KR102664215B1 - Lead-free dielectric ceramic composition with stable high-temperature dielectric properties and manufacturing method thereof - Google Patents

Abstract

The present invention is (Bi _0.65-2x Ba _0.35-2x Na _0.46x Sr _0.01x )(Fe _0.65-0.65x Ti _0.35-0.1x Nb _0.74x Zr _0.01x )O ₃ (however, 0 < x ≤ 0.1) BiFeO ₃ -BaTiO ₃ based lead-free dielectric ceramic composition and manufacturing method thereof are shown. The BiFeO ₃ -BaTiO ₃ based ceramic composition according to the present invention has a high dielectric constant (more than 1000) even in a high temperature range up to approximately 500°C and has excellent dielectric constant. It has temperature stability and has a high dielectric constant (above 1000) and low dielectric loss value (less than 0.1) even in the high temperature range up to approximately 320℃, and not only has excellent temperature stability of dielectric constant and dielectric loss value, but is also superior to the existing BaTiO ₃ system. Since the high _- temperature phase transition temperature is _very high compared to Control of dielectric constant and prevention of deterioration of dielectric loss can be effectively achieved by controlling sintering conditions according to a combination of two or more.

Description

Lead-free dielectric ceramic composition with stable high-temperature dielectric properties and manufacturing method thereof {LEAD-FREE DIELECTRIC CERAMIC COMPOSITION WITH STABLE HIGH-TEMPERATURE DIELECTRIC PROPERTIES AND MANUFACTURING METHOD THEREOF}

The present invention relates to a ceramic composition having a high dielectric constant with high temperature stability, and more specifically, to a BiFeO ₃ -BaTiO ₃ based ceramic composition with low dielectric loss even at high temperatures and excellent temperature stability of dielectric constant at high temperatures, and a method for manufacturing the same.

Multi-layer ceramic capacitor (MLCC) is a representative passive device that accounts for 60% of passive components in IT electronic circuits such as mobile phones, personal PCs, and digital displays. It separates noise from the power supply circuit of active devices such as ICs. It is an important device whose roles, such as decoupling, removing DC components from the signal, and flattening the signal, are comparable to those of semiconductors, which are representative active devices.

Recently, the use of MLCC in future mobility, including the 4th industry, is expected to increase rapidly. In order to strengthen competitiveness in line with the development of industrial technology, constant dielectric characteristics can be maintained even in extreme environments, and high dielectric capacitance and temperature stability are required. Research and development is actively underway on the development of dielectric materials with , electrode and co-sintering process technology in a reducing atmosphere, and post-BaTiO ₃ ceramic dielectric composition.

In particular, MLCCs used in future automobiles or at high temperatures require a ceramic composition that has high dielectric constant and low dielectric loss while also having excellent dielectric properties with excellent temperature stability of dielectric constant and dielectric loss values in the high temperature range of 150 ℃ or higher.

Korean Patent Publication No. 10-2021-0114671 (Publication date: 2021.09.24) Korean Patent Publication No. 10-2017-0062066 (Publication date: 2017.06.07)

The technical problem to be solved by the present invention is to provide BiFeO ₃ -BaTiO ₃ (BF-BT) based ceramics, which have high dielectric constant and low dielectric loss in a high temperature range and excellent dielectric properties with excellent temperature stability of dielectric constant and dielectric loss values. It provides composition.

In order to achieve the above technical problem, the present invention proposes a lead-free dielectric ceramic composition represented by the following chemical formula.

[Chemical formula]

(Bi _0.65-2x Ba _0.35-2x Na _0.46x Sr _0.01x )(Fe _0.65-0.65x Ti _0.35-0.1x Nb _0.74x Zr _0.01x )O ₃ (BFBT-NSNZ)

(In the above formula, 0 < x ≤ 0.1).

In addition, as the x value of the above chemical formula increases, a lead-free dielectric ceramic composition is proposed, characterized in that the temperature range having a dielectric constant (ε _r ) value that satisfies the following inequality in the temperature range of 25 to 500°C increases.

0.85 × ε _r150℃ ≤ ε _r ≤ 1.15 × ε _r150℃

(In the above inequality, ε _r150℃ is the dielectric constant value measured at 150℃).

In addition, in the above formula, x = 0.10, and a lead-free dielectric ceramic composition is proposed, characterized in that it has a dielectric constant (ε _r ) value that satisfies the above inequality in the temperature range of 88 to 500°C.

In addition, as the value of

In addition, a lead-free dielectric ceramic composition is proposed, where x = 0.10 in the above formula and has a dielectric loss value (tanδ) of 0.1 or less at 75 to 316°C.

In addition, as the x value increases in the above formula, a lead-free ceramic composition is proposed, which has an energy storage density of more than 0.6 J/cm ³ and an energy storage efficiency of more than 70% up to 100 kV/cm.

