Low dielectric loss and low temperature coefficient microwave dielectric ceramic and preparation method thereof

Abstract

The present application relates to a kind of low dielectric loss and low temperature coefficient microwave dielectric ceramic and its preparation method, the preparation method includes the following steps: after mixing zinc lanthanum titanate, strontium source and auxiliary raw material, sequentially forming and sintering, the low dielectric loss and low temperature coefficient microwave dielectric ceramic is prepared;The auxiliary raw material includes any one or combination of at least two of calcium carbonate, manganese dioxide or barium carbonate.The present application selects zinc lanthanum titanate and strontium titanate with good microwave dielectric properties as basic raw material to ensure the basic performance of ceramic;Introduce appropriate amount of calcium carbonate, manganese dioxide and barium carbonate, effectively reduce the dielectric loss of ceramic, and improve its temperature characteristics;The present application reduces production cost and technical difficulty by solid phase reaction method, while ensuring the uniformity and stability of ceramic, effectively reduces the dielectric loss of microwave dielectric ceramic, and improves its temperature characteristics, further improves the performance of ceramic.

Description

Technical Field

[0001] This invention relates to the field of microwave dielectric ceramics technology, and in particular to a microwave dielectric ceramic with low dielectric loss and low temperature coefficient and its preparation method. Background Technology

[0002] Microwave dielectric ceramics are important electronic materials widely used in mobile communications, satellite communications, and global positioning systems. Their main properties include low dielectric constant, low dielectric loss, high Q value, and near-zero temperature coefficient. However, traditional microwave dielectric ceramics often suffer from problems such as high dielectric loss and a large temperature coefficient, which severely affect their performance at high frequencies. Therefore, reducing the dielectric loss and improving the temperature characteristics of microwave dielectric ceramics is one of the important research directions in the field.

[0003] Existing solutions primarily aim to reduce dielectric loss and improve temperature characteristics by altering the composition and structure of the ceramic. For example, the microstructure of the ceramic can be changed by adding certain dopants, or the density and uniformity of the ceramic can be improved by adjusting the sintering process. Furthermore, some research attempts to improve the performance of microwave dielectric ceramics by introducing new ceramic systems.

[0004] CN108129146A discloses a method for preparing strontium titanate (SrTiO3) ceramics with high dielectric constant and low dielectric loss. The main technical solution is as follows: First, using SrCO3, TiO2, and Nb2O5 as raw materials, according to the chemical formula SrTi (1-1.25x) Nb x O3 is used to prepare the raw materials, which are then mixed by wet ball milling and dried to obtain a dry powder. The dry powder is placed in an electric furnace and calcined at a certain temperature for an appropriate time. After removal, it is further wet-milled, dried, and sieved to obtain fine strontium titanate ceramic powder. The powder is then dry-pressed into shape and sintered in a high-temperature electric furnace at 1420℃-1480℃ for 2 hours to obtain the desired strontium titanate ceramic. The strontium titanate ceramic obtained by this invention has excellent dielectric properties, with a dielectric constant maintained at 296-303, comparable to ordinary strontium titanate ceramics, while the Q×f value reaches nearly 7000 GHz, far exceeding that of ordinary strontium titanate ceramics. This invention has a simple process, is easy to scale up for production, and has high practical value.

[0005] CN107827453A discloses a method for preparing low dielectric loss strontium titanate ceramics. The preparation process is as follows: using high-purity (99.9%) SrTiO3 powder as raw material, and one or more of CaO, MgO, Al2O3, ZrO2, and Nb2O5 as additives, the mixture is wet-milled and mixed with the SrTiO3 powder, followed by pressureless sintering to prepare strontium titanate ceramics. Statistical analysis of numerous data shows that SrTiO3 ceramic samples doped with a certain amount of additives exhibit low dielectric loss and significantly improved dielectric properties. Typically, when 2wt% Nb2O5 is added, its Q×f value can reach 6281 GHz, approximately 5.5 times that of pure SrTiO3 (1145 GHz) ceramic samples. Furthermore, the preparation process of this invention is simple, highly controllable, and has good prospects for industrialization.

