-milled particle size D50 of 0.8 μm. The powder is dried at 80-100°C and granulated by adding 10-20 wt.% of an acrylic emulsion binder. Step 7: The ceramic raw material obtained in step 6 is pressed into a cylinder with a diameter of 15 mm and a height of 7 mm. The cylinder is heated to 450°C at a rate of 1°C / min and kept at that temperature for 2 hours to remove the binder. The cylinder is then heated to 825-900°C at a rate of 4°C / min and kept at that temperature for 1 hour to obtain (Zn 0.98- x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+zO3 microwave dielectric ceramic materials.

[0016] The above method was implemented, as shown in Tables 1 and 2 specifically: Table 1: Compositions and sintering temperatures of Examples 1 to 12

[0017] Table 2: Dielectric properties of Examples 1 to 12

[0018] It can be seen from Tables 1 and 2 that in x = 0.04, y = 0.02 and z = 0.06, 0.08, 0.1 range, the sintering temperature is between 825~900 o °C, the temperature coefficient of resonant frequency τ f values of the ceramic specimens are all between ±5 ppm / o °C, all of which are very excellent, and when z = 0.1 and the sintering temperature is 875 o °C (Example 9) (Zn 0.98-x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3 ceramic has the best microwave dielectric properties: ε r = 26.5 (@10GHz), tanδ = 1.21×10 -4 (@10GHz), Q×f = 77998GHz, τ f = 3.5 ppm / o °C, superior to the reports of the prior art, and can be applied to microwave and millimeter-wave passive integrated devices.

[0019] Figure 1 XRD diffraction patterns of Examples 7, 8, and 9. The main crystalline phase of the ceramic specimens under the three different examples is ZnTiO3 (JCPDS #58-0547), and Mg 2+ , Mn 2+ , Ni 2+ each doped ion is dissolved into the cation lattice position to form a solid solution with a ZnTiO3 structure. NiTiO3 has a positive frequency temperature coefficient (115 ppm / o °C), which can improve the temperature characteristics of the ZnTiO3 solid solution. In addition, as z increases, excessive Ti 4+On the one hand, it inhibits the formation of allotropic phases such as zinc titanate Zn2TiO4. On the other hand, excessive Ti forms TiO2. Since TiO2 has a positive temperature coefficient of 465 ppm / °C, the presence of a small amount of TiO2 can significantly improve the frequency temperature coefficient of ZnO-TiO2-based microwave dielectric ceramic materials.

[0020] Figure 2 Figure 465 ppm / °C is the SEM morphology of the cross-section of the sample in Example 9. It can be seen that the grains of the ceramic specimen grow sufficiently and the grain boundaries are clearly visible, indicating that sintering at low temperature (<900°C) can achieve densification, and there are only partial micropores at the grain boundaries.

[0021] In summary, in this example, the ZnO-TiO2-based microwave dielectric ceramic material was prepared by the sol-gel method, and Mg 2+ , Mn 2+ , Ni 2+ ions were introduced during the preparation process to achieve uniform and synergistic modification of ZnTiO3 during synthesis, thereby obtaining a ZnO-TiO2-based microwave dielectric ceramic material with excellent microwave dielectric properties and good temperature stability.

[0022] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A ZnO-TiO2-based microwave dielectric ceramic material, characterized in that, The chemical general formula of the ceramic material is: (Zn 0.98- x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3, where x = 0.02 to 0.05; y = 0.01 to 0.03; z = 0.06 to 0.1; Obtained by the sol-gel method, its main crystal phase is ZnTiO3, and the sintering temperature is 825 o °C to 900 o °C.

2. A ZnO-TiO2-based microwave dielectric ceramic material according to claim 1, characterized in that, When x = 0.04, y = 0.02 and z = 0.1, the dielectric constant of the material at the sintering temperature of 875 o °C is 26.5@10 GHz, the dielectric loss is 1.21×10 -4 @10 GHz, the Q×f value is 77998 GHz, and the frequency temperature coefficient is 3.5 ppm / o °C (-40~85 °C).

3. A preparation method of ZnO-TiO2-based microwave dielectric ceramic material, characterized in that, It includes the following steps: Step 1: Weigh the raw materials of Zn, Mg, Ti, Mn, and Ni according to the chemical general formula (Zn 0.98-x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3, where x = is 0.02 - 0.05; y = 0.01 - 0.03; z = 0.06 - 0.1; Step 2: Add the weighed ZnO and MgO powders into deionized water and stir to form a suspension; Mix concentrated nitric acid and deionized water in a volume ratio of 1:1 for dilution; Add the diluted nitric acid solution into the suspension and stir thoroughly until it is completely dissolved and clarified to form an inorganic solution; Step 3: Measure tetrabutyl titanate (C 16 H 36 O4Ti) solution and place it in a beaker. Add absolute ethanol according to a volume ratio of 1:1, and stir for 10 - 30 minutes for pre-hydrolysis to form an organic solution; Step 4: Add the inorganic solution prepared in Step 2 into the organic solution prepared in Step 3, stir for 10 - 30 minutes, then add the weighed Mn(NO3)2 and Ni(NO3)2 respectively, and continue to stir for 1 - 3 hours to form a gel; Step 5: Seal the gel prepared in Step 4 and place it in an oven at 60°C for aging for 4 - 10 hours, then place it in an oven at 80 - 100°C for drying. After that, pre - sinter the dry gel in an air atmosphere at 500 - 700°C for 2 - 5 hours; Step 6: Ball - mill the powder after pre - sintering in Step 5 according to the mass ratio of powder:zirconia balls:deionized water of 1:5:1, with the ball - milling particle size D50: 0.5 - 2μm. Take it out and dry it at 80°C - 100°C. Add 10 - 20wt.% acrylic emulsion binder to the prepared powder for granulation to obtain the green ceramic material; Step 7: Press the ceramic green body prepared in Step 6 into a mold. Heat it in a muffle furnace at a rate of 0.5 - 2 °C / min to 450 °C and hold for 2 hours to remove the binder. Then heat it at a rate of 2 - 8 °C / min to 825 - 900 °C and hold for 1 - 2 hours for sintering, thus obtaining the (Zn 0.78 Mg 0.2 ) 1-x (Mn 0.02 Ni y ) x Ti 1+z O3 microwave dielectric ceramic material.

4. The preparation method of a ZnO-TiO2-based microwave dielectric ceramic material according to claim 3, characterized in that, In step 7, the ceramic green material prepared in step 6 is pressed into a cylinder with a diameter of 15 mm and a height of 7 mm. It is heated in a muffle furnace at a rate of 1 °C / min to 450 °C and kept warm for 2 hours to remove the binder, and then heated at a rate of 4 °C / min to 825 - 900 °C and kept warm for 1 hour for sintering, thus obtaining the (Zn 0.98- x Mg x ) 1-y (Mn 1 / 2 Ni 1 / 2 ) y Ti 1+z O3 microwave dielectric ceramic material.

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