Laminated structure microwave dielectric ceramic and preparation method thereof

Abstract

The invention belongs to the field of ceramic materials, and particularly relates to a laminated structure microwave dielectric ceramic and a preparation method thereof. The laminated structure microwave dielectric ceramic provided by the invention comprises a first ZnWO4 layer, a TiO2 layer and a second ZnWO4 layer which are laminated in sequence, and the mass ratio of the TiO2 layer in the laminated structure microwave dielectric ceramic is less than or equal to 2%. The laminated structure microwave dielectric ceramic provided by the invention is of a sandwich structure; the top layer and the bottom layer are ZnWO4 and are used as matrixes of the ceramic material; and the interlayer is TiO2 and is used as a temperature compensation component of the ceramic material. Compared with the traditional multiphase mixed ZnWO4-based ceramic, the preparation method disclosed by the invention has the advantages that near-zero tau f adjustment of the ZnWO4 ceramic can be realized under the condition of relatively small TiO2 content, the ceramic material keeps a relatively high Q * f value, and coordinated control of microwave dielectric properties is realized. In addition, co-firing preparation of the microwave dielectric ceramic with the laminated structure at a relatively low temperature can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of ceramic materials, and particularly relates to a laminated structure microwave dielectric ceramic and a preparation method thereof. Background Art

[0002] Microwave dielectric ceramic materials generally refer to ceramics used as dielectric materials in microwave frequency band (300 MHz - 300 GHz) circuits to complete one or more functions, and are key materials for microwave components such as resonators and filters widely used in modern communication. Usually, microwave dielectric ceramics should have appropriate dielectric constant ( ε r ) to meet the usage requirements of different frequency bands, low dielectric loss (i.e., high Q × f value, where Q is the quality factor, f is the resonance frequency) and near-zero resonance frequency temperature coefficient (τ f ), to ensure the accuracy, efficiency and stability of information transmission. The progress of 5G / 6G mobile communication technology has promoted the continuous development of microwave components towards miniaturization, integration, high reliability, low power consumption, etc. At the same time, to meet the actual application requirements and reduce the R & D production cost, higher requirements are put forward for the development of microwave dielectric ceramics. In addition to having good microwave dielectric properties, ceramics also need to have a lower sintering temperature (<1050 °C) to meet the co-firing temperature requirements with electrode materials (such as the melting point of copper is 1085 °C) in the low temperature co-fired ceramic technology.

[0003] ZnWO 4 ceramics have relatively excellent microwave dielectric properties and have attracted wide attention. However, the relatively large τ f value (-60 ppm / °C) of this ceramic greatly limits its application in microwave components such as resonators. In addition, its sintering temperature is also relatively high (1100 - 1200 °C). The traditional modification method is to first add a temperature compensation component with a large opposite τ f to the matrix ceramic to adjust the τ f value. On this basis, a sintering aid is added to further reduce the sintering temperature. However, the second phase (temperature compensation component or sintering aid) introduced by the mixing and sintering method is likely to cause uneven local distribution of components, resulting in a large dielectric loss and large fluctuations in the microwave dielectric properties of the ceramic, making it difficult to meet the actual application requirements. Therefore, it is urgent to make targeted improvements to ZnWO 4 ceramics to make it meet the multi-functional requirements of good temperature stability, low loss and low temperature sintering. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a laminated microwave dielectric ceramic and a preparation method thereof. The laminated microwave dielectric ceramic provided by the present invention has both good temperature stability and low loss. The preparation method provided by the present invention preferably uses nano-scale raw materials, and the co-firing temperature of the laminated ceramic is low.

[0005] The present invention provides a laminated microwave dielectric ceramic, comprising a first ZnWO 4 layer, TiO 2 Layer and second ZnWO 4 layer; the TiO 2 The mass proportion of the layer in the laminated structure microwave dielectric ceramic is ≤2%.

[0006] Preferably, the TiO 2 The mass proportion of the layer in the laminated microwave dielectric ceramic is 0.5~1.5%.

[0007] Preferably, the first ZnWO 4 Layer and second ZnWO 4 The mass proportions of the layers in the laminated microwave dielectric ceramics are the same.

