CN117658624A - X8R type ceramic dielectric material and preparation method and application thereof - Google Patents
X8R type ceramic dielectric material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses an X8R type ceramic dielectric material, a preparation method and application thereof, and the preparation method comprises the following steps: (1) According to the stoichiometry BaTiO 3 ‑x Bi 4 Ti 3 O 12 ‑y Nb 2 O 5 ‑z NiO‑w Mn 3 O 4 Weighing raw materials to obtain medium material mixed powder; wherein x, y, z and w represent mole percent and are expressed as BaTiO 3 Based on the molar weight of (1) < x < 2.5%, 1) < xy is less than or equal to 2%, z is less than or equal to 0 and less than or equal to 1%, w is less than or equal to 0 and less than or equal to 1%, and z and w are not simultaneously 0; (2) Mixing the dielectric material mixed powder with a binder, grinding and granulating, aging and sieving, and tabletting to obtain a ceramic green body; (3) And discharging the glue of the ceramic green body, and sintering to obtain the X8R type ceramic dielectric material. The invention can generate the X8R type ceramic dielectric material with a core-shell structure.
Description
Technical Field
The invention belongs to the technical field of multifunctional electronic ceramic materials, and particularly relates to an X8R type ceramic dielectric material, and a preparation method and application thereof.
Background
The multilayer ceramic capacitor (Multi-Layer Ceramic Chip Capacitors, MLCC) has the advantages of small volume and good performance, is a basic passive component with the widest application and the largest dosage in the modern electronic industry, and is known as rice in the electronic industry.
The key point of preparing the high-performance MLCC is the material technology of dielectric ceramic powder, the dielectric thin-layer technology and the co-firing technology of ceramic powder and metal electrodes. The material technology of the dielectric ceramic powder material requires the functionality of the dielectric material. BaTiO 3 Is a classical MLCC medium material matrix, but BaTiO 3 The dielectric properties of (a) are poor in temperature stability, limiting their application in high temperature environments above curie temperature (about 125 c). The high-speed development of the modern electronic industry puts higher requirements on the temperature stability of MLCC, and in order to adapt to the working environment with higher temperature in the fields of automobile electronics, aerospace and the like, the high-speed development of the modern electronic industry puts higher demands on BaTiO 3 The material is doped and modified, and is regulated and controlled in structure, and the MLCC dielectric material with the capacitance temperature coefficient (Temperature Coefficients od Capacitance, TCC) meeting the X8R standard is significant, namely, when the capacitor operates at the temperature of-55 ℃ to 150 ℃, the capacitance floats within-15% to 15% on the basis of the nominal value. In addition, the co-firing of the ceramic powder and the metal electrode also provides requirements for the preparation performance of the dielectric material. Electrodes commonly used for MLCCs include noble metal electrodes (PMEs) containing Pd/Ag and common metal electrodes (BMEs) containing Ni/Cu. For PME MLCC, the preparation does not need to strictly control atmosphere, thereby ensuring the electrical insulation of the product and being simpler than BME MLCC preparation process. The PME electrode material with lower Pd content and higher Ag content can reduce the MLCC cost, but the higher Ag content limits the sintering temperature, and the dielectric material cofired with the Pd/Ag electrode with high Ag content needs to achieve better sintering quality at lower sintering temperature.
As described above, in view of practical production and application, it is important to develop an X8R type ceramic dielectric material having a low sintering temperature.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems in the related art to some extent. Therefore, the invention aims to provide an X8R type ceramic dielectric material, and a preparation method and application thereof. The ceramic dielectric material has good dielectric property and temperature stability, and can be used as a dielectric material for MLCC.
