Low-temperature rare earth pyrochlore microwave dielectric ceramic material and preparation method thereof

Abstract

The invention discloses a low-temperature rare earth pyrochlore microwave dielectric ceramic material and a preparation method thereof, the molecular formula of the ceramic material is La2Ce (2-5x / 4) VxO7, and x is greater than or equal to 0.02 and less than or equal to 0.08. The preparation method comprises the following steps: S1, weighing CeO2, La2O3 and V2O5 in proportion, and carrying out ball milling and mixing; s2, drying the product obtained in the step S1, calcining, preserving heat, and cooling along with a furnace; s3, LiF and MgF2 are weighed, the mass of LiF accounts for 0.5-1.0 wt% of the mass of the substance obtained in the step S2, the mass of MgF2 accounts for 0.75-1.5 wt% of the mass of the substance obtained in the step S2, and grinding and mixing are conducted; step S4, performing secondary ball milling on the product obtained in the step S2 and the product obtained in the step S3, and drying; and S5, preparing a blank from the powder obtained in the step S4, and sintering. The Q * f value is improved, and meanwhile the sintering temperature is remarkably reduced.

Description

Technical Field

[0001] The invention relates to ceramics and a preparation method thereof, in particular to a low-temperature rare earth pyrochlore type microwave dielectric ceramic material and a preparation method thereof. Background Art

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

[0003] There have been 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 replacement and second phase composite, but the effect is minimal, especially the quality factor ( Q × f value) and the resonant frequency temperature coefficient ( τ f ) cannot meet the practical application requirements at the same time. Based on this, some researchers considered replacing the B position with the rare earth element Ce to form an A2Ce2O7 (A=La, Sm, Nd) ceramic system, which has excellent microwave dielectric properties and ultra-high Q × f The sintering temperature is too high (over 1600°C). Therefore, how to improve the sintering performance of rare earth pyrochlore ceramic material system while ensuring the microwave dielectric properties of the material has become a key technical problem to be solved. 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 low-temperature rare earth pyrochlore type microwave dielectric ceramic material having both an ultra-high Q×f value and a small resonant frequency temperature coefficient. Another purpose of the present invention is to provide a method for preparing a rare earth pyrochlore type microwave dielectric ceramic material which is convenient and controllable and can reduce the sintering temperature.

[0005] Technical solution: The 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, 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 95481~118233GHz, and the resonant frequency temperature coefficient is -20~-26ppm / ℃.

[0007] The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material of the present invention comprises the following steps:

[0008] Step S1, weighing CeO2, La2O3, and V2O5 in proportion, and mixing by ball milling;

[0009] Step S2, drying, calcining, heat preservation, and cooling with the furnace;

[0010] 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;

[0011] Step S4, ball-milling the product obtained in step S2 and step S3 for a second time, and drying;

[0012] Step S5, preparing a blank from the powder obtained in step S4 and then sintering it to obtain a 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 hours, and the rotation speed is 200-250 r / min. CeO2, La2O3, and V2O5 powders are all analytically pure.

[0014] Furthermore, in step S2, the calcination temperature is 1000-1100°C and the holding time is 2-4h. If the calcination temperature is lower than 950°C, the powder contains the raw material phase, and the impurity phase is likely to appear in the subsequent sintering process; if the calcination temperature is higher than 1050°C, the powder particle size becomes larger, and the reaction activity becomes worse in the subsequent sintering process.

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

[0016] Furthermore, in step S4, the secondary ball milling is wet ball milling. The wet ball milling time is 8-12 hours, and the rotation speed is 250-300r / min. When the sintering temperature is lower than 1250°C, the sintering power of the ceramic material is insufficient, the density is reduced, and the performance is reduced; when 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 decrease in performance.

[0017] Furthermore, in 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.

[0018] Preparation principle: LiF and MgF2 are reacted at high temperature to obtain LiMgF3. Since n(LiF) / n(MgF2)>1, the final additive composition is LiF and LiMgF3. Not only is the sintering effect better than the simple combination of LiF and MgF2, but the final microwave dielectric properties are also improved. In addition, V 5+ A small amount of unequal substitution modification is performed on the Ce site in La2Ce2O7 to introduce an appropriate amount of cation vacancy defects, namely La2Ce (2-5x / 4) V x In O7, the sum of the number of Ce and V atoms is less than 2, which increases the diffusion and mass transfer power of the ceramic material, improves the sintering power, and then reduces the sintering temperature. The introduction of composite sintering aids and the strategy of alivalent ion replacement modification can both improve the sintering power, but the former is a low-melting point additive, and the latter is a structural defect-induced diffusion and mass transfer. The two have different modification ideas, which allows the two strategies to synergistically improve the sintering performance of rare earth pyrochlore ceramic materials and achieve the effect of "1+1>2".

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

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

[0021] 2. Select heterovalent ions to dope rare earth pyrochlore ceramic materials, and increase the sintering power of ceramic materials through structural defect-induced diffusion mass transfer, which can not only improve the resonant frequency temperature coefficient of ceramic materials, but also reduce their sintering temperature. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0025] Figure 4 This is a SEM image of the low-temperature rare earth pyrochlore type microwave dielectric ceramic material prepared in Comparative Example 3 of the present invention. 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. CeO2, La2O3, and V2O5 powders were all analytically pure.