[0008] The present invention provides a method for preparing the laminated microwave dielectric ceramic described in the above technical solution, comprising the following steps: a) ZnWO 4 The powder is mixed with the binder, ground and granulated to obtain ZnWO 4 Particles; b) TiO 2 The powder is mixed with the binder, ground and granulated to obtain TiO 2 Particles; There is no order of precedence between step a) and step b); c) Laying the ZnWO in layers in a mold 4 Particles, TiO 2 Particles and ZnWO 4 pelletizing, pressing, and obtaining a laminated ceramic green body; d) sintering the laminated structure ceramic green body to obtain laminated structure microwave dielectric ceramic.

[0009] Preferably, in step a), the ZnWO 4 The powder was prepared by the following steps: ZnO raw materials and WO 3 Raw materials according to ZnWO 4 The ingredients are mixed in a stoichiometric ratio, ground, dried, and sieved to obtain a mixed powder; the mixed powder is pre-sintered, ground again, dried again, and sieved again to obtain ZnWO 4 Powder.

[0010] Preferably, in step b), the TiO 2 powder is prepared according to the following steps: subjecting the TiO 2 raw material to pre-sintering, grinding, and sieving to obtain the TiO 2 powder.

[0011] Preferably, the ZnO raw material, the WO 3 raw material, and the TiO 2 raw material are all nano-scale raw materials.

[0012] Preferably, the temperature for pre-sintering the mixed powder is 800 - 900 °C, and the time is 2 - 6 h.

[0013] Preferably, the temperature for pre-sintering the TiO 2 raw material is 800 - 900 °C, and the time is 2 - 6 h.

[0014] Preferably, in step a), the particle size of the ZnWO 4 particles ≤ 0.25 mm (60 mesh).

[0015] Preferably, in step b), the particle size of the TiO 2 particles ≤ 0.25 mm (60 mesh).

[0016] Preferably, in steps a) and b), the binder is an aqueous PVA solution.

[0017] Preferably, step d) specifically includes: first degreasing the laminated structure ceramic green body at 550 - 650 °C for 2 - 6 h, and then sintering it at 1000 - 1050 °C for 2 - 6 h to obtain the laminated structure microwave dielectric ceramic.

[0018] Compared with the prior art, the present invention provides a laminated structure microwave dielectric ceramic and a preparation method thereof. The laminated structure microwave dielectric ceramic provided by the present invention has a "sandwich" structure; the top layer and the bottom layer are ZnWO 4 , serving as the matrix of the ceramic material; the interlayer is TiO 2 , serving as the temperature compensation component of the ceramic material. Compared with the traditional multi-phase mixed ZnWO 4 -based ceramic, the present invention can achieve near-zero τ 2 adjustment of the ZnWO 4 ceramic at a relatively low TiO f content, and keep the ceramic material with a relatively high Q × f value, realizing the coordinated control of microwave dielectric properties. The preparation method provided by the present invention combines the ZnWO 4 phase and the TiO 2After laminating the phases and then sintering, compared with the traditional ceramic preparation process of multi-phase mixed sintering, the present invention can limit the two-phase diffusion zone to a relatively shallow depth at the interface, which is beneficial to the coordinated control of microwave dielectric properties. At the same time, this diffusion zone can play the role of in-situ bonding of heterogeneous layers, which is beneficial to the good reliability of the all-ceramic structure. In addition, in the preferred technical solution provided by the present invention, nano-scale raw materials are used to prepare the microwave dielectric ceramic, which can reduce the sintering temperature of the matrix ceramic ZnWO 4 and achieve low-temperature co-sintering of the laminated structure microwave dielectric ceramic of ZnWO 4 and TiO 2 .

[0019] The experimental results show that: the present invention can sinter a microwave dielectric ceramic with good microwave dielectric properties at a relatively low temperature. The sintering temperature is as low as 1025 °C, and the relative dielectric constant of the microwave dielectric ceramic ε r is 17 - 20, Q × f the Q value is 45000 - 70000 GHz, and the resonance frequency temperature coefficient τ f is -20 - +30 ppm / °C. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0021] Figure 1 FIG. is a schematic structural diagram of the laminated structure microwave dielectric ceramic provided by the present invention; Figure 2 FIG. is a comparison diagram of the microwave dielectric properties of the ceramic materials of Examples 1 - 4 and Comparative Example 1 provided by the present invention.

