CN105523760B - A kind of preparation method of the sodium niobate ceramic material of the low-dielectric loss of stable anti-ferroelectricity - Google Patents

Abstract

The invention discloses a preparation method of a sodium niobate ceramic material with stable antiferroelectricity and low dielectric loss, belonging to the field of dielectric ceramic materials. The antiferroelectric phase in pure sodium niobate ceramics is stabilized by this method, and there is no electric field-induced ferroelectric phase under a high electric field of 100kV/cm, and the material has low dielectric loss (<2%). Preparation method: Weigh Na ₂ CO ₃ and Nb ₂ O ₅ according to the molar ratio of Na:Nb=1:1, put the two raw materials into a ball mill pot for ball milling, and use absolute ethanol as the grinding medium; then mix the obtained The powder is dry-milled by high-energy ball milling to obtain sodium niobate nano-powder, and the obtained nano-powder is directly pressurized without adding any binder, and then sintered into a ceramic body at 1350-1375°C. The determination of the stable antiferroelectric phase is obtained through electrical performance tests. The method of the invention is simple, and the energy consumption is low; the prepared sodium niobate ceramic material has relatively stable antiferroelectricity and low dielectric loss.

Description

Preparation of a Sodium Niobate Ceramic Material with Stable Antiferroelectricity and Low Dielectric Loss method

technical field

The invention belongs to the technical field of sodium niobate ceramic materials, and in particular relates to a preparation method of a sodium niobate ceramic material with stable antiferroelectricity and low dielectric loss.

Background technique

Sodium niobate (NaNbO ₃ ) is not only a key component in a variety of lead-free electronic ceramic systems, but its pure phase has important application prospects in energy storage capacitors, high-voltage power supply capacitors and other fields due to its antiferroelectric structure. Although theoretically pure sodium niobate is an antiferroelectric phase at room temperature, the sodium niobate ceramics prepared by conventional ceramic technology are prone to oxygen vacancies and alkali metal cation vacancies due to the volatilization and loss of alkali metals, and these vacancies form defect couples. Pole pair, it is very easy to induce the transformation of sodium niobate from antiferroelectricity to ferroelectricity under a weak electric field (Ge et al., J.Am.Ceram.Soc., 94, 4329–4334(2011)). Therefore, it is difficult to observe antiferroelectric behavior in the sodium niobate-based ceramic system reported in the literature. In order to obtain a stable antiferroelectric phase, the introduction of an additional second component stabilizer is an important method. Shimizu and Guo et al. introduced the second component of CaZrO ₃ or SrZrO ₃ to reduce the system tolerance factor and increase the average electronegativity, thereby stabilizing the antiferroelectric phase (Shimizu et al., Dalton Trans.44, 10763(2015 ) and Guo et al., J. Appl. Phys. 117, 214103 (2015)). However, this modification method obtains a binary complex phase ferroelectric system. In order to obtain a stable antiferroelectric pure sodium niobate unit phase, Shimizu et al. used calcination and sintering processes in a low-oxygen atmosphere to suppress the volatilization of alkali metal sodium, but their research results still failed to obtain a stable antiferroelectric phase (Shimizu et al. al., J. Am. Ceram. Soc., 97 [6] 1791–1796 (2014)). In addition, it should be noted that in order to obtain practical applications, sodium niobate ceramics also need to have low dielectric loss (<2%) to suppress the heat generation of components during operation.

The present invention combines the high-energy ball milling process with the buried powder sintering process, prepares sodium niobate nanopowder through the high-energy ball milling method, realizes one-step phase formation without calcination by ball milling, and thus obtains highly active nanopowder with narrow particle size distribution, and then through burying The powder sintering method suppresses the volatilization of sodium at high temperature, and prepares sodium niobate ceramic materials with high density, low defects and low dielectric loss. The electrical performance test proves that the stable antiferroelectric polarization behavior is obtained, and there is no antiferroelectric-ferroelectric behavior transition until the high-voltage breakdown electric field.

Contents of the invention

The purpose of this invention is to provide a kind of preparation method of the sodium niobate ceramics of stable antiferroelectricity and low dielectric loss, the material prepared by using this method has high density, low defect, low dielectric loss (<2%) , showing a relatively stable antiferroelectric phase.