In one aspect of the present invention, there is provided a method of preparing an X8R-type ceramic dielectric material, comprising:
(1) According to the stoichiometry BaTiO 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO-w Mn 3 O 4 Weighing BaTiO 3 、Bi 4 Ti 3 O 12 、Nb 2 O 5 NiO and Mn 3 O 4 Obtaining medium material mixed powder;
wherein x, y, z and w represent mole percent and are expressed as BaTiO 3 Based on the molar weight, x is more than or equal to 1% and less than or equal to 2.5%, y is more than or equal to 1% and less than or equal to 1%, z is more than or equal to 0 and less than or equal to 1%, w is more than or equal to 0 and less than or equal to 1%, and z and w are not simultaneously 0;
(2) Mixing the dielectric material mixed powder with a binder, grinding and granulating, aging and sieving, and tabletting to obtain a ceramic green body;
(3) And discharging the glue of the ceramic green body, and sintering to obtain the X8R type ceramic dielectric material.
In the preparation method of the invention, solid mass transfer occurs in the sintering process, and the doping element Bi, nb, ni, mn diffuses into BaTiO 3 Lattice, pseudo-cubic BaTiO can be obtained 3 And (3) a base ceramic. During sintering, due to different diffusion rates and mutual influence of doping elements, the doping elements are used for BaTiO 3 The diffusion of the grains is incomplete, forming an X8R type ceramic dielectric material with a core-shell structure. Specifically, nb is in BaTiO 3 The diffusion rate in the ceramic core-shell structure is low, the formation of the ceramic core-shell structure is promoted by the non-uniformity of diffusion, and Nb enters the BaTiO 3 Will pull down after latticeThe inner temperature, thereby increasing the low temperature dielectric constant; introducing transition metal oxide NiO, mn 3 O 4 Can be used for adjusting the proportion of the core shell; in addition, bi having a high Curie temperature and a low melting point 4 Ti 3 O 12 Can improve BaTiO by adding 3 Curie temperature of the ceramic and lower sintering temperature. The method can prepare the ceramic dielectric material with the doping concentration decreasing from the outer shell to the grain nucleus, and the formed core-shell structure is beneficial to improving the dielectric temperature stability, so that the ceramic dielectric material meets the X8R standard.
According to an embodiment of the invention, (z+w). Gtoreq.0.8%.
According to the embodiment of the invention, 0.8% to less than or equal to (z+w) to less than or equal to 1.3%, thereby further improving the dielectric property and temperature stability of the X8R type ceramic dielectric material.
According to an embodiment of the invention, bi 4 Ti 3 O 12 The preparation method comprises the following steps:
3, weighing bismuth source and titanium source according to the atomic mol ratio of Bi to Ti of (4-4.3), adding solvent, ball milling and mixing, and drying to obtain mixed powder;
calcining the mixed powder at 750-850 ℃ for 3-4 h to obtain Bi 4 Ti 3 O 12 。
According to an embodiment of the invention, the bismuth source comprises Bi 2 O 3 The titanium source comprises TiO 2 。
According to an embodiment of the present invention, in step (2), the binder includes at least one of an aqueous solution of polyvinyl alcohol and an ethanol solution of polyvinyl alcohol Ding Quanzhi.
According to an embodiment of the invention, the aging time is 2-5 hours. Therefore, the materials are mixed more uniformly.
According to an embodiment of the present invention, in the step (3), the conditions for discharging the glue include: heating to 500-600 deg.c and maintaining for 2-4 hr.
According to the embodiment of the invention, the temperature rising rate in the glue discharging stage is 2-3 ℃ per minute.
According to an embodiment of the present invention, the sintering conditions include: heating to 1140-1170 deg.c and sintering for 3-4 hr. Thus, a densified X8R-type ceramic can be obtained.
According to the embodiment of the invention, the pressure intensity in the tabletting molding is 2MPa to 6MPa.
According to an embodiment of the invention, the temperature rise rate in the sintering stage is 5 to 10 ℃/min.
In a second aspect of the present invention, there is provided an X8R-type ceramic dielectric material obtained by the above-described preparation method.
The crystal grain of the X8R type ceramic dielectric material prepared by the method has a core-shell structure, the core-shell structure is formed due to uneven distribution of doping elements in the ceramic crystal grain, a region almost without doping elements in the ceramic crystal grain is called a nucleus body, a region where the doping elements gather in the crystal grain is a shell, and the doping concentration from the shell to the nucleus body of the crystal grain is decreased, so that the formed core-shell structure is beneficial to improving the dielectric temperature stability. In addition, the existence of Ni and Mn balances the influence caused by Bi and Nb as donor doping, and dielectric loss is effectively reduced.