[0022] Attached Figure 1 Reference numerals: 1 is the first ZnWO 4 layer, 2 is the TiO 2 layer, 3 is the second ZnWO 4 layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0024] The present invention provides a laminated microwave dielectric ceramic, as Figure 1 shown, comprising a first ZnWO 4 layer 1, a TiO 2 layer 2, and a second ZnWO 4 layer 3, which are laminated in sequence.

[0025] In the laminated microwave dielectric ceramic provided by the present invention, the mass ratio of the TiO 2 layer 2 in the laminated microwave dielectric ceramic is ≤2%, preferably 0.5 - 1.5%, and specifically can be 0.5%, 0.6%, 0.7%, 0.71%, 0.8%, 0.9%, 1%, 1.1%, 1.18%, 1.2%, 1.3%, 1.4%, 1.41% or 1.5%.

[0026] In the laminated microwave dielectric ceramic provided by the present invention, the mass ratios of the first ZnWO 4 layer 1 and the second ZnWO 4 layer 3 in the laminated microwave dielectric ceramic are preferably the same.

[0027] In the laminated microwave dielectric ceramic provided by the present invention, the composition structure of the laminated microwave dielectric ceramic can be expressed as y 1 ZnWO 4 -xTiO 2 -y 2 ZnWO 4 , where x and y 1 , y 2 are mass percentages, and x + y 1 +y 2 = 1.

[0028] The laminated microwave dielectric ceramic provided by the present invention has a "sandwich" structure; the top layer and the bottom layer are ZnWO 4 , serving as the matrix of the ceramic material; the middle layer is TiO 2 , serving as the temperature compensation component of the ceramic material. Compared with the traditional multiphase mixed ZnWO 4 ceramic, the present invention can achieve near-zero τ 2 adjustment of the ZnWO 4 -based ceramic at a relatively low TiO f content, and keep the ceramic material with a relatively high Q × f value, realizing the coordinated control of microwave dielectric properties.

[0029] The present invention also provides a preparation method of the laminated microwave dielectric ceramic described in the above technical solution, comprising the following steps: a) ZnWO4 The powder is mixed and ground with a binder, granulated, to obtain ZnWO 4 particles; b) Mix and grind the TiO 2 powder with a binder, granulate, to obtain TiO 2 particles; There is no sequence between step a) and step b); c) Stack and lay the ZnWO 4 particles, TiO 2 particles and ZnWO 4 particles in sequence in a mold, press, to obtain a laminated structure ceramic green body; d) Sinter the laminated structure ceramic green body to obtain a laminated structure microwave dielectric ceramic.

[0030] In the preparation method provided by the present invention, in step a), the ZnWO 4 powder is preferably prepared according to the following steps: a1) After proportioning ZnO raw material and WO 3 raw material according to the stoichiometric ratio of ZnWO 4 , mix and grind, dry, sieve, to obtain a mixed powder; a2) Presinter the mixed powder, grind again, dry again, sieve again, to obtain ZnWO 4 powder.

[0031] In the above ZnWO 4 powder preparation steps provided by the present invention, in step a1), both the ZnO raw material and the WO 3 raw material are preferably nano-level raw materials; the way of the mixed grinding is preferably ball milling, zirconia balls and absolute ethanol are preferably added during the ball milling process, the rotation speed of the ball milling is preferably 200 - 400 r / min, specifically can be 200 r / min, 250 r / min, 300 r / min, 350 r / min or 400 r / min; the mesh number of the sieve for sieving is preferably 60 - 120 meshes, specifically can be 60 meshes (0.250 mm), 70 meshes (0.212 mm), 80 meshes (0.180 mm), 100 meshes (0.150 mm) or 120 meshes (0.125 mm).

[0032] In the above ZnWO 4In the powder preparation step, in step a2), the temperature of the pre-sintering is preferably 800-900 °C, specifically it can be 800 °C, 810 °C, 820 °C, 830 °C, 840 °C, 850 °C, 860 °C, 870 °C, 880 °C, 890 °C or 900 °C; the time of the pre-sintering is preferably 2-6 h, specifically it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h; the way of the re-grinding is preferably ball milling, zirconia balls and absolute ethanol are preferably added during the ball milling process, the rotation speed of the ball milling is preferably 200-400 r / min, specifically it can be 200 r / min, 250 r / min, 300 r / min, 350 r / min or 400 r / min; the mesh number of the sieve for the re-screening is preferably 60-120 meshes, specifically it can be 60 meshes, 70 meshes, 80 meshes, 100 meshes or 120 meshes.