In order to achieve the above object, the present invention adopts high-energy ball milling method to prepare sodium niobate nanopowder. It can be phased in a short time in a closed container at room temperature. Compared with the traditional calcination process, it does not require high temperature heating, and can realize the synthesis of narrow particle size distribution and high activity nanopowders, and at the same time inhibit the alkali during the preparation of precursor powders. The volatilization of metallic sodium. Subsequently, the buried powder sintering process is adopted for the sintering process of ceramic samples. Buried powder sintering is to create a protective atmosphere during the sintering process, inhibit the volatilization of alkali metal sodium, prevent the imbalance of material metering ratio, and achieve high density and low dielectric loss. , the reliable preparation of stoichiometric ratio sodium niobate ceramics, thus finally obtaining a stable antiferroelectric phase. Usually, in the non-stoichiometric niobate ceramic materials, defects such as oxygen vacancies will be generated due to the volatilization of sodium. These defects form dipole pairs to hinder the densification of the ceramic body and induce antiferroelectric-ferroelectric transition.

A kind of preparation method of the sodium niobate ceramic material of stable antiferroelectricity and low dielectric loss, it is characterized in that, comprises the steps:

(1) Weigh Na ₂ CO ₃ and Nb ₂ O ₅ powders according to the molar ratio Na:Nb=1:1 of the chemical formula NaNbO ₃ , put them into a ball mill jar, and after 12 hours of ball milling, a uniformly mixed powder is obtained . Since Na ₂ CO ₃ is easy to absorb water, in order to ensure the dosage ratio, Na ₂ CO ₃ was dried at 200°C before use, and absolute ethanol was selected as the grinding medium for mixing. Both Na ₂ CO ₃ and Nb ₂ O ₅ are micron-sized powders.

(2) Weigh the powder obtained in step (1) and put it into a high-energy ball mill tank for ball milling according to the fixed ball-to-material ratio. , and the ball milling time is 30-120min to obtain nanoscale ceramic powder; the reaction process is as follows:

Na ₂ CO ₃ +Nb ₂ O ₅ →2NaNbO ₃ +CO ₂ ↑

In this process, due to the continuous impact of the grinding balls, the particle size of the crushed powder is reduced to the nanometer scale, and the mechanical energy of the collision is continuously introduced into the powder, so that the mixed powder undergoes a diffusion reaction on the nanometer scale, and finally completes the above. reaction.

The ball milling conditions are preferably as follows: the ball-to-material ratio is 20:1, the ball milling speed is 800/min, and the ball milling time is 90 minutes, the phase formation effect and particle size dispersion of the powder sample obtained are the best, and the particle size distribution is 12-20nm sodium niobate nanopowder body; therefore preferably ball milling this powder as the ceramic sintering precursor powder in the present invention.

(3) directly pressing the ceramic powder obtained in step (2) into a green body without adding any binder.

(4) Sinter the green body obtained in step (3), the sintering conditions are: the rate of 7°C/min increases from room temperature to 650°C, then the rate of 3.4°C/min rises to 950°C, and then 4°C/min The speed is raised to 1350-1375 ° C for 2 hours and then cooled to room temperature with the furnace; at the same time, during the sintering process, the green body is buried in the powder obtained in step (2) for sintering.

The above materials of the present invention have a relatively stable antiferroelectric phase. Among them, the best sample is the ceramic sample obtained by sintering at 1365°C. Its density can reach 98%, the dielectric constant at room temperature ε _r =397, and the dielectric loss at room temperature tanδ=1.3%, which meets the requirements of high-quality ceramics.

Compared with other inventions, the present invention has the following significant advantages:

(1) This method simply mixes niobium pentoxide and sodium carbonate, which are cheap and easy to obtain, and transfers ball milling energy to the mixed powder at room temperature to obtain the target powder in a short time. This greatly reduces the material cost and simplifies the complexity of the preparation process.

(2) In the present invention, the high-energy ball milling method is selected to prepare nano-powders. The volatilization of a part of alkali metal sodium cannot be avoided during the preparation of powder by traditional high-temperature calcination, and the obtained powder has a large particle size and poor activity; while the high-energy ball milling method is to complete the target phase powder in a closed container at room temperature The synthesis avoids the volatilization of alkali metal sodium caused by heating. In addition, nano-scale powder has high sintering activity and defect density, which is beneficial to the later sintering densification. In the later sintering process, we further adopted the buried powder sintering method. The buried powder is mainly used to protect the green body during the sintering process and relieve the volatilization of alkali metal sodium in the green body, so as to achieve high density and low dielectric strength. Preparation of lossy (<2%) sodium niobate ceramics.

(3) The dielectric performance test data of the sodium niobate ceramic sample with low dielectric loss obtained by this method is not only the recognized Curie peak of T _C = 370 ° C, but also a new dielectric property of about T = 100 ° C peak, which has never been reported in the existing literature of sodium niobate. The appearance of this abnormal dielectric peak indicates that there is a stable antiferroelectric phase at room temperature, and the electrical test shows that the beam waist double hysteresis loop with antiferroelectric characteristics does not appear when the test electric field is increased to 100kv/cm A phase transition from antiferroelectric to ferroelectric, which means that the antiferroelectric performance of sodium niobate is stable.

