Non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic and preparation method thereof

Abstract

The application belongs to the field of microwave dielectric ceramic and its manufacturing, and particularly relates to a non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic and a preparation method thereof, which is suitable for low-temperature co-fired ceramic LTCC microwave devices and radio frequency communication fields. Under the premise of not introducing additional fluxing agents, the low-temperature sintering characteristics and the positive temperature frequency coefficient characteristics of BaV2O6 are fully utilized to realize the synchronous regulation of the sintering temperature of Li3Mg2NbO6 ceramic and the temperature coefficient of resonant frequency, while maintaining a relatively high quality factor. Considering that the vanadium component is prone to volatilization loss at an isothermal region close to or higher than 700 DEG C and 800-900 DEG C, a non-stoichiometric rich addition measure is adopted to weaken the local non-stoichiometry and defect increase phenomenon caused by vanadium volatilization, so as to reduce the dielectric loss, further improve and stabilize the Qxf of the composite system, and improve the sample batch consistency.

Description

Technical Field

[0001] This invention belongs to the field of microwave dielectric ceramics and their manufacturing, specifically relating to a non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic and its preparation method, applicable to low-temperature co-fired ceramic (LTCC) microwave devices and radio frequency communication fields. Background Technology

[0002] Low-temperature co-fired ceramics (LTCC) technology is one of the key technologies for achieving high integration, miniaturization, and high reliability in microwave and radio frequency devices, and has been widely used in mobile communications, satellite communications, radar systems, and radio frequency front-end modules. LTCC technology places high demands on the dielectric materials, typically requiring materials to achieve densification sintering below 900 °C, while simultaneously possessing a suitable dielectric constant, a high quality factor (Q×f), and a near-zero temperature coefficient of resonant frequency (τ). f This is to ensure that the device operates stably under varying temperature conditions.

[0003] Li3Mg2NbO6 microwave dielectric ceramics are known for their stable dielectric properties and high quality factor (Q×f can reach 8×10⁻⁶). 8 The material has attracted widespread attention due to its high GHz-level (GHz-scale) sintering temperature. However, it typically requires long-term sintering above 1200 °C to achieve densification, making it difficult to meet the low-temperature sintering requirements of the LTCC process. Furthermore, Li3Mg2NbO6 ceramics exhibit a large negative resonant frequency temperature coefficient (τ). f =-27.2 ppm / ℃), which limits its direct application in microwave devices with high temperature stability requirements.

[0004] To control the sintering temperature and temperature coefficient of resonant frequency of Li3Mg2NbO6 ceramics, current research typically employs methods such as introducing positive temperature coefficient (PTC) materials (e.g., TiO2, CaTiO3) and adding low-melting-point fluxes. However, these PTC materials often suffer from drawbacks such as high dielectric constant, high dielectric loss, and high sintering temperature. When combined with Li3Mg2NbO6, they tend to significantly increase the dielectric constant and decrease the quality factor, and are also unfavorable for low-temperature co-firing. Furthermore, while the introduction of fluxes can lower the sintering temperature, it often leads to the formation of a glassy phase at grain boundaries, affecting the high-frequency dielectric properties and long-term stability of the material.

[0005] Therefore, how to achieve synchronous control of the sintering temperature and resonant frequency temperature coefficient of Li3Mg2NbO6 ceramics while maintaining a high quality factor is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned problems or shortcomings and to solve the application issues of Li3Mg2NbO6 ceramics in LTCC technology, this invention provides a non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic and its preparation method, which is applicable to low-temperature co-fired ceramic (LTCC) microwave devices and radio frequency communication fields.

[0007] A non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic comprises Li3Mg2NbO6 phase and BaV2O6 phase, with a weight percentage of (100-x)%Li3Mg2NbO6+x%BaV2O6, wherein 25≤x≤40.

[0008] After pre-calcined materials were prepared from the Li3Mg2NbO6 and BaV2O6 phases respectively, they were mixed by solid-state method and composite sintered at 825~875℃ to obtain Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic. No additional flux or sintering aids were added during the preparation process. The dielectric constant ε of the Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic is... r The resonant frequency temperature coefficient is τ = 11.2~13.1, the quality factor Q×f is 11520~59680 GHz, and the temperature coefficient τ of the resonant frequency is τ = 11.2~13.1. f The concentration ranges from -18 to +5 ppm / ℃.