[0033] In the preparation method provided by the present invention, in step a), the binder is preferably an aqueous PVA solution; the content of PVA in the aqueous PVA solution is preferably 3-6 wt%, specifically it can be 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt% or 6 wt%.

[0034] In the preparation method provided by the present invention, in step a), after the granulation is preferably carried out screening; the mesh number of the sieve for the screening is preferably 60-120 meshes, specifically it can be 60 meshes, 70 meshes, 80 meshes, 100 meshes or 120 meshes.

[0035] In the preparation method provided by the present invention, in step a), the ZnWO 4 The particle size of the particles is preferably ≤0.25 mm, specifically it can be ≤0.25 mm, ≤0.212 mm, ≤0.18 mm, ≤0.15 mm or ≤0.125 mm.

[0036] In the preparation method provided by the present invention, in step b), the TiO 2 powder is preferably prepared according to the following steps: Pre-sinter, grind, and screen the TiO 2 raw materials to obtain TiO 2 powder.

[0037] In the above TiO provided by the present invention 2In the powder preparation step, the temperature of the pre-sintering is preferably 800-900 °C, specifically it can be 800 °C, 810 °C, 820 °C, 830 °C, 840 °C, 850 °C, 860 °C, 870 °C, 880 °C, 890 °C or 900 °C; the time of the pre-sintering is preferably 2-6 h, specifically it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h; the grinding method is preferably ball milling, zirconia balls and absolute ethanol are preferably added during the ball milling process, the rotation speed of the ball milling is preferably 200-400 r / min, specifically it can be 200 r / min, 250 r / min, 300 r / min, 350 r / min or 400 r / min; the mesh number of the sieve for sieving is preferably 60-120 meshes, specifically it can be 60 meshes, 70 meshes, 80 meshes, 100 meshes or 120 meshes.

[0038] In the preparation method provided by the present invention, in step b), the binder is preferably an aqueous PVA solution; the content of PVA in the aqueous PVA solution is preferably 3-6 wt%, specifically it can be 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt% or 6 wt%.

[0039] In the preparation method provided by the present invention, in step b), it is preferably sieved after granulation; the mesh number of the sieve for sieving is preferably 60-120 meshes, specifically it can be 60 meshes, 70 meshes, 80 meshes, 100 meshes or 120 meshes.

[0040] In the preparation method provided by the present invention, in step b), the TiO 2 particles preferably have a particle size of ≤0.25 mm, specifically it can be ≤0.25 mm, ≤0.212 mm, ≤0.18 mm, ≤0.15 mm or ≤0.125 mm.

[0041] In the preparation method provided by the present invention, the specific process of step c) preferably includes: first laying a layer of ZnWO 4 particles in the mold and pre-pressing; then laying a layer of TiO 4 particles on the ZnWO 2 particle layer and pre-pressing; then laying another layer of ZnWO 2 particles on the TiO 4 particle layer and pre-pressing; finally, performing overall pressing to obtain a laminated structure ceramic green body.

[0042] In the preparation method provided by the present invention, step d) preferably specifically includes: first debinding the laminated ceramic green body at 550-650 °C for 2-6 h, and then sintering at 1000-1050 °C for 2-6 h to obtain the laminated microwave dielectric ceramic. Among them, the debinding temperature can specifically be 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C, 630 °C, 640 °C or 650 °C; the debinding time can specifically be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h; the sintering temperature can specifically be 1000 °C, 1005 °C, 1010 °C, 1015 °C, 1020 °C, 1025 °C, 1030 °C, 1035 °C, 1040 °C, 1045 °C or 1050 °C; the sintering time can specifically be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h.

[0043] The preparation method provided by the present invention stacks the ZnWO 4 phase and the TiO 2 phase and then sinter them. Compared with the traditional ceramic preparation process of multi-phase mixed sintering, the present invention can limit the two-phase diffusion zone to a shallower depth at the interface, which is beneficial to the coordinated control of microwave dielectric properties. At the same time, this diffusion zone can play a role in in-situ bonding of heterogeneous layers, which is beneficial to the good reliability of the all-ceramic structure. In addition, in the preferred technical solution provided by the present invention, using nano-scale raw materials to prepare the microwave dielectric ceramic can reduce the sintering temperature of the matrix ceramic ZnWO 4 , and realize the low-temperature co-sintering of the ZnWO 4 and TiO 2 laminated microwave dielectric ceramic.