[0006] While existing technologies have improved the performance of microwave dielectric ceramics to some extent, several problems and limitations remain. First, current solutions often require complex fabrication processes and precise control, increasing production costs and technical difficulty. Second, existing ceramic systems often only achieve performance optimization within specific frequency ranges, limiting their use in a wider range of applications. Finally, while reducing dielectric loss and improving temperature characteristics, existing ceramic systems may sacrifice other ceramic properties, such as mechanical strength and chemical stability, which will affect the long-term reliability and stability of ceramic devices. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a microwave dielectric ceramic with low dielectric loss and low temperature coefficient, and its preparation method. This achieves effective reduction of dielectric loss and improvement of temperature characteristics of the microwave dielectric ceramic without sacrificing other ceramic properties such as mechanical strength and chemical stability. It also optimizes the performance of the microwave dielectric ceramic over a wider frequency range. Furthermore, it simplifies the preparation process of the microwave dielectric ceramic, reducing production costs and technical difficulty.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing microwave dielectric ceramics with low dielectric loss and low temperature coefficient. The preparation method includes the following steps: mixing lanthanum zinc titanate, strontium source and auxiliary raw materials, and then sequentially molding and sintering to prepare the microwave dielectric ceramics with low dielectric loss and low temperature coefficient. The auxiliary raw materials include any one or a combination of at least two of calcium carbonate, manganese dioxide or barium carbonate. Typical but non-limiting combinations include a combination of calcium carbonate and manganese dioxide, a combination of calcium carbonate and barium carbonate, or a combination of calcium carbonate, manganese dioxide and barium carbonate.

[0010] This invention selects lanthanum zinc titanate and strontium sources, which possess excellent microwave dielectric properties, as basic raw materials to ensure the fundamental properties of the ceramic. Simultaneously, the introduction of appropriate auxiliary materials as additives can effectively reduce the dielectric loss of the ceramic and improve its temperature characteristics. The solid-state reaction method for preparing microwave dielectric ceramics avoids the complex sintering process, thus greatly simplifying the preparation process and reducing production costs and technical difficulties. Furthermore, the solid-state reaction method can also ensure the uniformity and stability of the ceramic, further improving its performance.

[0011] Preferably, the mixing method includes mixing using a ball mill.

[0012] Preferably, the mixing time is 20h-28h, for example, it can be 20h, 22h, 24h, 26h or 28h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] Preferably, the molar ratio of the zinc lanthanum titanate to the strontium source is a:(1-a), where a is 0.45-0.65, for example, 0.45, 0.5, 0.55, 0.6 or 0.65, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, the strontium source includes strontium titanate.

[0015] Strontium titanate has low dielectric loss and excellent dielectric temperature stability, which can neutralize the high dielectric constant and high loss of lanthanum zinc titanate. When the strontium titanate content is low, the dielectric constant is high, and the dielectric loss and temperature coefficient will also increase; when the strontium titanate content is high, the dielectric constant decreases, the dielectric loss and temperature coefficient will decrease.

[0016] Preferably, the auxiliary raw material is a combination of calcium carbonate, manganese dioxide and barium carbonate.

[0017] Preferably, the amount of calcium carbonate used is 0.03wt%-0.2wt% of the total mass of zinc titanate, lanthanum titanate, strontium source and auxiliary raw materials, for example, it can be 0.03wt%, 0.05wt%, 0.07wt%, 0.08wt%, 0.1wt%, 0.13wt%, 0.15wt%, 0.17wt%, 0.19wt% or 0.2wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0018] Preferably, the amount of manganese dioxide used is 0.01wt%-0.04wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, for example, it can be 0.01wt%, 0.02wt%, 0.03wt% or 0.04wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the amount of barium carbonate used is 0.1wt%-0.3wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, for example, it can be 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt% or 0.3wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0020] By adjusting the proportions of lanthanum zinc titanate, strontium titanate, calcium carbonate, manganese dioxide, and barium carbonate, the dielectric loss of microwave dielectric ceramics can be effectively reduced, the Q×F value increased, and the temperature characteristics improved without sacrificing other ceramic properties such as mechanical strength and chemical stability. Furthermore, this optimized formulation can achieve performance optimization of microwave dielectric ceramics over a wider frequency range.

[0021] Preferably, the mixture is stirred before molding for 4-6 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the stirring involves adding a PVA solution, a dispersant, and an antifoaming agent.

[0023] Preferably, the mass concentration of the PVA solution is 7%-10%, for example, it can be 7%, 8%, 9% or 10%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the amount of PVA solution added is 15wt%-30wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, for example, it can be 15wt%, 20wt%, 25wt% or 30wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0025] Preferably, the dispersant comprises ammonia or ammonium citrate.

