Composite microwave dielectric ceramic and preparation method thereof

Abstract

The application belongs to the technical field of electronic ceramics, and particularly relates to a composite microwave dielectric ceramic and a preparation method thereof, the preparation method comprising the following steps: obtaining a molar ratio (1-x):x of MgAl2O4 ceramic powder and MgTa2O6 ceramic powder, according to the molar ratio, weighing the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder and uniformly mixing the same, drying, sieving, granulating and pressing the ceramic powder after uniform mixing into blocks to obtain a ceramic green body, and performing sintering treatment on the ceramic green body to obtain the composite microwave dielectric ceramic.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic ceramics, and particularly relates to a composite microwave dielectric ceramic and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the 5G network and the Internet of Things era, the demand for high-performance microwave dielectric ceramics and components thereof is becoming more and more urgent, so as to expect them to provide more excellent performance at a higher working frequency. Since low polarization rate at high frequency is conducive to reducing noise and inductive crosstalk, it significantly reduces the signal transmission delay of the dielectric In recent years, the working frequency of 5G communication has a general trend of millimeter wave, and one of the core materials is a microwave dielectric ceramic with a medium-low dielectric constant (ε r ≤20).

[0003] In order to meet the wide bandwidth, the clarity and accuracy of information transmission, the low delay and the temperature stability, the microwave dielectric ceramic needs to have an ultra-low dielectric loss f (Q>10000 at the working frequency f), a high quality factor Qxf and a near-zero resonance frequency temperature coefficient τ f .

[0004] MgAl2O4 spinel is a low-cost high-frequency low-loss microwave dielectric ceramic, which has a high quality factor (ε r =7.5, Qxf=100000 GHz), but its temperature coefficient has a large negative value (τ f =-70 ppm / ℃), which makes it difficult to meet the application requirements. MgTa2O6 generally has a high Qxf value (Qxf>60000 GHz) and a moderate dielectric constant (ε r =30), but its resonance frequency temperature coefficient has a large positive value (τ f =30 ppm / ℃), which also cannot meet the use requirements. SUMMARY

[0005] In view of the above problems, the application designs a preparation method of a composite microwave dielectric ceramic, which comprises the following steps:

[0006] A molar ratio (1-x):x of MgAl2O4 ceramic powder and MgTa2O6 ceramic powder is obtained, according to the molar ratio, the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are weighed and uniformly mixed;

[0007] The ceramic powder after uniform mixing is dried, sieved, granulated and pressed into a block to obtain a ceramic body.

[0008] The ceramic body is subjected to sintering treatment to obtain a composite microwave dielectric ceramic.

[0009] Preferably, based on preset parameters and preset formulas of the composite microwave dielectric ceramic, the volume fraction of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder is obtained,

[0010] Based on the volume fraction, the molar ratio (1-x):x of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder is obtained, wherein 0.3≤x≤0.8.

[0011] Preferably, the preset parameters include a dielectric constant, a quality factor and a resonance frequency temperature coefficient,

[0012] The preset formulas include formula (1), formula (2) and formula (3),

[0013] The formula (1) is: lnε th =v1 lnε r1 +v2lnε r2 ,

[0014] Wherein, ε th represents the dielectric constant of the composite microwave dielectric ceramic, ε r1 represents the dielectric constant of the MgAl2O4 ceramic end component, ε r2 represents the dielectric constant of the MgTa2O6 ceramic end component, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0015] The formula (2) is: Q -1 =v1Q1 -1 +v2Q2 -1 ,

[0016] Wherein, Q -1 represents the loss tangent value of the composite microwave dielectric ceramic, Q1 -1 represents the loss tangent value of the MgAl2O4 ceramic, Q2 -1 represents the loss tangent value of the MgTa2O6 ceramic, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0017] The formula (3) is: τ f =v1τ f1 +v2τ f2 ,

[0018] Wherein, τ f represents the resonance frequency temperature coefficient of the composite microwave dielectric ceramic, τ f1 represents the resonance frequency temperature coefficient of the MgAl2O4 ceramic, τ f2The resonant frequency temperature coefficient of the MgTa2O6 ceramic is represented as v1, the volume fraction of the MgAl2O4 ceramic powder is represented as v2, and the volume fraction of the MgTa2O6 ceramic powder is represented as v3.