Description of drawings

Figure 1: The X-ray diffraction (XRD) pattern of the powder sample obtained when the ball-to-material ratio is 20:1, the ball milling speed is 800/min, and the ball milling time is 90 minutes.

Figure 2: The powder sample obtained when the ball-to-material ratio is 20:1, the ball milling speed is 800/min, and the ball milling time is 90 minutes. Figures: (a) low magnification transmission electron microscope image; (b) EDS energy spectrum; (c) high magnification TEM image, (d) Selected area electron diffraction image.

Fig. 3: the ceramic sample accompanying drawing that embodiment 2 obtains:

(a) SEM image, (b) grain size distribution image

Fig. 4: X-ray diffraction pattern (XRD) of the ceramic sample obtained in Example 2.

Figure 5: Dielectric temperature curves and loss curves of ceramic samples obtained in Example 2 at different frequencies.

Figure 6: P-E loop of the ceramic sample obtained in Example 2 at room temperature.

Detailed ways

The substantive characteristics and remarkable advantages of the present invention are further illustrated below through the examples, but the present invention is not limited to the following examples.

The NaNbO ₃ precursor powder was synthesized. The precursor powder was prepared from low-priced Na ₂ CO ₃ and Nb ₂ O ₅ raw materials. The reaction process was as follows: Na ₂ CO ₃ +Nb ₂ O ₅ →2NaNbO ₃ +CO ₂ ↑(1 )

Firstly, Na ₂ CO ₃ was dried at 200°C for 12 hours, and then two raw materials, Na ₂ CO ₃ and Nb ₂ O ₅ were weighed and put into a ball mill with a molar ratio of Na:Nb=1:1. Mix the materials in the planetary ball mill for 12 hours; the powder obtained by mixing the materials is weighed according to the fixed ball-to-material ratio and put into a high-energy ball mill tank for ball milling. The ball milling conditions are: the ball-to-material ratio is 15:1~20:1, and the ball milling speed is 600~1000 /min, the ball milling time is 30-120min; in this process, due to the continuous impact of the grinding balls, the particle size of the crushed powder is reduced to the nanometer scale, and the mechanical energy generated in the collision is continuously transmitted into the powder, so that the mixed powder The solid diffusion reaction occurs on the nanometer scale, and the reaction in the above reaction formula (1) is finally completed. Na ₂ CO ₃ is easy to absorb water, which is not conducive to the purpose of short-term phase formation, so absolute ethanol is selected as the grinding medium for mixing.

Both Na ₂ CO ₃ and Nb ₂ O ₅ are micron-sized powders.

Example 1:

The ball milling conditions are as follows: the ball-to-material ratio is 15:1, the ball milling speed is 1000/min, and the ball milling time is 90 minutes. The NaNbO ₃ powder prepared by high-energy ball milling is directly molded under a pressure of 800 MPa without adding any binder. The diameter is 11.5 mm, and the thickness is about 1.5 mm; then the rate of 7 ° C / min is raised from room temperature to 650 ° C, then the rate of 3.4 ° C / min is increased to 950 ° C, and the rate of 4 ° C / min is increased to 1350 ° C. The powder is sintered and kept for 2 hours to obtain the target ceramic material.

Example 2:

The ball milling conditions are as follows: the ball-to-material ratio is 20:1, the ball milling speed is 800/min, and the ball milling time is 90 minutes. The NaNbO ₃ powder prepared by high-energy ball milling is directly molded under a pressure of 800 MPa without adding any binder. The diameter is 11.5 mm, and the thickness is about 1.5 mm; then the rate of 7 ° C / min is raised from room temperature to 650 ° C, then the rate of 3.4 ° C / min is increased to 950 ° C, and the rate of 4 ° C / min is increased to 1365 ° C. The powder is sintered and kept for 2 hours to obtain the target ceramic material. It can be seen from Figures 5 and 6 that there is a new dielectric peak around T=100°C, which has never been reported in the existing literature on sodium niobate. The appearance of this abnormal dielectric peak indicates that there is a stable antiferroelectric phase at room temperature, and the electrical test shows that the beam waist double hysteresis loop with antiferroelectric characteristics does not appear when the test electric field is increased to 100kV/cm A phase transition from antiferroelectric to ferroelectric, which means that the antiferroelectric performance of sodium niobate is stable.

Example 3:

The ball milling conditions are as follows: the ball-to-material ratio is 30:1, the ball milling speed is 600/min, and the ball milling time is 120 minutes. The NaNbO ₃ powder prepared by high-energy ball milling is directly molded under a pressure of 800 MPa without adding any binder. The diameter is 11.5mm, and the thickness is about 1.5mm; then the rate of 7°C/min is raised from room temperature to 650°C, the rate of 3.4°C/min is raised to 950°C, and the rate of 4°C/min is raised to 1375°C to bury the powder After sintering and heat preservation for 2 hours, the target ceramic material is obtained.