[0026] Preferably, the amount of dispersant added is 0.01wt%-0.03wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, for example, it can be 0.01wt%, 0.02wt% or 0.03wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0027] Preferably, the defoamer comprises zinc alcohol.

[0028] Preferably, the amount of defoamer added is 0.005wt%-0.02wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, for example, it can be 0.005wt%, 0.01wt%, 0.015wt% or 0.02wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0029] Preferably, the molding process includes sequential spray granulation and tableting.

[0030] Preferably, the water content of the spray granulation is 0.2%-0.5%, for example, it can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the particle size distribution of the spray granulation is 75%-90% of 160-200 mesh, for example, it can be 75%, 80%, 85% or 90%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the molding density of the tablet is 3.5 g / cm³. 3 -3.7g / cm 3 For example, it could be 3.5g / cm³ 3 3.6g / cm 3 Or 3.7g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0033] Molding density affects the performance of microwave dielectric ceramics. When the molding density is low, the distance between the powders is large. During sintering, the grain growth will fill the gaps between the powders, resulting in more pores, lower sintering density, and poor material performance. When the molding density is high, the blank is prone to cracking, and the mold is also prone to damage.

[0034] Preferably, the forming equipment includes a 20T press.

[0035] Preferably, the sintering is carried out in an air atmosphere.

[0036] Preferably, the sintering includes a first sintering and a second sintering performed sequentially.

[0037] Preferably, the heating rate of the first sintering is 1℃ / min-2℃ / min, for example, it can be 1℃ / min, 1.5℃ / min or 2℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the holding temperature for the first sintering is 500℃-700℃, for example, it can be 500℃, 550℃, 600℃, 650℃ or 700℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] This invention removes organic matter from the ceramic blank by adjusting the holding temperature during the first sintering, thereby preventing the dielectric ceramic from cracking due to binder removal during subsequent sintering.

[0040] Preferably, the holding time for the first sintering is 2h-6h, for example, it can be 2h, 3h, 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the heating rate of the secondary sintering is 2℃ / min-3℃ / min, for example, it can be 2℃ / min, 2.5℃ / min or 3℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the holding temperature for the secondary sintering is 1300℃-1350℃, for example, it can be 1300℃, 1310℃, 1320℃, 1330℃, 1340℃ or 1350℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] The secondary sintering temperature has a significant impact on the properties of microwave dielectric ceramics. When the secondary sintering temperature is too low, it is not conducive to grain growth, resulting in increased porosity and deteriorated performance. When the secondary sintering temperature is too high, it can lead to side reactions and the formation of impurity phases, which also deteriorates the material properties.

[0044] Preferably, the holding time for the secondary sintering is 4h-8h, for example, it can be 4h, 5h, 6h, 7h or 8h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the sintering process is followed by cooling.

[0046] Preferably, the cooling includes reducing the temperature from the holding temperature of the secondary sintering to 550°C-600°C, for example, 550°C, 570°C, 590°C or 600°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Preferably, the cooling rate is 1℃ / min-2.5℃ / min, for example, it can be 1℃ / min, 1.5℃ / min, 2℃ / min or 2.5℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] Preferably, the method for preparing the zinc lanthanum titanate includes the following steps:

[0049] Lanthanum source, zinc source and titanium source are ball-milled and mixed, dried and pre-calcined to obtain the zinc lanthanum titanate.

[0050] Preferably, the lanthanum source includes lanthanum oxide.

[0051] Preferably, the lanthanum source is calcined before mixing.

[0052] Preferably, the calcination holding temperature is 900℃-1100℃, for example, it can be 900℃, 950℃, 1000℃, 1050℃ or 1200℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] Preferably, the calcination holding time is 1h-3h, for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] Preferably, the zinc source includes zinc oxide.

[0055] Preferably, the titanium source includes titanium dioxide.

[0056] Preferably, the ball milling and mixing time is 16h-28h, for example, it can be 16h, 18h, 20h, 22h, 24h, 26h or 28h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] Preferably, the drying and pre-firing process includes drying and pre-firing performed sequentially.