[0019] Preferably, the preparation step of the MgAl2O4 ceramic powder comprises:

[0020] MgO and Al2O3 are mixed in a molar ratio of 1:1 to obtain a mixture A by ball milling with zirconia balls as grinding balls and anhydrous ethanol as the ball milling medium.

[0021] The mixture A is sequentially subjected to drying, sieving and calcination to obtain the MgAl2O4 ceramic powder.

[0022] Preferably, the drying temperature during the drying treatment of the mixture A is 60-80℃.

[0023] The calcination temperature during the calcination treatment of the mixture A is 1250-1400℃, and the holding time is 4-10h.

[0024] Preferably, the preparation step of the MgTa2O6 ceramic powder comprises:

[0025] MgO and Ta2O5 are mixed in a molar ratio of 1:1 to obtain a mixture B by ball milling with zirconia balls as grinding balls and anhydrous ethanol as the ball milling medium.

[0026] The mixture B is subjected to drying, sieving and calcination to obtain the MgTa2O6 ceramic powder.

[0027] Preferably, the drying temperature during the drying treatment of the mixture B is 60-80℃.

[0028] The calcination temperature during the calcination treatment of the mixture B is 1150-1250℃, and the holding time is 4-10h.

[0029] Preferably, the drying temperature of the ceramic powder is 60-80℃.

[0030] Preferably, the sintering temperature of the ceramic green body is 1550-1575℃, and the holding time is 4-12h.

[0031] The application also designs a composite microwave dielectric ceramic prepared by the above preparation method. The composite microwave dielectric ceramic has a dielectric constant ε r =14-24.97, a quality factor Qxf=133187-182822GHz, and a resonant frequency temperature coefficient τ f =-8.26-28.51ppm / ℃.

[0032] Compared with the prior art, the application has the following beneficial effects:

[0033] (1) The application takes MgAl2O4 with a negative resonant frequency temperature coefficient as the main crystal phase, and introduces MgTa2O6 with a different structure, high quality factor and positive resonant frequency temperature coefficient as the second phase. Since the structure of the tetragonal phase MgTa2O6 is different from that of the cubic phase MgAl2O4, the chemical reaction between the two phases is limited to the greatest extent. Therefore, the coexistence of the two phases makes the resonant frequency temperature coefficients of the composite microwave dielectric ceramic compensate each other to achieve a near-zero effect, which can be used for 5G high-frequency communication.

[0034] (2) MgTa2O6 is a low-temperature phase, and its grain growth rate is relatively fast, forming polygonal large grains. MgAl2O4 is a high-temperature phase, and its grain growth rate is relatively slow, forming fine equiaxed grains. The small MgAl2O4 grains can play a pinning effect to inhibit the grain growth of MgTa2O6, thereby forming a uniform and dense microstructure, which is not only beneficial to improving the quality factor of the composite microwave dielectric ceramic, but also beneficial to promoting the densification of the composite microwave dielectric ceramic, thereby reducing the sintering temperature of the composite microwave dielectric ceramic.

[0035] (3) By adjusting the molar ratio of MgAl2O4 and MgTa2O6 (1-x):x, the dielectric constant of the composite microwave dielectric ceramic can be flexibly adjusted, and the adjustable range of the dielectric constant is relatively large, which can reach 14-24.97. In addition, a high quality factor of 133187-196483 GHz and a continuously adjustable resonant frequency temperature coefficient can be obtained, so that the composite microwave dielectric ceramic can meet different bandwidths and be applied to 5G high-frequency communication, which is beneficial to improving the clarity, accuracy and temperature stability of information transmission, and reducing the delay.

[0036] (4) During the sintering process, Al 3+ and Ta 5+ occur solid solution, and part of Al 3+ solidifies into the MgTa2O6 lattice, so that the crystal structure of MgAl2O4 and MgTa2O6 is improved. Al 3+ and Ta 5+ deviate from the normal valence, causing the [AlO6] and [TaO6] oxygen octahedra to twist, which is beneficial to optimizing the dielectric constant, resonant frequency temperature coefficient and quality factor of the composite microwave dielectric ceramic. In addition, the solid solution of Al 3+ and Ta 5+ can activate the lattice and reduce the sintering activation energy, which is beneficial to further reducing the sintering temperature. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a scanning electron microscope (SEM) photo of the composite microwave dielectric ceramic prepared in the embodiment of the application.

