A laminated structure microwave dielectric ceramic and its preparation method

Abstract

The present invention belongs to the field of ceramic materials, and particularly relates to a laminated microwave dielectric ceramic and a preparation method thereof. The laminated microwave dielectric ceramic provided by the present invention comprises a first ZnWO4 layer, a TiO2 layer, and a second ZnWO4 layer which are laminated in sequence; the mass proportion of the TiO2 layer in the laminated microwave dielectric ceramic is ≤2%. The laminated microwave dielectric ceramic provided by the present invention has a "sandwich" structure; the top layer and the bottom layer are ZnWO4, serving as the matrix of the ceramic material; the interlayer is TiO2, serving as the temperature compensation component of the ceramic material. Compared with the traditional multi-phase mixed ZnWO4-based ceramic, the present invention can achieve near-zero τ f adjustment of the ZnWO4 ceramic with a relatively small content of TiO2, and keep the ceramic material at a relatively high Q × f value, realizing the coordinated control of microwave dielectric properties. In addition, the present invention can realize the co-firing preparation of the laminated microwave dielectric ceramic at a relatively low temperature.

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 bands (300 MHz - 300 GHz) circuits to perform 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 a suitable 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 a 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-sintering temperature requirements with electrode materials (such as the melting point of copper is 1085 °C) in the low-temperature co-fired ceramic technology.

[0003] The microwave dielectric properties of ZnWO4 ceramics are relatively excellent, which has 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 prone to cause uneven local distribution of components, which will bring a large dielectric loss and cause large fluctuations in the microwave dielectric properties of the ceramic, making it difficult to meet the actual application requirements. Therefore, it is urgent to carry out targeted improvement on ZnWO4 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 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%.

[0006] Preferably, the mass proportion of the TiO2 layer in the laminated microwave dielectric ceramic is 0.5-1.5%.

[0007] Preferably, the first ZnWO4 layer and the second ZnWO4 layer have the same mass proportion in the laminated structure microwave dielectric ceramic.

[0008] The present invention provides a method for preparing the laminated microwave dielectric ceramic described in the above technical solution, comprising the following steps:

[0009] a) mixing ZnWO4 powder and a binder, grinding and granulating to obtain ZnWO4 particles;

[0010] b) mixing TiO2 powder and a binder, grinding and granulating to obtain TiO2 particles;

[0011] There is no order of precedence between step a) and step b);

[0012] c) stacking the ZnWO4 particles, TiO2 particles and ZnWO4 particles in sequence in a mold and pressing to obtain a laminated ceramic green body;

[0013] d) sintering the laminated structure ceramic green body to obtain laminated structure microwave dielectric ceramic.

[0014] Preferably, in step a), the ZnWO4 powder is prepared according to the following steps: after mixing the ZnO raw material and the WO3 raw material according to the stoichiometric ratio of ZnWO4, mixing and grinding, drying, and sieving to obtain a mixed powder; pre-sintering the mixed powder, grinding again, drying again, and sieving again to obtain ZnWO4 powder.

[0015] Preferably, in step b), the TiO2 powder is prepared according to the following steps: pre-sintering, grinding and sieving the TiO2 raw material to obtain TiO2 powder.

[0016] Preferably, the ZnO raw material, WO3 raw material and TiO2 raw material are all nanoscale raw materials.

[0017] Preferably, the temperature for pre-sintering the mixed powder is 800 - 900 °C, and the time is 2 - 6 h.

[0018] Preferably, the temperature for pre-sintering the TiO2 raw material is 800 - 900 °C, and the time is 2 - 6 h.

[0019] Preferably, in step a), the particle size of the ZnWO4 particles ≤ 0.25 mm (60 mesh).

[0020] Preferably, in step b), the particle size of the TiO2 particles ≤ 0.25 mm (60 mesh).

[0021] Preferably, in steps a) and b), the binder is an aqueous PVA solution.

[0022] Preferably, step d) specifically includes: first degumming the laminated 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 a laminated microwave dielectric ceramic.

