CN105152647A - Sintering temperature-sensitive bismuth titanate-based lead-free dielectric ceramic material - Google Patents

Abstract

The present invention discloses preparation and electrical property characterization of a sintering temperature-sensitive bismuth titanate-based lead-free dielectric ceramic material, wherein the chemical general formula of the ceramic is Bi4Ti3O12, primary pre-burning is performed at a temperature of 800 DEG C by using a traditional solid-phase method, and sintering is performed at two different temperatures such as 1100 DEG C and 1150 DEG C. According to the present invention, the Curie temperature is 663 DEG C when the sintering temperature is 1100 DEG C, the relative dielectric constant close to the Curie temperature achieves more than or equal to 76.7, while the Curie temperature is 656 DEG C when the sintering temperature is 1150 DEG C, the relative minimum dielectric constant close to the Curie temperature can achieve 22.67, such that the preferred ceramic sheet achieving the relative dielectric constant of more than or equal to 76.7 has the small dielectric loss; the activation energy of the prepared ceramic sheet is 0.50-0.73 through electric mode coefficient calculation; and when the sintering temperature is only increased by 50 DEG C, the significant changes are generated in the value and the change trends of the dielectric constant, the dielectric loss and the like of the material.

Description

A bismuth titanate-based lead-free dielectric ceramic material sensitive to sintering temperature

technical field

The invention belongs to the technical field of preparation of electronic ceramic components, in particular to a bismuth titanate-based lead-free dielectric ceramic sensitive to sintering temperature, which is a new perovskite layered structure with high dielectric constant and low dielectric loss If the sintering temperature is slightly changed, the dielectric constant, dielectric loss and activation energy of the ceramic will change significantly.

Background technique

With the in-depth study of ferroelectric memory materials, bismuth layer-structured ferroelectric materials (bismuth layer-structured ferroelectric: BLSF) have attracted great interest. The general formula of BLSF can be expressed as: (Bi ₂ O ₂ ) ²⁺ ( A _m-1 B _m O _3m+1 ) ^2- (m can be taken from 1 to 6). Among them, bismuth titanate (Bi ₄ Ti ₃ O ₁₂ , referred to as BIT) is a typical ferroelectric material with bismuth layer structure, which has low processing temperature, high Curie temperature (Tc), and good remanent polarization strength. , high dielectric constant, low dielectric loss, good ferroelectric and piezoelectric properties, anti-fatigue characteristics, and lead-free have become one of the candidate materials for new memory, and it is also a hot spot in the research of BLSF materials. It has good ferroelectric properties and is most likely to become one of the materials for manufacturing non-volatile ferroelectric memory. It has a wide range of applications, whether in industry, agriculture, national defense, scientific research, or in daily life. At the same time, its unique electrical, optical, and optoelectronic properties also have broad application prospects in modern microelectronics, micro-electromechanical systems, and information storage. Its good photocatalytic properties under visible light make it widely used in industrial water processing is possible.

However, with the development of science and technology, people have higher and higher requirements for the performance of BIT materials. Although the research on BIT ferroelectric materials has made great progress, the research still shows that BIT materials still have poor sintering compactness, pressure Low electrical activity and large coercive field Ec are not conducive to polarization, resulting in low piezoelectric performance, so it cannot fully meet the needs of industrial and commercial development for higher quality. Because BIT already has strong piezoelectric and ferroelectric properties, this time we mainly study the factors that affect its dielectric properties. By changing the sintering temperature and then affecting its microstructure, the experiment prepared a new type of information material with high dielectric properties and low loss, so that BIT can be better used for science and better for human beings.

Contents of the invention

The object of the present invention is to provide a bismuth titanate-based lead-free dielectric ceramic material sensitive to sintering temperature, whose general chemical formula is: Bi ₄ Ti ₃ O ₁₂ . Compared with other lead-free piezoelectric ceramics, the prepared ceramic has the characteristics of high dielectric constant, small dielectric loss, high resistivity, and sensitivity to sintering temperature.