In addition, in another aspect of the invention, the present invention is a method of manufacturing the lead-free dielectric ceramic composition, including (a) Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, TiO ₂ powder, BaCO ₃ powder, Na ₂ CO ₃ powder, Nb ₂ O ₅ powder, SrCO ₃ powder, and ZrO ₂ powder, pulverizing and calcining a mixed powder to produce raw material powder, and (b) forming a molded body using the raw material powder prepared in step (a). Lead-free dielectric ceramic composition comprising the step of manufacturing and then sintering Propose a manufacturing method.

The BiFeO ₃ -BaTiO ₃ based ceramic composition according to the present invention not only has a high dielectric constant (more than 1000) and a dielectric loss value (0.1 or less) even in a high temperature range of up to approximately 250°C, but also has excellent temperature stability of the dielectric constant and dielectric loss values. In addition, because the high-temperature phase transition temperature is very high compared to the existing BaTiO ₃ system, it can be used more stably in high temperature areas.

In addition, the overall dielectric properties of the BiFeO ₃ -BaTiO ₃ based ceramic composition according to the present invention are effectively controlled by controlling the dielectric constant and preventing deterioration of dielectric loss by adjusting the sintering conditions according to one or a combination of two or more selected from the type and content of additives. It can be done.

Figure 1 is a room temperature XRD pattern of BFBT-NSNZ ceramics manufactured in an example of the present application.
Figure 2(a) is the room temperature polarization-electric field ( PE ) hysteresis loop of the BFBT-NSNZ ceramics prepared in the examples of the present application, and Figure 2(b) shows the BFBT-NSNZ ceramics (x = 0.10) under various electric fields, respectively. These are the room temperature energy storage density ( W _store ) and energy storage efficiency (η) measurement results.
3(a) and 3(b) show the temperature dependence and dielectric constant of the dielectric constant ( ε _r ) of the BFBT-NSNZ ceramics (0 ≤ x ≤ 0.10) prepared in the examples of the present application at frequencies of 10 kHz and 100 kHz, respectively. This is a graph showing the temperature stability of the constant, and Figure 3(c) is a graph showing the temperature dependence of dielectric loss (tan δ ≤ 0.1).

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Since the embodiments according to the concept of the present invention can make various changes and have various forms, specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiments according to the concept of the present invention to a specific disclosed form, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The terms used in this specification are merely used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “include” or “have” are intended to indicate the existence of a described feature, number, step, operation, component, part, or combination thereof, but are not intended to indicate the presence of one or more other features or numbers. It should be understood that this does not exclude in advance the possibility of the existence or addition of steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in more detail through examples.

Embodiments according to the present specification may be modified into various other forms, and the scope of the present specification is not to be construed as being limited to the embodiments described in detail below. The embodiments of this specification are provided to more completely explain the present specification to those with average knowledge in the art.

<Example> Synthesis and characterization of BFBT-NSNZ ceramics

In this example, (Bi _0.65-2x Ba _0.35-2x Na _0.46x Sr _0.01x )(Fe _0.65-0.65x Ti _0.35-0.1x Nb _0.74x Zr _0.01x )O ₃ (however, 0 ≤ x ≤ 0.10) The indicated lead-free dielectric ceramic (BFBT-NSNZ) was synthesized through a known solid-state reaction method.

First, each of Bi ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , BaCO ₃ , Na ₂ CO ₃ , Nb ₂ O ₅ , SrCO ₃ and ZrO ₂ (99.9% Sigma Aldrich Co., St. Louis, MO) was dried. The powder was weighed according to the stoichiometric ratio and ball milled in ethanol with zirconia balls for 24 hours to prepare a slurry, dried at 100°C, calcined at 800°C for 5 hours, and then ball milled again for 6 hours. .

Subsequently, the calcined powder was compression molded into a disk-shaped ceramic specimen with a diameter of 10 mm at a pressure of 98 MPa and sintered at a temperature of 1000°C for 3 hours in an alumina crucible. After polishing the sintered pellets, silver (Ag) paste was applied to both sides and fired at a temperature of 650°C for 30 minutes to form electrodes, and then electrical measurements were performed.

Figure 1 shows the XRD pattern in the 2θ (20 - 70°) range of sintered BFBT-NSNZ ceramics. The ceramic specimen showed a single-phase perovskite structure without a noticeable secondary phase, indicating that BNBT-NS successfully diffused into the BF-BT lattice to form a stable solid solution. For reference, the dotted line in the XRD pattern represents the peak of Si used as an internal standard material. All BFBT-NSNZ ceramics were observed to have pseudocubic symmetry, as no obvious peak splitting was observed, and all ceramic compositions had similar crystal structures without significant differences in peak positions and relative intensities. It was confirmed to have. The relative density of the specimen was confirmed to be over 95%.

