A high-temperature impedance x7r dielectric ceramic material, and a preparation method and application thereof

Abstract

The application relates to the technical field of ceramic materials, in particular to a high-temperature impedance X7R dielectric ceramic material and a preparation method and application thereof, raw materials of the high-temperature impedance X7R dielectric ceramic material include main powder, a dopant, a dispersing agent and a binder, the main powder is prepared by ball milling, pre-sintering BaTiO3, Na 0.5 Bi 0.5 TiO3 at a molar ratio of 9:1, the pre-sintering temperature is 1200-1400 DEG C, and the pre-sintering time is 2-4 h; the dopant is obtained by pre-sintering Nb2O5, a transition metal oxide MeO and MgCO3, the pre-sintering temperature is 650-750 DEG C, and the pre-sintering time is 1-2 h; in terms of molar parts, the main powder is 100 molar parts, the Nb2O5 is 0.1-1.0 molar parts, the MgCO3 is 0.1-1.0 molar parts, and the transition metal oxide MeO is 0.1-3.0 molar parts. The temperature characteristic of the dielectric ceramic is improved, and the temperature stability meets the X7R dielectric material standard formulated by the American Electronics Association.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, and in particular to a high-temperature impedance X7R dielectric ceramic material, its preparation method, and its application. Background Technology

[0002] Currently, there are three main types of dielectric materials commonly used in MLCCs: lead-based composite perovskite systems, tungsten bronze structures, and BaTiO3 systems. Firstly, while lead-based composite perovskite systems have low sintering temperatures, their high lead content reduces reliability and poses significant environmental hazards. Secondly, although tungsten bronze structures have high dielectric constants, their dielectric losses are also high, and the high mobility of alkali metals makes the dielectric properties of MLCCs unstable. In contrast, the BaTiO3 system, with its strong spontaneous polarization and high dielectric constant, is the mainstream choice for high-dielectric-constant MLCCs. However, since the Curie temperature of BaTiO3 is approximately 125°C, it is difficult to meet the ±15% TCC change rate requirement under high-temperature conditions (>125°C). For specialized industries such as military and aerospace, the upper limit of operating temperature is generally above 150°C. Therefore, it is necessary to improve the dielectric temperature characteristics of BaTiO3 through doping modification, element control, and process optimization to obtain stable capacitance-dielectric-temperature characteristics over a wide temperature range. Summary of the Invention

[0003] In view of this, the purpose of this invention is to propose a high-temperature impedance X7R dielectric ceramic material, its preparation method and application, so as to solve the problem of high capacitance change rate of current ceramic dielectric materials under high temperature conditions above 125℃.

[0004] To achieve the above objectives, this invention provides a high-temperature impedance X7R dielectric ceramic material, the raw materials of which include a main powder, a dopant, a dispersant, and a binder, wherein the main powder consists of BaTiO3 and Na... 0.5 Bi 0.5 TiO3 was prepared by ball milling and pre-calcination at a molar ratio of 9:1, with a pre-calcination temperature of 1200–1400°C and a pre-calcination time of 2–4 h. The dopant was obtained by pre-calcining Nb2O5, transition metal oxide MeO, and MgCO3 at a pre-calcination temperature of 650–750°C and a pre-calcination time of 1–2 h. In molar amounts, the main powder was 100 molars, and the Nb2O5, MgCO3, and MeO were 0.1–1.0 molars, respectively.

[0005] The BaTiO3 particles have a size of 150–500 nm and are prepared by a solid-state method. The main powder in the ceramic powder formulation (referring to BaTiO3 and Na, by molar percentage) 0.5 Bi 0.5The amount of the doped powder (Nb2O5, MeO, MgCO3) is 0.3-5 mol% of the total amount of the powder.

[0006] The BaTiO3-based main phase provides ferroelectric phase polarization performance, NBT is used as a peak-shifting agent to move the Curie peak to a high temperature to meet the high temperature stability requirement, Nb is used as a donor dopant to promote the formation of a core-shell structure, and MeO is used as an acceptor dopant to compensate for the Nb 5+ Ti 4+ The charge imbalance caused by the ions and the adjustment of the distribution of the doped elements, and MgCO3 is used to inhibit grain growth and reduce dielectric loss.

