A low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material and its preparation method

Abstract

The present invention discloses a low-temperature rare earth pyrochlore-type microwave dielectric ceramic material and a preparation method thereof. The molecular formula of the ceramic material is La2Ce (2‑5x / 4) V x O7, where 0.02 ≤ x ≤ 0.08. The preparation method includes the following steps: Step S1, weighing CeO2, La2O3, and V2O5 in proportion and ball-milling and mixing them; Step S2, drying the product obtained in Step S1, calcining it, keeping it warm, and cooling it with the furnace; Step S3, weighing LiF and MgF2, where the mass of LiF is 0.5-1.0 wt% of the mass of the product obtained in Step S2, and the mass of MgF2 is 0.75-1.5 wt% of the mass of the product obtained in Step S2, and grinding and mixing them; Step S4, performing secondary ball-milling on the product obtained in Step S2 and the product obtained in Step S3, and drying; Step S5, preparing a blank from the powder obtained in Step S4 and sintering it. The present invention improves Q × f value and significantly reduces the sintering temperature at the same time.

Description

Technical Field

[0001] The present invention belongs to ceramics and their manufacturing methods, and specifically relates to a low-temperature rare earth pyrochlore-type microwave dielectric ceramic material and its preparation method. Background Art

[0002] As an important electronic component, microwave dielectric ceramics have an important impact on the operating frequency, signal transmission efficiency, stability, and reliability of communication devices. With the rapid development of modern communication technology, the requirements for the performance of communication devices are also getting higher and higher, that is, devices need to be more miniaturized and integrated. Compared with traditional metal dielectric materials, passive devices prepared from microwave dielectric ceramic materials have the advantages of low dielectric loss, controllable dielectric constant, light weight, and high integration.

[0003] There have been early reports on the research of pyrochlore-type microwave dielectric ceramic materials (A2B2O7, A = Re, B = Ti, Sn). Researchers have tried to improve their microwave dielectric properties through traditional modification methods such as ion substitution and second-phase composite, but with little effect. In particular, the quality factor ( Q × f value) and the temperature coefficient of resonant frequency ( τ f ) cannot meet the actual application simultaneously. On this basis, some researchers considered replacing the B site with the rare earth element Ce to form the A2Ce2O7 (A = La, Sm, Nd) ceramic system, which has excellent microwave dielectric properties, combining a super-high Q × f value and a small temperature coefficient of resonant frequency, but the sintering temperature is too high (exceeding 1600 °C). Therefore, on the premise of ensuring the microwave dielectric properties of the material, how to improve the sintering performance of the rare earth pyrochlore-type ceramic material system has become a key technical problem to be solved urgently. Summary of the Invention

[0004] Object of the Invention: In order to overcome the deficiencies in the prior art, the object of the present invention is to provide a low-temperature rare earth pyrochlore-type microwave dielectric ceramic material with both a super-high Q×f value and a small temperature coefficient of resonant frequency. Another object of the present invention is to provide a preparation method for a rare earth pyrochlore-type microwave dielectric ceramic material that is convenient to control and can reduce the sintering temperature.

[0005] Technical Solution: A low-temperature rare earth pyrochlore-type microwave dielectric ceramic material described in the present invention has a molecular formula of La2Ce (2-5x / 4) V x O7, where 0.02 ≤ x ≤ 0.08.

[0006] Furthermore, the relative dielectric constant of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is 25.12 - 26.93, the quality factor is 95481 - 118233 GHz, and the resonant frequency temperature coefficient is -20 - -26 ppm / °C.

[0007] The preparation method of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material described in the present invention includes the following steps:

[0008] Step S1: Weigh CeO2, La2O3, and V2O5 in proportion and mix them by ball milling.

[0009] Step S2: Dry the product obtained in Step S1, calcine it, keep it warm, and then cool it in the furnace.

[0010] Step S3: Weigh LiF and MgF2. The mass of LiF is 0.5 - 1.0 wt% of the mass of the product obtained in Step S2, and the mass of MgF2 is 0.75 - 1.5 wt% of the mass of the product obtained in Step S2. Grind and mix them, and then calcine.

[0011] Step S4: Perform secondary ball milling on the product obtained in Step S2 and the product obtained in Step S3, and then dry.

[0012] Step S5: Prepare a blank from the powder obtained in Step S4 and then sinter it to obtain the rare-earth pyrochlore-type microwave dielectric ceramic material.

