A low-loss rare earth pyrochlore-based microwave dielectric ceramic material and its preparation method

Abstract

The present invention discloses a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material and a preparation method thereof. The chemical formula of the low-loss rare-earth pyrochlore-based microwave dielectric ceramic material is Nd 2‑ x Gd x Ce 2‑y Ge y O7, where 0.04 ≤ x ≤ 0.08 and 0.01 ≤ y ≤ 0.04. The preparation method includes the following steps: weighing CeO2, Nd2O3, Gd2O3, and GeO2 according to the stoichiometric ratio, and performing primary ball milling and mixing; drying, calcining, heat preservation, and furnace cooling; performing secondary ball milling and drying; sintering and low-temperature heat preservation followed by furnace cooling. The present invention realizes the synthesis of the (Nd, Gd)2(Ce, Ge)2O7 solid solution through the strategy of A and B site co-modification, improves the loss characteristics of the rare-earth pyrochlore ceramic material, and enhances the Q×f value of the ceramic material; it can inhibit the valence change of the Ce element, reduce structural defects, and ensure the sintering densification of the material.

Description

Technical Field

[0001] The present invention belongs to ceramic materials and their preparation methods, and specifically relates to a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material and a preparation method thereof. Background Art

[0002] Multilayer ceramic capacitors can achieve the miniaturization of devices and have excellent dielectric properties, meeting the development requirements of microwave communication technology and increasing their proportion in the microwave communication field. With the in-depth development of 5G mobile communication, new requirements are put forward for high-performance microwave communication technology and materials, such as an acceptable dielectric constant ε r , a high quality factor Q×f, and a resonance frequency temperature coefficient τ f close to zero. These materials are applied to the fifth-generation cellular system (5G) and have outstanding characteristics such as high capacity, high speed, and low latency.

[0003] Rare-earth pyrochlore-based microwave dielectric ceramic materials (A2B2O7) have been studied and reported by many scholars as a classic microwave dielectric ceramic material system. Generally, light rare-earth elements such as Y, La, Sm, etc. can be selected for the A site in the pyrochlore structure, and elements such as Ti, Zr, Sn, Ce, etc. are selected for the B site. The overall microwave dielectric properties of this material system are good, but the dielectric loss characteristics (Q×f value) still need to be improved (usually, Q×f < 60000 GHz). Therefore, preparing a low-loss rare-earth pyrochlore-based 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-loss rare-earth pyrochlore-based microwave dielectric ceramic material, and another object of the present invention is to provide a convenient and controllable preparation method for the rare-earth pyrochlore-based microwave dielectric ceramic material.

[0005] Technical Solution: A low-loss rare-earth pyrochlore-based microwave dielectric ceramic material described in the present invention has a chemical formula of Nd 2-x Gd x Ce 2-y Ge y O7, where 0.04 ≤ x ≤ 0.08 and 0.01 ≤ y ≤ 0.04.

[0006] Furthermore, its relative dielectric constant is 22.52 - 24.98, the quality factor is 136457 - 154620 GHz, and the resonance frequency temperature coefficient is -9 to -15 ppm / °C.

[0007] A preparation method for the low-loss rare-earth pyrochlore-based microwave dielectric ceramic material described in the present invention includes the following steps:

[0008] Step S1: Weigh CeO2, Nd2O3, Gd2O3, and GeO2 according to the stoichiometric ratio and conduct primary ball milling and mixing.

[0009] Step S2: Dry the product obtained in Step S1, calcine it, hold it at a constant temperature, and then cool it in the furnace.

[0010] Step S3: Conduct secondary ball milling on the product obtained in Step S2 and then dry it.

[0011] Step S4: Sinter the product obtained in Step S3, hold it at a low temperature, and then cool it in the furnace to finally obtain a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material.

[0012] Furthermore, in Step S1, the feeding order for primary ball milling is to first add CeO2 and grinding balls into the ball milling tank, then add Gd2O3 and GeO2, and finally add Nd2O3.