[0044] For the sake of clarity, the following will be described in detail through the following examples and comparative examples.

[0045] Example 1 (y 1 ZnWO 4 -xTiO 2 -y 2 ZnWO 4 , x = 0.71 wt%, y 1 =y 2 = 49.645 wt%) (1) ZnWO 4 Raw material batching: Mix the nano-scale ZnO raw material and the nano-scale WO 3 raw material according to the chemical equation ZnWO 4Ingredients are prepared; then, they are mixed and ball-milled. During the ball-milling process, zirconia balls and absolute ethanol are added. The ball-milling speed is 300 r / min, and the ball-milling time is 4 h. After the ball-milling is completed, it is dried and sieved through a 80-mesh sieve to obtain a mixed powder of ZnO and WO 3 ; (2)ZnWO 4 Pre-sintering of raw materials: The mixed powder obtained in step (1) is pre-sintered at 850 °C for 4 h, then subjected to secondary ball-milling. The ball-milling conditions are the same as those in step (1); after the ball-milling is completed, it is dried and sieved through a 80-mesh sieve to obtain ZnWO 4 powder; (3)TiO 2 Pre-sintering of raw materials: The nano-level TiO 2 raw material is pre-sintered at 850 °C for 4 h, then ball-milled. The ball-milling conditions are the same as those in step (1); after the ball-milling is completed, it is dried and sieved through a 80-mesh sieve to obtain TiO 2 powder; (4)Preparation of granulated powder: The powders obtained in steps (2) and (3) are respectively added with an appropriate amount of PVA aqueous solution (concentration 5 wt%), ground, granulated, and sieved through a 80-mesh sieve to obtain ZnWO 4 particles and TiO 2 particles; (5)Preparation of laminated structure ceramic green body: The particles obtained in step (4) are arranged in the geometric structure form of ZnWO 4 in the lower layer, TiO 2 in the middle layer, and ZnWO 4 in the upper layer. First, ZnWO 4 particles with a mass fraction of 49.645 wt% are added to the mold for pre-pressing, then TiO 2 particles with a mass fraction of 0.71 wt% are added for pre-pressing, then ZnWO 4 particles with a mass fraction of 49.645 wt% are added for pre-pressing, and finally overall pressing is carried out to obtain a ceramic green body with a "sandwich"-type laminated structure; (6)Sintering of laminated structure ceramic: The ceramic green body obtained in step (5) is first degummed at 600 °C for 4 h to remove the PVA binder, and then sintered at 1025 °C for 4 h to obtain a laminated structure of 49.645 wt% ZnWO 4 -0.71 wt% TiO 2 -49.645 wt% ZnWO 4 ceramic; (7)Testing of microwave dielectric properties of laminated structure ceramic: The upper and lower surfaces of the ceramic obtained in step (6) are polished, and then the microwave dielectric properties of the sample are tested using a network analyzer and a matching fixture. The test results are: relative dielectric constant ε r=17.69, Q × f Value = 66260GHz, resonant frequency temperature coefficient = -16.4ppm / ℃.