[0013] Furthermore, in Step S1, the ball milling is wet ball milling, the ball milling time is 24 - 36 h, and the rotation speed is 200 - 250 r / min. The CeO2, La2O3, and V2O5 powders are all of analytical purity.

[0014] Furthermore, in Step S2, the calcination temperature is 1000 - 1100 °C, and the heat preservation time is 2 - 4 h. If the calcination temperature is lower than 950 °C, the raw material phase is contained in the powder, and impurity phases are likely to appear during the subsequent sintering process; if the calcination temperature is higher than 1050 °C, the particle size of the powder becomes larger, and the reaction activity becomes poor during the subsequent sintering process.

[0015] Furthermore, in Step S3, the grinding is manual grinding, the grinding time is 15 - 30 min. The calcination temperature is 450 - 550 °C, and the time is 15 - 30 min. If the calcination temperature is lower than 450 °C, LiF and MgF2 cannot form the LiMgF3 phase; if the calcination temperature is higher than 550 °C, the particle size of the powder becomes larger, and the effect as a sintering aid becomes poor.

[0016] Further, in step S4, the secondary ball milling is wet ball milling. The time of wet ball milling is 8 - 12 h, and the rotation speed is 250 - 300 r / min. If the sintering temperature is lower than 1250°C, the sintering driving force of the ceramic material is insufficient, the density decreases, and the performance deteriorates; if the sintering temperature is higher than 1350°C, the ceramic grains grow abnormally, and the grains are coated during the grain growth process, resulting in an increase in porosity, a decrease in density, and a deterioration in performance.

[0017] Further, in step S5, the sintering temperature is 1250 - 1350°C, and after sintering, it is kept warm for 4 - 6 h, and then cooled with the furnace.

[0018] Preparation principle: The additive LiF and MgF2 are used to obtain LiMgF3 through a prior high-temperature solid-phase reaction. Since n(LiF) / n(MgF2)>1, the final auxiliary agent components are LiF and LiMgF3. Not only is the sintering aid effect better than the simple combination of LiF and MgF2, but the final microwave dielectric properties are also improved; in addition, V 5+ is used to perform a small amount of inequivalent substitution modification on the Ce site in La2Ce2O7, introducing an appropriate amount of cation vacancy defects, that is, in La2Ce (2-5x / 4) V x O7, the sum of the number of Ce and V atoms is less than 2, thereby increasing the diffusion mass transfer driving force of the ceramic material, improving the sintering driving force, and further reducing the sintering temperature. The introduction of the composite sintering aid and the strategy of hetero-valent ion substitution modification can both improve the sintering driving force. However, the former is a low-melting-point additive, and the latter is structure defect-induced diffusion mass transfer. The modification ideas of the two are different, enabling the two strategies to synergistically improve the sintering performance of rare-earth pyrochlore ceramic materials, achieving the effect of "1 + 1 > 2".

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

[0020] 1. By means of the strategy of premixing + calcination, LiF and MgF2 are converted into a LiMgF3 + LiF composite sintering aid, which improves the Q×f value of rare-earth pyrochlore ceramic materials and significantly reduces their sintering temperature;

[0021] 2. Selecting hetero-valent ions to dope and modify rare-earth pyrochlore ceramic materials, and inducing diffusion mass transfer through structure defects, increases the sintering driving force of the ceramic materials. It can not only improve the resonance frequency temperature coefficient of the ceramic materials but also reduce their sintering temperature. Description of the drawings

[0022] Figure 1 is the XRD pattern of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material prepared in Example 3 of the present invention;

[0023] Figure 2XRD pattern of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material prepared in Comparative Example 2 of the present invention;

[0024] Figure 3 SEM images of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material prepared in Example 3 of the present invention;

[0025] Figure 4 SEM images of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material prepared in Comparative Example 3 of the present invention. Detailed implementation manners

[0026] Materials, reagents, instruments, etc. used in the following examples can be obtained from commercial sources unless otherwise specified. Experimental methods without specific conditions noted in the examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. CeO2, La2O3, and V2O5 powders are all of analytical grade.

[0027] Example 1

[0028] A preparation method of a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material La2Ce 1.975 V 0.02 O7, comprising the following steps:

[0029] Step S1: Weigh 33.99 g of CeO2, 32.58 g of La2O3, and 0.18 g of V2O5 powders and ball-mill them by the wet ball-milling method at a rotation speed of 200 r / min for 24 h.

[0030] Step S2: After drying the product obtained in Step S1, place it in a high-temperature muffle furnace and calcine it at 1000 °C for 2 h, then cool it down with the furnace.