[0023] Compared with the prior art, the present invention provides a laminated microwave dielectric ceramic and a preparation method thereof. The laminated microwave dielectric ceramic provided by the present invention has a "sandwich" structure; the top layer and the bottom layer are ZnWO4, serving as the matrix of the ceramic material; the interlayer is TiO2, serving as the temperature compensation component of the ceramic material. Compared with the traditional multi-phase mixed ZnWO4-based ceramics, the present invention can achieve near-zero τ f adjustment of ZnWO4 ceramics with a relatively small TiO2 content, and keep the ceramic material with a relatively high Q × f value, realizing the coordinated control of microwave dielectric properties. In the preparation method provided by the present invention, after laminating the ZnWO4 phase and the TiO2 phase, sintering is carried out. 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 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-level raw materials to prepare the microwave dielectric ceramic can reduce the sintering temperature of the matrix ceramic ZnWO4 and realize the low-temperature co-sintering of the ZnWO4 and TiO2 laminated microwave dielectric ceramic.

[0024] 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 × fwith a value of 45000 to 70000 GHz and a temperature coefficient of resonance frequency τ f is -20 to +30 ppm / °C. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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 use in 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, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0026] Figure 1 is a schematic structural diagram of the laminated structure microwave dielectric ceramic provided by the present invention;

[0027] Figure 2 is a comparison chart of the microwave dielectric properties of the ceramic materials of Examples 1 to 4 and Comparative Example 1 provided by the present invention.

[0028] APPENDIX Figure 1 Marking description: 1 is the first ZnWO4 layer, 2 is the TiO2 layer, and 3 is the second ZnWO4 layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] 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.

[0030] The present invention provides a laminated structure microwave dielectric ceramic, as Figure 1 shown, including a first ZnWO4 layer 1, a TiO2 layer 2, and a second ZnWO4 layer 3 laminated in sequence.

[0031] In the laminated structure microwave dielectric ceramic provided by the present invention, the mass ratio of the TiO2 layer 2 in the laminated structure microwave dielectric ceramic is ≤2%, preferably 0.5 to 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%.

[0032] In the laminated structure microwave dielectric ceramic provided by the present invention, the mass ratios of the first ZnWO4 layer 1 and the second ZnWO4 layer 3 in the laminated structure microwave dielectric ceramic are preferably the same.

[0033] In the laminated structure microwave dielectric ceramic provided by the present invention, the composition structure of the laminated structure microwave dielectric ceramic can be expressed as y1ZnWO4 - xTiO2 - y2ZnWO4, where x, y1, and y2 are mass percentages, and x + y1 + y2 = 1.

[0034] The laminated structure microwave dielectric ceramic provided by the present invention has a "sandwich" structure; the top layer and the bottom layer are ZnWO4, serving as the matrix of the ceramic material; the middle layer is TiO2, serving as the temperature compensation component of the ceramic material. Compared with the traditional multi-phase mixed ZnWO4 ceramic, the present invention can achieve near-zero τ of the ZnWO4-based ceramic with a relatively small TiO2 content f adjustment, and keep the ceramic material with a relatively high Q × f value, realizing the coordinated control of microwave dielectric properties.

[0035] The present invention also provides a preparation method of the laminated structure microwave dielectric ceramic described in the above technical solution, including the following steps:

[0036] a) Mix and grind ZnWO4 powder with a binder, and granulate to obtain ZnWO4 particles;

[0037] b) Mix and grind TiO2 powder with a binder, and granulate to obtain TiO2 particles;

[0038] There is no sequence requirement between step a) and step b);

[0039] c) Stack and lay the ZnWO4 particles, TiO2 particles, and ZnWO4 particles in sequence in a mold, and press to obtain a green body of the laminated structure ceramic;

[0040] d) Sinter the green body of the laminated structure ceramic to obtain the laminated structure microwave dielectric ceramic.

[0041] In the preparation method provided by the present invention, in step a), the ZnWO4 powder is preferably prepared according to the following steps:

[0042] a1) After proportioning ZnO raw material and WO3 raw material according to the stoichiometric ratio of ZnWO4, mix and grind, dry, and screen to obtain a mixed powder;

[0043] a2) Pre-sinter the mixed powder, grind again, dry again, and screen again to obtain ZnWO4 powder.