According to an embodiment of the invention, the X8R-type ceramic dielectric material is pseudocubic BaTiO 3 And (3) a base ceramic.
According to the embodiment of the invention, the dielectric constant at 25 ℃ and the test frequency of 1kHz is 1875-2370, and the dielectric loss is less than 1.5%.
In a third aspect of the present invention, there is provided the use of the X8R ceramic dielectric material according to the second aspect of the present invention in the preparation of an MLCC.
According to the embodiment of the invention, the dielectric material can be co-fired with a silver-palladium electrode, wherein the palladium content in the silver-palladium electrode is 25-30 wt%, and the co-firing temperature is 1140-1150 ℃. Thus, modified BaTiO 3 Sintering temperature of ceramic is purer than BaTiO 3 The sintering temperature of the ceramic (1300 ℃) is reduced, and the ceramic can be used as a dielectric material for the practical production of PME MLCC.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 shows Bi synthesized in example 1 4 Ti 3 O 12 Powder XRD pattern;
FIG. 2 is an XRD pattern of the ceramic dielectric of example 1;
FIG. 3 is a TEM image of the ceramic dielectric of example 1;
FIG. 4 is a SEM image of a cross-section of a ceramic dielectric of example 1;
FIG. 5 is a graph showing the dielectric constant and dielectric loss versus temperature of the ceramic dielectric of example 1;
FIG. 6 is a SEM image of a cross-section of a ceramic dielectric of example 2;
FIG. 7 is a graph of dielectric constant and dielectric loss versus temperature for the ceramic dielectric of example 2;
FIG. 8 is a graph of dielectric constant and dielectric loss versus temperature for the ceramic dielectric of example 3;
FIG. 9 is a graph of the temperature coefficient of capacitance and dielectric loss versus temperature for the ceramic dielectric of example 6;
FIG. 10 is a graph of the temperature coefficient of capacitance and dielectric loss versus temperature for the ceramic dielectric of comparative example 1;
FIG. 11 is a graph of the temperature coefficient of capacitance and dielectric loss versus temperature for the ceramic dielectric of comparative example 2.
Detailed Description
The following detailed description of the embodiments of the invention is intended to be illustrative of the invention and is not to be taken as limiting the invention. In one aspect of the present invention, a method for preparing an X8R-type ceramic dielectric material is provided, comprising the steps of:
(1) According to the stoichiometry BaTiO 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO-w Mn 3 O 4 Weighing BaTiO 3 、Bi 4 Ti 3 O 12 、Nb 2 O 5 NiO and Mn 3 O 4 Obtaining medium material mixed powder;
(2) Mixing the dielectric material mixed powder with a binder, grinding and granulating, aging and sieving, and tabletting to obtain a ceramic green body;
(3) And discharging the glue of the ceramic green body, and sintering to obtain the X8R type ceramic dielectric material.
In the preparation method of the invention, solid mass transfer occurs in the sintering process, and the doping element Bi, nb, ni, mn diffuses into BaTiO 3 Lattice, pseudo-cubic BaTiO can be obtained 3 And (3) a base ceramic. During sintering, due to different diffusion rates and mutual influence of doping elements, the doping elements are used for BaTiO 3 The diffusion of the grains is incomplete, forming an X8R type ceramic dielectric material with a core-shell structure. Specifically, nb is in BaTiO 3 The diffusion rate in the ceramic core-shell structure is low, the formation of the ceramic core-shell structure is promoted by the non-uniformity of diffusion, and Nb enters the BaTiO 3 The Curie temperature is lowered after the crystal lattice, so that the low-temperature dielectric constant is improved; introducing transition metal oxide NiO, mn 3 O 4 Can be used for adjusting the proportion of the core shell; in addition, bi having a high Curie temperature and a low melting point 4 Ti 3 O 12 Can improve BaTiO by adding 3 Curie temperature of the ceramic and lower sintering temperature. The method can prepare the ceramic dielectric material with the doping concentration decreasing from the outer shell to the grain nucleus, and the formed core-shell structure is beneficial to improving the dielectric temperature stability, so that the ceramic dielectric material meets the X8R standard.
