Perovskite type fluoride microwave dielectric ceramic material and preparation method thereof

Abstract

The invention discloses a perovskite type fluoride microwave dielectric ceramic material and a preparation method thereof, the chemical composition of the microwave dielectric ceramic material is K < 1-x > NaxMg < 1-y > CayF < 3 + z > Na2B4O7, x is greater than or equal to 0.01 and less than or equal to 0.03, y is greater than or equal to 0.01 and less than or equal to 0.05, and z is greater than or equal to 0.5 and less than or equal to 1.0; and z is the mass percent of Na2B4O7 relative to the mass percent of K < 1-x > Na < x > Mg < 1-y > Ca < y > F < 3 >. The preparation method comprises the following steps: weighing KF, NaF, MgF2 and CaF2 powder according to a stoichiometric ratio, grinding, barreling and uniformly mixing; calcining and preserving heat; the preparation method comprises the following steps: weighing Na2B4O7 powder, carrying out high-temperature melting, carrying out heat preservation and water cooling to form glass residues, carrying out coarse grinding, and crushing to obtain Na2B4O7 glass powder; uniformly mixing the powder; sintering is performed after blank making. According to the invention, high quality factor and near-zero temperature coefficient of resonance frequency of the KMgF3-based microwave dielectric ceramic material are realized.

Description

Technical Field

[0001] The invention relates to ceramic materials and a preparation method thereof, in particular to a perovskite-type fluoride microwave dielectric ceramic material and a preparation method thereof. Background Art

[0002] With the continuous development of mobile communications, researchers have successfully developed a large number of microwave dielectric ceramic materials. Despite this, microwave dielectric ceramic materials with excellent dielectric properties and low sintering temperature are still the research hotspots of microwave materials today. With the popularization of 5G mobile communications, millimeter wave communication technology requires ceramic materials to meet the requirements of low dielectric constant (ε r <10), high Q value (Q×f>60000GHz), near-zero resonant frequency temperature coefficient (-10ppm / ℃<τ f <10ppm / ℃) and other indicators.

[0003] Most fluoride microwave dielectric ceramic materials are concentrated in alkali metal or alkaline earth metal fluorides, such as CaF2, BaF2, MgF2, SrF2 and LiF. Among them, the binary composite fluoride KMgF3 has low phonon energy and large bandgap width, and is a microwave dielectric ceramic material with great application potential. However, this type of composite fluoride system cannot simultaneously meet high quality factor and near-zero resonant frequency temperature coefficient, which is also the key technical problem that the present invention needs to solve. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a perovskite fluoride microwave dielectric ceramic material with a high quality factor and a near-zero resonant frequency temperature coefficient. Another purpose of the present invention is to provide a method for preparing a perovskite fluoride microwave dielectric ceramic material that reduces the sintering temperature and improves the microwave dielectric properties.

[0005] Technical solution: The perovskite fluoride microwave dielectric ceramic material described in the present invention has the following chemical composition: K 1-x Na x Mg 1-y Ca y F3+zNa2B4O7, where 0.01≤x≤0.03, 0.01≤y≤0.05, 0.5≤z≤1.0; z is the ratio of Na2B4O7 to K 1-x Na x Mg 1-y Ca y Mass percentage of F3.

[0006] Furthermore, the relative dielectric constant of the perovskite fluoride microwave dielectric ceramic material is 7.25 to 8.14, the quality factor is 50245 to 65747 GHz, and the resonant frequency temperature coefficient is -8 to -14 ppm / °C.

[0007] The method for preparing the above-mentioned perovskite-type fluoride microwave dielectric ceramic material comprises the following steps:

[0008] Step 1, weigh KF, NaF, MgF2 and CaF2 powders according to the stoichiometric ratio, and mix them evenly by grinding and tumbling;

[0009] Step 2, calcining the product obtained in step 1 and keeping the temperature;

[0010] Step 3, weighing Na2B4O7 powder according to the stoichiometric ratio, melting the Na2B4O7 powder at high temperature, keeping the temperature and water cooling to form glass slag, coarsely grinding the glass slag and then ball milling to obtain Na2B4O7 glass powder;

[0011] Step 4, mixing the product obtained in step 2 and step 3 uniformly by dry rolling;

[0012] Step 5, taking out the powder obtained in step 4, forming a blank and then sintering it to obtain a perovskite-type fluoride microwave dielectric ceramic material.