In order to achieve the purpose of the invention, the invention provides a preparation method of lead-free dielectric ceramics, the method comprising the following steps:

(1) The reactants are TiO ₂ and Bi ₂ O ₃ (the purity is 99%, the use of high-purity reactants can reduce the impact of impurities on the reaction results), and the reactants are measured by the general chemical formula after cooling to room temperature in a desiccator The specific weight was obtained, and the sample was processed and prepared by the traditional solid phase method. The specific formula is as follows:

raw material Bi ₂ O ₃ TiO ₂ Dosage (g) 7.9545 2.0455

(2) Powders were mixed in isopropanol and ball milled with stabilized zirconia grind for 24 hours and dried. The dried powder was calcined at a temperature of 800° C. for 2 hours. After the calcining, the powder was ball milled for 12 hours, and then the powder was ground and granulated.

(3) Press the above-mentioned granular body into a circular sheet green sheet with a single-axis steel mold machine, and refer to the examples for specific dimensions, and cold isostatic pressing under a pressure of 200 MPa. The sample was then equally divided into two parts and loaded into two closed alumina crucibles to minimize the loss of volatile bismuth oxide, one was sintered at 1100 °C for 2-3 hours, and the other was sintered at 1150 °C Sinter for 2-3 hours. In this experiment, increasing the sintering temperature by 50℃ is the key to exploring the dielectric properties of Bi ₄ Ti ₃ O ₁₂ .

(4) A part of the ceramic sheet is ground to powder, which is a single phase by X-ray diffraction analysis.

(5) Grinding and polishing another part of the calcined ceramic sheet to a thickness of 0.9 mm for dielectric measurement. Gold powder is applied to the front and back sides, fired into electrodes in a furnace at 800°C, and high-temperature impedance spectroscopy is measured in a non-conductive wire-tube furnace; the IS data is corrected by the geometry of the sample (thickness/area of the particles) , and analyzed using ZView software. The relative permittivity and dielectric loss are tested by an impedance analyzer at 20°C to 600°C.

After testing, the sintering temperature is 1100°C and the Curie point is 663°C. At this time, the relative permittivity near the Curie point is above 76.7. The sintering temperature is 1150°C. The Curie point is 656°C, and the relative permittivity is above 22.67. It can be seen that the dielectric properties of the ceramic sheet samples at 1100 °C are significantly better than those at 1150 °C.

(6) Use the electron microscope to study the cross-sectional structure of the ceramic sheet. The cross-sections of the ceramic slices were polished, thermally etched at 990°C for 11 hours, and then coated with gold. Electron probe microanalysis was performed at 20 kV using microprobes in randomly selected areas of 12 groups.

(7) Research and microscopic analysis of the cross-sectional structure of the ceramic sheet by electron microscopy.

The present invention has the following characteristics:

(1) The traditional solid-state sintering method is used to mix the raw materials TiO ₂ and Bi ₂ O ₃ according to the stoichiometric ratio. A new BIT material was successfully synthesized.

(2) In the present invention, ceramic sheets with different dielectric properties are obtained by sintering at different temperatures from 1040°C to 1180°C, which are used to explore the influence of temperature on material properties under different chemical reactions, and select the best performance (1100°C) and The two special temperature points where the performance reverses (1150°C) are analyzed in detail, and then the dielectric material that is most suitable for practical applications is screened out, and the performance of BIT lead-free dielectric ceramics is improved.

(3) The present invention carries out the high-temperature impedance spectrum analysis in the impedance analyzer after confirming that the experimental material is the theoretical material by XRD diffraction analysis, obtains the relative permittivity value and the dielectric loss value of the material, and analyzes with Zview software, obtains The electrical performance data of various aspects of ceramic materials have been obtained, which has important reference value.

(4) The present invention carries out the impedance spectrum analysis measurement data and shows that the material has high dielectric constant and low dielectric loss below the Curie temperature, and the log (σ/ohm ^-1 cm ^-1 ) VS1000/T curve shows that the activation energy of the material is at Between 0.50 and 0.73.