[0058] Preferably, the drying temperature is 120℃-180℃, for example, it can be 120℃, 140℃, 150℃, 160℃, 170℃ or 180℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, the drying and heat preservation time is 12h-20h, for example, it can be 12h, 14h, 16h, 18h or 20h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0060] Preferably, the preheating rate is 1℃ / min-3℃ / min, for example, it can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min or 3℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] Preferably, the preheating temperature is 1150℃-1250℃, for example, it can be 1150℃, 1170℃, 1190℃, 1200℃, 1210℃, 1230℃ or 1250℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0062] The pre-firing temperature has a significant impact on the performance of microwave dielectric ceramics. When the pre-firing temperature is high, the hardness of the powder is high, resulting in a larger particle size of the second-milled powder, which leads to an increase in the dielectric loss of the material and a decrease in the Q×F value. When the pre-firing temperature is low, the lanthanum zinc titanate phase cannot be completely formed, and there will be side reactions during the subsequent composite sintering with strontium titanate, which will affect the performance of microwave dielectric ceramics.

[0063] Preferably, the preheating time is 2h-6h, for example, it can be 2h, 3h, 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0065] (1) The lanthanum source, zinc source and titanium source are ball-milled and mixed, dried at 200℃-250℃ for 12h-20h, and then pre-calcined at 1150℃-1250℃ for 2h-6h to obtain lanthanum zinc titanate.

[0066] (2) The zinc lanthanum titanate, strontium source and auxiliary raw materials are mixed and spray granulation and pressing are performed in sequence. After primary sintering and secondary sintering in air atmosphere, the microwave dielectric ceramic with low dielectric loss and low temperature coefficient is obtained by cooling.

[0067] In a second aspect, the present invention provides a microwave dielectric ceramic with low dielectric loss and low temperature coefficient, wherein the microwave dielectric ceramic is prepared according to the preparation method described in the first aspect.

[0068] Preferably, the dielectric loss tanδ of the low dielectric loss and low temperature coefficient microwave dielectric ceramic is less than 10.2, for example, it can be 2.9, 3, 5, 7, 9 or 10.2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] Preferably, the temperature coefficient of the low dielectric loss and low temperature coefficient microwave dielectric ceramic is less than 12.5 between -40℃ and 125℃. For example, it can be 4, 6, 8, 10, 12 or 12.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] Compared with the prior art, the present invention has at least the following beneficial effects:

[0071] (1) In this invention, zinc lanthanum titanate and strontium source with good microwave dielectric properties are selected as basic raw materials to ensure the basic properties of ceramics; at the same time, an appropriate amount of auxiliary raw materials are introduced as additives, which can effectively reduce the dielectric loss of ceramics and improve their temperature characteristics.

[0072] (2) By adjusting the proportions of zinc lanthanum titanate, strontium source and auxiliary raw materials, this invention can effectively reduce the dielectric loss of microwave dielectric ceramics and improve their temperature characteristics without sacrificing other properties of ceramics such as mechanical strength and chemical stability. At the same time, this optimized formula can also achieve performance optimization of microwave dielectric ceramics in a wider frequency range.

[0073] (3) The present invention uses a simple solid-state reaction method to prepare microwave dielectric ceramics, avoiding the complex sintering process, thereby greatly simplifying the preparation process of microwave dielectric ceramics and reducing production costs and technical difficulties; in addition, the solid-state reaction method can ensure the uniformity and stability of ceramics, further improving the performance of ceramics.

[0074] (4) Through the above-mentioned technical means, the present invention can effectively solve the problems of high dielectric loss and poor temperature characteristics of microwave dielectric ceramics, and at the same time simplify the ceramic preparation process, reduce production costs and technical difficulties. Detailed Implementation

[0075] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0076] In the following examples, the purity of lanthanum oxide is 99.7 wt%, the purity of zinc oxide is 99.7 wt%, the purity of titanium dioxide is 99.7 wt%, the purity of calcium carbonate is 99.5 wt%, the purity of manganese dioxide is 99.5 wt%, and the purity of barium carbonate is 99 wt%.

[0077] Example 1

[0078] This embodiment provides a method for preparing microwave dielectric ceramics with low dielectric loss and low temperature coefficient, the preparation method comprising the following steps:

[0079] (a) According to La(Zn) 0.5 Ti 0.5 3. Weigh out lanthanum oxide, zinc oxide, and titanium dioxide according to the molecular formula. Lanthanum oxide needs to be calcined at 1000℃ for 2 hours before mixing. Add the lanthanum oxide to a ball mill and mix thoroughly. The mixture should be prepared as follows: raw materials: deionized water: zirconium oxide balls. The material was fed at a weight ratio of 1:1, rotated at 60 r / min, and ball-milled for 24 h. Then, 30 ml of dispersant ammonium citrate was added to obtain the ball-milled material.