[0013] Furthermore, in step 1, KF and NaF powders are first ground for 15 to 30 minutes, recorded as powder A, and MgF2 and CaF2 powders are ground for 30 to 60 minutes, recorded as powder B; and then powder A and powder B are evenly mixed by dry rolling. The speed of rolling is 100 to 180 r / min, and the time is 12 to 18 hours.

[0014] Furthermore, in step 2, the calcination temperature is 550-750° C., and the holding time is 2-4 hours.

[0015] Furthermore, in step 3, the heating rate of high temperature melting is 5-10° C., the temperature is 700-800° C., and the holding time is 0.5-1.0 h.

[0016] Furthermore, in step 4, the rotation speed of dry rolling is 150-250 r / min, and the time is 16-24 h.

[0017] Furthermore, in step five, the sintering temperature is 750-900° C., kept at this temperature for 4-8 hours, and cooled along with the furnace.

[0018] Preparation principle: The present invention uses Na with similar ionic radius + , Ca 2+ Replace K at position A in KMgF3 + 、Mg at B 2+, forming a solid solution structure. Compared with the problem that single ion replacement modification can only improve the material Q×f value, Na / Ca synergistic replacement modification can not only significantly improve the crystal structure of KMgF3, but also reduce the loss caused by the anharmonic term in the ideal crystal, thereby greatly improving the material quality factor (Q×f value). In addition, Na / Ca synergistic replacement modification can reduce the electronegativity difference of ions in the material crystal structure. The smaller the electronegativity difference, the higher the resonant frequency temperature coefficient τ f The smaller the absolute value.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0020] 1. The high quality factor and near-zero resonant frequency temperature coefficient of KMgF3-based microwave dielectric ceramic materials are achieved through the method of synergistic modification (Na / Ca) of ion substitution at A and B sites;

[0021] 2. Selecting Na2B4O7 glass powder as a sintering aid effectively reduces the sintering temperature of ceramic materials without reducing the dielectric properties of the materials;

[0022] 3. The raw material premixing process (NaF+KF, MgF2+CaF2) is beneficial to strengthen the contact process between the fluoride raw materials and optimize the replacement modification of Na / Ca ions, thereby further improving the microwave dielectric properties of ceramic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an XRD pattern of the perovskite fluoride microwave dielectric ceramic material prepared in Example 2 of the present invention;

[0024] Figure 2 is a SEM image of the perovskite fluoride microwave dielectric ceramic material prepared in Example 2 of the present invention;

[0025] Figure 3 is a SEM image of the perovskite fluoride microwave dielectric ceramic material prepared in Comparative Example 3 of the present invention; Figure 4 This is the XRD diagram of the microwave dielectric ceramic material prepared in Comparative Example 4. DETAILED DESCRIPTION

[0026] Unless otherwise specified, the materials, reagents, instruments, etc. used in the following examples can be obtained from commercial sources. Experimental methods without specific conditions in the examples are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0027] Example 1

[0028] A method for preparing a perovskite fluoride microwave dielectric ceramic material comprises the following steps:

[0029] (1) Fluoride ceramic component is K 0.99 Na 0.01 Mg 0.97 Ca 0.03 F3+0.5wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders by manual grinding for 15 minutes, and then grind and mix MgF2 and CaF2 powders for 30 minutes.

[0030] (2) The premixed four fluoride powders were ball milled at a speed of 100 r / min for 12 h using a dry rolling method.

[0031] (3) The milled powder was placed in a high-temperature muffle furnace and calcined at 550°C for 2 h.

[0032] (4) Weigh Na2B4O7 powder according to the proportion and put it into a corundum crucible, place the corundum crucible in a muffle furnace for high-temperature melting at 700°C, with a heating rate of 5°C / min and a holding time of 0.5 h. The melt is water-cooled to form glass slag, which is coarsely ground and then ball-milled to obtain Na2B4O7 glass powder.

[0033] (5) The calcined powder was mixed evenly with Na2B4O7 glass powder by dry rolling at a rotation speed of 150 r / min and a ball milling time of 18 h.

[0034] (6) After ball milling, the powder is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 750°C for 4 hours. After cooling in the furnace, a perovskite-type fluoride microwave dielectric ceramic material is obtained.

