CN102875146B - A kind of layered perovskite structure ceramics and preparation method thereof - Google Patents

Abstract

The invention provides layered perovskite structural ceramic and a preparation method thereof. The preparation method includes mixing well titanate compounds, bismuth compounds, lanthanum compounds, iron compounds, cobalt compounds and complexing agent in solvent, heating, evaporating and burning to obtain powder, and pre-sintering, preforming and sintering to obtain the layered perovskite structural ceramic structurally shown in a formula (I). Compared with ceramics prepared in prior art by solid phase sintering process, and the layered perovskite structural ceramic is prepared by solution process and sintering process. The preparation method has the advantages that the raw materials are spread evenly by the solution process, and the single-phase perovskite structural material is easy to obtain; the power prepared by the solution process has high reactivity, sintering temperature is low, the processes of ball-milling, binder removal and the like are avoided, and preparation cycle is shortened; by introducing lanthanum ions ferroelectric properties of the layered perovskite structural ceramic are improved, cobalt ions and ferric ions are coupled so that ferromagnetic properties of the ceramic are improved. The formula (I) is Bi7-xLaxFe1.5Co1.5Ti3O21.

Description

A kind of layered perovskite structure ceramics and preparation method thereof

technical field

The invention belongs to the technical field of ceramic materials, and in particular relates to a layered perovskite structure ceramic and a preparation method thereof.

Background technique

Magnetoelectric multiferroic materials refer to materials that exhibit ferroelectric order and ferromagnetic/antiferromagnetic order at the same time in a certain temperature range, and there is a certain coupling between them. In recent years, because multiferroic materials can not only be used in the research and development of ferroelectric and magnetic devices, but more importantly, they can use the coupling between magnetoelectricity, that is, the application of an electric field can control the ferromagnetic polarization and the application of a magnetic field can control the ferromagnetic polarization. Electric polarization provides an additional degree of freedom for the design and application of devices, thus showing extremely attractive applications in emerging spintronics, multi-state information storage, electrically driven ferromagnetic resonators, and magnetically regulated piezoelectric sensors. prospect.

Among the discovered multiferroic materials, bismuth-based layered perovskite structure materials have received widespread attention because they contain Bi-O layers as space charge reservoirs and insulating layers, which can effectively reduce the leakage current in the materials. BiFeO ₃ (BFO) with simple perovskite ABO ₃ -type structure is a lead-free and environmentally friendly material with ferroelectric Curie temperature and antiferromagnetic Neel temperature much higher than room temperature, but its pure phase material The preparation of BFO is difficult, and the high concentration of oxygen vacancies and the existence of low-valent Fe ²⁺ ions in the material easily lead to high leakage conductance, which destroys its ferroelectric properties and limits the application of BFO materials. Bismuth titanate (Bi ₄ Ti ₃ O ₁₂ , BTO) is also a typical bismuth-containing layered perovskite structure, which has a high Curie temperature and spontaneous polarization, and its strong ferroelectricity comes from Bi ³⁺ The 6s ² lone electron pair of the ion.

The combination of BFO materials and BTO materials can form a layered perovskite multiferroic structure with the structural formula Bi _n+1 Fe _n-3 Ti ₃ O _3(n+1) (where n is an integer equal to or greater than 3, BFTO). Material, two bismuth oxide layers (Bi ₂ O ₂ ) ²⁺ contain three titanium oxide (Ti-O) octahedrons and one or more (Fe-O) octahedrons, and their multiferroics are derived from iron electric unit (BTO) and multiferroic unit (BFO). BFTO can effectively utilize the insulating effect of the bismuth oxide layer to suppress the leakage current of the magnetic unit due to oxygen vacancies and Fe multivalent states, but it still exhibits room temperature antiferromagnetism, which is limited in practical applications. The research results show that A-site doping can improve the ferroelectric properties of the material and reduce the leakage current of the sample; B-site doping can improve the ferromagnetic properties of the material.

The Chinese patent with the publication number CN102167584A discloses a five-layer structure bismuth titanocobaltate ceramic material with multiferroic properties and its preparation method. Cobalt ions are doped at the B site to realize the coupling between iron and cobalt ions. Further, the ferromagnetic properties of the material are improved, but the ferroelectric properties of the material are not improved, and the solid phase sintering process is adopted, and the sintering temperature is relatively high. The Chinese patent with the publication number CN 101704669A discloses a layered structure titanium iron cobaltate lanthanum bismuth ceramic with multiferroic properties and its preparation method, which is doped with high-valence lanthanum ions at the A site and Co ions at the B site , improve the ferroelectric and ferromagnetic properties of the material at the same time, but its preparation method is also a solid phase reaction method, which needs to go through ball milling, pre-synthesis, molding, plastic discharge and sintering processes, the preparation cycle is long, and it is not easy to obtain pure phase powder .

Contents of the invention

In view of this, the technical problem to be solved by the present invention is to provide a layered perovskite structure ceramic and a preparation method thereof, the ceramic has good ferroelectric properties and ferromagnetic properties, and the preparation cycle is short.

The present invention provides a layered perovskite structure ceramic, as shown in formula (I):

Bi _7-x La _x Fe _1.5 Co _1.5 Ti ₃ O ₂₁ (I)

Among them, 0.2≤x≤1.5.

The invention provides a method for preparing layered perovskite structure ceramics, comprising the following steps:

A) The bismuth source compound, lanthanum source compound, iron source compound, cobalt source compound and titanate compound are mixed according to the ratio of metal ion Bi:La:Fe:Co:Ti=7-x:x:1.5:1.5:3 Soluble in solvent, add complexing agent to mix and stir, adjust pH value to 5~7, heat, evaporate to dryness and burn into powder, and obtain powder after pre-calcination, wherein 0.2≤x≤1.5;

B) Pressing the powder into tablets and sintering to obtain layered perovskite structure ceramics.