In the present invention, stoichiometric BaTiO 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO-w Mn 3 O 4 Wherein x, y, z and w each represent: by BaTiO 3 Based on the molar amount of Bi 4 Ti 3 O 12 、Nb 2 O 5 NiO and Mn 3 O 4 The mol percent is more than or equal to 1 percent and less than or equal to 2.5 percent, and is more than or equal to 1 percent and less than or equal to 2 percent of x, more than or equal to 0 and less than or equal to 1 percent of z, more than or equal to 0 and less than or equal to 1 percent of w, and z and w are not simultaneously 0. In other words, relative to 1mol of BaTiO 3 ，Bi 4 Ti 3 O 12 The dosage of (C) is 0.01 mol-0.025 mol, nb 2 O 5 The amount of NiO is 0.01 to 0.02mol, the amount of NiO is 0 to 0.01mol, mn 3 O 4 The amount of NiO and Mn is 0 to 0.01mol 3 O 4 The total amount of (2) is not 0.
Specifically, in the stoichiometric formula, z=0, 0 < w.ltoreq.1%, or 0 < z.ltoreq.1%, w=0, or 0 < z.ltoreq.1%, 0 < w.ltoreq.1%.
In some embodiments, in BaTiO 3 The molar quantity of (z+w) is more than or equal to 0.8 percent.
Further, 0.8% or less (z+w) or less 1.3%, for example, 0.8%, 1%, 1.3%, etc., whereby the core-shell ratio of the core-shell structure is regulated to improve the dielectric stability of the material.
In some embodiments, in step (1), bi 4 Ti 3 O 12 The preparation method comprises the following steps:
3, weighing bismuth source and titanium source according to the atomic mol ratio of Bi to Ti of (4-4.3), adding solvent, ball milling and mixing, wherein the solvent can adopt absolute ethyl alcohol and the like, and drying to obtain mixed powder;
calcining the mixed powder at 750-850 ℃ for 3-4 hours, for example, at 750-800 ℃ and 850 ℃ for 3-4 hours, etc., to obtain single-phase Bi 4 Ti 3 O 12 。
As some examples, the atomic molar ratio of Bi to Ti is, for example, 4.02:3, 4.1:3, 4.2:3, etc.
In some embodiments, the bismuth source comprises Bi 2 O 3 The titanium source comprises TiO 2 。
In some embodiments, in step (2), the binder comprises at least one of an aqueous solution of polyvinyl alcohol (PVA) and an ethanol solution of polyvinyl butyral ester (PVB). The concentration of the binder is not particularly limited and may be selected according to the actual conditions. In general, the mass concentration of the polyvinyl alcohol in the aqueous solution of the polyvinyl alcohol is 5wt% to 8wt%; the mass concentration of the polyvinyl butyral ester in the ethanol solution of the polyvinyl butyral Ding Quanzhi is 5-8 wt%.
In some embodiments, in step (2), the aging time is 2h to 5h, e.g., the aging time is 2h, 3h, 4h, 5h, etc., whereby the binder solvent is volatilized after the blank is aged.
In some embodiments, in step (2), the mesh number of the screen is 130 mesh to 200 mesh, e.g., 130 mesh, 140 mesh, 160 mesh, 175 mesh, 180 mesh, 200 mesh, etc. Therefore, the dispersed powder with the particle size close to that of the powder is obtained, the powder is convenient to tablet, and the problem that the powder is easy to crack due to uneven stress during agglomeration and tablet pressing is avoided.
In some embodiments, in step (3), the pressure in the tablet forming is 2MPa to 6MPa, for example, 2MPa, 4MPa, 5MPa, 6MPa, etc.
