MgNb2O6 dielectric ceramic with excessive Mg and preparation method of MgNb2O6 dielectric ceramic

Abstract

The invention discloses MgNb2O6 dielectric ceramic with excessive Mg and a preparation method of the MgNb2O6 dielectric ceramic, and belongs to the technical field of dielectric ceramics, MgNb2O6 + x mol.% MgO (x is greater than 0 and less than or equal to 3) dielectric ceramic is prepared by adopting a solid-phase reaction method, and excessive Mg ions do not change the phase structure of the ceramic but can inhibit abnormal growth of ceramic crystal grains, so that the crystal grains are more uniform. Besides, along with the increase of excessive Mg ions, the dielectric constant epsilon r and the quality factor Q * f of the MgNb2O6 ceramic are in a trend of firstly increasing and then decreasing, and when x is equal to 2, the ceramic has the optimal dielectric properties that epsilon r is equal to 20.37, Q * f is equal to 85 and 410 GHz, and tauf is equal to-62.21 ppm / DEG C.

Description

Technical Field

[0001] This invention belongs to the field of dielectric ceramics technology, specifically a MgNb2O6 dielectric ceramic with excess Mg and its preparation method. Background Technology

[0002] With the development of active phased array radar and mobile communication technologies, microwave ferrite devices are evolving towards miniaturization, broadband, and high power. Microstrip circulators designed based on novel ferrite-dielectric ceramic composite substrates inherit the high dielectric constant, low loss, and tunable performance characteristics of dielectric ceramics, enabling miniaturization, high power, and ultra-wideband design of circulators. Conventional ferrite materials typically have a dielectric constant below 14, which is low and hinders device miniaturization. Dielectric ceramics, on the other hand, come in a wide variety, with dielectric constants ranging from 6 to 150.

[0003] In the 5G era, dielectric constant 20 ceramics are the core material for fabricating dielectric filters. For ferrite-dielectric-ceramic composite substrates used in circulators, dielectric constant 20 ceramics are also the preferred choice. As the outer ring for ferrite impedance matching, they not only reduce device size but also exhibit low dielectric loss. Currently, there are relatively few types of dielectric constant 20 ceramics used in engineering applications. With the increasing reliance on ceramics in ferrite-dielectric-ceramic composite substrates, there is an urgent need to develop more high-performance dielectric constant 20 ceramics. Summary of the Invention

[0004] Based on the demand for ferrite-dielectric ceramic composite substrates, this invention uses MgNb2O6 ceramic as the optimization target. Without changing the dielectric constant of 20, the phase structure, microstructure and dielectric properties of MgNb2O6 ceramic are optimized by excess Mg ions.

[0005] The technical solution of the present invention is as follows: a MgNb2O6 dielectric ceramic with excess Mg, wherein the dielectric ceramic is stoichiometric according to MgNb2O6 + x mol.% MgO, where x = greater than 0 and less than or equal to 3.

[0006] Furthermore, the dielectric ceramic is made from MgO and Nb2O5.

[0007] Preferably, X=2.

[0008] This invention also provides a method for preparing MgNb2O6 dielectric ceramic with excess Mg, comprising the following steps: using compounds MgO and Nb2O5 as raw materials, MgNb2O6 + x mol.%MgO is stoichiometrically weighed, where x is greater than 0 and less than or equal to 3; ball milling, drying, and pre-firing; ball milling and drying again; sieving; adding PVA for granulation; pressing into green body; and sintering the green body.

[0009] Furthermore, the sintering temperature is 1375℃ and the time is 4 hours.