[0035] Example 2

[0036] A method for preparing a perovskite fluoride microwave dielectric ceramic material comprises the following steps:

[0037] (1) Fluoride ceramic component is K 0.98 Na 0.02 Mg 0.95 Ca 0.05 F3+0.75wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders for 20 minutes by manual grinding, and then grind and mix MgF2 and CaF2 powders for 40 minutes.

[0038] (2) The premixed four fluoride powders were ball milled at a speed of 150 r / min for 14 h using a dry rolling method.

[0039] (3) The milled powder is placed in a high-temperature muffle furnace and calcined at 600°C for 4 hours.

[0040] (4) Weigh Na2B4O7 powder according to the proportion and put it into a corundum crucible, place the corundum crucible in a muffle furnace for high-temperature melting at 750°C, with a heating rate of 6°C / min and a holding time of 1 hour. The melt is water-cooled to form glass slag, which is coarsely ground and then ball-milled to obtain Na2B4O7 glass powder.

[0041] (5) The calcined powder was mixed evenly with Na2B4O7 glass powder by dry rolling at a rotation speed of 175 r / min and a ball milling time of 16 h.

[0042] (6) After ball milling, the powder is pressed into a green compact and placed in a high-temperature muffle furnace for sintering at a temperature of 800°C for 8 hours. After cooling in the furnace, a perovskite-type fluoride microwave dielectric ceramic material is obtained.

[0043] Example 3

[0044] A method for preparing a perovskite fluoride microwave dielectric ceramic material comprises the following steps:

[0045] (1) Fluoride ceramic component is K 0.97 Na 0.03 Mg 0.97 Ca 0.03 F3+1.0wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders for 25 minutes by manual grinding, and then grind and mix MgF2 and CaF2 powders for 50 minutes.

[0046] (2) The premixed four fluoride powders were ball milled at a speed of 130 r / min for 16 h using a dry rolling method.

[0047] (3) The milled powder is placed in a high-temperature muffle furnace and calcined at 700°C for 3 h.

[0048] (4) Weigh Na2B4O7 powder according to the proportion and put it into a corundum crucible, place the corundum crucible in a muffle furnace for high-temperature melting at 800°C, with a heating rate of 8°C / min and a holding time of 1 hour. The melt is water-cooled to form glass slag, which is coarsely ground and then ball-milled to obtain Na2B4O7 glass powder.

[0049] (5) The calcined powder was mixed evenly with Na2B4O7 glass powder by dry rolling at a rotation speed of 200 r / min and a ball milling time of 20 h.

[0050] (6) After ball milling, the powder is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 750° C. for 6 h. After cooling in the furnace, a perovskite-type fluoride microwave dielectric ceramic material is obtained.

[0051] Example 4

[0052] A method for preparing a perovskite fluoride microwave dielectric ceramic material comprises the following steps:

[0053] (1) Fluoride ceramic component is K 0.98 Na 0.02 Mg 0.99 Ca 0.01 F3+0.75wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders for 30 minutes by manual grinding, and then grind and mix MgF2 and CaF2 powders for 60 minutes.

[0054] (2) The premixed four fluoride powders were ball milled at a speed of 180 r / min for 14 h using a dry rolling method.

[0055] (3) The milled powder is placed in a high-temperature muffle furnace and calcined at 750°C for 2 h.

[0056] (4) Weigh Na2B4O7 powder according to the proportion and put it into a corundum crucible, place the corundum crucible in a muffle furnace for high-temperature melting at 800°C, with a heating rate of 5°C / min and a holding time of 0.5 h. The melt is water-cooled to form glass slag, which is coarsely ground and then ball-milled to obtain Na2B4O7 glass powder.

[0057] (5) The calcined powder was mixed evenly with Na2B4O7 glass powder by dry rolling at a rotation speed of 250 r / min and a ball milling time of 24 h.

[0058] (6) After ball milling, the powder is pressed into a green compact and placed in a high-temperature muffle furnace for sintering at a temperature of 900°C for 4 hours. After cooling in the furnace, a perovskite-type fluoride microwave dielectric ceramic material is obtained.

[0059] Example 5

[0060] A method for preparing a perovskite fluoride microwave dielectric ceramic material comprises the following steps:

[0061] (1) Fluoride ceramic component is K 0.99 Na 0.01 Mg 0.95 Ca 0.05F3+1.0wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders for 25 minutes by manual grinding, and then grind and mix MgF2 and CaF2 powders for 40 minutes.