[0013] Furthermore, in Step S1, the primary ball milling is wet ball milling, the ball milling time is 18 - 24 h, and the rotation speed is 250 - 300 r / min.

[0014] Furthermore, in Step S2, the calcination temperature is 1150 - 1250 °C, and the holding time is 3 - 5 h. If the calcination temperature is lower than 1150 °C, the raw material phase remains in the powder, and impurity phases are likely to appear during the subsequent sintering process. If the calcination temperature is higher than 1250 °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 secondary ball milling is wet ball milling, the ball milling time is 6 - 12 h, and the rotation speed is 300 - 350 r / min.

[0016] Furthermore, in Step S3, the drying temperature is 70 - 90 °C, and the drying time is 8 - 12 h.

[0017] Furthermore, in Step S4, the sintering temperature is 1450 - 1550 °C, and after sintering, it is held for 1 - 2 h. If the holding temperature is lower than 1 h, the growth of ceramic grains is insufficient, which is not conducive to final sintering densification. If the holding time is higher than 2 h, due to insufficient oxygen in the air atmosphere, some of the Ce elements in the ceramic components change their valence states from tetravalent to trivalent, resulting in an increase in cation defects in the pyrochlore structure.

[0018] Further, in step S4, the low-temperature heat preservation is to cool down to 1250-1350 °C at a cooling rate of 5-10 °C / min and then heat preserve for 12-18 h. The long-time low-temperature heat preservation can not only inhibit the valence state transformation process of part of the Ce element, but also promote the sintering densification of the ceramic material. When the heat preservation temperature is lower than 1250 °C or the heat preservation time is lower than 12 h or the cooling rate is higher than 10 °C / min, the sintering densification decreases. When the heat preservation temperature is lower than 1350 °C or the heat preservation time is higher than 18 h or the cooling rate is lower than 5 °C / min, the effect of inhibiting the valence state transformation of the Ce element becomes worse.

[0019] Preparation principle: Using Nd2Ce2O7 with a pyrochlore structure as the matrix, Gd2O3 and GeO2 are introduced as ion substitution modifiers during the wet ball milling process. After high-temperature calcination, Gd 3+ and Ge 4+ occupy the A-site and B-site of the pyrochlore structure respectively to form a pyrochlore solid solution phase. Among them, the ionic radius of Ge 4+ is much smaller than that of Ce 4+ , and the ion substitution ratio should be controlled not to be too high; Ce element is easily reduced and undergoes valence state changes (Ce 4+ →Ce 3+ ) during high-temperature (above 1450 °C) sintering in an air atmosphere, resulting in an increase in the cation defect concentration in the pyrochlore structure, thus deteriorating the loss characteristics of the material. In addition, the sintering temperature of the Ce-based pyrochlore structure ceramic material is relatively high (~1500 °C), and too low sintering temperature cannot meet the sintering densification. Therefore, the present invention solves this problem through a sintering process of (short-time high-temperature sintering + long-time low-temperature heat preservation). The short-time (1-2 h) high-temperature sintering can promote the sintering densification of the ceramic material, and the long-time (12-18 h) low-temperature heat preservation can not only assist in improving the sintering densification through grain growth, but also reduce the high-temperature valence state change of the Ce element.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0021] 1. The synthesis of (Nd, Gd)2(Ce,Ge)2O7 solid solution is achieved through the strategy of A-site and B-site co-modification, improving the loss characteristics of the rare earth pyrochlore ceramic material and enhancing the Q×f value of the ceramic material;

[0022] 2. The sintering process of (short-time high-temperature sintering + long-time low-temperature heat preservation) is selected, which inhibits the valence state change of the Ce element at the B-site in the pyrochlore structure, reduces the structural defects while ensuring the sintering densification of the material, thereby enhancing the Q×f value of the ceramic material to meet the application requirements of 5G mobile communication microwave devices. Description of the Drawings

[0023] Figure 1It is the XRD pattern of the low-temperature rare earth pyrochlore-based microwave dielectric ceramic material prepared in Example 3 of the present invention;

[0024] Figure 2 It is the SEM image of the low-temperature rare earth pyrochlore-based microwave dielectric ceramic material prepared in Example 3 of the present invention;

[0025] Figure 3 It is the SEM image of the low-temperature rare earth pyrochlore-based microwave dielectric ceramic material prepared in Comparative Example 3. Detailed implementation mode

[0026] The materials, reagents, instruments, etc. used in the following examples can be obtained from commercial sources unless otherwise specified. The experimental methods without specific conditions in the examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. The CeO2, Nd2O3, Gd2O3, and GeO2 powders are all of analytical purity.