[0010] Compared with existing technologies, (1) this invention uses a solid-state reaction method to prepare MgNb2O6 + x mol.% MgO (x > 0 and ≤ 3) dielectric ceramics, and (2) studies the effects of different Mg ion contents on the ceramic phase structure, microstructure and dielectric properties. Excess Mg ions do not change the ceramic phase structure, but can inhibit abnormal growth of ceramic grains and make the grains more uniform. (3) With the increase of excess Mg ions, the dielectric constant ε of MgNb2O6 ceramics increases. r The quality factor Q × f shows a trend of first increasing and then decreasing. At x=2, the ceramic exhibits the best dielectric properties: ε r =20.37, Q×f=85,410 GHz, τ f = -62.21ppm / °C. Attached Figure Description

[0011] Figure 1 This is the XRD pattern of MgNb2O6 + x mol.% MgO ceramic; Figure 2 TC is the texture coefficient of the (400), (231) and (621) diffraction peaks of MgNb2O6 + x mol.% MgO ceramics; Figure 3 The following are SEM images of MgNb2O6 + x mol.% MgO ceramics: (a) x = 0; (b) x = 1; (c) x = 2; (d) x = 3; Figure 4 The bulk density and relative compactness of MgNb2O6 + x mol.% MgO ceramics; Figure 5 The dielectric properties of MgNb2O6 + xmol.% MgO ceramic; Figure 6 The dielectric constant ε of MgNb₂O₆ + x mol.% MgO ceramic is... r and relative density; Figure 7 The temperature coefficient τ of the resonant frequency of MgNb₂O₆ + x mol.% MgO ceramic is... f And the degree of order S. Detailed Implementation

[0012] The technical solution of the present invention will be further explained below with reference to the accompanying drawings.

[0013] This experiment used high-purity compounds MgO and Nb2O5 as raw materials. The raw materials were stoichiometrically prepared according to the formula MgNb2O6 + x mol.%MgO (x=0~3). After ball milling and drying, the raw materials were pre-fired, ball milled again, dried, and sieved. Then, an appropriate amount of PVA was added for granulation. The granules were pressed into cylindrical ceramic green bodies with a diameter of 15 mm and a thickness of 7.5 mm. The green bodies were then sintered at 1375℃ for 4 h.

[0014] The crystal phase composition of the samples was analyzed using a Rigaku D / max-2500 X-ray diffractometer with step scanning at a step size of 0.02° and a step length of 0.5 s / step, covering a 2θ angle range of 10–80°. The surface microstructure of the samples was analyzed using a FEI Quanta 200 scanning electron microscope. The ceramic density was tested using the Archimedes' displacement method. The dielectric constant and quality factor of the materials were measured using a Keysight N5232B network analyzer, and the temperature coefficient of resonant frequency τ was measured using a precision thermostat. f The test temperature range is 25-85℃.

[0015] The MgNb2O6 ceramic was modified by introducing excess MgO, and the XRD test results are as follows: Figure 1 As shown in the figure, as the excess MgO increases from 0 to 3 mol.%, only the MgNb2O6 phase (ICSD-PDF#88-0708) is observed in the XRD patterns of all ceramics, and no second phase is found. However, in the XRD patterns, the diffraction peaks corresponding to the (400), (231), and (621) crystal planes show different degrees of preferred orientation.

[0016] Figure 2 The texture coefficients TC corresponding to the (400), (231), and (621) diffraction peaks are calculated. With increasing excess MgO, the texture coefficients TC of the (400) and (621) diffraction peaks gradually increase. The (400) diffraction peak is a superlattice diffraction peak, and its relative intensity reflects the degree of order in the crystal structure. Furthermore, when no excess MgO is introduced, the (231) diffraction peak has a high texture coefficient, TC of 14.32%, which leads to a distinct preferred orientation of the MgNb2O6 ceramic grains. With increasing excess MgO, the texture coefficient of the (231) diffraction peak decreases significantly, indicating a decrease in the preferred orientation of the ceramic grains.

[0017] Figure 3SEM images of MgNb2O6 ceramics with 0-3 mol.% MgO are shown. For MgNb2O6 ceramics without excess MgO, more pores appear at the grain boundaries, and abnormal grain growth occurs, resulting in an uneven microstructure. This is mainly related to the high texture coefficient of the (231) diffraction peak at this point. As the excess MgO increases, the abnormal grain growth disappears, the grains become more uniform, and the pores at the grain boundaries gradually decrease. When 2 mol.% MgO is introduced, the ceramic has the densest and most uniform microstructure. However, as the MgO content increases to 3 mol.%, the pores at the grain boundaries gradually increase again.