[0038] Figure 2 The schematic diagram of the cell parameter of the embodiment of the present application changing with x.

[0039] Figure 3 The EDS energy spectrum of the element detection result of the embodiment of the present application. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application.

[0041] Embodiment 1

[0042] The embodiment provides a preparation method of a composite microwave dielectric ceramic, comprising the following steps:

[0043] Step 1: preparing MgAl2O4 ceramic powder:

[0044] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium, MgO and Al2O3 are mixed in a molar ratio of 1:1 for ball milling to obtain a mixture A;

[0045] The mixture A is subjected to drying treatment at 60 DEG C, and then subjected to calcination treatment at 1250 DEG C for 4h to obtain the MgAl2O4 ceramic powder.

[0046] Step 2: preparing MgTa2O6 ceramic powder:

[0047] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium, MgO and Ta2O5 are mixed in a molar ratio of 1:1 for ball milling to obtain a mixture B;

[0048] The mixture B is subjected to drying treatment at 60 DEG C, and then subjected to calcination treatment at 1150 DEG C for 4h to obtain the MgTa2O6 ceramic powder.

[0049] Step 3: based on preset parameters and preset formulas of the composite microwave dielectric ceramic, the volume fraction of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder is obtained,

[0050] wherein the preset parameters include dielectric constant, quality factor and resonance frequency temperature coefficient,

[0051] the preset formulas include formula (1), formula (2) and formula (3),

[0052] The formula (1) is: lnε th =v1 lnε r1 +v2lnε r2 ,

[0053] wherein ε th represents the dielectric constant of the composite microwave dielectric ceramic, ε r1 represents the dielectric constant of the MgAl2O4 ceramic end component, ε r1 = 7.5, ε r2 represents the dielectric constant of the MgTa2O6 ceramic end component, ε r2 = 30, vi represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0054] The formula (2) is: Q -1 = vi Qi -1 + v2 Q2 -1 ,

[0055] wherein Q -1 represents the loss tangent of the composite microwave dielectric ceramic, Qi -1 represents the loss tangent of the MgAl2O4 ceramic, Qi -1 = 0.000125, Q2 -1 represents the loss tangent of the MgTa2O6 ceramic, Q2 -1 = 0.00005, vi represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0056] The formula (3) is: τ f = vi τ f1 + v2 τ f2 ,

[0057] wherein τ f represents the resonant frequency temperature coefficient of the composite microwave dielectric ceramic, τ f1 represents the resonant frequency temperature coefficient of the MgAl2O4 ceramic, τ f1 = -70 ppm / °C, τ f2 represents the resonant frequency temperature coefficient of the MgTa2O6 ceramic, τ f2 = +30 ppm / °C, vi represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0058] Step 4: Based on the three formulas of Step 3, the volume fractions of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are obtained,

[0059] Based on volume fraction, the molar ratio (1-x):x of MgAl2O4 ceramic powder and MgTa2O6 ceramic powder is obtained, where 0.3≤x≤0.8. By adjusting the molar ratio (1-x):x in this embodiment, the dielectric constant, temperature coefficient of resonant frequency, and quality factor of the composite microwave dielectric ceramic can be flexibly adjusted. In this embodiment, x=0.3.

[0060] Step 5: Weigh out MgAl2O4 ceramic powder and MgTa2O6 ceramic powder in a molar ratio of 0.7:0.3 according to the molar ratio in Step 4 and mix them evenly.

[0061] The uniformly mixed ceramic powder is dried, sieved, granulated, and pressed into blocks to obtain a ceramic green body; wherein the drying temperature of the ceramic powder is 60℃.

[0062] Step 6: Sinter the ceramic blank at 1550℃ and hold for 4 hours to obtain composite microwave dielectric ceramic.