[0009] The BaV2O6 phase adopts a vanadium volatilization compensation strategy, according to BaV... (2+δ) The vanadium was prepared by non-stoichiometric batching of O6, wherein 0.04 ≤ δ ≤ 0.1. The vanadium volatilization compensation strategy is used to compensate for the vanadium volatilization loss generated during the pre-calcination and composite sintering of the BaV2O6 phase, so as to reduce the dielectric loss caused by the increase of point defects and grain boundary defects due to local non-stoichiometry, thereby improving and stabilizing the Q×f of the composite system and improving the consistency of sample batches.

[0010] Preferably, the best overall performance is obtained when x=30 and the sintering temperature is 850℃.

[0011] Preferably, δ = 0.08.

[0012] Preferably, the preparation method of the above-mentioned non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic includes the following steps:

[0013] Step 1: Pre-calcined materials of Li3Mg2NbO6 phase and BaV2O6 phase were prepared separately.

[0014] Preparation of Li3Mg2NbO6 pre-calcined material: The component raw materials are weighed according to the Li3Mg2NbO6 stoichiometric ratio, ball-milled, dried, and sieved, and then pre-calcined at 950~1050℃ for 2~4 h; Preparation of BaV2O6 pre-calcined material: The component raw materials are prepared using BaV2O6 with excess vanadium source. (2+δ) O6 non-stoichiometric ingredients are ball-milled, dried, and sieved, and then pre-calcined at 450~550℃ for 1~2 hours.

[0015] Step 2: Mix the two-phase pre-calcined material prepared in Step 1 with (100-x)%Li3Mg2NbO6 + x%BaV2O6 at a mass fraction of x=25~40 wt%, and then ball mill, dry, granulate and shape it in sequence.

[0016] Step 3: After debinding, sinter at a low temperature of 825~875℃ to obtain Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic. No other flux is added during the preparation process.

[0017] Preferably, the sintering temperature in step 3 is 850°C.

[0018] Preferably, the preparation of the BaV2O6 pre-calcined material includes: mixing BaCO3 and V2O5 in a BaV source excess δ. (2+δ) O6 was prepared in a non-stoichiometric ratio, and anhydrous ethanol was added. The mixture was ball-milled at 250-300 rpm for 4-6 hours. After drying and sieving, the mixture was pre-calcined at 450-550℃ with a temperature increase of 3-5℃ / min, and held at that temperature for 1-2 hours. The pre-calcined BaV2O6 material was then obtained by cooling in the furnace.

[0019] Preferably, the preparation of the Li3Mg2NbO6 pre-calcined material includes: mixing Li2CO3, MgO and Nb2O5 according to the stoichiometric ratio of Li3Mg2NbO6; adding anhydrous ethanol and ball milling at 250~300 rpm for 4~6 h; drying and sieving; pre-calcining at 3~5℃ / min to 950~1050℃ and holding for 2~4 h; and cooling with the furnace to obtain the Li3Mg2NbO6 pre-calcined material.

[0020] Preferably, the glue removal process in step 3 is a segmented glue removal process: heating to 200℃ and holding for 1~3 hours, then heating to 450~600℃ and holding for 2~6 hours.

[0021] This invention is the first to achieve synchronous control of the sintering temperature and resonant frequency temperature coefficient of Li3Mg2NbO6 ceramics without introducing additional flux, by fully utilizing the low-temperature sintering characteristics and positive temperature frequency coefficient characteristics of BaV2O6, while maintaining a high quality factor.