[0046] Example 2 (y 1 ZGar 4 -xTiO 2 -y 2 ZGar 4 ,x=1.10wt%,y 1 =y 2 =49.45 wt%) (1) ZnWO 4 Raw material ingredients: Nano-ZnO raw materials and nano-WO 3 Raw materials according to ZnWO 4 The ingredients were prepared in a stoichiometric ratio; then, the mixture was ball-milled, and zirconium oxide balls and anhydrous ethanol were added during the ball-milling process. The ball-milling speed was 300 r / min and the ball-milling time was 4 h. After the ball-milling was completed, the mixture was dried and passed through an 80-mesh sieve to obtain ZnO and WO 3 Mixed powder; (2) ZnWO 4 Raw material pre-sintering: The mixed powder obtained in step (1) was pre-sintered at 850°C for 4 hours, and then subjected to secondary ball milling. The ball milling conditions were the same as those in step (1). After the ball milling, the mixed powder was dried and passed through an 80-mesh sieve to obtain ZnWO 4 Powder; (3) TiO 2 Raw material pre-sintering: Nano-sized TiO 2 The raw materials were pre-sintered at 850°C for 4 h and then ball-milled under the same conditions as in step (1). After the ball-milling, they were dried and passed through an 80-mesh sieve to obtain TiO 2 Powder; (4) Preparation of granulated powder: The powders prepared in step (2) and step (3) were added with an appropriate amount of PVA aqueous solution (concentration 5 wt%), ground, granulated, and passed through an 80-mesh sieve to obtain ZnWO 4 Particles and TiO 2 Particles; (5) Preparation of laminated ceramic greenware: The particles prepared in step (4) are placed in a ZnWO 4 , middle layer TiO 2 and upper ZnWO 4 The geometric structure is as follows: first, 49.45wt% ZnWO is added into the mold. 4 The particles were pre-pressed and then 1.10 wt% TiO 2 The particles were pre-pressed and then 49.45wt% ZnWO was added.4 The particles are pre-pressed and finally integrally pressed to obtain a green ceramic body with a "sandwich"-type laminated structure; (6) Sintering of the laminated structure ceramic: The green ceramic body obtained in step (5) is first degummed at 600 °C for 4 h to remove the PVA binder, and then sintered at 1025 °C for 4 h to obtain a laminated structure of 49.45 wt% ZnWO 4 -1.10 wt% TiO 2 -49.45 wt% ZnWO 4 ceramic; (7) Microwave dielectric property test of the laminated structure ceramic: The upper and lower surfaces of the ceramic obtained in step (6) are polished, and then the microwave dielectric properties of the sample are tested using a network analyzer and a matching fixture. The test results are: relative dielectric constant ε r = 18.93, Q × f value = 58230 GHz, temperature coefficient of resonant frequency = +4.6 ppm / °C.

[0047] Example 3 (y 1 ZnWO 4 -xTiO 2 -y 2 ZnWO 4 , x = 1.18 wt%, y 1 = y 2 = 49.41 wt%) (1) ZnWO 4 Raw material batching: The nano-ZnO raw material and the nano-WO 3 raw materials are batched according to the chemical equation ZnWO 4 ; After that, they are mixed and ball-milled. Zirconia balls and absolute ethanol are added during the ball-milling process. The ball-milling speed is 300 r / min, and the ball-milling time is 4 h; After the ball-milling is completed, it is dried and sieved through an 80-mesh sieve to obtain a mixed powder of ZnO and WO 3 ; (2) Pre-sintering of ZnWO 4 raw materials: The mixed powder obtained in step (1) is pre-sintered at 850 °C for 4 h, and then subjected to secondary ball-milling. The ball-milling conditions are the same as those in step (1); After the ball-milling is completed, it is dried and sieved through an 80-mesh sieve to obtain ZnWO 4 powder; (3) Pre-sintering of TiO 2 raw materials: The nano-TiO 2 raw materials are pre-sintered at 850 °C for 4 h, and then ball-milled. The ball-milling conditions are the same as those in step (1); After the ball-milling is completed, it is dried and sieved through an 80-mesh sieve to obtain TiO 2 powder; (4)Preparation of granulated powder: The powders obtained in steps (2) and (3) are respectively added with an appropriate amount of PVA aqueous solution (concentration 5 wt%), ground, granulated, and sieved through a 80-mesh sieve to obtain ZnWO 4 particles and TiO 2 particles; (5)Preparation of laminated ceramic green body: The particles obtained in step (4) are arranged in the geometric structure form of ZnWO 4 in the lower layer, TiO 2 in the middle layer, and ZnWO 4 in the upper layer. First, add ZnWO 4 particles with a mass fraction of 49.41 wt% to the mold for pre-pressing, then add TiO 2 particles with a mass fraction of 1.18 wt% for pre-pressing, then add ZnWO 4 particles with a mass fraction of 49.41 wt% for pre-pressing, and finally perform overall pressing to obtain a ceramic green body with a "sandwich"-type laminated structure; (6)Sintering of laminated ceramic: The ceramic green body obtained in step (5) is first debinded at 600 °C for 4 h to remove the PVA binder, and then sintered at 1025 °C for 4 h to obtain a laminated structure of 49.41 wt% ZnWO 4 -1.18 wt% TiO 2 -49.41 wt% ZnWO 4 ceramic; (7)Testing of microwave dielectric properties of laminated ceramic: The upper and lower surfaces of the ceramic obtained in step (6) are polished, and then the microwave dielectric properties of the sample are tested using a network analyzer and a supporting fixture. The test results are: relative dielectric constant ε r = 19.21, Q × f value = 55530 GHz, temperature coefficient of resonant frequency = +16.0 ppm / °C.