[0063] This embodiment lowers the densification temperature of the composite microwave dielectric ceramic to 1550℃. The principle behind this is that MgTa2O6, as the low-temperature phase, has a faster grain growth rate, forming large polygonal grains, while MgAl2O4, as the high-temperature phase, has a slower grain growth rate, forming fine equiaxed grains. Figure 1 As shown in (a), two types of grains with different morphologies and contrasts can be observed. The fine equiaxed grains belong to the cubic MgAl2O4 phase, while the larger polygonal grains belong to the tetragonal MgTa2O6 phase, indicating that the two phases can coexist.

[0064] The small MgAl2O4 grains act as pinning agents, significantly inhibiting the grain growth of MgTa2O6. At x = 0.3, a uniform and dense microstructure is formed, which is beneficial to improving the quality factor of the composite microwave dielectric ceramic.

[0065] During the sintering process, Al 3+ With Ta 5+ Solid solution occurs, leading to structural changes in the two crystalline phases, MgAl₂O₄ and MgTa₂O₆, specifically reflected in changes in cell parameters and grain elemental analysis results. For example... Figure 2 As shown, the cell parameters of the two phases MgAl2O4 and MgTa2O6 decrease monotonically with x, and Ta... 5+ The ionic radius is Al 3+ The ionic radius is Both have an oxygen octahedral [Al / TaO6] coordination relationship. 3+ Replace Ta 5+ This leads to cell shrinkage. For example... Figure 3As shown, Spots 1-3 are detected, the element ratio of spot2 conforms to the stoichiometric ratio of MgAl2O4, and Spots 1 and 3 conform to the stoichiometric ratio of MgTa2O6, which can prove that the ceramic product prepared in this embodiment is a composite ceramic. In addition, the existence of Al element on the MgTa2O6 grain is also detected, which proves that part of Al 3+ is dissolved into the crystal lattice.

[0066] This solid solution phenomenon makes the Al 3+ and Ta 5+ deviate from the normal valence, the Al-O and Ta-O bond length increases, and the Al / Ta valence is lower than the theoretical +3 and +5 valence, indicating that the rigidity of the [Al / TaO6] oxygen octahedron is weakened and the ionicity is enhanced, finally optimizing the dielectric constant, the resonant frequency temperature coefficient and the quality factor of the composite microwave dielectric ceramic, so that it obtains higher measured values than the calculated values of formulas (1)-(3). The composite microwave dielectric ceramic prepared in this embodiment is measured to have a dielectric constant ε r = 14.00, a quality factor Qxf = 133187 GHz, and a resonant frequency temperature coefficient τ f = -8.26 ppm / ℃, which meets the application requirements of K15 series microwave dielectric ceramics.

[0067] Embodiment 2

[0068] This embodiment provides a preparation method of a composite microwave dielectric ceramic, comprising the following steps:

[0069] Step 1: Preparation of MgAl2O4 ceramic powder:

[0070] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium. MgO and Al2O3 are mixed by ball milling at a molar ratio of 1:1 to obtain a mixture A.

[0071] The mixture A is dried at 70℃, and then calcined at 1350℃ for 7h to obtain the MgAl2O4 ceramic powder.

[0072] Step 2: Preparation of MgTa2O6 ceramic powder:

[0073] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium. MgO and Ta2O5 are mixed by ball milling at a molar ratio of 1:1 to obtain a mixture B.

[0074] The mixture B is dried at 70℃, and then calcined at 1200℃ for 7h to obtain the MgTa2O6 ceramic powder.

[0075] Step 3: based on preset parameters and preset formulas of the composite microwave dielectric ceramic, the volume fractions of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are obtained,

[0076] wherein the preset parameters include a dielectric constant, a quality factor and a resonance frequency temperature coefficient,

[0077] the preset formulas include formula (1), formula (2) and formula (3),

[0078] the formula (1) is: lnε th = v1lnε r1 + v2lnε r2 ,

[0079] wherein ε th represents a dielectric constant of the composite microwave dielectric ceramic, ε r1 represents a dielectric constant of the MgAl2O4 ceramic component, ε r1 = 7.5, ε r2 represents a dielectric constant of the MgTa2O6 ceramic component, ε r2 = 30, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder;

[0080] the formula (2) is: Q -1 = v1Q1 -1 + v2Q2 -1 ,

[0081] wherein Q -1 represents a loss tangent value of the composite microwave dielectric ceramic, Q1 -1 represents a loss tangent value of the MgAl2O4 ceramic, Q1 -1 = 0.000125, Q2 -1 represents a loss tangent value of the MgTa2O6 ceramic, Q2 -1 = 0.00005, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder;