[0022] BaV2O6 is a microwave dielectric ceramic material with a low sintering temperature and a positive temperature coefficient of resonant frequency (sintering temperature 550 ℃, holding time 1 h; τ f = +28.2 ppm / ℃), its sintering temperature is significantly lower than that of Li3Mg2NbO6 ceramics, and its dielectric constant is moderate (ε r =11.2), and low dielectric loss (Q×f = 42790 GHz). Therefore, this invention uses BaV2O6 as a composite phase to form a two-phase composite with Li3Mg2NbO6, in order to achieve low-temperature sintering without introducing additional flux and to address the negative τ of Li3Mg2NbO6. f Compensation and regulation are implemented. However, the quality factor of BaV2O6 single-phase ceramics is relatively low and τ f The vanadium content is relatively high, making it difficult to use alone as a high-performance microwave dielectric ceramic material. Furthermore, BaV₂O₆, as a vanadium-containing phase, has a low melting / softening temperature range. During heat treatment processes such as pre-sintering or subsequent composite sintering, the vanadium component is more prone to volatilization loss (e.g., loss in the form of volatile species such as V₂O₅) in isotherms near or above 700℃ and 800~900℃. This may lead to an increase in point defects or grain boundary defects in the BaV₂O₆ phase, resulting in increased dielectric loss, decreased quality factor, and potential performance fluctuations between sample batches. Without effective compensation and control of vanadium volatilization, it is difficult to achieve low-temperature sintering and temperature coefficient control while further stabilizing and improving the Q×f value of the composite system and obtaining repeatable excellent microwave dielectric properties.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] (1) Introducing a low-temperature densifiable and τ-sensitive material into the Li3Mg2NbO6 material system. f The presence of a positive BaV2O6 phase allows the composite system to achieve low-temperature sintering densification at 825–875℃;

[0025] (2) The positive τ of BaV2O6 f The negative τ of Li3Mg2NbO6 f It has a compensating effect, making the composite ceramic τ f It can be adjusted to a near-zero range, improving temperature stability;

[0026] (3) It can maintain a high Q×f without introducing other fluxes, avoiding performance degradation caused by glass phase or high dielectric loss conditioning phase;

[0027] (4) XRD results show that no new phase was generated after recombination, the system is stable, which is beneficial to obtaining repeatable microwave dielectric properties.

[0028] (5) By adopting a volatilization compensation strategy based on the non-stoichiometry of vanadium source, the local non-stoichiometry and defect increase caused by vanadium volatilization can be reduced, thereby reducing dielectric loss, further improving and stabilizing the Q×f of the composite system, and improving the consistency of sample batches. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the preparation process of the present invention; Figure 2 The XRD pattern of the non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic is shown in the example.

[0030] The specific implementation methods are described in further detail below with reference to the accompanying drawings.

[0031] A method for preparing a non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic, such as... Figure 1 As shown, the specific steps are as follows:

[0032] Step 1: Pre-calcined materials of Li3Mg2NbO6 phase and BaV2O6 phase were prepared separately.

[0033] Preparation of Li3Mg2NbO6 pre-calcined material: Analytical grade Li2CO3, MgO, and Nb2O5 were mixed according to the stoichiometric ratio of Li3Mg2NbO6, and anhydrous ethanol and ball milling media were added for ball milling (250~300 rpm, 4~6 h). The mixture was then dried (100~120℃) and sieved (80~120 mesh). The powder was placed in an alumina crucible and heated to 950~1050℃ at a rate of 3~5℃ / min, held for 2~4 h, and then cooled in the furnace to obtain Li3Mg2NbO6 pre-calcined material.

[0034] Preparation of BaV2O6 pre-calcined material: Analytical pure BaCO3 and V2O5 were mixed according to BaV2O6... (2+δ) The O6 is prepared in a non-stoichiometric ratio, where 0.04≤δ≤0.1, with the optimal δ being 0.08. After ball milling, mixing, drying, and sieving, the powder is placed in an alumina crucible and heated to 450~550℃ at 3~5℃ / min and held for 1~2 h. The powder is then cooled in the furnace to obtain BaV2O6 pre-calcined material.

[0035] Step 2: Li3Mg2NbO6-BaV2O6 composite and secondary ball milling.

[0036] The two-phase pre-calcined materials of Li3Mg2NbO6 and BaV2O6 were weighed and mixed at a mass ratio of (100-x)%Li3Mg2NbO6 + x%BaV2O6, with 25≤x≤40. Anhydrous ethanol and ball milling media were added and the mixture was ball-milled for 6~12 h. The mixture was then dried and sieved.

[0037] Step 3, Granulation, Molding and Debinding: Add PVA aqueous solution (5~10wt%) as binder to the composite powder obtained in Step 2, grind evenly and granulate, and then perform uniaxial dry pressing. Debind the green body according to the following procedure: heat to 200℃ and hold for 1~3 h, then heat to 450~600℃ and hold for 2~6 h.

[0038] Low-temperature sintering: After debinding, the temperature is raised to 825~875℃ and held for 2~4 h (preferably 3 h) for sintering, and then cooled to room temperature with the furnace to obtain non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic; no additional flux is added during the entire process.