[0080] (b) The ball milling material prepared in step (a) is placed in an oven to dry at a temperature of 150°C for 16 hours. After drying, the powder is passed through a 60-mesh sieve, loaded into an alumina crucible, and placed in an air sintering furnace for pre-firing. The temperature is increased to a maximum of 1200°C at a rate of 2°C / min and held for 4 hours to obtain lanthanum zinc titanate.

[0081] (c) The zinc lanthanum titanate and strontium titanate described in step (b) are mixed in a ratio of 0.57La(Zn) 0.5 Ti 0.5 Zinc lanthanum titanate and strontium titanate were weighed out according to the ratio of 3+0.43SrTiO3, and auxiliary materials were added to the ball mill for ball milling and mixing. The amount of CaCO3 was 0.08wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials, the amount of MnO2 was 0.02wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials, and the amount of BaCO3 was 0.2wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials. The materials were added according to the weight ratio of raw materials:deionized water:zirconia balls = 2:2:5, the mixing time was 24h, and the mixing speed was 60r / min to obtain the mixture.

[0082] (d) The mixture described in step (c) is loaded into a mixing tank, and an 8% PVA solution is added. The amount added is 20 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. The amount of dispersant ammonium citrate added is 0.03 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. The amount of defoamer zinc alcohol added is 0.02 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. After stirring for 5 hours, spray granulation is performed. The water content of the spray granules is 0.3%, and the particle size distribution of the spray granules is 80% of 160-200 mesh, to obtain spherical particles.

[0083] (e) The spherical particles described in step (d) are pressed into Z14×7 discs using a 20T press, with a molding density of 3.6 g / cm³. 3 The discs were placed in high-temperature air for sintering. The sintering process was as follows: the first sintering was to heat the discs from room temperature to 700°C at a rate of 1.5°C / min and hold them at that temperature for 4 hours; the second sintering was to heat the discs to the maximum sintering temperature of 1340°C at a rate of 2.5°C / min and hold them at that temperature for 5 hours; then the discs were cooled to 600°C at a rate of 2°C / min and cooled in the furnace to obtain the microwave dielectric ceramic with low dielectric loss and low temperature coefficient.

[0084] Example 2

[0085] This embodiment provides a method for preparing microwave dielectric ceramics with low dielectric loss and low temperature coefficient, the preparation method comprising the following steps:

[0086] (a) According to La(Zn) 0.5Ti 0.5 3. Weigh out lanthanum oxide, zinc oxide, and titanium dioxide according to the molecular formula. Lanthanum oxide needs to be calcined at 1100℃ for 1 hour before mixing. Add these to a ball mill and mix thoroughly. The mixture should be prepared as follows: raw materials: deionized water: zirconium oxide balls. The material was fed at a weight ratio of 1:1, the rotation speed was 60 r / min, and the ball milling time was 16 h. Then, 30 ml of dispersant ammonium citrate was added to obtain the ball milling material.

[0087] (b) The ball milling material prepared in step (a) was placed in an oven and dried at 180°C for 12 hours. After drying, the powder was passed through a 60-mesh sieve, and the material was placed in an air sintering furnace for pre-firing. The temperature was increased to a maximum of 1250°C at a rate of 3°C / min and held for 2 hours to obtain lanthanum zinc titanate.

[0088] (c) Mix the zinc lanthanum titanate and strontium titanate described in step (b) at a ratio of 0.65La(Zn) 0.5 Ti 0.5 Zinc lanthanum titanate and strontium titanate were weighed out according to the ratio of 3+0.35SrTiO3, and auxiliary materials were added to the ball mill for ball milling and mixing. The amount of CaCO3 was 0.2wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials, the amount of MnO2 was 0.04wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials, and the amount of BaCO3 was 0.3wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials. The materials were added according to the weight ratio of raw materials:deionized water:zirconia balls = 2:2:5, the mixing time was 28h, and the mixing speed was 60r / min to obtain the mixture.

[0089] (d) The mixture described in step (c) is loaded into a mixing tank, and a 7% PVA solution is added. The amount added is 30 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. The amount added as dispersant ammonium citrate is 0.01 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. The amount added as defoamer zinc alcohol is 0.005 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. After stirring for 6 hours, spray granulation is performed. The water content of the spray granules is 0.5%, and the particle size distribution of the spray granules is 90% of 160-200 mesh, to obtain spherical particles.