[0082] the formula (3) is: τ f = v1τ f1 + v2τ f2 ,

[0083] wherein τ f represents a resonance frequency temperature coefficient of the composite microwave dielectric ceramic, τ f1 represents a resonance frequency temperature coefficient of the MgAl2O4 ceramic, τ f1 = -70 ppm / ℃, τ f2 represents a resonance frequency temperature coefficient of the MgTa2O6 ceramic, τf2 = + 30 ppm / °C, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0084] Step 4: Based on the three formulas of Step 3, the volume fractions of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are obtained,

[0085] Based on the volume fractions, the molar ratio (1-x):x of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder is obtained, wherein 0.3≤x≤0.8. By adjusting the molar ratio (1-x):x of the present embodiment, the dielectric constant, the resonant frequency temperature coefficient, and the quality factor of the composite microwave dielectric ceramic can be flexibly adjusted. In the present embodiment, x = 0.4.

[0086] Step 5: According to the molar ratio of Step 4, the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are weighed in a molar ratio of 0.6:0.4 and uniformly mixed.

[0087] The uniformly mixed ceramic powder is dried, sieved, granulated, and pressed into a block to obtain a ceramic green body. The drying temperature of the ceramic powder is 70°C.

[0088] Step 6: The ceramic green body is sintered at 1560°C for 8h to obtain a composite microwave dielectric ceramic.

[0089] As shown in Figure 1 (b), two different morphologies and different contrast grains can be observed. The small equiaxed grains belong to the cubic MgAl2O4 phase, and the larger polygonal grains belong to the tetragonal MgTa2O6 phase, indicating that the two phases can coexist. The small MgAl2O4 grains play a pinning effect, significantly inhibiting the grain growth of MgTa2O6, and when x = 0.4, a uniform and dense microstructure is formed, which is beneficial to improve the quality factor of the composite microwave dielectric ceramic. In addition, as shown in Figure 1 (g), when x = 0.4, the backscattered electron image exhibits obvious atomic number light and dark contrast. The darker grains represent the MgAl2O4 phase with low atomic number, and the brighter grains represent the MgTa2O6 phase with high atomic number. With the increase of x, the MgAl2O4 grains decrease, proving that the two phases coexist, and the phase content change trend is consistent with the design.

[0090] According to the calculations of the formulas (1)-(3) of the present embodiment, when x = 0.4, a K15 series microwave dielectric ceramic with a dielectric constant ε r of about 15 and a resonant frequency temperature coefficient τ fabout -21.4 ppm / ℃, and a quality factor Qxf is above 150000 GHz. However, Al 3+ occurs solid solution with Ta 5+ , which can optimize the dielectric constant, the temperature coefficient of resonant frequency, and the quality factor of the composite microwave dielectric ceramic. The dielectric constant ε r = 16.46, the quality factor Qxf = 179526 GHz, and the temperature coefficient of resonant frequency τ f = 3.35 ppm / ℃ of the composite microwave dielectric ceramic prepared in the embodiment meet the application requirements of K15 series microwave dielectric ceramics.

[0091] Embodiment 3

[0092] The embodiment provides a preparation method of a composite microwave dielectric ceramic, including the following steps.

[0093] Step 1: preparing MgAl2O4 ceramic powder

[0094] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium. MgO and Al2O3 are mixed in a molar ratio of 1:1 to obtain a mixture A.

[0095] The mixture A is subjected to drying treatment at 80℃, and then is subjected to calcination treatment at 1400℃ and is kept for 10 h to obtain the MgAl2O4 ceramic powder.

[0096] Step 2: preparing MgTa2O6 ceramic powder

[0097] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium. MgO and Ta2O5 are mixed in a molar ratio of 1:1 to obtain a mixture B.

[0098] The mixture B is subjected to drying treatment at 80℃, and then is subjected to calcination treatment at 1250℃ and is kept for 10 h to obtain the MgTa2O6 ceramic powder.