[0062] (2) The premixed four fluoride powders were ball milled at a speed of 150 r / min for 18 h using a dry rolling method.

[0063] (3) The milled powder was placed in a high-temperature muffle furnace and calcined at 650°C for 4 h.

[0064] (4) Weigh Na2B4O7 powder according to the proportion and put it into a corundum crucible, place the corundum crucible in a muffle furnace for high-temperature melting at 700°C, with a heating rate of 10°C / min and a holding time of 1.0 h. The melt is water-cooled to form glass slag, which is coarsely ground and then ball-milled to obtain Na2B4O7 glass powder.

[0065] (5) The calcined powder was mixed evenly with Na2B4O7 glass powder by dry rolling at a rotation speed of 225 r / min and a ball milling time of 22 h.

[0066] (6) After ball milling, the powder is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 850°C for 8 hours. After cooling in the furnace, a perovskite-type fluoride microwave dielectric ceramic material is obtained.

[0067] Comparative Example 1

[0068] A method for preparing a microwave dielectric ceramic material comprises the following steps:

[0069] Fluoride ceramic component is KMg 0.95 Ca 0.05F3+0.75wt%Na2B4O7, weigh KF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix MgF2 and CaF2 powders by manual grinding for 40 minutes. The three pre-mixed fluoride powders are ball-milled at a speed of 150r / min for 14 hours by dry rolling method. The milled powder is placed in a high-temperature muffle furnace and calcined at 600℃ for 4 hours. At the same time, weigh Na2B4O7 powder according to proportion and put it into a corundum crucible, and place the corundum crucible in a muffle furnace for high-temperature melting at 750℃, with a heating rate of 6℃ / min and a holding time of 1h. After water cooling, the melt forms glass slag, which is coarsely ground and ball-milled to obtain Na2B4O7 glass powder. The calcined powder is evenly mixed with Na2B4O7 glass powder by dry rolling method, with a speed of 175r / min and a ball-milling time of 16h. The powder after ball milling is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 800°C for 8 hours. After cooling in the furnace, a microwave dielectric ceramic material is obtained.

[0070] Comparative Example 2

[0071] A method for preparing a microwave dielectric ceramic material comprises the following steps:

[0072] Fluoride ceramic components are K 0.98 Na 0.02 MgF3+0.75wt%Na2B4O7, weigh KF, NaF, MgF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders by manual grinding for 20 minutes. The three pre-mixed fluoride powders are ball-milled at a speed of 150r / min for 14h by dry rolling method. The milled powder is placed in a high-temperature muffle furnace and calcined at 600℃ for 4h. At the same time, weigh Na2B4O7 powder according to proportion and put it into a corundum crucible, and place the corundum crucible in a muffle furnace for high-temperature melting at 750℃, with a heating rate of 6℃ / min and a holding time of 1h. After water cooling, the melt forms glass slag, which is coarsely ground and ball-milled to obtain Na2B4O7 glass powder. The calcined powder is evenly mixed with Na2B4O7 glass powder by dry rolling method, with a speed of 175r / min and a ball-milling time of 16h. The powder after ball milling is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 800°C for 8 hours. After cooling in the furnace, a microwave dielectric ceramic material is obtained.

[0073] Comparative Example 3

[0074] A method for preparing a microwave dielectric ceramic material comprises the following steps:

[0075] Fluoride ceramic components are K 0.98 Na 0.02 Mg0.95 Ca 0.05 F3+0.75wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, grind and mix KF and NaF powders by hand grinding for 20 minutes, and then grind and mix MgF2 and CaF2 powders for 40 minutes. The pre-mixed four fluoride powders are ball-milled at a speed of 150r / min for 14 hours by dry rolling method. The rolled powder is placed in a high-temperature muffle furnace and calcined at 600℃ for 4 hours. The calcined powder is pressed and sintered in a high-temperature muffle furnace at a sintering temperature of 800℃ for 8 hours. After cooling with the furnace, a microwave dielectric ceramic material is obtained.