[0027] Example 1

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

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

[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., keep it warm for 2 hours, and cool it along with the furnace.

[0031] Step S3, weigh 0.33g LiF and 0.50g MgF2 powder, grind and mix them by hand grinding for 15 minutes, and place the ground powder in a high-temperature muffle furnace for calcination at 450°C for 15 minutes to obtain additive components of LiF and LiMgF3. The additives LiF and MgF2 are 0.5wt% and 0.75wt% of the mass of the substance obtained in step S2, respectively.

[0032] Step S4, ball-milling the product obtained in step S2 and the product obtained in step S3 for a second time to mix them evenly by wet ball milling, with a rotation speed of 250 r / min, a ball milling time of 8 h, and drying.

[0033] Step S5, the powder obtained in step S4 is pressed and placed in a high-temperature muffle furnace for sintering at a sintering temperature of 1300°C for 4 hours. After cooling in 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 1.975 V 0.02 O7.

[0034] Example 2

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

[0036] Step S1, weigh 33.56g CeO2, 32.58g La2O3 and 0.36g V2O5 powders and ball mill them at a speed of 225r / min for 28h by wet ball milling.

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

[0038] Step S3, weigh 0.47g LiF and 0.70g MgF2 powder, grind and mix them by hand grinding for 20min, and calcine the ground powder in a high-temperature muffle furnace at 500℃ for 30min to obtain additive components of LiF and LiMgF3. The additives LiF and MgF2 are 0.7wt% and 1.05wt% of the mass of the substance obtained in step S2, respectively.

[0039] Step S4, ball-milling the product obtained in step S2 and the product obtained in step S3 for a second time to mix them evenly by wet ball milling, with a rotation speed of 275 r / min, a ball milling time of 9 h, and drying.

[0040] Step S5, the powder obtained in step S4 is pressed and placed in a high-temperature muffle furnace for sintering at a sintering temperature of 1350°C for 5 hours. After cooling in 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 1.95 V 0.04 O7.

[0041] Example 3

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

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

[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., keep it warm for 4 hours, and cool it with the furnace.

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

[0046] Step S4, ball-milling the product obtained in step S2 and the product obtained in step S3 for a second time to mix them evenly by wet ball milling, with a rotation speed of 300 r / min and a ball milling time of 10 h, and then drying.

[0047] Step S5, the powder compact obtained in step S4 is placed in a high-temperature muffle furnace for sintering at a sintering temperature of 1250°C for 6 hours. After cooling in 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 low-temperature rare earth pyrochlore type microwave dielectric ceramic material La2Ce 1.925 V 0.06 The preparation method of O7 comprises the following steps:

[0050] Step S1, weigh 33.13 g CeO2, 32.58 g La2O3 and 0.54 g V2O5 powders and ball mill them at a speed of 225 r / min for 30 h using a 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 hours, and cool it along with the furnace.

[0052] Step S3, weigh 0.60g LiF and 0.89g MgF2 raw material powders, grind and mix them by hand grinding for 25min, and place the ground powder in a high-temperature muffle furnace for calcination at 550°C for 30min to obtain additive components of LiF and LiMgF3. The additives LiF and MgF2 are 0.9wt% and 1.35wt% of the mass of the substance obtained in step S2, respectively.

[0053] Step S4, ball-milling the product obtained in step S2 and the product obtained in step S3 for a second time to mix them evenly by wet ball milling, with a rotation speed of 275 r / min and a ball milling time of 11 h, and then drying.

[0054] Step S5, the powder obtained in step S4 is pressed and placed in a high-temperature muffle furnace for sintering at a sintering temperature of 1350°C for 5 hours. After cooling in 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 1.925 V 0.06 O7.

[0055] Example 5

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

[0057] Step S1, weigh 32.70g CeO2, 32.58g La2O3 and 0.72g V2O5 powders and ball mill them at a speed of 200r / min for 26h 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 hours, and cool it with the furnace.

[0059] Step S3, weigh 0.66g LiF and 0.99g MgF2 raw material powders, grind and mix them by hand grinding for 30min, and place the ground powder in a high-temperature muffle furnace for calcination at 500℃ for 15min to obtain additive components of LiF and LiMgF3. The additives LiF and MgF2 are 1.0wt% and 1.5wt% of the mass of the substance obtained in step S2, respectively.

[0060] Step S4, ball-milling the product obtained in step S2 and the product obtained in step S3 for a second time to mix them evenly by wet ball milling, with a rotation speed of 250 r / min, a ball milling time of 12 h, and drying.