[0090] (e) The spherical particles described in step (d) are pressed into Z14×7 discs using a 20T press, with a molding density of 3.7 g / cm³. 3 The discs were placed in high-temperature air for sintering. The first sintering was carried out by heating from room temperature to 600°C at a rate of 2°C / min and holding for 2 hours. The second sintering was carried out by heating to the maximum sintering temperature of 1350°C at a rate of 3°C / min and holding at the maximum sintering temperature of 1350°C for 4 hours. Then, the temperature was cooled to 550°C at a rate of 2.5°C / min and cooled with the furnace to obtain the microwave dielectric ceramic with low dielectric loss and low temperature coefficient.

[0091] Example 3

[0092] This embodiment provides a method for preparing microwave dielectric ceramics with low dielectric loss and low temperature coefficient, the preparation method comprising the following steps:

[0093] (a) According to La(Zn) 0.5 Ti 0.5 3. Weigh out lanthanum oxide, zinc oxide, and titanium dioxide according to the molecular formula. Lanthanum oxide needs to be calcined at 900℃ for 3 hours before mixing. Add these to a ball mill and mix thoroughly. The mixture should be prepared as follows: raw materials: deionized water: zirconium oxide balls. The material was fed at a weight ratio of 1:1, rotated at 60 r / min, and ball-milled for 28 h. Then, 30 ml of dispersant ammonium citrate was added to obtain the ball-milled material.

[0094] (b) The ball milling material prepared in step (a) was placed in an oven and dried at 120°C for 20 hours. After drying, the powder was passed through a 60-mesh sieve, and the material was placed in an air sintering furnace for pre-firing. The temperature was increased to a maximum of 1150°C at a rate of 1°C / min and held for 6 hours to obtain lanthanum zinc titanate.

[0095] (c) The zinc lanthanum titanate and strontium titanate described in step (b) are mixed in a ratio of 0.45La(Zn) 0.5 Ti 0.5 Zinc lanthanum titanate and strontium titanate were weighed out according to the ratio of 3+0.55SrTiO3, and auxiliary materials were added to the ball mill for ball milling and mixing. The amount of CaCO3 was 0.03wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials, the amount of MnO2 was 0.01wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials, and the amount of BaCO3 was 0.1wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary materials. The materials were added according to the weight ratio of raw materials:deionized water:zirconia balls = 2:2:5, the mixing time was 20h, and the mixing speed was 60r / min to obtain the mixture.

[0096] (d) The mixture described in step (c) is loaded into a mixing tank, and a 10% PVA solution is added. The amount added is 15 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. The amount of dispersant ammonium citrate added is 0.03 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. The amount of defoamer zinc alcohol added is 0.02 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials. After stirring for 4 hours, spray granulation is performed. The water content of the spray granules is 0.2%, and the particle size distribution of the spray granules is 75% of 160-200 mesh, to obtain spherical particles.

[0097] (e) The spherical particles described in step (d) are pressed into Z14×7 discs using a 20T press, with a molding density of 3.5 g / cm³.3 The discs were placed in high-temperature air for sintering. The first sintering was performed by heating from room temperature to 500°C at a rate of 1°C / min and holding for 6 hours. The second sintering was performed by heating to the maximum sintering temperature of 1300°C at a rate of 2°C / min and holding at the maximum sintering temperature of 1300°C for 8 hours. Then, the temperature was reduced to 600°C at a rate of 1°C / min and cooled in the furnace to obtain the microwave dielectric ceramic with low dielectric loss and low temperature coefficient.

[0098] Example 4

[0099] The only difference between this embodiment and Embodiment 1 is that, except for step (c), which is based on 0.66La(Zn) 0.5 Ti 0.5 Except for the ratio of 0.34SrTiO3, the rest of the ratio is the same as in Example 1.

[0100] Example 5

[0101] The only difference between this embodiment and Embodiment 1 is that, except for step (c), which is based on 0.43La(Zn) 0.5 Ti 0.5 Except for the ratio of 0.57SrTiO3, the rest of the ratio is the same as in Example 1.

[0102] Example 6

[0103] The only difference between this embodiment and Example 1 is that, except that in step (c), the amount of MnO2 used is 0.05 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, everything else is the same as in Example 1.