[0044] In the above-mentioned ZnWO4 powder preparation steps provided by the present invention, in step a1), both the ZnO raw material and the WO3 raw material are preferably nanoscale raw materials; the preferred way of mixing and grinding is ball milling. Preferably, zirconia balls and absolute ethanol are added during the ball milling process. The preferred rotation speed of the ball milling is 200 - 400 r / min, specifically 200 r / min, 250 r / min, 300 r / min, 350 r / min, or 400 r / min; the preferred mesh number of the sieve for sieving is 60 - 120 mesh, specifically 60 mesh (0.250 mm), 70 mesh (0.212 mm), 80 mesh (0.180 mm), 100 mesh (0.150 mm), or 120 mesh (0.125 mm).

[0045] In the above-mentioned ZnWO4 powder preparation steps provided by the present invention, in step a2), the preferred temperature for pre-sintering is 800 - 900 °C, specifically 800 °C, 810 °C, 820 °C, 830 °C, 840 °C, 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, or 900 °C; the preferred time for pre-sintering is 2 - 6 h, specifically 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, or 6 h; the preferred way of re-grinding is ball milling. Preferably, zirconia balls and absolute ethanol are added during the ball milling process. The preferred rotation speed of the ball milling is 200 - 400 r / min, specifically 200 r / min, 250 r / min, 300 r / min, 350 r / min, or 400 r / min; the preferred mesh number of the sieve for re-sieving is 60 - 120 mesh, specifically 60 mesh, 70 mesh, 80 mesh, 100 mesh, or 120 mesh.

[0046] In the preparation method provided by the present invention, in step a), the preferred binder is an aqueous PVA solution; the content of PVA in the aqueous PVA solution is preferably 3 - 6 wt%, specifically 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%.

[0047] In the preparation method provided by the present invention, in step a), it is preferably sieved after granulation; the preferred mesh number of the sieve for sieving is 60 - 120 mesh, specifically 60 mesh, 70 mesh, 80 mesh, 100 mesh, or 120 mesh.

[0048] In the preparation method provided by the present invention, in step a), the preferred particle size of the ZnWO4 particles is ≤0.25 mm, specifically ≤0.25 mm, ≤0.212 mm, ≤0.18 mm, ≤0.15 mm, or ≤0.125 mm.

[0049] In the preparation method provided by the present invention, in step b), the TiO2 powder is preferably prepared according to the following steps:

[0050] The TiO2 raw material is pre-sintered, ground, and sieved to obtain TiO2 powder.

[0051] In the above TiO2 powder preparation steps provided by the present invention, 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, and preferably zirconia balls and absolute ethanol are 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 mesh, specifically it can be 60 mesh, 70 mesh, 80 mesh, 100 mesh or 120 mesh.

[0052] 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%.

[0053] In the preparation method provided by the present invention, in step b), after granulation, it is preferably sieved; the mesh number of the sieve for sieving is preferably 60 - 120 mesh, specifically it can be 60 mesh, 70 mesh, 80 mesh, 100 mesh or 120 mesh.

[0054] In the preparation method provided by the present invention, in step b), the particle size of the TiO2 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.

[0055] In the preparation method provided by the present invention, the specific process of step c) preferably includes: first laying a layer of ZnWO4 particles in the mold and pre-pressing; then laying a layer of TiO2 particles on the ZnWO4 particle layer and pre-pressing; then laying another layer of ZnWO4 particles on the TiO2 particle layer and pre-pressing; finally performing overall pressing to obtain a laminated structure ceramic green body.

[0056] In the preparation method provided by the present invention, step d) preferably specifically includes: first, subjecting the laminated ceramic green body to debinding at 550-650 °C for 2-6 h, and then sintering at 1000-1050 °C for 2-6 h to obtain a laminated microwave dielectric ceramic. Among them, the temperature of the debinding 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 time of the debinding 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 temperature of the sintering 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 time of the sintering 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.

[0057] In the preparation method provided by the present invention, after laminating the ZnWO4 phase and the TiO2 phase 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 at 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 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 ZnWO4 and achieve low-temperature co-sintering of the ZnWO4 and TiO2 laminated microwave dielectric ceramic.