[0007] In the mixed powder composed of the main powder and the doped powder synthesized by the traditional solid phase method, a small amount of one or more of the submicron or nanometer transition metal element oxides and other additive components are added, which are uniformly mixed by a wet method and dried to obtain a dielectric ceramic for MLCC. During calcination, the softening temperature of part of the additives is low, which will be dissolved into a liquid phase first. As the temperature rises, the liquid phase increases, gradually wrapping the solid phase BaTiO3 grains that have not had time to grow, forming a shell-core structure, which inhibits the further growth of the barium titanate grains, and finally a fine-grained dielectric ceramic is obtained, which improves the temperature characteristics of the dielectric ceramic. The temperature stability meets the X7R dielectric material standard established by the American Electronics Association.

[0008] If the dopant does not contain the aforementioned composition, the dielectric ceramic material prepared cannot meet the X7R standard and has good high-temperature impedance characteristics and low dielectric loss factor.

[0009] The Me in the transition metal oxide MeO is any one or more of Fe, Ni, Co, and Mn.

[0010] The amount of the dispersant added is 0.5-5 parts by mass based on 100 parts by mass of the mixed powder composed of the main powder and the dopant, and the amount of the binder added is 5-15 parts by mass.

[0011] The dispersant includes a polyethylene oxide resin. The dispersant of the present application is not particularly limited, but for the purpose of achieving the aforementioned dispersion, the dispersant can be a polyethylene oxide resin and other resins.

[0012] The binder includes a polyvinyl acetal resin. The binder of the present application is not particularly limited, but for the purpose of achieving the aforementioned binding, the binder is a polyvinyl acetal resin and other resins.

[0013] The preparation method of the high-temperature impedance X7R dielectric ceramic material includes the following steps:

[0014] S1, take the formula amount of BaTiO3 and Na 0.5 Bi 0.5 TiO3, mixed by 9:1 molar percentage after ball milling, pre-sintered into BT-NBT ceramic powder, the main powder is obtained; wherein, the pre-sintering temperature is 1200-1400℃, and the pre-sintering time is 2-4h;

[0015] S2, take the formula amount of Nb2O5, MeO and MgCO3, pre-sintered at 650-750℃ for 1-2h to synthesize the dopant;

[0016] S3, after mixing the main powder obtained in S1 with the dopant obtained in S2, add a dispersant and grind to obtain a powder mixture;

[0017] S4, add a binder and a solvent to the powder mixture, and after mixing, form a ceramic slurry;

[0018] S5, after the ceramic slurry is shaped and dried, a sheet is obtained;

[0019] S6, sinter the sheet to obtain a high-temperature impedance X7R dielectric ceramic material.

[0020] The particle size D50 of the powder mixture in S3 is 0.340-0.355μm, and the specific surface area is 3.5-3.6m 2 / g.

[0021] The solvent in S4 includes one or more of water, anhydrous ethanol or toluene.

[0022] The sintering temperature in S6 is 1230-1350℃, the sintering atmosphere is 0.5-3.5% H2-N2 by volume fraction, and the sintering time is 4 hours.

[0023] The application of the high-temperature impedance X7R dielectric ceramic material in a multilayer ceramic capacitor.

[0024] The main reason for the significant decrease in dielectric constant of traditional BaTiO3-based dielectric materials above 125℃ is the ferroelectric-paraelectric phase transition of BaTiO3 above the Curie temperature, which causes the dielectric constant to decrease significantly. Therefore, it is necessary to move the Curie temperature peak to a higher temperature to meet the high-temperature performance requirements. 0.5 Bi 0.5 TiO3 has a high phase transition temperature (320℃), and has a similar ABO3-type perovskite structure as BaTiO3, so it can form a solid solution with BaTiO3. 0.5 Bi 0.5Na / Bi ions in TiO3 can jointly substitute Ba ions in A site of BaTiO3 in a ratio of 1:1, which can greatly affect the Ti-O bond energy in the adjacent Ti-O octahedron, so that the Curie temperature of BaTiO3 is moved to the high temperature direction.