[0099] Step 3: based on preset parameters and preset formulas of the composite microwave dielectric ceramic, the volume fraction of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder is obtained,

[0100] wherein the preset parameters include a dielectric constant, a quality factor, and a temperature coefficient of resonant frequency,

[0101] the preset formulas include formula (1), formula (2), and formula (3),

[0102] the formula (1) is: lnε th = v1 lnε r1 + v2 lnε r2 ,

[0103] wherein ε th represents the dielectric constant of the composite microwave dielectric ceramic, ε r1 represents the dielectric constant of the MgAl2O4 ceramic end component, ε r1 = 7.5, ε r2 represents the dielectric constant of the MgTa2O6 ceramic end component, ε r2 = 30, vi represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0104] The formula (2) is: Q -1 = vi Qi -1 + v2 Q2 -1 ,

[0105] wherein Q -1 represents the loss tangent of the composite microwave dielectric ceramic, Qi -1 represents the loss tangent of the MgAl2O4 ceramic, Qi -1 = 0.000125, Q2 -1 represents the loss tangent of the MgTa2O6 ceramic, Q2 -1 = 0.00005, vi represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0106] The formula (3) is: τ f = vi τ f1 + v2 τ f2 ,

[0107] wherein τ f represents the resonant frequency temperature coefficient of the composite microwave dielectric ceramic, τ f1 represents the resonant frequency temperature coefficient of the MgAl2O4 ceramic, τ f1 = -70 ppm / °C, τ f2 represents the resonant frequency temperature coefficient of the MgTa2O6 ceramic, τ f2 = +30 ppm / °C, vi represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0108] Step 4: Based on the three formulas of Step 3, the volume fractions of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder, vi and v2, are obtained.

[0109] Based on the volume fraction, the molar ratio (1-x):x of MgAl2O4 ceramic powder and MgTa2O6 ceramic powder is obtained, wherein 0.3≤x≤0.8. By adjusting the molar ratio (1-x):x of the embodiment, the dielectric constant, the resonant frequency temperature coefficient, and the quality factor of the composite microwave dielectric ceramic can be flexibly adjusted, and in the embodiment, x=0.5.

[0110] Step 5: According to the molar ratio of step 4, MgAl2O4 ceramic powder and MgTa2O6 ceramic powder are taken in a molar ratio of 0.5:0.5 and mixed uniformly.

[0111] The mixed ceramic powder is dried, sieved, granulated, and pressed into a block to obtain a ceramic green body; wherein the drying temperature of the ceramic powder is 80℃.

[0112] Step 6: The ceramic green body is sintered at 1575℃ and kept for 12h to obtain a composite microwave dielectric ceramic.

[0113] As shown in Figure 1 (c), two different morphologies and different contrast grains can be observed. The small equiaxed grains belong to the cubic MgAl2O4 phase, and the larger polygonal grains belong to the tetragonal MgTa2O6 phase, indicating that the two phases can coexist. The small MgAl2O4 grains play a pinning role, significantly inhibiting the grain growth of MgTa2O6, and when x=0.5, a uniform and dense microstructure is formed, which is beneficial to improve the quality factor of the composite microwave dielectric ceramic.

[0114] The composite microwave dielectric ceramic prepared in the embodiment has a dielectric constant ε r =18.69, a quality factor Q×f=150557GHz, and a resonant frequency temperature coefficient τ f =10.94ppm / ℃, which meets the application requirements of K20 series microwave dielectric ceramics.

[0115] Embodiment 4

[0116] The embodiment provides a preparation method of a composite microwave dielectric ceramic, comprising the following steps:

[0117] Step 1: Preparation of MgAl2O4 ceramic powder:

[0118] Zirconia balls are used as grinding balls, and anhydrous ethanol is used as a ball milling medium. MgO and Al2O3 are mixed in a molar ratio of 1:1 and ball milled to obtain a mixture A.

[0119] The mixture A is dried at 70℃, and then calcined at 1300℃ and kept for 7h to obtain MgAl2O4 ceramic powder.

[0120] Step 2: Preparation of MgTa2O6 ceramic powder:

[0121] MgO and Ta2O5 were mixed in a molar ratio of 1:1 and ball milled with zirconia balls as grinding balls and anhydrous ethanol as a ball milling medium to obtain a mixture B;

[0122] The mixture B was dried at 70°C, and then calcined at 1200°C for 7h to obtain MgTa2O6 ceramic powder.