In a word, the ceramic prepared by the method of the invention has a large dielectric constant, a small dielectric loss and is sensitive to the sintering temperature, and the electrical properties of the ceramic can be changed by changing the sintering temperature.

Description of drawings

Figure 1 is an XRD diffraction pattern, and diffraction analysis shows that the ceramic sheet obtained by the experimental reaction is a single phase, which is consistent with the theoretical material;

Figure 2 shows the curve of the relative dielectric constant measured with the temperature of the material environment when the material is pre-fired at 800°C and sintered at 1100°C;

Figure 3 shows the curve of the relative dielectric constant measured with the temperature of the material environment when the material is pre-fired at 800°C and sintered at 1150°C;

Figure 4 shows the curve of the dielectric loss tgδ measured with the temperature of the material environment when the material is pre-fired at 800 °C and sintered at 1100 °C;

Figure 5 shows the curve of the dielectric loss tgδ measured by the material pre-fired at 800°C and sintered at 1150°C with the temperature of the material environment;

Figure 6 shows the fitting line of two groups of materials log(σ/ohm-1cm-1) changing with 1000/T (the slope represents the activation energy);

Figure 7 shows the electron micrographs obtained when the material was pre-fired at 800°C and sintered at 1100°C;

Figure 8 shows the electron micrographs obtained when the material was pre-fired at 800°C and sintered at 1150°C.

Detailed ways

The present invention will be described in more detail below by means of examples, but the following examples are only illustrative, and the protection scope of the present invention is not limited by these examples.

Embodiment one: preparation of piezoelectric ceramics

Chemical formula: 3TiO ₂ +2Bi ₂ O ₃ →Bi ₄ Ti ₃ O ₁₂

Two kinds of raw material powders, TiO ₂ and Bi ₂ O ₃ are used, weighed according to the general chemical formula, the reactant is cooled to room temperature in a desiccator, and dried, and the mass of TiO ₂ is 2.0455g, and the mass of Bi ₂ O ₃ is 7.9545g , the samples were processed by traditional solid-phase methods. The specific procedure was as follows: the powders were mixed in isopropanol and ball milled with stabilized zirconia grind for 24 hours and dried. The dry powder is pre-fired at 800°C for 2 hours. After pre-fired, the powder is ball milled for 12 hours, and then the powder is re-ground and shaped into pellets, and pressed into tablets with a green uniaxial steel mold. , pressed into a disc size (area 0.6951cm, diameter 0.941cm, thickness 0.168cm), and cold isostatic pressing at a pressure of 200 MPa. Then put the sample into a closed alumina crucible and sinter at 1100° C. for 2-3 hours to obtain a sintered ceramic sheet, the sample number is a.

The procedure is the same as above, pre-fire at 800°C for 2 hours, sinter at 1150°C for 2-3 hours, sample number is b.

Embodiment two: the dielectric property measurement of piezoelectric ceramic material sample

(1) Figure 1 is an XRD diffraction pattern. The diffraction analysis shows that the ceramic sheet obtained by the experimental reaction is a single phase, which is consistent with the theoretical material.

(2) Relative permittivity measurement

Figure 2 shows that the relative dielectric constant of sample a was pre-fired at 800°C and calcined at 1100°C as a function of the ambient temperature of the sample. The relative permittivity rises faster at lower temperatures below the Curie temperature. It increases sharply near the Curie point _Tc = 663℃, and the peak value of r reaches 205.4, 131.6 and 76.7 at three different frequencies of 100kHz, 250kHz and 1MHz, respectively, and drops sharply after Tc. By comparing the data, it can be found that the higher the frequency, the smaller the relative permittivity.

Figure 3 shows that the sample b was prefired at 800°C and the ceramic sheet was sintered at 1150°C as a function of the relative permittivity of the sample as a function of the ambient temperature of the sample. The general trend of relative permittivity changing with temperature is similar to that in Figure 2. It increases slowly at first, and then increases slightly faster near the Curie point T _c = 656°C. The peak values of r near the Curie temperature for three different frequencies of 100kHz, 250kHz and 1MHz are respectively After reaching 49.61, 34.70 and 22.67, the dielectric constant value tends to decrease slightly. Compared with the data obtained when the sample was sintered at 1100 °C, the dielectric constant is significantly reduced, indicating that the increase in sintering temperature will lead to a decrease in the dielectric properties of the material.