[0039] Figure 2 The XRD pattern of the Li3Mg2NbO6-BaV2O6 two-phase composite after sintering shows that only the diffraction peaks of Li3Mg2NbO6 and BaV2O6 are present, and no new phase is detected, indicating that no chemical reaction occurs between the two phases to form a new phase during the composite sintering process.

[0040] Table 1 shows the dielectric properties of the (100-x)% Li3Mg2NbO6 + x% BaV2O6 composite ceramic sample without the vanadium volatilization compensation strategy at different x values ​​and sintering temperatures.

[0041] Table 1:

[0042] x value Sintering temperature (°C) <![CDATA[Dielectric constant (ɛ r ).]]> Quality factor Q×f (GHz) <![CDATA[Temperature coefficient of resonant frequency τ f (ppm / °C)]]> 25 825 12.7 19230 -18 25 850 12.8 24330 -16 25 875 13.1 27760 -16 30 825 12.2 33130 -4 30 850 12.6 49180 -6 30 875 12.9 38560 -6 35 825 11.7 26190 -1 35 850 11.9 31590 -4 35 875 12.0 27040 -2 40 825 11.2 17550 3 40 850 11.6 19710 5 40 875 11.7 11520 5

[0043] To verify the effect of the vanadium volatilization compensation strategy adopted in this invention on dielectric properties, composite ceramics were prepared under the optimal process conditions in Table 1 (70 wt% Li3Mg2NbO6 + 30 wt% BaV2O6, held at 850℃ for 2-4 h); the difference being that the BaV2O6 phase pre-sintered material used was BaV (2+δ) O6 was added in a non-stoichiometric ratio (0.04 ≤ δ ≤ 0.1), and vanadium volatilization was compensated by adjusting the δ value. The ε values ​​of samples under different δ compensation conditions were analyzed. r Q×f and τ f The tests were compared, with the uncompensated baseline sample with δ=0 used as a control. The results are shown in Table 2.

[0044] Table 2:

[0045] δ value <![CDATA[Dielectric constant (ɛ r ).]]> Quality factor Q×f (GHz) <![CDATA[Temperature coefficient of resonance frequency τ f (ppm / °C)]]> 0 12.6 49180 -6 0.04 12.7 52230 -7 0.06 12.7 52970 -7 0.08 12.7 59680 -6 0.1 12.8 56020 -7

[0046] Note: δ=0 represents the baseline sample data (ε) for x=30 and 850℃ in Table 1. r =12.6, Q×f=49180 GHz, τ f =-6ppm / ℃).

[0047] As shown in Table 1, without employing a vanadium volatilization compensation strategy, the Li3Mg2NbO6-BaV2O6 composite system can achieve good dielectric property control within a low-temperature sintering range of 825–875 °C. Using Li3Mg2NbO6 as the main phase, supplemented with low-temperature sinterable BaV2O6 with a positive temperature coefficient, in a weight ratio of (100–x)%Li3Mg2NbO6 + x%BaV2O6 (25 ≤ x ≤ 40), the dielectric constant of the material can be maintained within a moderate range of 11.2–13.1, the quality factor Q×f reaches 11520–49180 GHz, and the temperature coefficient of the resonant frequency τ... f The ppm / ℃ can be continuously adjusted from -18 ppm / ℃ to +5 ppm / ℃. The optimal overall performance (ε) is achieved when x = 30 and the sintering temperature is 850℃. r ≈12.6, Q×f≈49180 GHz, τ f (≈-6ppm / ℃), indicating that without adding any other flux, the present invention can simultaneously achieve low-temperature sintering densification of Li3Mg2NbO6-based ceramics and effective compensation and control of the temperature frequency coefficient, while maintaining a high quality factor, thereby solving the problem of excessively high sintering temperature and τ in the Li3Mg2NbO6 system. f A technical problem with a negative bias.

[0048] As shown in Table 2, the results of the preferred embodiments indicate that using BaV... (2+δ) Following the vanadium volatilization compensation strategy with O6, the quality factor Q×f of the composite ceramic was further improved. Compared to the baseline sample with δ = 0 (Q×f = 49180 GHz), Q×f increased to 59680 GHz when δ = 0.08, an improvement of approximately 20%, and τ f The vanadium content remains within the near-zero range of -7 to -6 ppm / ℃, indicating that vanadium overcompensation can effectively reduce losses caused by volatilization and improve the quality factor. Meanwhile, when δ further increases to 0.1, Q×f decreases slightly to 56020 GHz, indicating that there is an optimal range for vanadium overcompensation. Excessive vanadium overcompensation may lead to increased local nonstoichiometry deviations in the BaV2O6 phase, an increase in point defects or grain boundary defects, or the formation of trace amounts of a second phase (such as a vanadium-rich phase), thereby increasing dielectric loss and decreasing the quality factor.