[0123] Step 3: Based on the preset parameters and preset formulas of the composite microwave dielectric ceramic, the volume fractions of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder were obtained,

[0124] wherein the preset parameters include dielectric constant, quality factor and resonance frequency temperature coefficient,

[0125] the preset formulas include formula (1), formula (2) and formula (3),

[0126] the formula (1) is: lnε th = v1 lnε r1 + v2 lnε r2 ,

[0127] wherein ε th represents the dielectric constant of the composite microwave dielectric ceramic, ε r1 represents the dielectric constant of the MgAl2O4 ceramic end component, ε r1 = 7.5, ε r2 represents the dielectric constant of the MgTa2O6 ceramic end component, ε r2 = 30, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder;

[0128] the formula (2) is: Q -1 = v1Q1 -1 + v2Q2 -1 ,

[0129] wherein Q -1 represents the loss tangent value of the composite microwave dielectric ceramic, Q1 -1 represents the loss tangent value of the MgAl2O4 ceramic, Q1 -1 = 0.000125, Q2 -1 represents the loss tangent value of the MgTa2O6 ceramic, Q2 -1 = 0.00005, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder;

[0130] The formula (3) is: τ f = v1τ f1 + v2τ f2 ,

[0131] Wherein, τ f represents the resonant frequency temperature coefficient of the composite microwave dielectric ceramic, τ f1 represents the resonant frequency temperature coefficient of the MgAl2O4 ceramic, τ f1 =-70ppm / ℃, τ f2 represents the resonant frequency temperature coefficient of the MgTa2O6 ceramic, τ f2 =+30ppm / ℃, v1 represents the volume fraction of the MgAl2O4 ceramic powder, and v2 represents the volume fraction of the MgTa2O6 ceramic powder.

[0132] Step 4: Based on the three formulas of step 3, the volume fractions of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are obtained,

[0133] Based on the volume fractions, the molar ratio (1-x):x of the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder is obtained, wherein 0.3≤x≤0.8. By adjusting the molar ratio (1-x):x of the embodiment, the dielectric constant, the resonant frequency temperature coefficient, and the quality factor of the composite microwave dielectric ceramic can be flexibly adjusted, and in the embodiment, x=0.6.

[0134] Step 5: According to the molar ratio of step 4, the MgAl2O4 ceramic powder and the MgTa2O6 ceramic powder are weighed in a molar ratio of 0.4:0.6 and uniformly mixed.

[0135] The uniformly mixed ceramic powder is dried, sieved, granulated, and pressed into a block to obtain a ceramic green body; wherein the drying temperature of the ceramic powder is 70℃.

[0136] Step 6: The ceramic green body is sintered at 1570℃ and kept for 10h to obtain a composite microwave dielectric ceramic.

[0137] As shown in Figure 1 (d), two different morphologies and different contrast grains can be observed. The small equiaxed grains belong to the cubic MgAl2O4 phase, and the larger polygonal grains belong to the tetragonal MgTa2O6 phase, indicating that the two phases can coexist. The small MgAl2O4 grains play a pinning effect, significantly inhibiting the grain growth of MgTa2O6, and when x=0.6, a uniform and dense microstructure is formed, which is beneficial to improve the quality factor of the composite microwave dielectric ceramic. In addition, as shown in Figure 1(h) as shown, when x = 0.6, the backscattered electron image exhibits obvious atomic number contrast, the darker grains represent the low atomic number MgAl2O4 phase, and the brighter grains represent the high atomic number MgTa2O6 phase, with the increase of x, the MgAl2O4 grains decrease, which proves that the two phases coexist, and the phase content change trend is consistent with the design.

[0138] The composite microwave dielectric ceramic prepared in the example is measured to have a dielectric constant ε r = 21.84, a quality factor Qxf = 182822 GHz, and a resonance frequency temperature coefficient τ f = 13.13 ppm / ℃, which meets the application requirements of K20 series microwave dielectric ceramics.

[0139] Example 5

[0140] The difference between the example and example 1 is that x = 0.7 in the example.