Figure 2(a) shows the room temperature polarization-electric field ( PE ) hysteresis loop of BFBT-NSNZ ceramics with a composition of 0.00 ≤ x ≤ 0.10. It can be observed that NSNZ has a significant effect on the polarization and coercive field of BF35BT ceramics. The BFBT-NSNZ ceramics with x = 0 show typical ferroelectric behavior with high remnant polarization ( P _r ) and high coercive field ( E _c ). When NSNZ was added to BF35BT ceramics, the PE hysteresis curve became thinner and both P _r and E _c continued to decrease. Therefore, the long-range ferroelectric order that dominates in pure BF35BT ceramics can be disturbed by the addition of NSNZ and converted to a relaxed ferroelectric state. The room temperature energy storage density ( W _store ) and energy storage efficiency (η) at x = 0.10 are shown in Figure 2(b), which means that W _store increases to 0.131 as the applied electric field increases. It shows an increase from 0.569 J/cm ³ . Meanwhile, η also increased from 74% to 78%. Compared with the results according to existing literature, BFBT-NSNZ ceramics exhibit excellent energy storage performance, suggesting that BFBT-NSNZ may be a suitable material for energy storage applications.

The temperature dependence of dielectric constant ( ε _r ) and dielectric loss (tan δ ) as a function of NSNZ concentration in BF35BT ceramics from room temperature to 500 °C at frequencies of 10 kHz and 100 kHz is shown in Figure 3. Referring to Figure 3(a), the BF35BT ceramics with x = 0 exhibited leakage behavior, but when NSNZ was added to the BF35BT ceramics, the maximum dielectric permittivity (ε _m ) dropped sharply and the temperature-invariant smooth dielectric constant was wide. Appears in range. Figure 3(b) shows the temperature dependence of the dielectric constant at 100 kHz for BFBT-NSNZ with 0 ≤ x ≤ 0.10, with reference to which the dielectric constant ( ε ) at x = 0.04 is 1449 ± It was found to be 15%. Additionally, the BFBT-NSNZ ceramics with x = 0.10 showed the widest dielectric temperature stability range with a dielectric constant of 1134 ± 15% from 88 °C to 500 °C. As the NSNZ content of BF35BT increased, the temperature range with a stable ε value (ε ± 15%, 100 kHz) expanded from 105 ℃ to 412 ℃, using the dielectric constant value at 150 ℃ as a reference point. In this example, the temperature range over which the BFBT-NSNZ ceramics with x = 0.10 has a stable dielectric constant is larger than that of the previously reported BF35BT ceramics. For reference, the results of comparing the dielectric temperature stability range between the lead-free ceramic according to the present invention and the known lead-free ceramic are shown in Table 1 below.

<Table 1> Comparison of dielectric temperature stability ranges of the present invention and known lead-free dielectric ceramics

Additionally, the temperature dependence of dielectric loss (tan δ ) was reduced by the addition of NSNZ. BFBT-based ceramics generally have high dielectric loss, but as NSNZ concentration increased, the relatively wide stable temperature range with dielectric loss below 0.1 (tan δ ≤ 0.1) increased. The stable range of dielectric loss at x = 0.10 was 75 ℃ ~ 316 ℃.

The present invention is not limited to the above-mentioned embodiments, but can be manufactured in various different forms, and those skilled in the art will be able to form other specific forms without changing the technical idea or essential features of the present invention. You will be able to understand that this can be implemented. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive.

Claims (7)

A lead-free ceramic composition represented by the following chemical formula:
[Chemical formula]
(Bi _0.65-2x Ba _0.35-2x Na _0.46x Sr _0.01x )(Fe _0.65-0.65x Ti _0.35-0.1x Nb _0.74x Zr _0.01x )O ₃
(In the above formula, 0 < x ≤ 0.1). According to paragraph 1,
As the value of x in the above formula increases,
A lead-free ceramic composition characterized by an increasing temperature range having a dielectric constant (ε _r ) value that satisfies the following inequality in the temperature range of 25 to 500°C:
0.85 × ε _r150℃ ≤ ε _r ≤ 1.15 × ε _r150℃
(In the above inequality, ε _r150℃ is the dielectric constant value measured at 150℃). According to paragraph 2,
In the above formula, x = 0.10,
A lead-free ceramic composition characterized by having a dielectric constant (ε _r ) value that satisfies the above inequality in the temperature range of 88 to 500°C. According to paragraph 1,
As the value of x increases in the above formula,
A lead-free ceramic composition characterized by an increasing temperature range with a dielectric loss value (tanδ) of 0.1 or less in the temperature range of 25 to 500°C. According to clause 4,
In the above formula, x = 0.10,
A lead-free ceramic composition characterized by having a dielectric loss value (tanδ) of 0.1 or less at 75 to 316°C. According to paragraph 1,
As the value of x increases in the above formula,
A lead-free ceramic composition characterized by an energy storage density of more than 0.6 J/cm ³ and an energy storage efficiency of more than 70% up to 100 kV/cm. (a) Grinding a mixed powder containing Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, TiO ₂ powder, BaCO ₃ powder, Na ₂ CO ₃ powder, Nb ₂ O ₅ powder, SrCO ₃ powder, and ZrO ₂ powder Preparing raw material powder by calcination; and
(b) manufacturing a molded body using the raw material powder prepared in step (a) and then sintering it.
The lead-free ceramic composition according to paragraph 1 Manufacturing method.