[0048] Example 4 (y 1 ZnWO 4 -xTiO 2 -y 2 ZnWO 4 , x = 1.41 wt%, y 1 = y 2 = 49.295 wt%) (1)ZnWO 4 Raw material batching: The nano-ZnO raw material and nano-WO 3 raw material are mixed according to the chemical equation ZnWO 4Ingredients are prepared; then, they are mixed and ball-milled. During the ball-milling process, zirconia balls and absolute ethanol are added. The ball-milling speed is 300 r / min, and the ball-milling time is 4 h. After the ball-milling is completed, it is dried and sieved through a 80-mesh sieve to obtain a mixed powder of ZnO and WO 3 ; (2)ZnWO 4 Pre-sintering of raw materials: The mixed powder obtained in step (1) is pre-sintered at 850 °C for 4 h, and then secondary ball-milling is carried out. The ball-milling conditions are the same as those in step (1); after the ball-milling is completed, it is dried and sieved through a 80-mesh sieve to obtain ZnWO 4 powder; (3)TiO 2 Pre-sintering of raw materials: The nanoscale TiO 2 raw material is pre-sintered at 850 °C for 4 h, and then ball-milled. The ball-milling conditions are the same as those in step (1); after the ball-milling is completed, it is dried and sieved through a 80-mesh sieve to obtain TiO 2 powder; (4)Preparation of granulated powder: The powders obtained in step (2) and step (3) are respectively added with an appropriate amount of PVA aqueous solution (concentration 5 wt%), ground, granulated, and sieved through a 80-mesh sieve to obtain ZnWO 4 particles and TiO 2 particles; (5)Preparation of laminated structure ceramic green body: The particles obtained in step (4) are arranged in the geometric structure form of the lower layer of ZnWO 4 , the middle layer of TiO 2 and the upper layer of ZnWO 4 . First, ZnWO 4 particles with a mass fraction of 49.295 wt% are added to the mold for pre-pressing, then TiO 2 particles with a mass fraction of 1.41 wt% are added for pre-pressing, and then ZnWO 4 particles with a mass fraction of 49.295 wt% are added for pre-pressing, and finally overall pressing is carried out to obtain a ceramic green body with a "sandwich"-type laminated structure; (6)Sintering of laminated structure ceramic: The ceramic green body obtained in step (5) is first degummed at 600 °C for 4 h to remove the PVA binder, and then sintered at 1025 °C for 4 h to obtain a laminated structure of 49.295 wt% ZnWO 4 -1.41 wt% TiO 2 -49.295 wt% ZnWO 4 ceramic; (7)Measurement of microwave dielectric properties of laminated structure ceramic: The upper and lower surfaces of the ceramic obtained in step (6) are polished, and then the microwave dielectric properties of the sample are measured using a network analyzer and a matching fixture. The test results are: relative dielectric constant ε r= 19.92, Q × f Value = 45060 GHz, temperature coefficient of resonant frequency = +28.9 ppm / °C.