[0058] For the sake of clarity, the following will be described in detail through the following examples and comparative examples.

[0059] Example 1 (y1ZnWO4-xTiO2-y2ZnWO4, x = 0.71 wt%, y1 = y2 = 49.645 wt%)

[0060] (1) ZnWO4 raw material batching: Mix nano-scale ZnO raw material and nano-scale WO3 raw material according to the chemical formula ZnWO4; then, perform ball milling, adding zirconia balls and anhydrous ethanol during the ball milling process, with a ball milling speed of 300 r / min and a ball milling time of 4 h; after the ball milling is completed, dry and pass through an 80-mesh sieve to obtain a mixed powder of ZnO and WO3;

[0061] (2) Pre-sintering of ZnWO4 raw materials: Pre-sinter the mixed powder obtained in step (1) at 850 °C for 4 h, and then perform secondary ball milling, with the ball milling conditions the same as in step (1); after the ball milling is completed, dry and pass through an 80-mesh sieve to obtain ZnWO4 powder;

[0062] (3) Pre-sintering of TiO2 raw materials: The nano-sized TiO2 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, the raw materials were dried and passed through an 80-mesh sieve to obtain TiO2 powder.

[0063] (4) Preparation of granulated powder: Add an appropriate amount of PVA aqueous solution (concentration 5 wt%) to the powders prepared in step (2) and step (3), grind, granulate, and pass through an 80-mesh sieve to obtain ZnWO4 particles and TiO2 particles, respectively;

[0064] (5) Preparation of laminated ceramic green body: The particles prepared in step (4) are placed in a geometric structure of a lower ZnWO4 layer, a middle TiO2 layer and an upper ZnWO4 layer. First, 49.645 wt% of ZnWO4 particles are added to the mold for pre-pressing. Then, 0.71 wt% of TiO2 particles are added for pre-pressing. Then, 49.645 wt% of ZnWO4 particles are added for pre-pressing. Finally, the whole is pressed to obtain a "sandwich" type laminated ceramic green body.

[0065] (6) Sintering of laminated ceramics: The ceramic green body prepared in step (5) was first debonded at 600°C for 4 hours to remove the PVA binder, and then sintered at 1025°C for 4 hours to obtain a laminated structure of 49.645wt% ZnWO4-0.71wt% TiO2-49.645wt% ZnWO4 ceramics;

[0066] (7) Microwave dielectric properties test of laminated ceramics: The upper and lower surfaces of the ceramics obtained in step (6) were polished, and then the microwave dielectric properties of the samples were tested using a network analyzer and a matching fixture. The test results were: relative dielectric constant ε r =17.69, Q × f Value = 66260GHz, resonant frequency temperature coefficient = -16.4ppm / ℃.

[0067] Example 2 (y1ZnWO4-xTiO2-y2ZnWO4, x=1.10wt%, y1=y2=49.45wt%)

[0068] (1) ZnWO4 raw material preparation: Nano-ZnO raw material and nano-WO3 raw material are prepared according to the stoichiometric ratio of ZnWO4; then, the mixture is ball-milled, and zirconium oxide balls and anhydrous 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, the mixture is dried and passed through an 80-mesh sieve to obtain a mixed powder of ZnO and WO3;

[0069] (2) Pre-sintering of ZnWO4 raw materials: After pre-sintering the mixed powder obtained in step (1) at 850 °C for 4 h, secondary ball milling is carried out, and 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 ZnWO4 powder;

[0070] (3) Pre-sintering of TiO2 raw materials: After pre-sintering the nano-TiO2 raw materials at 850 °C for 4 h, ball milling is carried out, and 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 TiO2 powder;

[0071] (4) Preparation of granulated powder: Add the powders obtained in step (2) and step (3) respectively to an appropriate amount of PVA aqueous solution (concentration 5 wt%), grind, granulate, and sieve through a 80-mesh sieve to obtain ZnWO4 particles and TiO2 particles respectively;