[0104] Example 7

[0105] The only difference between this embodiment and Example 1 is that, except that MnO2 is not added in step (c) and the amount of CaCO3 used is 0.1 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, everything else is the same as in Example 1.

[0106] Example 8

[0107] The only difference between this embodiment and Example 1 is that, except that in step (c), the amount of CaCO3 used is 0.02 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, everything else is the same as in Example 1.

[0108] Example 9

[0109] The only difference between this embodiment and Example 1 is that, except that in step (c), the amount of CaCO3 used is 0.3 wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials, everything else is the same as in Example 1.

[0110] Example 10

[0111] The only difference between this embodiment and Embodiment 1 is that, except that the preheating temperature in step (b) is 1300°C, everything else is the same as in Embodiment 1.

[0112] Example 11

[0113] The only difference between this embodiment and Embodiment 1 is that, except that the preheating temperature in step (b) is 1100°C, everything else is the same as in Embodiment 1.

[0114] Example 12

[0115] The only difference between this embodiment and Embodiment 1 is that, except that the molding density in step (e) is 3.4 g / cm³. 3 Except for the above, everything else is the same as in Example 1.

[0116] Example 13

[0117] The only difference between this embodiment and Embodiment 1 is that the holding temperature for the second sintering in step (e) is changed from 1340°C to 1290°C. All other aspects are the same as in Embodiment 1.

[0118] Example 14

[0119] The only difference between this embodiment and Embodiment 1 is that the holding temperature for the second sintering in step (e) is changed from 1340°C to 1360°C. All other aspects are the same as in Embodiment 1.

[0120] Test methods

[0121] The low dielectric loss and low temperature coefficient microwave dielectric ceramics prepared in Examples 1-14 were used to test the performance of the ceramic wafers using a network analyzer and a dedicated resonant cavity. The results are shown in Table 1.

[0122] Table 1

[0123]

[0124]

[0125] The test results show that:

[0126] (1) As can be seen from Examples 1-14, the present invention selects lanthanum zinc titanate and strontium titanate as basic raw materials to ensure the basic performance of ceramics; introduces appropriate amounts of calcium carbonate, manganese dioxide and barium carbonate to effectively reduce the dielectric loss of ceramics and improve their temperature characteristics; the present invention reduces production costs and technical difficulties through solid-state reaction method; at the same time, it ensures the uniformity and stability of ceramics, effectively reduces the dielectric loss of microwave dielectric ceramics and improves their temperature characteristics, and further improves the performance of ceramics.

[0127] (2) As can be seen from Examples 1 and 4-5, the present invention regulates the performance of microwave dielectric ceramics by adjusting the ratio of zinc lanthanum titanate and strontium titanate. When the strontium titanate content is low, the dielectric constant is high, the dielectric loss and temperature coefficient will also increase; when the strontium titanate content is high, the dielectric constant decreases, the Q×F value decreases, and the temperature coefficient Tf also decreases.

[0128] (3) As can be seen from Examples 1 and 6-9, the present invention can reduce dielectric loss and increase Q×F value by adjusting the amount of auxiliary raw materials including calcium carbonate, manganese dioxide and barium carbonate.

[0129] (4) As can be seen from Examples 1 and 10-11, the present invention regulates the performance of microwave dielectric ceramics by controlling the pre-sintering temperature. When the pre-sintering temperature is high, the sintering density of the material is high and the particle size of the powder is large, which leads to an increase in the dielectric loss of the material and a decrease in the Q×F value. When the pre-sintering temperature is low, the zinc lanthanum phase cannot be completely formed, and there will be side reactions when it is sintered with strontium titanate in the subsequent process, which will affect the performance of microwave dielectric ceramics.

[0130] (5) As can be seen from Examples 1 and 12, the present invention regulates the performance of microwave dielectric ceramics by adjusting the molding density. When the molding density is low, the distance between the powders is large. During sintering, the grain growth will make up for the gaps between the powders, resulting in more pores, lower sintering density, and poor material performance. When the molding density is high, the product cracking rate is high, the performance deteriorates, and the yield is low.

[0131] (6) As can be seen from Examples 1 and 13-14, the present invention regulates the performance of microwave dielectric ceramics by controlling the secondary sintering temperature. When the secondary sintering temperature is low, it is not conducive to grain growth, resulting in increased porosity and deterioration of performance. When the secondary sintering temperature is high, it will lead to side reactions and generate impurity phases, which will also lead to deterioration of material performance.