[0061] Step S5, the powder obtained in step S4 is pressed and placed in a high-temperature muffle furnace for sintering at a sintering temperature of 1300°C for 4 hours. After cooling in 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 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 0.8wt% and 1.2wt% respectively. According to the stoichiometric ratio, 34.42gCeO2 and 32.58g La2O3 powders are weighed and ball milled at a speed of 250r / min for 36h by wet ball milling. The dried powder is placed in a high-temperature muffle furnace and calcined at 1050℃ for 4h. According to the stoichiometric ratio, 0.54gLiF and 0.81gMgF2 raw material powders are weighed, and the two are first ground and mixed by manual grinding for 25min, and the ground powder is placed in a high-temperature muffle furnace and calcined at 450℃ for 20min. The above two calcined powders are mixed evenly by wet ball milling, with a speed of 300r / min and a ball milling time of 10h. The powder after ball milling is pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 1400°C for 6 hours. The microwave dielectric ceramic material is obtained after cooling in the furnace.

[0064] Comparative Example 2

[0065] The components of low-temperature rare earth pyrochlore microwave dielectric ceramic materials are La2Ce 1.9375 V 0.05 O7, the mass percentage of additives LiF and MgF2 compared to the total mass of CeO2, La2O3, and V2O5 are 0.8wt% and 1.2wt%, respectively. According to the stoichiometric ratio, 33.35g CeO2, 32.58g La2O3, 0.45g V2O5, 0.53g LiF and 0.80g MgF2 powders were weighed and ball milled at a speed of 250r / min for 36h by wet ball milling. The dried powder was calcined at 1050℃ in a high-temperature muffle furnace for 4h. The calcined powder was mixed evenly by wet ball milling, with a speed of 300r / min and a ball milling time of 10h. After ball milling, the powder was pressed and sintered in a high-temperature muffle furnace at a sintering temperature of 1450℃ and a holding time of 6h. After cooling with the furnace, a microwave dielectric ceramic material was obtained.

[0066] Comparative Example 3

[0067] The components of low-temperature rare earth pyrochlore microwave dielectric ceramic materials are La2Ce 1.9375 V 0.05 O7. According to the stoichiometric ratio, 33.35g CeO2, 32.58g La2O3 and 0.45g V2O5 powders were weighed and ball-milled at a speed of 250r / min for 36h by wet ball milling. The dried powder was calcined at 1050℃ in a high-temperature muffle furnace for 4h. The calcined powder was mixed evenly by wet ball milling at a speed of 300r / min and a ball milling time of 10h. The ball-milled powder was pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 1500℃ for 6h. After cooling in the furnace, a microwave dielectric ceramic material was obtained.

[0068] Table 1 Properties of materials obtained in various embodiments and comparative examples

[0069]

[0070] Table 1 shows the microwave dielectric properties and sintering properties of the microwave dielectric ceramic materials obtained in Examples 1 to 5 and Comparative Examples 1 to 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, and is the optimal embodiment. The phase composition is as follows Figure 1 As shown, the phase composition is La2Ce 1.9375 V 0.05 O7 solid solution phase, LiMgF3 and LiF phase cannot be detected by XRD due to their low content. Comparative Example 1 prepared a ceramic sample without adding V2O5. 5+ Adenovalent substitution modification, τ f The absolute value increased significantly, and the sintering temperature rose to 1400°C; in Comparative Example 2, LiF and MgF2 were not ground and mixed separately and calcined, but were mixed and calcined with CeO2, La2O3, and V2O5 powders in a ball milling process, such as Figure 2 As shown in the figure, the intervention of LiF and MgF2 causes CeO2, La2O3, and V2O5 to be unable to form a single rare earth pyrochlore phase, and the microwave dielectric properties and sintering properties are greatly reduced. The formation of the impurity phase CeO2 causes the stoichiometric ratio of Ce and V to change. Therefore, the main crystal phase adopts La2 (Ce, Comparative Example 3 prepared a ceramic sample without adding LiF and MgF2, which was different from Example 3 (such as Figure 3 Compared with the modified composite additives, the sintering density decreases, such as Figure 4As shown in the figure, there are obvious pores inside the ceramic block. Q × f The value dropped significantly and the sintering temperature increased to 1500℃.

Claims

1. A low-temperature rare earth pyrochlore type microwave dielectric ceramic material, characterized in that: Its molecular formula is La2Ce (2-5x / 4) V x O7, 0.02 ≤ x ≤0.

08.

2. The low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 1, characterized in that: Its relative dielectric constant is 25.12~26.93, the quality factor is 95481~118233GHz, and the resonant frequency temperature coefficient is -20~ -26ppm / ℃.

3. A method for preparing a low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to any one of claims 1 to 2, 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.

4. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 3, 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.

5. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 3, characterized in that: In step S2, the calcination temperature is 1000-1100° C., and the holding time is 2-4 hours.

6. The low-temperature rare earth pyrochlore type microwave dielectric ceramic material and the preparation method thereof according to claim 3, characterized in that: In step S3, the grinding is manual grinding, and the grinding time is 15 to 30 minutes.

7. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 3, characterized in that: In step S3, the calcination temperature is 450-550° C. and the calcination time is 15-30 min.

8. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 3, characterized in that: In the step S4, the secondary ball milling is wet ball milling.

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

10. The method for preparing the low-temperature rare earth pyrochlore type microwave dielectric ceramic material according to claim 3, 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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