[0018] To obtain ceramic density data more directly, the bulk density and relative density of MgNb2O6 + xmol.% MgO ceramic were obtained using the Archimedes displacement method, as shown below. Figure 4 As shown, with the increase of excess MgO from 0 to 3 mol.%, the bulk density and relative density of MgNb2O6 ceramics showed a trend of first increasing and then decreasing, with the maximum value occurring when the MgO content was 2 mol.%. This trend is consistent with the microstructure of the ceramics in the SEM images. Therefore, adding a certain amount of MgO contributes to the densification and homogenization of MgNb2O6 ceramic grains.

[0019] Figure 5 The dielectric properties of MgNb2O6 ceramics with excess MgO were shown. For the Q × f value, as the MgO content increased from x = 0 to x = 3, the Q × f value of MgNb2O6 ceramics showed a trend of first increasing and then decreasing, with the maximum value appearing at x = 2, at which point the Q × f value was 85,410 GHz. Generally speaking, the Q × f value of ceramics is affected by both intrinsic and extrinsic factors

[11] . Intrinsic factors are mainly closely related to the crystal structure of the dielectric material, because intrinsic loss is mainly generated by the interaction between the alternating electric field and the lattice vibration. Extrinsic factors are inevitable sources of influence in the preparation process of ceramic materials, and are mainly closely related to raw materials, preparation process, phase structure, number of grain boundaries, grain growth, density and doping.

[0020] The dielectric constant ε of ceramics r It is closely related to relative density. Generally speaking, increasing the relative density of ceramics can significantly increase ε. r This is because in non-dense ceramics, the dielectric constant of pores is 1, and the presence of a large number of pores will lead to a decrease in the dielectric constant of the ceramic. Figure 5 For MgNb2O6 + x mol.% MgO ceramic ε r The graph shows the relationship between relative density and density. As can be seen from the graph, both exhibit a consistent trend.

[0021] exist Figure 1 In the obtained XRD patterns, we found that excess MgO promoted the relative intensity of the (400) superlattice diffraction peak in MgNb2O6 ceramics. Since the (400) superlattice diffraction peak is closely related to the ceramic's degree of order, we calculated the degree of order S in MgNb2O6 + x mol.% MgO ceramics. By comparing the degree of order S with the temperature coefficient of resonant frequency τ... f We found that the trends of change between the two are consistent, therefore we established a similar... Figure 7 The relationship diagram shown illustrates this. The reason why both exhibit the same trend may be that in MgNb2O6 ceramics with higher order, the crystal structure maintains higher symmetry, thus possessing a larger negative τ. f This means it tends to move closer to 0 ppm / ℃. Regarding the temperature coefficient τ of the resonant frequency... f Its value gradually increases with the increase of excess Mg ions, mainly due to the influence of the ceramic's degree of order.

Claims

1. A MgNb₂O₆ dielectric ceramic with excess Mg, characterized in that, The dielectric ceramic is stoichiometric according to MgNb2O6 + x mol.%MgO, where x is greater than 0 and less than or equal to 3.

2. The MgNb₂O₆ dielectric ceramic with excess Mg according to claim 1, characterized in that, The dielectric ceramic is made from MgO and Nb2O5.

3. The MgNb₂O₆ dielectric ceramic with excess Mg according to claim 1, characterized in that, X=2。 4. A method for preparing MgNb2O6 dielectric ceramic with excess Mg, characterized in that, Includes the following steps: Using compounds MgO and Nb2O5 as raw materials, the mixture is prepared according to the stoichiometric ratio of MgNb2O6 + xmol.%MgO, where x is greater than 0 and less than or equal to 3. After ball milling and drying, the mixture is pre-calcined, ball milled and dried again, sieved, and then PVA is added for granulation. The mixture is then pressed into green bodies and sintered.

5. The method for preparing MgNb₂O₆ dielectric ceramic with excess Mg according to claim 4, characterized in that, The sintering temperature was 1375℃ and the time was 4 hours.

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