In some embodiments, in step (3), the conditions for discharging the glue include: heating to 500-600 ℃, for example, heating to 500 ℃, 550 ℃, 600 ℃, and the like, and preserving heat for 2-4 hours, for example, preserving heat for 2 hours, 3 hours, 4 hours, and the like. Thus, the organic matters in the green body are removed completely, and the shape and the size are unchanged.
In some embodiments, in step (3), the temperature rise rate in the paste ejection stage is 2 ℃/min to 3 ℃/min, such as 2 ℃/min, 3 ℃/min, and the like.
In some embodiments, in step (3), the sintering conditions include: heating to 1140-1170 deg.C, sintering for 3-4 h, for example, heating to 1140 deg.C, 1150 deg.C, 1170 deg.C, etc., and sintering at this temperature for 3h, 4h, etc., thereby producing ceramic with high densification degree.
In some embodiments, in step (3), the temperature rising rate of the sintering stage is 5 ℃/min to 10 ℃/min, for example, the temperature rising rate is 5 ℃/min, 6 ℃/min, 8 ℃/min, 10 ℃/min, and the like, so that the sintering efficiency can be improved, and the cracking problem caused by too fast temperature rising can be avoided.
In a second aspect of the invention, an X8R type ceramic dielectric material prepared by the preparation method in the first aspect is provided.
The crystal grain of the X8R type ceramic dielectric material has a core-shell structure, the core-shell structure is formed due to the fact that doping elements are unevenly distributed in ceramic crystal grains, in the ceramic crystal grains, the area almost without the doping elements is called a nucleus body, the area where the doping elements gather in the crystal grains is a shell, the doping concentration from the shell to the nucleus body of the crystal grains is decreased, and the formed core-shell structure is beneficial to improving the dielectric temperature stability. In addition, the existence of Ni and Mn balances the influence caused by Bi and Nb as donor doping, and dielectric loss is effectively reduced.
In some embodiments, the X8R ceramic dielectric material is pseudocubic BaTiO 3 And (3) a base ceramic.
In some embodiments, the dielectric constant at 25 ℃ at a test frequency of 1kHz is 1875-2370, e.g., 1875, 2090, 2115, 2130, 2370, 2185, etc., corresponding to a dielectric loss of less than 1.5%, e.g., 0.8%, 1.14%, 1.21%, 1.3%, 1.36%, 1.47%, etc.
In a third aspect of the present invention, there is provided a use of the X8R-type ceramic dielectric material of the second aspect in the preparation of an MLCC, comprising: and co-firing the ceramic green body and a silver-palladium electrode.
In some embodiments, the palladium content in the silver palladium electrode is 25wt% to 30wt%, e.g., 25wt%, 28wt%, 30wt%, etc., the cofiring temperature is 1140 ℃ to 1170 ℃, e.g., the cofiring temperature is 1140 ℃, 1150 ℃, 1160 ℃, 1170 ℃, etc. Therefore, the ceramic green body and the silver-palladium electrode can be co-fired at a lower temperature, the dielectric temperature stability of the co-fired ceramic meets the X8R standard, and meanwhile, the ceramic has lower dielectric loss, and can be used as a dielectric material in the actual production of PME MLCC.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not limiting in any way.
The following examples are presented to illustrate the X8R type ceramic dielectrics of the present invention and methods of making and using the same.
Example 1
1) 6.7844g Bi is weighed 2 O 3 And 1.6773g TiO 2 Adding absolute ethyl alcohol, ball milling and mixing for 10 hours, drying at 100 ℃ to obtain mixed powder, calcining at 850 ℃ for 4 hours, and obtaining Bi through solid phase reaction 4 Ti 3 O 12 Pre-pulverizing;
2) According to the chemicalStoichiometric BaTiO 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 Taking BaTiO from z NiO 3 、Bi 4 Ti 3 O 12 、Nb 2 O 5 NiO, wherein x, y, z and w represent mole percent, expressed as BaTiO 3 Based on the molar weight of the mixture, x is 1.54%, y is 2%, z is 0.8% and w is 0%, and the mixture is ball-milled, mixed and dried to obtain medium material mixed powder;
3) Adding 5wt% of polyvinyl alcohol aqueous solution into the mixed powder obtained in the step 2), grinding and granulating, aging for 2 hours, sieving with a 130-mesh screen, taking 0.4g of powder, and tabletting under 2MPa by using a tabletting mold with the diameter of 10mm to obtain a wafer green body;
4) Heating the wafer green body to 600 ℃ at a speed of 2 ℃/min, preserving heat for 2 hours to perform glue discharging, and heating to 1150 ℃ at a speed of 10 ℃/min to sinter for 4 hours to obtain an X8R type ceramic dielectric medium;
5) And (3) polishing and polishing the obtained ceramic dielectric, coating medium-temperature silver paste on the upper surface and the lower surface of the ceramic dielectric, and heating to 600 ℃ at a heating rate of 5 ℃/min for 11min to obtain the wafer capacitor.