[0076] Comparative Example 4

[0077] A method for preparing a microwave dielectric ceramic material comprises the following steps:

[0078] Fluoride ceramic components are K 0.98 Na 0.02 Mg 0.95 Ca 0.05 F3+0.75wt%Na2B4O7, weigh KF, NaF, MgF2 and CaF2 raw material powders according to the stoichiometric ratio, and ball mill the four fluoride powders at a speed of 150r / min for 14h by dry rolling method. The milled powder is placed in a high-temperature muffle furnace and calcined at 600℃ for 4h. At the same time, weigh Na2B4O7 powder according to proportion and put it into a corundum crucible, and place the corundum crucible in a muffle furnace for high-temperature melting at 750℃, with a heating rate of 6℃ / min and a holding time of 1h. After water cooling, the melt forms glass slag, which is coarsely ground and ball milled to obtain Na2B4O7 glass powder. The calcined powder is evenly mixed with Na2B4O7 glass powder by dry rolling method, with a speed of 175r / min and a ball milling time of 16h. The powder after ball milling is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 800°C for 8 hours. After cooling in the furnace, a microwave dielectric ceramic material is obtained.

[0079] Table 1 Performance of materials obtained in Examples 1 to 5 and Comparative Examples 1 to 4

[0080]

[0081] Examples 1 to 5 of the present invention are the microwave dielectric properties and sintering properties of perovskite fluoride microwave dielectric ceramic materials under different formulations and process conditions, among which the ceramic sample prepared in Example 2 has the highest quality factor and the best resonant frequency temperature coefficient, and is the optimal example. Figure 1As shown, the main phase is KMgF3. Comparative Example 1 prepared a ceramic sample without adding NaF, and Comparative Example 2 prepared a ceramic sample without adding CaF2. The quality factor and resonant frequency temperature coefficient were not ideal. Comparative Example 3 prepared a ceramic sample without adding Na2B4O7 glass powder. Figure 2 (Example 2) and Figure 3 As shown in (Comparative Example 3), the addition of glass additives is beneficial to the sintering density of ceramic materials and greatly reduces the sintering temperature. Comparative Example 4 does not use the raw material premixing process, and the quality factor of the ceramic material decreases.

Claims

1. A perovskite fluoride microwave dielectric ceramic material, characterized in that: Its chemical composition is: K 1-x Na x Mg 1- y Ca y F3+zNa2B4O7, where 0.01≤x≤0.03, 0.01≤y≤0.05, 0.5≤z≤1.0; z is the ratio of Na2B4O7 to K 1- x Na x Mg 1-y Ca y Mass percentage of F3.

2. The perovskite fluoride microwave dielectric ceramic material according to claim 1, characterized in that: Its relative dielectric constant is 7.25 to 8.14, its quality factor is 50245 to 65747 GHz, and its resonant frequency temperature coefficient is -8 to -14 ppm / °C.

3. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 1 or 2, characterized in that: The following steps are involved: Step 1, weigh KF, NaF, MgF2 and CaF2 powders according to the stoichiometric ratio, and mix them evenly by grinding and rolling; Step 2, calcining the product obtained in step 1 and keeping the temperature; Step 3, weighing Na2B4O7 powder according to the stoichiometric ratio, melting the Na2B4O7 powder at high temperature, keeping the temperature and water cooling to form glass slag, coarsely grinding the glass slag and then ball milling to obtain Na2B4O7 glass powder; Step 4, mixing the product obtained in step 2 and step 3 uniformly by dry rolling; Step 5, taking out the powder obtained in step 4, forming a blank and then sintering it to obtain a perovskite type fluoride microwave dielectric ceramic material.

4. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: In the step 1, the KF and NaF powders are first ground for 15 to 30 minutes, which are recorded as powder A, and the MgF2 and CaF2 powders are ground for 30 to 60 minutes, which are recorded as powder B; and then the powders A and B are mixed evenly by dry rolling.

5. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: The rotation speed of the rolling mill is 100-180 r / min, and the time is 12-18 hours.

6. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: In the step 2, the calcination temperature is 550-750° C., and the insulation time is 2-4 hours.

7. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: In the step three, the heating rate of high temperature melting is 5-10°C and the temperature is 700-800°C.

8. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: In the step 3, the insulation time is 0.5 to 1.0 h.

9. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: In the step 4, the rotation speed of the dry rolling mill is 150 to 250 r / min, and the time is 16 to 24 hours.

10. The method for preparing a perovskite fluoride microwave dielectric ceramic material according to claim 3, characterized in that: In the step 5, the sintering temperature is 750-900° C., the temperature is kept for 4-8 hours, and the furnace is cooled.

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