[0025] In order to make the medium system have good dielectric constant and temperature stability, it is necessary to form a core-shell structure in the crystal grain. Nb is selected as a donor element to dope and substitute Ti ions in B site of BaTiO3. The addition of Nb makes the phase transition peak (shell peak) of the dielectric material in the high temperature region be depressed and widened, and the phase transition peak (core peak) in the low temperature region moves to the low temperature direction. In addition, the donor doping can also reduce the oxygen vacancy and enhance the high temperature stability. Due to the superposition and flattening of the shell peak and the core peak, the temperature stability of the overall dielectric temperature curve is obviously improved.

[0026] MeO is used as an acceptor element for doping. As a transition metal element, MeO can affect the reaction between the donor element Nb and BT in the (1-x)BaTiO3-xNa 0.5 Bi 0.5 TiO3-Nb2O5 system, which can affect the reaction between the donor element Nb and BT, and then adjust the diffusion and distribution of Nb in the crystal grain, that is, affect the core / shell ratio and relative strength in the crystal grain, and improve the temperature stability of the system. In addition, the acceptor doping can reduce the dielectric loss and bound free moving electrons, and enhance the insulation impedance.

[0027] Due to the effect of the grain size, the grain size of BaTiO3 should not be too large. Therefore, in order to refine the grain and improve the dielectric constant, Mg 2+ ions have a low diffusion rate in the BaTiO3 crystal grain, so Mg element is used for B site doping, so that Ba(Ti x Mg 1-x )O3 in paraelectric phase is formed outside the crystal grain to wrap the pure phase BaTiO3. In addition, the relatively dense shell layer can also inhibit the further diffusion of other doping elements in the crystal grain, which is beneficial to form a suitable micro core-shell structure.

[0028] Advantages of the present application:

[0029] The present application adopts BaTiO3-Na 0.5 Bi 0.5The ceramic dielectric material is prepared by using TiO3-Nb2O5-MeO-MgCO3 system, adding a small amount of sub-micron or nano-sized transition metal element oxides in the main powder, mixing uniformly, drying, and calcining to obtain the dielectric porcelain material for MLCC. In the calcining process, the softening temperature of part of the additives is low, which is dissolved as liquid phase first. With the increase of temperature, the liquid phase increases, gradually wrapping the solid phase BaTiO3 grains which have not grown up yet, forming a shell-core structure, which inhibits the further growth of the barium titanate grains, and finally solid-solubilizes into fine-grained dielectric ceramic, which improves the temperature characteristics of the dielectric ceramic, and the temperature stability meets the X7R dielectric material standard formulated by the American Electronics Association.

[0030] When barium titanate is sintered in a reducing atmosphere, it is easy to lose oxygen at high temperature and become a semiconductor. Magnesium, calcium, manganese and other compounds play the role of acceptor in the calcining process of the porcelain dielectric, and the oxygen vacancy concentration caused by them is greater than that caused by oxygen volatilization, so that the barium titanate can also maintain high insulation resistivity when sintered in a reducing atmosphere. The present application meets the X7R dielectric porcelain material formula, and has good high-temperature impedance characteristics and low dielectric loss factor (tan δ). BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only a part of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0032] Figure 1 The preparation flow chart of the high-temperature impedance X7R dielectric ceramic material of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application more clear, the following will further illustrate the present application in combination with specific embodiments.