Example 2
X8R-type ceramic dielectric and wafer capacitor were prepared as in example 1, except that the dielectric material powder mixture was prepared according to the stoichiometric formula BaTiO 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO-w Mn 3 O 4 The feed amount was controlled so that x was 1.54%, y was 2%, z was 0.8%, and w was 0.5%.
Example 3
X8R-type ceramic dielectric and wafer capacitor were prepared as in example 1, except that BaTiO was stoichiometrically 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -w Mn 3 O 4 The amount of the feed was controlled so that x was 1.54%, y was 1% and w was 1%.
Example 4
X8R-type ceramic dielectric and wafer capacitor were prepared as in example 1, except that BaTiO was stoichiometrically 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO controls the feed amount such that x is 2.04%, y is 1% and z is 0.8%.
Example 5
X8R-type ceramic dielectric and wafer capacitor were prepared as in example 1, except that BaTiO was stoichiometrically 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO controls the feed amount such that x is 2.04%, y is 1% and z is 1%.
Example 6
Other operations are the same as in example 2, except steps 4) and 5):
4) Silver palladium electrode paste (Ag/Pd: the mass ratio is 7: 3) Baking in an oven at 120deg.C for 30min;
5) Heating the wafer green body coated with the silver-palladium electrode to 600 ℃ at a speed of 2 ℃/min, preserving heat for 2 hours to remove glue, and then heating to 1150 ℃ at a speed of 10 ℃/min to sinter for 4 hours to obtain the wafer capacitor.
Comparative example 1
Other operations are the same as example 1, except that z is 0, i.e., niO is removed based on example 1.
Comparative example 2
Other operations are the same as example 4, except that z is 0%, i.e., niO is removed based on example 4, as in example 4.
Bi of example 1 4 Ti 3 O 12 Characterization tests were performed on the pre-fabricated powders, the ceramic dielectrics of examples 1 to 6 and comparative examples 1 to 2, and wafer capacitors.
1. For Bi synthesized in example 1 4 Ti 3 O 12 XRD test of the powder shows that the powder is shown in figure 1, and compared with PDF card 72-1019, the powder has the same diffraction peak, and the single-phase Bi is successfully prepared 4 Ti 3 O 12 The powder is used as a raw material reagent.
2. XRD testing of the ceramic of example 1 showed that no peak was separated at 45℃as shown in FIG. 2, which proves that pseudocubic BaTiO was produced 3 . XRD patterns of examples 2 to 6 and comparative examples 1 to 2 are similar to those of example 1, showing that sintering at 1150℃produces pseudocubic BaTiO 3 。
3. As a result of TEM characterization of the ceramic dielectric of example 1, as shown in FIG. 3, it is apparent from FIG. 3 that the grains have circular regions with ferroelectric domain stripes, and no stripes outside the circles, demonstrating that the synthesized ceramic has a core-shell structure due to the fact that BaTiO 3 The ceramic has ferroelectricity at room temperature, the undoped nucleus retains ferroelectricity at room temperature, and the doped BaTiO 3 The base ceramic, i.e. the corresponding shell, has no ferroelectricity at room temperature.
4. The ceramic dielectrics of examples 1 and 2 were microscopically characterized in cross section and as a result, see fig. 4 and 6, respectively, it is understood from fig. 4 and 6 that the corresponding dielectric materials were densified at a sintering temperature of 1150 ℃.