[0031] Step S3: Weigh 0.33 g of LiF and 0.50 g of MgF2 powders, first grind and mix them by hand for 15 min, then place the ground powder in a high-temperature muffle furnace and calcine it at 450 °C for 15 min to obtain an additive component of LiF and LiMgF3. The additives LiF and MgF2 are 0.5 wt% and 0.75 wt% of the mass of the product obtained in Step S2, respectively.

[0032] Step S4: Mix the product obtained in Step S2 and the product obtained in Step S3 by secondary ball-milling in a wet ball-milling manner until they are uniformly mixed. The rotation speed is 250 r / min, and the ball-milling time is 8 h, then dry it.

[0033] Step S5: Compress the powder compact obtained in Step S4 and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1300 °C, and the holding time is 4 h. After cooling with the furnace, a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is obtained. Through XRD characterization, the molecular formula of the obtained low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is La2Ce 1.975 V 0.02 O7.

[0034] Example 2

[0035] A preparation method of a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material La2Ce 1.95 V 0.04 O7, comprising the following steps:

[0036] Step S1: Weigh 33.56 g of CeO2, 32.58 g of La2O3 and 0.36 g of V2O5 powder and ball-mill them by the wet ball-milling method at a rotation speed of 225 r / min for 28 h.

[0037] Step S2: After drying the product obtained in Step S1, place it in a high-temperature muffle furnace for calcination at 1025 °C for 3 h, and cool with the furnace.

[0038] Step S3: Weigh 0.47 g of LiF and 0.70 g of MgF2 powder. First, grind and mix the two by hand for 20 min. Place the ground powder in a high-temperature muffle furnace for calcination at 500 °C for 30 min to obtain an additive with components of LiF and LiMgF3. The additives LiF and MgF2 are 0.7 wt% and 1.05 wt% of the mass of the product obtained in Step S2, respectively.

[0039] Step S4: Through the wet ball-milling method, mix the product obtained in Step S2 and the product obtained in Step S3 for secondary ball-milling to be evenly mixed. The rotation speed is 275 r / min, and the ball-milling time is 9 h. Then dry it.

[0040] Step S5: Compress the powder obtained in Step S4 and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1350 °C, and the holding time is 5 h. After cooling with the furnace, a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is obtained. Through XRD characterization, the molecular formula of the obtained low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is La2Ce 1.95 V 0.04 O7.

[0041] Example 3

[0042] A preparation method of a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material La2Ce 1.9375 V 0.05 O7, comprising the following steps:

[0043] Step S1: Weigh 33.35 g of CeO2, 32.58 g of La2O3 and 0.45 g of V2O5 powders, and ball-mill them at a rotation speed of 250 r / min for 36 h by the wet ball-milling method.

[0044] Step S2: After drying the product obtained in Step S1, place it in a high-temperature muffle furnace and calcine it at 1050 °C for 4 h, and then cool it down with the furnace.

[0045] Step S3: Weigh 0.53 g of LiF and 0.80 g of MgF2 raw material powders, first grind and mix them by hand for 25 min, place the ground powder in a high-temperature muffle furnace and calcine it at 450 °C for 20 min to obtain an additive with components of LiF and LiMgF3. The additives LiF and MgF2 are 0.8 wt% and 1.2 wt% of the mass of the product obtained in Step S2, respectively.

[0046] Step S4: By means of wet ball-milling, secondarily ball-mill and mix evenly the product obtained in Step S2 and the product obtained in Step S3 at a rotation speed of 300 r / min for 10 h, and then dry it.

[0047] Step S5: Press the powder obtained in Step S4 into a green body and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1250 °C, and the holding time is 6 h. After cooling with the furnace, a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is obtained. After XRD characterization, the molecular formula of the obtained low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is La2Ce 1.9375 V 0.05 O7.

[0048] Example 4

[0049] A preparation method of a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material La2Ce 1.925 V 0.06 O7, comprising the following steps:

[0050] Step S1: Weigh 33.13 g of CeO2, 32.58 g of La2O3 and 0.54 g of V2O5 powders, and ball-mill them at a rotation speed of 225 r / min for 30 h by the wet ball-milling method.

[0051] Step S2: After drying the product obtained in Step S1, place it in a high-temperature muffle furnace and calcine it at 1075 °C for 3 h, and then cool it down with the furnace.