[0132] In summary, this invention selects lanthanum zinc titanate and strontium titanate as basic raw materials to ensure the basic properties of the ceramic; introduces appropriate amounts of calcium carbonate, manganese dioxide, and barium carbonate to effectively reduce the dielectric loss of the ceramic and improve its temperature characteristics; this invention reduces production costs and technical difficulties through a solid-state reaction method; at the same time, it ensures the uniformity and stability of the ceramic, effectively reduces the dielectric loss of microwave dielectric ceramics and improves their temperature characteristics, further enhancing the performance of the ceramic.

[0133] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing microwave dielectric ceramics with low dielectric loss and low temperature coefficient, characterized in that, The preparation method includes the following steps: After mixing zinc lanthanum titanate, strontium source and auxiliary materials, the mixture is successively formed and sintered to prepare the microwave dielectric ceramic with low dielectric loss and low temperature coefficient. The auxiliary raw materials include any one or a combination of at least two of calcium carbonate, manganese dioxide, or barium carbonate.

2. The preparation method according to claim 1, characterized in that, The molar ratio of lanthanum zinc titanate to strontium source is a:(1-a), where a is 0.45-0.

65. Preferably, the strontium source includes strontium titanate.

3. The preparation method according to claim 1 or 2, characterized in that, The auxiliary raw material is a combination of calcium carbonate, manganese dioxide and barium carbonate; Preferably, the amount of calcium carbonate used is 0.03wt%-0.2wt% of the total mass of zinc titanate, lanthanum titanate, strontium source and auxiliary raw materials; Preferably, the amount of manganese dioxide used is 0.01wt%-0.04wt% of the total mass of zinc titanate, lanthanum, strontium source, and auxiliary raw materials; Preferably, the amount of barium carbonate used is 0.1wt%-0.3wt% of the total mass of zinc lanthanum titanate, strontium source and auxiliary raw materials.

4. The preparation method according to any one of claims 1-3, characterized in that, The molding process includes sequential spray granulation and tableting. Preferably, the water content of the spray granulation is 0.2%-0.5%; Preferably, the molding density of the tablet is 3.5 g / cm³. 3 -3.7g / cm 3 .

5. The preparation method according to any one of claims 1-4, characterized in that, The sintering is carried out in an air atmosphere; Preferably, the sintering includes a first sintering and a second sintering performed sequentially; Preferably, the holding temperature for the first sintering is 500℃-700℃; Preferably, the holding time for the first sintering is 2h-6h; Preferably, the holding temperature for the secondary sintering is 1300℃-1350℃; Preferably, the holding time for the secondary sintering is 4h-8h.

6. The preparation method according to any one of claims 1-5, characterized in that, The sintering process is followed by cooling. Preferably, the cooling includes reducing the temperature from the holding temperature of the secondary sintering to 550°C-600°C; Preferably, the cooling rate is 1℃ / min-2.5℃ / min.

7. The preparation method according to any one of claims 1-6, characterized in that, The preparation method of the zinc lanthanum titanate includes the following steps: Lanthanum source, zinc source and titanium source are ball-milled and mixed, dried and pre-calcined to obtain the zinc lanthanum titanate; Preferably, the lanthanum source includes lanthanum oxide; Preferably, the zinc source includes zinc oxide; Preferably, the titanium source includes titanium dioxide.

8. The preparation method according to claim 7, characterized in that, The drying and pre-firing process includes drying and pre-firing performed sequentially. Preferably, the drying temperature is 120℃-180℃; Preferably, the drying and heat preservation time is 12h-20h; Preferably, the pre-firing temperature is 1150℃-1250℃; Preferably, the preheating time is 2-6 hours.

9. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The lanthanum source, zinc source and titanium source are ball-milled and mixed, dried at 200℃-250℃ for 12h-20h, and then pre-calcined at 1150℃-1250℃ for 2h-6h to obtain lanthanum zinc titanate. (2) The zinc lanthanum titanate, strontium source and auxiliary raw materials are mixed and spray granulation and pressing are performed in sequence. After one sintering and two sintering in air atmosphere, the microwave dielectric ceramic with low dielectric loss and low temperature coefficient is obtained by cooling.

10. A microwave dielectric ceramic with low dielectric loss and low temperature coefficient, characterized in that, The microwave dielectric ceramic is prepared by the preparation method according to any one of claims 1-9.

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