5. The wafer capacitors of examples 1 to 6 and comparative examples 1 to 2 were tested for the change of dielectric constant and dielectric loss with temperature at a temperature ranging from-55 ℃ to 150 ℃ under 1kHz by a Novocontrol instrument to obtain corresponding curves of the change of dielectric constant and dielectric loss with temperature of the ceramic dielectric; based on the curves of the dielectric constants of the ceramic dielectrics of the example 6 and the comparative examples 1 to 2 changing with temperature, the TCC calculation of the temperature coefficient was performed to obtain the corresponding curves of the temperature coefficient and the dielectric loss of the ceramic dielectrics changing with temperature.
Wherein the temperature coefficientC T Is a capacitance value at T temperature within a temperature range of-55 ℃ to 150 ℃, C 25℃ Is a capacitance value of 25 ℃.
The results of the dielectric constants and dielectric losses of the ceramic dielectrics of examples 1 to 3 at 1kHz as a function of temperature are shown in fig. 5, 7 and 8, with the ordinate epsilon representing the dielectric constant and tan delta representing the dielectric loss. FIG. 5 is a graph showing the relationship between the dielectric constant and the dielectric loss of the ceramic of example 1 and temperature, and it can be seen from FIG. 5 that the dielectric constant changes smoothly with temperature, satisfying the X8R standard, but the dielectric loss increases with increasing temperature; FIG. 7 is a graph showing the relationship between the dielectric constant and the dielectric loss of the ceramic of example 2 and the temperature, wherein the dielectric constant changes smoothly with temperature, meets X8R standard, and has lower dielectric loss as shown in FIG. 7; FIG. 8 is a graph showing the relationship between the dielectric constant and the dielectric loss of the ceramic of example 3 and the temperature, wherein the dielectric constant changes smoothly with temperature, meets X8R standard, and has lower dielectric loss as shown in FIG. 8; the high Wen Juli peak is more pronounced due to the lower Nb content.
FIG. 9 is a graph showing the relationship between the capacitance and dielectric loss of the ceramic dielectric material of example 6 and the temperature T (-50 ℃ to 150 ℃), wherein one ordinate tan delta represents the dielectric loss and the other ordinate represents the capacitance TCC; as can be seen from fig. 9, the ceramic green body of example 6 was co-fired with a silver-palladium electrode at 1150 ℃ and the dielectric temperature stability of the resulting ceramic dielectric met the X8R standard while having lower dielectric loss, indicating that the ceramic could be applied as a dielectric in a PME MLCC. The dielectric constant, dielectric loss versus temperature graphs of examples 1-3 and the temperature coefficient, dielectric loss versus temperature graph of example 6 are common in that they have a high Wen Juli peak (around 130 ℃) and a less pronounced low Wen Kuanfeng, the bimodal character being caused by the core-shell structure-the high Wen Juli peak being caused by the grain nuclei (almost no doping element BaTiO) 3 ) The low Wen Kuanfeng is determined by the grain shell (the doping elements Bi, nb, ni, mn are aggregated and there is a concentration gradient).
FIG. 10 is a graph showing the relationship between the temperature coefficient (TCC) and the dielectric loss (tan delta) of the ceramic dielectric in comparative example 1 and temperature. As can be seen from fig. 10, the change in the capacitance temperature of comparative example 1 satisfies the X8R standard, but the dielectric loss increases to 20% at high temperature. The reason for this is probably due to the absence of NiO and Mn 3 O 4 As acceptor doping, while Bi and Nb as donor impurities doping increases the number of weak linking ions in the ceramic, resulting in increased dielectric losses at high temperatures.
FIG. 11 is a graph showing the relationship between the temperature coefficient (TCC) and the dielectric loss (tan delta) of the ceramic of comparative example 2 and temperature. As can be seen from FIG. 11, the ceramic has a temperature coefficient of up to 20% at 150 ℃ and does not meet the X8R standard. The reason for this is probably due to the absence of NiO and Mn 3 O 4 Regulating, in grainThe housing is in an excessive proportion resulting in a severely depressed peak at high Wen Juli.