[0049] Comparative Example 1 (ZnWO 4 ) (1) ZnWO 4 Raw material batching: Nano-scale ZnO raw material and nano-scale WO 3 raw material were batched according to the chemical equation ZnWO 4 ; After that, they were mixed and ball-milled. Zirconia balls and absolute ethanol were added during the ball-milling process. The ball-milling speed was 300 r / min and the ball-milling time was 4 h; After the ball-milling was completed, it was dried and passed through an 80-mesh sieve to obtain a mixed powder of ZnO and WO 3 . (2) ZnWO 4 Raw material pre-sintering: The mixed powder obtained in step (1) was pre-sintered at 850 °C for 4 h, then subjected to secondary ball-milling, and the ball-milling conditions were the same as in step (1); After the ball-milling was completed, it was dried and passed through an 80-mesh sieve to obtain ZnWO 4 powder. (3) ZnWO 4 Ceramic green body: The powder obtained in step (2) was added with an appropriate amount of PVA aqueous solution (concentration 5 wt%), ground, granulated, passed through an 80-mesh sieve, and then poured into a mold for pressing to obtain a ceramic green body; (4) ZnWO 4 Ceramic sintering: The ceramic green body obtained in step (3) was first degummed at 600 °C for 4 h to remove the PVA binder, and then sintered at 1025 °C for 4 h to obtain ZnWO 4 ceramic. (5) ZnWO 4 Microwave dielectric property test of ceramic: The upper and lower surfaces of the ceramic obtained in step (4) were polished, and then the microwave dielectric properties of the sample were tested using a network analyzer and a supporting fixture. The test results were: relative dielectric constant ε r = 15.74, Q × f Value = 81780 GHz, temperature coefficient of resonant frequency = -72.9 ppm / °C.

[0050] Based on the microwave dielectric property test results of the ceramic materials in Examples 1 to 4 and Comparative Example 1, a graph of the change of microwave dielectric properties with the mass percentage of TiO 2 was plotted, and the results are as Figure 2 shown. It can be seen through Figure 2 that through the "sandwich" laminated structure design, at a relatively small TiO 2At a content (when the mass percentage is 1.10 wt%), the near-zero τ of ZnWO 4 ceramics can be achieved, f regulated, and the ceramic material can maintain a relatively high Q × f value, realizing the coordinated control of the microwave dielectric properties of the ceramics.

[0051] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A laminated microwave dielectric ceramic, characterized in that: It comprises a first ZnWO4 layer, a TiO2 layer and a second ZnWO4 layer stacked in sequence; the mass proportion of the TiO2 layer in the laminated microwave dielectric ceramic is ≤2%.

2. The laminated microwave dielectric ceramic according to claim 1, characterized in that: The mass proportion of the TiO2 layer in the laminated microwave dielectric ceramic is 0.5-1.5%.

3. The laminated microwave dielectric ceramic according to claim 1, characterized in that: The first ZnWO4 layer and the second ZnWO4 layer have the same mass proportion in the laminated structure microwave dielectric ceramic.

4. A method for preparing a laminated microwave dielectric ceramic according to any one of claims 1 to 3, characterized in that: The following steps are involved: a) mixing ZnWO4 powder and a binder, grinding and granulating to obtain ZnWO4 particles; b) mixing TiO2 powder and a binder, grinding and granulating to obtain TiO2 particles; There is no order of precedence between step a) and step b); c) stacking the ZnWO4 particles, TiO2 particles and ZnWO4 particles in sequence in a mold and pressing to obtain a laminated ceramic green body; d) sintering the laminated structure ceramic green body to obtain laminated structure microwave dielectric ceramic.

5. The preparation method according to claim 4, characterized in that: In step a), the ZnWO4 powder is prepared according to the following steps: The ZnO raw material and the WO3 raw material are mixed according to the stoichiometric ratio of ZnWO4, then ground, dried, and sieved to obtain a mixed powder; the mixed powder is pre-sintered, ground again, dried again, and sieved again to obtain ZnWO4 powder; In step b), the TiO2 powder is prepared according to the following steps: The TiO2 raw material is pre-sintered, ground, and sieved to obtain TiO2 powder.

6. The preparation method according to claim 5, characterized in that: The ZnO raw material, WO3 raw material and TiO2 raw material are all nano-scale raw materials.

7. The preparation method according to claim 5, characterized in that: The mixed powder is pre-sintered at a temperature of 800-900°C for 2-6 hours; The TiO2 raw material is pre-sintered at a temperature of 800-900°C for a time of 2-6 hours.

8. The preparation method according to claim 4, characterized in that: In step a), the particle size of the ZnWO4 particles is ≤0.25 mm; In step b), the particle size of the TiO2 particles is ≤0.25 mm.

9. The preparation method according to claim 4, characterized in that: In step a) and step b), the binder is a PVA aqueous solution.

10. The preparation method according to claim 4, characterized in that: Step d) specifically includes: The laminated structure ceramic green body is firstly debinded at 550-650° C. for 2-6 hours, and then sintered at 1000-1050° C. for 2-6 hours to obtain a laminated structure microwave dielectric ceramic.

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