[0027] Example 1

[0028] A preparation method of a low-loss rare earth pyrochlore-based microwave dielectric ceramic material Nd 1.96 Gd 0.04 Ce 1.99 Ge 0.01 O7, comprising the following steps:

[0029] (1) Weigh 34.25 g of CeO2 powder, 32.97 g of Nd2O3 powder, 0.72 g of Gd2O3 powder, and 0.10 g of GeO2 powder according to the stoichiometric ratio, and ball mill them at a speed of 200 r / min for 18 h by wet ball milling (primary ball milling).

[0030] (2) Place the dried powder from step (1) in a high-temperature muffle furnace for calcination, heat it to 1150 °C at a rate of 3 °C / min, hold for 3 h, and cool it with the furnace.

[0031] (3) Mix the calcined powder from step (2) evenly by wet ball milling (secondary ball milling) at a speed of 300 r / min for 6 h, and dry it at 70 °C for 8 h.

[0032] (4) Press the powder obtained in step (3) into a green body and place it in a high-temperature muffle furnace for sintering. The heating rate is 3 °C / min, the sintering temperature is 1450 °C, hold for 1 h, then cool to 1250 °C at a rate of 5 °C / min, hold for 12 h, and cool it with the furnace. After that, obtain the low-temperature rare earth pyrochlore-based microwave dielectric ceramic material Nd 1.96 Gd 0.04 Ce 1.99 Ge 0.01 O7.

[0033] Example 2

[0034] Preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.95 Gd 0.05 Ce 1.98 Ge 0.02 O7, comprising the following steps:

[0035] (1) Weigh 34.08 g of CeO2 powder, 32.81 g of Nd2O3 powder, 0.91 g of Gd2O3 powder, and 0.21 g of GeO2 powder according to the stoichiometric ratio, and ball-mill them at a speed of 275 r / min for 20 h by the wet ball-milling (primary ball-milling) method.

[0036] (2) Place the dried powder from step (1) in a high-temperature muffle furnace for calcination, heat it to 1200 °C at a rate of 3 °C / min, hold for 4 h, and then cool it with the furnace.

[0037] (3) Mix the calcined powder from step (2) evenly by wet ball-milling (secondary ball-milling) at a speed of 325 r / min for 8 h, and dry it at 75 °C for 9 h.

[0038] (4) Press the powder obtained in step (3) into a compact and place it in a high-temperature muffle furnace for sintering. The heating rate is 3 °C / min, the sintering temperature is 1500 °C, hold for 1 h, then cool it to 1350 °C at a rate of 8 °C / min, hold for 14 h, and then cool it with the furnace. After that, a low-temperature rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.95 Gd 0.05 Ce 1.98 Ge 0.02 O7 is obtained.

[0039] Example 3

[0040] Preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.94 Gd 0.06 Ce 1.97 Ge 0.03 O7, comprising the following steps:

[0041] (1) Weigh 33.91 g of CeO2 powder, 32.64 g of Nd2O3 powder, 1.09 g of Gd2O3 powder, and 0.31 g of GeO2 powder according to the stoichiometric ratio, and ball-mill them at a speed of 300 r / min for 22 h by the wet ball-milling (primary ball-milling) method.

[0042] (2) Place the dried powder after (primary ball-milling) in a high-temperature muffle furnace for calcination, heat it to 1200 °C at a rate of 3 °C / min, hold for 3 h, and then cool it with the furnace.