The specific amounts of the raw materials used and the dielectric properties of the ceramic dielectrics used in examples 1 to 6 and comparative examples 1 to 2 are shown in Table 1.
TABLE 1
As can be seen from Table 1, the dielectric constants of the products of examples 1 to 6 at 25℃and test frequency of 1kHz are 1875 to 2370, the corresponding dielectric losses are less than 1.5%, and the TCC floating absolute values are 7% to 14%, all of which are less than 15%, indicating that the ceramic dielectrics of examples 1 to 6 all meet the X8R standard.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (10)
1. A method for preparing an X8R ceramic dielectric material, comprising the steps of:
(1) According to chemistryMetering BaTiO 3 -x Bi 4 Ti 3 O 12 -y Nb 2 O 5 -z NiO-w Mn 3 O 4 Weighing BaTiO 3 、Bi 4 Ti 3 O 12 、Nb 2 O 5 NiO and Mn 3 O 4 Obtaining medium material mixed powder;
wherein x, y, z and w represent mole percent and are expressed as BaTiO 3 Based on the molar weight, x is more than or equal to 1% and less than or equal to 2.5%, y is more than or equal to 1% and less than or equal to 1%, z is more than or equal to 0 and less than or equal to 1%, w is more than or equal to 0 and less than or equal to 1%, and z and w are not simultaneously 0;
(2) Mixing the dielectric material mixed powder with a binder, grinding and granulating, aging and sieving, and tabletting to obtain a ceramic green body;
(3) And discharging the glue of the ceramic green body, and sintering to obtain the X8R type ceramic dielectric material.
2. The method of producing an X8R ceramic dielectric material according to claim 1, wherein (z+w) is 0.8% or more;
alternatively, 0.8% or less (z+w) or less than 1.3%.
3. The method for producing an X8R-type ceramic dielectric material according to claim 1, wherein in the step (1), bi 4 Ti 3 O 12 The preparation method comprises the following steps:
weighing bismuth source and titanium source according to the atomic mol ratio of Bi to Ti of (4-4.3) to 3, adding solvent, ball milling and mixing, and drying to obtain mixed powder;
calcining the mixed powder at 750-850 ℃ for 3-4 h to obtain Bi 4 Ti 3 O 12 ；
Optionally, the bismuth source comprises Bi 2 O 3 The titanium source comprises TiO 2 。
4. The method of producing an X8R ceramic dielectric material according to claim 1, wherein in step (2), the binder comprises at least one of an aqueous polyvinyl alcohol solution and an ethanol polyvinyl butyral ester solution;
optionally, the aging time is 2-5 hours.
5. The method of claim 1, wherein in the step (3), the conditions for discharging the paste include: heating to 500-600 ℃, and preserving heat for 2-4 h;
optionally, the temperature rising rate of the glue discharging stage is 2-3 ℃/min.
6. The method of producing an X8R ceramic dielectric material according to claim 1, wherein in step (3), the sintering conditions include: heating to 1140-1170 ℃ and sintering for 3-4 h;
optionally, in the tabletting forming, the pressure is 2-6 MPa;
optionally, the temperature rise rate in the sintering stage is 5 ℃/min to 10 ℃/min.
7. An X8R ceramic dielectric material prepared by the method of any one of claims 1-6.
8. The X8R-type ceramic dielectric material of claim 7, wherein the X8R-type ceramic dielectric material is pseudocubic BaTiO 3 And (3) a base ceramic.
9. The X8R ceramic dielectric material of claim 7, wherein the X8R ceramic dielectric material has a dielectric constant of 1875-2370 at a test frequency of 1kHz at 25 ℃ and a corresponding dielectric loss of less than 1.5%.
10. Use of the X8R ceramic dielectric material according to any one of claims 7-9 for the preparation of an MLCC, comprising: co-firing the ceramic green body with a silver-palladium electrode;
optionally, the palladium content in the silver-palladium electrode is 25-30wt%, and the cofiring temperature is 1140-1170 ℃.
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