Comparative example 1:

The ball milling conditions are as follows: the ball-to-material ratio is 20:1, the ball milling speed is 800/min, and the ball milling time is 90 minutes. The NaNbO ₃ powder prepared by high-energy ball milling is directly molded under a pressure of 800 MPa without adding any binder. The diameter is 11.5mm and the thickness is about 1.5mm; then the rate of 7°C/min is raised from room temperature to 650°C, then the rate of 3.4°C/min is raised to 950°C, and the rate of 4°C/min is raised to 1330°C for sintering , heat preservation for 2 hours, and the target ceramic material is obtained.

Comparative example 2:

The ball milling conditions are: the ball-to-material ratio is 20:1, the ball milling speed is 800/min, and the ball milling time is 90 minutes. The NaNbO ₃ powder prepared by high-energy ball milling is directly molded under the pressure of 800MPa without adding any binder. The diameter is 11.5mm, and the thickness is about 1.5mm; then the rate of 7°C/min is raised from room temperature to 650°C, then the rate of 3.4°C/min is raised to 950°C, and the rate of 4°C/min is raised to 1380°C. The powder is sintered and kept for 2 hours to obtain the target ceramic material.

Comparative example 3:

The ball milling conditions are as follows: the ball-to-material ratio is 30:1, the ball milling speed is 400/min, and the ball milling time is 120 minutes. The NaNbO ₃ powder prepared by high-energy ball milling is directly molded under a pressure of 800 MPa without adding any binder. The diameter is 11.5 mm, and the thickness is about 1.5 mm; then the rate of 7 ° C / min is raised from room temperature to 650 ° C, then the rate of 3.4 ° C / min is increased to 950 ° C, and the rate of 4 ° C / min is increased to 1365 ° C for sintering , heat preservation for 2 hours, and the target ceramic material is obtained.

Table 1 The relevant performance parameter comparison table of the above-mentioned embodiment and comparative example ceramic sample

Relative density Dielectric constant Dielectric loss Antiferroelectricity Comparative example 1 83% 200 46% Have Comparative example 2 93% 308 5.7% Have Comparative example 3 89% 171 39% none Example 1 95% 285 1.64% Have Example 2 98% 397 1.3% Have

Example 3 96% 373 1.89% Have

Claims (4)

1. a kind of preparation method of the sodium niobate ceramic material of the low dielectric loss of stable antiferroelectricity, is characterized in that, comprises the steps: (1) Weigh Na ₂ CO ₃ and Nb ₂ O ₅ powders according to the molar ratio Na:Nb=1:1 of the chemical formula NaNbO ₃ , put them into a ball mill jar, and after 12 hours of ball milling, a uniformly mixed powder is obtained ; Na ₂ CO ₃ is dried at 200°C before use, and absolute ethanol is used as the grinding medium for mixing; Na ₂ CO ₃ and Nb ₂ O ₅ are both micron-sized powders; (2) Weigh the powder obtained in step (1) and put it into a high-energy ball mill tank for ball milling according to the fixed ball-to-material ratio. , and the ball milling time is 30-120min to obtain nanoscale ceramic powder; the reaction process is as follows: Na ₂ CO ₃ +Nb ₂ O ₅ →2NaNbO ₃ +CO ₂ ↑; (3) directly pressing the ceramic powder body obtained in step (2) into a green body without adding any binding agent; (4) Sinter the green body obtained in step (3), the sintering conditions are: the rate of 7°C/min increases from room temperature to 650°C, then the rate of 3.4°C/min rises to 950°C, and then 4°C/min The speed is raised to 1350-1375 ° C for 2 hours and then cooled to room temperature with the furnace; at the same time, during the sintering process, the green body is buried in the powder obtained in step (2) for sintering. 2. according to the preparation method of the sodium niobate ceramic material of the low dielectric loss of a kind of stable antiferroelectricity claimed in claim 1, it is characterized in that, step (2) ball milling condition is: ball-to-material ratio is 20:1 , the ball milling speed is 800r/min, and the ball milling time is 90min to obtain a powder with a particle size distribution of 12-20nm sodium niobate nanopowder. 3. according to the preparation method of a kind of sodium niobate ceramic material with stable antiferroelectricity and low dielectric loss according to claim 1, it is characterized in that step (4) is raised to 1365 ℃ for 2 hours. 4. The sodium niobate ceramic material with stable antiferroelectricity and low dielectric loss prepared according to any method of claims 1-3.