[0043] (3) Mix the powder after calcination in step (2) evenly by wet ball milling (secondary ball milling), with a rotation speed of 300 r / min, a ball milling time of 10 h, and drying at 80 °C for 10 h.

[0044] (4) Press the powder obtained in step (3) into a green body and sinter it in a high-temperature muffle furnace. The heating rate is 3 °C / min, the sintering temperature is 1500 °C, hold for 2 h, then cool to 1250 °C at a cooling rate of 10 °C / min, hold for 16 h, and cool with the furnace to obtain a low-temperature rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.94 Gd 0.06 Ce 1.97 Ge 0.03 O7.

[0045] Example 4

[0046] A preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.93 Gd 0.07 Ce 1.98 Ge 0.02 O7, comprising the following steps:

[0047] (1) Weigh 34.08 g of CeO2 powder, 32.47 g of Nd2O3 powder, 1.27 g of Gd2O3 powder, and 0.21 g of GeO2 powder according to the stoichiometric ratio, and ball mill them at a rotation speed of 275 r / min for 20 h by wet ball milling (primary ball milling).

[0048] (2) Place the dried powder in step (1) into a high-temperature muffle furnace for calcination, heat it to 1150 °C at a rate of 3 °C / min, hold for 5 h, and cool with the furnace.

[0049] (3) Mix the powder after calcination in step (2) evenly by wet ball milling (secondary ball milling), with a rotation speed of 325 r / min, a ball milling time of 8 h, and drying at 85 °C for 11 h.

[0050] (4) Press the powder obtained in step (3) into a green body and sinter it in a high-temperature muffle furnace. The heating rate is 3 °C / min, the sintering temperature is 1450 °C, hold for 2 h, then cool to 1300 °C at a cooling rate of 5 °C / min, hold for 18 h, and cool with the furnace to obtain a low-temperature rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.93 Gd 0.07 Ce 1.98 Ge 0.02 O7.

[0051] Example 5

[0052] A low-loss rare-earth pyrochlore-based microwave dielectric ceramic material Nd 1.92 Gd0.08 Ce 1.96 Ge 0.04 Preparation method of NdGdCeGeO7, comprising the following steps:

[0053] (1) Weigh 33.73 g of CeO2 powder, 32.30 g of Nd2O3 powder, 1.45 g of Gd2O3 powder, and 0.42 g of GeO2 powder according to the stoichiometric ratio, and ball-mill them by wet ball-milling (primary ball-milling) at a rotation speed of 250 r / min for 24 h.

[0054] (2) Place the powder dried in step (1) in a high-temperature muffle furnace for calcination, heat it up to 1250 °C at a rate of 3 °C / min, hold for 5 h, and then cool it down with the furnace.

[0055] (3) Mix the powder calcined in step (2) evenly by wet ball-milling (secondary ball-milling) at a rotation speed of 350 r / min for 12 h, and dry it at 90 °C for 12 h.

[0056] (4) Press the powder obtained in step (3) into a compact and place it in a high-temperature muffle furnace for sintering. The heating rate is 3 °C / min, the sintering temperature is 1550 °C, hold for 1 h, then cool it down to 1300 °C at a rate of 8 °C / min, hold for 12 h, and then cool it down with the furnace to obtain the low-temperature rare-earth pyrochlore-based microwave dielectric ceramic material NdGdCeGeO7. 1.92 Gd 0.08 Ce 1.96 Ge 0.04 O7.

[0057] Comparative Example 1

[0058] The remaining steps of this comparative example are the same as those of Example 3, and the only difference is that: Gd2O3 is omitted from the raw materials, and the mass of Nd2O3 is 33.65 g.

[0059] Comparative Example 2

[0060] The remaining steps of this comparative example are the same as those of Example 3, and the only difference is that: GeO2 is omitted from the raw materials, and the mass of CeO2 is 34.42 g.

[0061] Comparative Example 3

[0062] The remaining steps of this comparative example are the same as those of Example 3, and the only difference is that: in step S4, the low-temperature holding is omitted, that is, the sintering temperature is 1500 °C, and after holding for 18 h, it is cooled down with the furnace.