[0034] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present application should be understood as the usual meaning understood by those skilled in the art to which the present application belongs. The words such as "include" or "contain" mean that the elements or objects before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0035] The properties of the powder used in the present application are shown in Table 1:

[0036] Table 1: Selection of raw powder used

[0037] No. Raw material name Particle morphology Particle size specification 1 BaTiO3 Spherical or spheroidal 150-500 nm 2 Na 0.5 Bi 0.5 TiO3]]> Spherical or spheroidal 150-300 nm 3 [Nb2O5] Spherical or spheroidal 30-40 nm 4 MgCO3 Spherical or spheroidal 30-50 nm 5 MeO Spherical or spheroidal 30-60 nm

[0038] The present application is embodied as follows:

[0039] Example 1

[0040] The preparation method of the high-temperature resistant X7R dielectric ceramic material in this example is carried out according to the following steps:

[0041] The main phase BaTiO3 and Na 0.5 Bi 0.5 TiO3 are mixed by the solid phase method at a molar percentage of 9:1 (the material selection is shown in Table 1), and sintered at a sintering temperature of 1300°C for 3h to obtain the main powder; Nb2O5, MgCO3, MeO, etc. are mixed by the solid phase method according to a certain ratio (the material mixing ratio is shown in Table 2), and sintered at a sintering temperature of 700°C for 2h to obtain the dopant; based on 100 parts by mass of the mixed powder composed of the main powder and the dopant, 20% by mass of toluene solvent, 20% by mass of ethanol solvent and 1% by mass of dispersant AKM-0531 are added respectively. After mixing uniformly, a vertical bead mill is used for grinding for 3.5 hours, thereby obtaining a slurry mixture with a particle size D50 = 0.340-0.355um and a specific surface area BET = 3.5-3.6m 2 / g, and then 6% by weight of PVB (polyvinyl butyral resin) is added to the powder mixture, and uniformly mixed to obtain a slurry, and the slurry is dried and pressed into a compact.

[0042] Examples 2-6

[0043] Examples 2-6 are all manufactured by a method similar to that of Example 1. The difference is that the amount of Nb2O5 is changed in Examples 2-6, and the specific conditions and evaluation results are shown in Table 2.

[0044] Table 2: Amount of main powder and dopant added in Examples 1-6 and corresponding test results

[0045]

[0046] As can be seen from Table 2, the addition of the donor doping element Nb makes the dielectric material form a core-shell structure, and as the amount of addition increases, the proportion of the shell layer inside the grain decreases. The addition of Nb makes the phase transition peak (shell peak) in the high-temperature region of the dielectric material be depressed and broadened, and the phase transition peak (core peak) in the low-temperature region moves to the low-temperature direction, making the room temperature dielectric constant K value significantly increase.

[0047] Preferably, when the doping amount of the donor element Nb2O5 is 0.2mol%, the TCC of the dielectric material at -55°C-125°C is not greater than 15% and the dielectric constant K value reaches 2586, and the dielectric loss is less than 5%.

[0048] Examples 7-10

[0049] Examples 7-10 were manufactured in a similar manner to Example 1. The difference is that Examples 7-10 changed the amount of Ni2O3, and the specific conditions and evaluation results are shown in Table 3 below.

[0050] Table 3: Main powder, dopant addition amount, and corresponding test results of Examples 7-10

[0051]

[0052] As can be seen from Table 3, when the acceptor element Ni2O3 is used for doping, the donor element Nb 5+ In the case of doping substitution Ti 4+ causes charge imbalance, so the form of donor-acceptor co-doping is used to reduce oxygen vacancies and free electrons. In addition, the slow diffusion speed of MgCO3 can inhibit abnormal grain growth, adjust the core-shell ratio, and reduce dielectric loss.

[0053] Preferably, when the doping amount of the acceptor element Ni2O3 is 1.0 mol%, the TCC of the dielectric material at -55°C to 125°C is not greater than 15% and the dielectric constant K value reaches 2586, and the dielectric loss is less than 5%.

[0054] Examples 11-14

[0055] Examples 11-14 were manufactured in a similar manner to Example 1. The difference is that Examples 11-13 changed the element category of MeO, and Example 14 changed the addition amount of MgCO3, and the specific conditions and evaluation results are shown in Table 4 below.