[0072] (5) Preparation of laminated structure ceramic green body: Arrange the particles obtained in step (4) in the geometric structure form of ZnWO4 in the lower layer, TiO2 in the middle layer, and ZnWO4 in the upper layer. First, add ZnWO4 particles with a mass fraction of 49.45 wt% to the mold for pre-pressing, then add TiO2 particles with a mass fraction of 1.10 wt% for pre-pressing, then add ZnWO4 particles with a mass fraction of 49.45 wt% for pre-pressing, and finally perform overall pressing to obtain a ceramic green body with a "sandwich"-type laminated structure;

[0073] (6) Sintering of laminated structure ceramic: First, degrease the ceramic green body obtained in step (5) at 600 °C for 4 h to remove the PVA binder, and then sinter it at 1025 °C for 4 h to obtain a laminated structure 49.45 wt% ZnWO4-1.10 wt% TiO2-49.45 wt% ZnWO4 ceramic;

[0074] (7) Microwave dielectric property test of laminated structure ceramic: Polish the upper and lower surfaces of the ceramic obtained in step (6), and then use a network analyzer and a matching fixture to test the microwave dielectric properties of the sample. The test results are: relative dielectric constant ε r = 18.93, Q × f value = 58230 GHz, resonant frequency temperature coefficient = +4.6 ppm / °C.

[0075] Example 3 (y1ZnWO4-xTiO2-y2ZnWO4, x = 1.18 wt%, y1 = y2 = 49.41 wt%)

[0076] (1)ZnWO4 raw material batching: Nano-ZnO raw material and nano-WO3 raw material are batched according to the chemical equation ZnWO4; 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 WO3;

[0077] (2)Pre-sintering of ZnWO4 raw material: The mixed powder prepared 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 a 80-mesh sieve to obtain ZnWO4 powder;

[0078] (3)Pre-sintering of TiO2 raw material: Nano-TiO2 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 TiO2 powder;

[0079] (4)Preparation of granulated powder: The powders prepared 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 ZnWO4 particles and TiO2 particles respectively;

[0080] (5)Preparation of laminated structure ceramic green body: The particles prepared in step (4) are arranged in the geometric structure form of ZnWO4 in the lower layer, TiO2 in the middle layer, and ZnWO4 in the upper layer. First, ZnWO4 particles with a mass fraction of 49.41 wt% are added to the mold for pre-pressing, then TiO2 particles with a mass fraction of 1.18 wt% are added for pre-pressing, and then ZnWO4 particles with a mass fraction of 49.41 wt% are added for pre-pressing. Finally, overall pressing is carried out to obtain a ceramic green body with a "sandwich"-type laminated structure;

[0081] (6)Sintering of laminated structure ceramic: The ceramic green body prepared 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 49.41 wt% ZnWO4-1.18 wt% TiO2-49.41 wt% ZnWO4 ceramic;

[0082] (7)Measurement of microwave dielectric properties of laminated structure ceramic: The upper and lower surfaces of the ceramic prepared in step (6) are polished, and then the microwave dielectric properties of the sample are measured 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 resonance frequency = +16.0 ppm / °C.

[0083] Example 4 (y1ZnWO4-xTiO2-y2ZnWO4, x = 1.41 wt%, y1 = y2 = 49.295 wt%)

[0084] (1) Preparation of ZnWO4 raw material ingredients: The nano-ZnO raw material and nano-WO3 raw material are proportioned according to the chemical formula ZnWO4; then, 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 a 80-mesh sieve to obtain a mixed powder of ZnO and WO3;

[0085] (2) Pre-sintering of ZnWO4 raw materials: The mixed powder prepared 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 a 80-mesh sieve to obtain ZnWO4 powder;

[0086] (3) Pre-sintering of TiO2 raw materials: The nano-TiO2 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 TiO2 powder;

[0087] (4) Preparation of granulated powder: The powders prepared 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 ZnWO4 particles and TiO2 particles respectively;

[0088] (5) Preparation of laminated structure ceramic green body: The particles prepared in step (4) are in the geometric structure form of ZnWO4 in the lower layer, TiO2 in the middle layer, and ZnWO4 in the upper layer. First, 49.295 wt% of ZnWO4 particles are added to the mold for pre-pressing, then 1.41 wt% of TiO2 particles are added for pre-pressing, and then 49.295 wt% of ZnWO4 particles are added for pre-pressing, and finally overall pressing is carried out to obtain a ceramic green body with a "sandwich"-type laminated structure;