[0063] Table 1 shows the microwave dielectric properties and sintering properties of the low-loss rare-earth pyrochlore-based microwave dielectric ceramic materials obtained in Examples 1 to 5 under different formulations and process conditions. Among them, the ceramic sample prepared in Example 3 has the highest quality factor and a near-zero temperature coefficient of resonant frequency, making it the optimal example. The phase composition is as shown in Figure 1 and is the solid solution phase of Nd 1.94 Gd 0.06 Ce 1.97 Ge 0.03 O7, with the structure of (Nd,Gd)2(Ce,Ge)2O7. In Comparative Example 1 and Comparative Example 2, ceramic samples without adding Gd2O3 and without adding GeO2 were prepared respectively. The lack of the synergistic modification effect of ion substitution led to a significant decrease in the Q×f value and a slight increase in the absolute value of τ f . In Comparative Example 3, the step of low-temperature heat preservation was missing during the sintering process. Part of Ce 4+ had its valence state transformed into Ce 3+ in the high-temperature environment, increasing the ionic defects in the pyrochlore structure. In addition, under the action of low-temperature heat preservation, the ceramic grains of the ceramic sample in Example 3 were fine and uniform, and there were no obvious pores, as shown in Figure 2 . While the particle size of the ceramic sample in Comparative Example 3 was large and the uniformity was poor, as shown in Figure 3 . A certain amount of large pores appeared inside the ceramic, and the sintering densification was not good. Therefore, the Q×f value decreased significantly and the absolute value of τ f increased significantly.

[0064] Table 1 Material properties obtained in Examples 1-5 and Comparative Examples 1-3

[0065] .

Claims

1. A preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material, characterized in that, It includes the following steps: Step S1: Weigh CeO2, Nd2O3, Gd2O3, and GeO2 according to the stoichiometric ratio and conduct primary ball milling and mixing; Step S2: Dry the product obtained in Step S1, calcine it, hold it at a constant temperature, and then cool it in the furnace; Step S3: Conduct secondary ball milling on the product obtained in Step S2 and then dry it; Step S4: Sinter the product obtained in Step S3, hold it at a low temperature, and then cool it in the furnace to finally obtain a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material; The chemical formula of the low-loss rare-earth pyrochlore-based microwave dielectric ceramic material is Nd 2-x Gd x Ce 2-y Ge y O7, where 0.04 ≤ x ≤ 0.08, 0.01 ≤ y ≤ 0.04; In Step S4, the sintering temperature is 1450~1550°C, and the holding time after sintering is 1~2 h; In Step S4, the low-temperature holding is to cool down to 1250~1350°C at a cooling rate of 5~10°C / min and then hold it for 12~18 h.

2. The preparation method of the low-loss rare earth pyrochlore-based microwave dielectric ceramic material according to claim 1, characterized in that: The relative dielectric constant of the low-loss rare-earth pyrochlore-based microwave dielectric ceramic material is 22.52~24.98, the quality factor is 136457~154620 GHz, and the resonant frequency temperature coefficient is -9~ -15 ppm / °C.

3. The preparation method of a low-loss rare earth pyrochlore-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S1, the feeding sequence for the primary ball milling is to first add CeO2 and grinding balls into the ball milling tank, then add Gd2O3 and GeO2, and finally add Nd2O3.

4. The preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S1, the primary ball milling is wet ball milling, the ball milling time is 18~24 h, and the rotation speed is 250~300 r / min.

5. The preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material according to claim 1, wherein: In Step S2, the calcination temperature is 1150~1250°C, and the holding time is 3~5 h.

6. The preparation method of a low-loss rare earth pyrochlore-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S3, the secondary ball milling is wet ball milling, the ball milling time is 6~12 h, and the rotation speed is 300~350 r / min.

7. The preparation method of a low-loss rare-earth pyrochlore-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S3, the drying temperature is 70~90°C, and the drying time is 8~12 h.

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