See Table 1 for the dielectric constant values at the Curie point (T _c ) under different conditions

Table 1 Relative permittivity at the Curie point at different sintering temperatures

(3) Dielectric loss measurement data

Figure 4 shows that the tgδ curve of sample a is sintered at 1100 °C with temperature, and the loss tangent angle is almost 0 at 150 °C, which can be ignored, and then increases slowly and then decreases. By comparing the data, it can be found that the higher the frequency, the smaller the dielectric loss.

Figure 5 shows the curve of tgδ versus temperature for sample b sintered at 1150°C

When sintered at 1150°C, the loss angle increases significantly compared to the low sintering temperature, and the overall trend continues to rise, which has a greater impact on the dielectric properties.

The dielectric loss values at the Curie point under different conditions are shown in Table 2.

Table 2 Dielectric loss value at Curie point at different sintering temperatures

(4) log(σ/ohm-1cm-1) VS1000/T activation energy and Z* impedance diagram measurement data

Figure 6 shows that the log(σ/ohm-1cm-1) of the two samples changes with 1000/T and the fitting line (the slope represents the activation energy).

The above figure shows that Ea is greater than 0.5, and the activation energy is between 0.50 and 0.73. Ceramic samples at both sintering temperatures are good insulating materials.

(5) Microstructure measurement and analysis

The results shown in Figure 7 and Figure 8 show that the grain size of the sample at 1100 °C is significantly smaller than that at 1150 °C, and the distribution is relatively uniform.

Claims (3)

1., to a bismuth titanate based unleaded dielectric ceramic material for sintering temperature sensitivity, it is characterized in that chemical general formula is: Bi ₄ti ₃o ₁₂, through 800 DEG C of pre-burnings, 1100 DEG C of sintering form, and relative permittivity reaches more than 76.7.

2., to a bismuth titanate based unleaded dielectric ceramic material for sintering temperature sensitivity, it is characterized in that chemical general formula is: Bi ₄ti ₃o ₁₂through 800 DEG C of pre-burnings, 1150 DEG C of sintering form, and relative permittivity reaches more than 22.67.

3., to a preparation method for the bismuth titanate based unleaded dielectric ceramic material of sintering temperature sensitivity, it is characterized in that step is:

(1) selection purity is the reactant TiO of 99% ₂and Bi ₂o ₃, reactant is cooled to room temperature in moisture eliminator, is then measured than weighing by chemical general formula;

(2) powder mixes and carries out 24 hours ball millings and drying with stable zirconium oxide abrasive ball in Virahol.By the powder of drying 800 DEG C of pre-burnings, the time is 2 hours, after each pre-burning, by powder ball milling 12 hours, is more again again ground by this coccoid and is configured as granular;

(3) above-mentioned granular solid is pressed into disk green sheet, and under 200 MPa pressure isostatic cool pressing, sample is divided into two portions, and a part of sample loads the alumina crucible closed, to reduce the loss of volatile oxidation bismuth as far as possible, at 1100 DEG C of sintering 2-3 hour; Another part sample loads the alumina crucible closed, to reduce the loss of volatile oxidation bismuth as far as possible, at 1150 DEG C of sintering 2-3 hour;

(4) test, a ceramic plate part is ground to powder, is single-phase by X-ray diffraction analysis;

Ceramic plate grinding and polishing to the thickness of 0.9mm of another part calcining carries out Dielectric measuring, and bronze is applied to contrary parallel surface, and coated sheet is fired into electrode in 800 DEG C of stoves, and carries out the measurement of high temperature impedance spectrum in the threaded pipe type stove of non-conductive; Relative permittivity and dielectric loss are tested at 20 DEG C ~ 600 DEG C by electric impedance analyzer;

(5) cross-section structure of Electronic Speculum to ceramic plate is used to study and microanalysis.