[0052] Step S3: Weigh 0.60 g of LiF and 0.89 g of MgF2 raw material powders. First, grind and mix the two for 25 min by manual grinding. Then, place the ground powder in a high-temperature muffle furnace and calcine it at 550 °C for 30 min to obtain a promoter with components of LiF and LiMgF3. The additives LiF and MgF2 are 0.9 wt% and 1.35 wt% of the amounts obtained in step S2, respectively.

[0053] Step S4: Perform secondary ball milling and mixing of the product obtained in step S2 and the product obtained in step S3 by wet ball milling to make them uniformly mixed. The rotation speed is 275 r / min, the ball milling time is 11 h, and then dry it.

[0054] Step S5: Press the powder obtained in step S4 into a green body and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1350 °C and the holding time is 5 h. After cooling with the furnace, a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is obtained. Through XRD characterization, the molecular formula of the obtained low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is La2Ce 1.925 V 0.06 O7.

[0055] Example 5

[0056] A preparation method of a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material La2Ce 1.9 V 0.08 O7, comprising the following steps:

[0057] Step S1: Weigh 32.70 g of CeO2, 32.58 g of La2O3, and 0.72 g of V2O5 powders and ball mill them at a rotation speed of 200 r / min for 26 h by wet ball milling.

[0058] Step S2: After drying the product obtained in step S1, place it in a high-temperature muffle furnace and calcine it at 1100 °C for 2 h, and then cool it with the furnace.

[0059] Step S3: Weigh 0.66 g of LiF and 0.99 g of MgF2 raw material powders. First, grind and mix the two for 30 min by manual grinding. Then, place the ground powder in a high-temperature muffle furnace and calcine it at 500 °C for 15 min to obtain a promoter with components of LiF and LiMgF3. The additives LiF and MgF2 are 1.0 wt% and 1.5 wt% of the amounts obtained in step S2, respectively.

[0060] Step S4: Perform secondary ball milling and mixing of the product obtained in step S2 and the product obtained in step S3 by wet ball milling to make them uniformly mixed. The rotation speed is 250 r / min, the ball milling time is 12 h, and then dry it.

[0061] Step S5: Press the powder compact obtained in Step S4 and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1300 °C, the holding time is 4 h, and after cooling with the furnace, a low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is obtained. After XRD characterization, the molecular formula of the obtained low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material is La2Ce 1.9 V 0.08 O7.

[0062] Comparative Example 1

[0063] The components of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material are La2Ce2O7, and the mass percentages of the additives LiF and MgF2 compared to the total mass of CeO2 and La2O3 are 0.8 wt% and 1.2 wt% respectively. Weigh 34.42 g of CeO2 powder and 32.58 g of La2O3 powder according to the stoichiometric ratio and ball-mill them at a speed of 250 r / min for 36 h by the wet ball-milling method. Place the dried powder in a high-temperature muffle furnace and calcine it at 1050 °C for 4 h. Weigh 0.54 g of LiF and 0.81 g of MgF2 raw material powders according to the stoichiometric ratio, first grind and mix them by hand for 25 min, and place the ground powder in a high-temperature muffle furnace and calcine it at 450 °C for 20 min. Mix the above two calcined powders evenly by wet ball-milling, with a rotation speed of 300 r / min and a ball-milling time of 10 h. Press the ball-milled powder and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1400 °C, the holding time is 6 h, and after cooling with the furnace, a microwave dielectric ceramic material is obtained.

[0064] Comparative Example 2

[0065] The components of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material are La2Ce 1.9375 V 0.05 O7, and the mass percentages of the additives LiF and MgF2 compared to the total mass of CeO2, La2O3, and V2O5 are 0.8 wt% and 1.2 wt% respectively. Weigh 33.35 g of CeO2, 32.58 g of La2O3, 0.45 g of V2O5, 0.53 g of LiF, and 0.80 g of MgF2 powders according to the stoichiometric ratio and ball-mill them at a speed of 250 r / min for 36 h by the wet ball-milling method. Place the dried powder in a high-temperature muffle furnace and calcine it at 1050 °C for 4 h. Mix the calcined powder evenly by wet ball-milling, with a rotation speed of 300 r / min and a ball-milling time of 10 h. Press the ball-milled powder and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1450 °C, the holding time is 6 h, and after cooling with the furnace, a microwave dielectric ceramic material is obtained.