[0049] In summary, the present invention has a simple process and controllable cost, and has the prospect and value for application and promotion in LTCC microwave devices and related fields.

Claims

1. A non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic, characterized in that: It includes Li3Mg2NbO6 phase and BaV2O6 phase, which are (100-x)%Li3Mg2NbO6+x%BaV2O6 by weight percentage, where 25≤x≤40; The Li3Mg2NbO6 and BaV2O6 phases were separately pre-calcined, then mixed by a solid-state method and composite sintered at 825–875 °C to obtain Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramics. No additional flux or sintering aids were added during the preparation process. The dielectric constant ε of the Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramics is... r The resonant frequency temperature coefficient is τ = 11.2–13.1, the quality factor Q×f is 11520–59680 GHz, and the temperature coefficient τ of the resonant frequency is τ = 11.2–13.

1. f The concentration ranges from -18 to +5 ppm / ℃. The BaV2O6 phase adopts a vanadium volatilization compensation strategy, according to BaV... (2+δ) O6 was prepared by non-stoichiometric proportioning of ingredients, wherein 0.04≤δ≤0.

1.

2. The non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in claim 1, characterized in that: The x=30 and the sintering temperature is 850℃.

3. The non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in claim 1, characterized in that: The value is δ=0.

08.

4. The preparation method of the non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in any one of claims 1-3, characterized in that: Step 1: Pre-calcined materials of Li3Mg2NbO6 phase and BaV2O6 phase were prepared separately. Preparation of Li3Mg2NbO6 pre-calcined material: The component raw materials are weighed according to the Li3Mg2NbO6 metric ratio, ball-milled, dried, and sieved, and then pre-calcined at 950~1050℃ for 2~4 h; Preparation of BaV2O6 pre-calcined material: The component raw materials are prepared using BaV2O6 with excess vanadium source. (2+δ) O6 non-stoichiometric ingredients are ball-milled, dried, and sieved, and then pre-calcined at 450~550℃ for 1~2 hours. Step 2: Mix the two-phase pre-calcined material prepared in Step 1 with (100-x)%Li3Mg2NbO6 + x%BaV2O6 at a mass fraction of x=25~40 wt%, and then ball mill, dry, granulate and shape it in sequence. Step 3: After debinding, sinter at a low temperature of 825~875℃ to obtain Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic.

5. The preparation method of the non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in claim 4, characterized in that: The sintering temperature in step 3 is 850℃.

6. The preparation method of the non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in claim 4, characterized in that: The preparation of the BaV2O6 pre-calcined material includes: mixing BaCO3 and V2O5 with an excess of vanadium source δ. (2+δ) O6 was prepared in a non-stoichiometric ratio, and anhydrous ethanol was added and ball-milled at 250-300 rpm for 4-6 h. After drying and sieving, the mixture was pre-calcined at 450-550℃ with a temperature increase of 3-5℃ / min, and held at that temperature for 1-2 h. The pre-calcined BaV2O6 material was then obtained by cooling in the furnace.

7. The preparation method of the non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in claim 4, characterized in that: The preparation of the Li3Mg2NbO6 pre-calcined material includes: mixing Li2CO3, MgO and Nb2O5 according to the stoichiometric ratio of Li3Mg2NbO6; adding anhydrous ethanol and ball milling at 250~300 rpm for 4~6 h; drying and sieving; pre-calcining at 3~5℃ / min to 950~1050℃ and holding for 2~4 h; and cooling with the furnace to obtain the Li3Mg2NbO6 pre-calcined material.

8. The preparation method of the non-stoichiometric Li3Mg2NbO6-BaV2O6 composite LTCC dielectric ceramic as described in claim 4, characterized in that: The glue removal process in step 3 is a segmented glue removal process: heat up to 200℃ and keep it at that temperature for 1~3 hours, then heat up to 450~600℃ and keep it at that temperature for 2~6 hours.

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