[0141] As shown in Figure 1 (e), two grains with different morphologies and different contrasts can be observed. The small equiaxed grains belong to the cubic MgAl2O4 phase, and the larger polygonal grains belong to the tetragonal MgTa2O6 phase, which indicates that the two phases can coexist. The small MgAl2O4 grains play a pinning effect, which significantly inhibits the grain growth of MgTa2O6, and a uniform grain size and dense microstructure are formed when x = 0.7, which is beneficial to improve the quality factor of the composite microwave dielectric ceramic.

[0142] The composite microwave dielectric ceramic prepared in the example is measured to have a dielectric constant ε r = 23.45, a quality factor Qxf = 159350 GHz, and a resonance frequency temperature coefficient τ f = 26.19 ppm / ℃.

[0143] Example 6

[0144] The difference between the example and example 1 is that x = 0.8 in the example.

[0145] As shown in Figure 1 (f), two grains with different morphologies and different contrasts can be observed. The small equiaxed grains belong to the cubic MgAl2O4 phase, and the larger polygonal grains belong to the tetragonal MgTa2O6 phase, which indicates that the two phases can coexist. The small MgAl2O4 grains play a pinning effect, which significantly inhibits the grain growth of MgTa2O6, and a uniform grain size and dense microstructure are formed when x = 0.8, which is beneficial to improve the quality factor of the composite microwave dielectric ceramic.

[0146] The composite microwave dielectric ceramic prepared in the example has a dielectric constant ε r = 24.97, a quality factor Qxf = 161459 GHz, and a resonance frequency temperature coefficient τ f = 28.51 ppm / °C.

[0147] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the present application; based on the examples of the present application, all other examples obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application. Although the present application is described in detail with reference to the foregoing examples, a person of ordinary skill in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the examples of the present application.

Claims

1. A method for preparing a composite microwave dielectric ceramic, characterized in that, Includes the following steps: Obtain the molar ratio (1-x):x of MgAl2O4 ceramic powder and MgTa2O6 ceramic powder. Weigh the MgAl2O4 ceramic powder and MgTa2O6 ceramic powder according to the molar ratio and mix them evenly. Where 0.3 ≤ x ≤ 0.8; The uniformly mixed ceramic powder is dried, sieved, granulated, and pressed into blocks to obtain ceramic green bodies; The ceramic blank is sintered to obtain a composite microwave dielectric ceramic. The sintering temperature of the ceramic blank is 1550~1575℃, and the holding time is 4-12h.

2. The method for preparing composite microwave dielectric ceramics according to claim 1, characterized in that, The preparation steps of the MgAl2O4 ceramic powder include: Using zirconia balls as grinding media and anhydrous ethanol as the milling medium, MgO and Al2O3 were mixed and milled at a molar ratio of 1:1 to obtain mixture A. Mixture A was subjected to drying, sieving, and calcination in sequence to obtain MgAl2O4 ceramic powder.

3. The method for preparing composite microwave dielectric ceramics according to claim 2, characterized in that, The drying temperature for drying mixture A is 60-80℃. The calcination temperature for the mixture A is 1250-1400℃, and the holding time is 4-10h.

4. The method for preparing composite microwave dielectric ceramics according to claim 1, characterized in that, The preparation steps of the MgTa2O6 ceramic powder include: Using zirconia balls as grinding media and anhydrous ethanol as the milling medium, MgO and Ta₂O₅ were mixed and milled in a 1:1 molar ratio to obtain mixture B. Mixture B was dried, sieved, and calcined to obtain MgTa2O6 ceramic powder.

5. The method for preparing composite microwave dielectric ceramics according to claim 4, characterized in that, The drying temperature for drying mixture B is 60-80℃. The calcination temperature for the mixture B is 1150-1250℃, and the holding time is 4-10h.

6. The method for preparing composite microwave dielectric ceramics according to claim 1, characterized in that, The drying temperature of the ceramic powder is 60-80℃.

7. A composite microwave dielectric ceramic, characterized in that, The composite microwave dielectric ceramic is prepared by any one of the preparation methods described in claims 1-6.

8. The composite microwave dielectric ceramic according to claim 7, characterized in that, The dielectric constant of the composite microwave dielectric ceramic ε r =14~24.97, quality factor Q × f =133187~182822GHz, temperature coefficient of resonant frequency τ f =-8.26~28.51 ppm / °C.

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