[0056] Table 4: Main powder, dopant addition amount, and corresponding test results of Examples 11-14

[0057]

[0058] As can be seen from Table 4, when the acceptor element MeO is used for doping, the diffusion and distribution of Nb in the grain are adjusted, and the free-moving electrons are bound, the core / shell ratio and relative strength in the grain are adjusted, and the dielectric loss is reduced. In addition, the slow diffusion speed of MgCO3 can inhibit abnormal grain growth, adjust the core-shell ratio, and reduce dielectric loss.

[0059] Those skilled in the art should understand that the above discussion of any embodiment is only exemplary, and is not intended to suggest that the present application is limited to these examples; under the idea of the present application, the above embodiments or technical features among different embodiments can also be combined, and the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for the sake of brevity. Any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A high temperature resistance X7R dielectric ceramic material, whose raw materials include main powder, dopant, dispersant and binder, characterized in that, The main powder is made of BaTiO3, Na 0.5 Bi 0.5 TiO3 in a molar ratio of 9:1 by ball milling and pre-sintering, the pre-sintering temperature is 1200-1400℃, and the pre-sintering time is 2-4h; the dopant is obtained by pre-sintering of Nb2O5, transition metal oxide MeO and MgCO3, the pre-sintering temperature is 650-750℃, and the pre-sintering time is 1-2h; in terms of molar parts, the main powder is 100 molar parts, the Nb2O5 is 0.1-1.0 molar parts, the MgCO3 is 0.1-1.0 molar parts, and the transition metal oxide MeO is 0.1-3.0 molar parts; in the transition metal oxide MeO, Me is any one or more of Fe, Ni, Co and Mn, and in terms of 100 mass parts of the mixed powder composed of the main powder and the dopant, the addition amount of the dispersant is 0.5-5 mass parts, and the addition amount of the binder is 5-15 mass parts.

2. The high temperature resistant X7R dielectric ceramic material according to claim 1, characterized in that, The dispersant includes a polyethylene oxide resin.

3. The high temperature resistant X7R dielectric ceramic material according to claim 1, characterized in that, The binder includes a polyvinyl acetal resin.

4. The process for the preparation of high temperature resistant X7R dielectric ceramic material according to any one of claims 1 to 3, characterized in that, The method includes the following steps: S1, take the formula amount of BaTiO3 and Na 0.5 Bi 0.5 TiO3, mixed by 9:1 in molar percentage, ball milled, pre-fired into BT-NBT ceramic powder, and the main powder is obtained; wherein, the pre-fired temperature is 1200~1400℃, and the pre-fired time is 2~4h; S2. Taking a formula amount of Nb2O5, MeO and MgCO3, pre-sintering at 650-750°C for 1-2 hours to synthesize a dopant; S3. Mixing the main powder obtained in S1 with the dopant obtained in S2, adding a dispersant and grinding to obtain a powder mixture; S4. Adding a binder and a solvent to the powder mixture, mixing to form a ceramic slurry; S5. Forming and drying the ceramic slurry to obtain a sheet; S6. Sintering the sheet to obtain a high-temperature resistance X7R dielectric ceramic material.

5. The method of claim 4, wherein the high temperature resistance X7R dielectric ceramic material is prepared by the steps of: mixing and kneading the above-mentioned components; and molding the mixture. The particle size D50 of the powder mixture in S3 is 0.340-0.355 μm, and the specific surface area is 3.5-3.6 m 2 / g.

6. The method of claim 4, wherein the high temperature resistance X7R dielectric ceramic material is prepared by the steps of: mixing and kneading the above-mentioned components; and molding the mixture. The solvent in S4 includes one or more of water, anhydrous ethanol or toluene.

7. The method for preparing the high-temperature impedance X7R dielectric ceramic material according to claim 4, characterized in that, The sintering temperature in S6 is 1230-1350°C, the sintering atmosphere is 0.5-3.5% H2-N2 by volume fraction, and the sintering time is 4 hours.

8. Use of the high-temperature resistance X7R dielectric ceramic material according to any one of claims 1-3 in a multilayer ceramic capacitor.

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