[0066] Comparative Example 3

[0067] The components of the low-temperature rare-earth pyrochlore-type microwave dielectric ceramic material are La2Ce 1.9375 V 0.05 O7. Weigh 33.35 g of CeO2, 32.58 g of La2O3, and 0.45 g of V2O5 powder according to the stoichiometric ratio and ball-mill them by the wet ball-milling method at a speed of 250 r / min for 36 h. Place the dried powder in a high-temperature muffle furnace and calcine it at 1050 °C for 4 h. Mix the calcined powder evenly by the wet ball-milling method at a speed of 300 r / min for 10 h. Press the ball-milled powder into a compact and sinter it in a high-temperature muffle furnace at a sintering temperature of 1500 °C for 6 h, and cool it with the furnace to obtain the microwave dielectric ceramic material.

[0068] Table 1 Performance of materials obtained in each example and comparative example

[0069]

[0070] Table 1 shows the microwave dielectric properties and sintering properties of the microwave dielectric ceramic materials obtained in Examples 1-5 and Comparative Examples 1-3 under different formulations and process conditions. The relative dielectric constant and quality factor were measured according to T / CECA 107-2024, and the resonant frequency temperature coefficient was measured according to GB / T6427-1999. Among them, the ceramic sample prepared in Example 3 has the highest quality factor, the smallest absolute value of the resonant frequency temperature coefficient, and the lowest sintering temperature, which is the optimal example. The phase composition is as Figure 1 shown, and the phase composition is La2Ce 1.9375 V 0.05 O7 solid solution phase. The LiMgF3 and LiF phases cannot be detected by XRD due to their low content. Comparative Example 1 prepared a ceramic sample without adding V2O5, lacking the hetero-valent substitution modification of V 5+ , and the absolute value of τ f increased significantly, and the sintering temperature rose to 1400 °C; in Comparative Example 2, LiF and MgF2 were not separately ground, mixed, and calcined, but were mixed and calcined with CeO2, La2O3, and V2O5 powder during the first ball-milling process. As Figure 2 shown, the intervention of LiF and MgF2 prevented CeO2, La2O3, and V2O5 from forming a single rare-earth pyrochlore phase, and both the microwave dielectric properties and sintering properties decreased significantly. The formation of the impurity phase CeO2 changed the stoichiometric ratio of Ce and V. Therefore, the main crystal phase is expressed in the form of La2(Ce, V)2O7 solid solution. Comparative Example 3 prepared a ceramic sample without adding LiF and MgF2. Compared with Example 3 (as Figure 3 shown), the modification of the composite additive was lacking, and the sintering density decreased. As Figure 4As shown, there are obvious pores inside the ceramic block. Therefore, Q × f The value drops significantly, and the sintering temperature rises to 1500 °C.

Claims

1. A method for preparing a low-temperature rare earth pyrochlore type microwave dielectric ceramic material, characterized in that: The following steps are involved: Step S1, weighing CeO2, La2O3, and V2O5 in proportion, and mixing by ball milling; Step S2, drying, calcining, heat preservation, and cooling with the furnace; Step S3, weighing LiF and MgF2, wherein the mass of LiF is 0.5-1.0wt% of the mass of the substance obtained in step S2, and the mass of MgF2 is 0.75-1.5wt% of the mass of the substance obtained in step S2, grinding and mixing, and calcining; Step S4, ball-milling the product obtained in step S2 and step S3 for a second time, and drying; Step S5, preparing a blank from the powder obtained in step S4 and then sintering it to obtain a low-temperature rare earth pyrochlore type microwave dielectric ceramic material; The molecular formula of the low-temperature rare earth pyrochlore type microwave dielectric ceramic material is La2Ce (2-5x / 4) V x O7, 0.02 ≤ x ≤0.

08.

2. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: The low-temperature rare earth pyrochlore microwave dielectric ceramic material has a relative dielectric constant of 25.12 to 26.93, a quality factor of 95481 to 118233 GHz, and a resonant frequency temperature coefficient of -20 to -26 ppm / °C.

3. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: In the step S1, the ball milling is wet ball milling, the ball milling time is 24-36 hours, and the rotation speed is 200-250 r / min.

4. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: In step S2, the calcination temperature is 1000-1100° C., and the holding time is 2-4 hours.

5. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: In step S3, the grinding is manual grinding, and the grinding time is 15 to 30 minutes.

6. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: In step S3, the calcination temperature is 450-550° C. and the calcination time is 15-30 min.

7. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: In the step S4, the secondary ball milling is wet ball milling.

8. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 7, characterized in that: The wet ball milling time is 8-12 hours, and the rotation speed is 250-300 r / min.

9. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: In the step S5, the sintering temperature is 1250-1350° C., and the sintering temperature is kept for 4-6 hours, followed by cooling with the furnace.

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