[0089] (6) Sintering of laminated structure ceramic: The ceramic green body prepared 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 49.295 wt% ZnWO4-1.41 wt% TiO2-49.295 wt% ZnWO4 ceramic with a laminated structure;

[0090] (7) Microwave dielectric property test of laminated structure ceramic: The upper and lower surfaces of the ceramic prepared in step (6) are polished, and then the microwave dielectric properties of the sample are tested by using a network analyzer and a supporting fixture. The test results are: relative dielectric constant εr = 19.92, Q × f Value = 45060 GHz, temperature coefficient of resonant frequency = +28.9 ppm / °C.

[0091] Comparative Example 1 (ZnWO4)

[0092] (1) ZnWO4 raw material batching: Nano-scale ZnO raw material and nano-scale WO3 raw material were batched according to the chemical equation ZnWO4; then, they were mixed and ball-milled. Zirconia 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, it was dried and passed through an 80-mesh sieve to obtain a mixed powder of ZnO and WO3.

[0093] (2) Pre-sintering of ZnWO4 raw materials: The mixed powder obtained in step (1) was pre-sintered at 850 °C for 4 h, then subjected to secondary ball-milling. 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 ZnWO4 powder.

[0094] (3) ZnWO4 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.

[0095] (4) Sintering of ZnWO4 ceramics: 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 ZnWO4 ceramics.

[0096] (5) Microwave dielectric property test of ZnWO4 ceramics: The upper and lower surfaces of the ceramics obtained in step (4) were polished, and then the microwave dielectric properties of the samples 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.

[0097] Based on the microwave dielectric property test results of the ceramic materials in Examples 1 - 4 and Comparative Example 1, a graph of the change in microwave dielectric properties with the mass percentage of TiO2 was plotted. The results are as Figure 2 shown. It can be seen that through the "sandwich" laminated structure design, near-zero τ of ZnWO4 ceramics can be achieved at a relatively low TiO2 content (when the mass percentage is 1.10 wt%), and the ceramic material can maintain a relatively high Figure 2 × f adjustment, and keep the ceramic material with a relatively high Q × fThe values achieve the coordinated control of the ceramic microwave dielectric properties.

[0098] 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 structure microwave dielectric ceramic, characterized in that, It includes a first ZnWO4 layer, a TiO2 layer, and a second ZnWO4 layer that are stacked in sequence; the mass ratio of the TiO2 layer in the laminated structure microwave dielectric ceramic is ≤ 2%.

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

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

4. A method for preparing the laminated structure microwave dielectric ceramic according to any one of claims 1 to 3, characterized in that, It includes the following steps: a) Mix and grind ZnWO4 powder with a binder, and granulate to obtain ZnWO4 particles; b) Mix and grind TiO2 powder with a binder, and granulate to obtain TiO2 particles; There is no sequence between step a) and step b); c) Lay the ZnWO4 particles, TiO2 particles, and ZnWO4 particles in sequence in a mold, and press to obtain a green body of the laminated structure ceramic; d) Sinter the green body of the laminated structure ceramic to obtain a 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: After proportioning ZnO raw material and WO3 raw material according to the chemical stoichiometry of ZnWO4, mix and grind, dry, and screen to obtain a mixed powder; pre-sinter the mixed powder, grind again, dry again, and screen again to obtain ZnWO4 powder; In step b), the TiO2 powder is prepared according to the following steps: Pre-sinter the TiO2 raw material, grind, and screen 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-level raw materials.

7. The preparation method according to claim 5, characterized in that, The temperature for pre-sintering the mixed powder is 800 - 900 °C, and the time is 2 - 6 h; The temperature for pre-sintering the TiO2 raw material is 800 - 900 °C, and the time is 2 - 6 h.

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, wherein In step a) and step b), the binder is an aqueous PVA solution.

10. The preparation method according to claim 4, wherein, Step d) specifically includes: First, degrease the green body of the laminated structure ceramic at 550 - 650 °C for 2 - 6 h, and then sinter it at 1000 - 1050 °C for 2 - 6 h to obtain a laminated structure microwave dielectric ceramic.

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