Preferably, the bismuth source compound is selected from one of bismuth nitrate, bismuth subnitrate, bismuth oxide, bismuth subcarbonate and bismuth oxalate.

Preferably, the lanthanum source compound is selected from one of lanthanum nitrate, lanthanum carbonate, lanthanum oxide, lanthanum oxalate and lanthanum acetate.

Preferably, the iron source compound is selected from one of ferric nitrate, ferric oxide, ferric oxide and ferric oxalate.

Preferably, the cobalt source compound is selected from one of cobalt nitrate, cobalt oxide, cobalt oxalate and cobalt acetate.

Preferably, the complexing agent is selected from one or more of ethylenediaminetetraacetic acid, citric acid and glycine.

Preferably, the molar ratio of the complexing agent to the total number of metal ions is 1-2.5:1.

Preferably, the pre-burning temperature is 700°C~800°C, and the time is 2~4h.

Preferably, the sintering is hot press sintering or muffle furnace sintering.

The invention provides a layered perovskite structure ceramic and a preparation method thereof. In the method, a titanate compound, a bismuth source compound, a lanthanum source compound, an iron source compound, a cobalt source compound and a complexing agent are mixed in a certain proportion. Mix and stir in a solvent, adjust the pH value to 5~7, heat, evaporate to dryness and burn into powder, and obtain powder after pre-calcination; press the powder into tablets and sinter to obtain layered calcium with the structure of formula (I) Titanium structure ceramics. Compared with the preparation of titanium iron cobaltate lanthanum bismuth ceramics by using solid phase sintering process in the prior art, the present invention adopts solution method and sintering process to prepare layered perovskite structure ceramics. First, the solution method is used to prepare the raw materials evenly, and the resulting powder has finer particles and uniform components, and it is easy to obtain materials with a single-phase layered perovskite structure; secondly, the powder prepared by the solution method has higher reactivity , so that the sintering temperature is relatively low, and there is no need to go through processes such as ball milling and plastic discharge, which shortens the preparation cycle; again, the introduction of lanthanum ions improves the leakage current caused by the oxygen vacancies caused by the volatilization of bismuth ions on the one hand, and on the other hand On the one hand, the difference in radii between lanthanum and bismuth ions will lead to distortion of the crystal lattice, which improves the ferroelectric properties of ceramics, and at the same time, the coupling of cobalt ions and iron ions improves the ferromagnetic properties of ceramics.

The experimental results show that the layered perovskite structure ceramics prepared by the present invention are six-layer structure single-phase layered perovskite structure ceramics, and the remanent polarization is 1.35~2.61 under the condition that the measured electric field is 100kV/cm μC/cm ² , the coercive field is 23~40kV/cm, under the condition of measuring electric field 150kV/cm, the remnant polarization is 4.99~7.48μC/cm ² , the coercive field (2E _c ) is 67~88kV /cm, at room temperature, the residual magnetic susceptibility is 1.12~2.60emu/g, and the coercive field (2H _c ) is 250~360 Oe.

Description of drawings

Fig. 1 is the X-ray diffraction figure of the layered perovskite structure ceramics that makes in the embodiment of the present invention 1;

Fig. 2 is the scanning electron micrograph of the layered perovskite structure ceramics obtained in Example 1 of the present invention;

Fig. 3 is the ferroelectric performance measurement diagram of the layered perovskite structure ceramics obtained in Example 1 of the present invention;

Fig. 4 is a measurement diagram of the ferromagnetic properties of the layered perovskite structure ceramics prepared in Example 1 of the present invention.

Detailed ways

The present invention provides a layered perovskite structure ceramic, as shown in formula (I):

Bi _7-x La _x Fe _1.5 Co _1.5 Ti ₃ O ₂₁ (I)

Among them, 0.2≤x≤1.5, preferably 0.4≤x≤1.3, more preferably 0.6≤x≤1.2.

The structure of the layered perovskite structure ceramics with the formula (I) structure in the present invention is that 3 titanium oxide (Ti-O) octahedra are sandwiched between two bismuth oxide layers ((Bi ₂ O ₂ ) ²⁺ ) , 1.5 iron oxide (Fe-O) octahedra and 1.5 cobalt oxide (Co-O) octahedra.

In the perovskite structure ceramics, due to the multivalent state of the magnetic ion iron ion and the oxygen vacancy caused by the volatilization of the bismuth element, it is easy to cause an increase in the leakage current. The bismuth-containing oxygen layer of the layered perovskite structure ceramics of the present invention can play the role of a space charge reservoir and an insulating layer, and can reduce the leakage current caused by the multivalent state of magnetic ions Fe; the A-site is doped with non-volatile rare earth The element lanthanum ions can reduce the leakage current increased due to the volatilization of bismuth ions, providing the ferroelectric properties of layered perovskite structure ceramics; doping cobalt ions at the B site, both iron and cobalt have a sub-d electron layer structure The magnetic particles can be coupled to improve the ferromagnetic properties of the ceramic material. Therefore, the layered perovskite structure ceramics provided by the invention have good ferroelectric properties and ferromagnetic properties.

The present invention also provides a corresponding preparation method for the layered perovskite structure ceramics, including the following steps: A) dissolving titanate compounds, bismuth source compounds, lanthanum source compounds, iron source compounds and cobalt source compounds in proportion Solvent, add complexing agent and mix and stir, adjust the pH value to 5~7, heat, evaporate to dryness and burn into powder, and obtain powder after pre-calcination; B) Press the powder into tablets and sinter to obtain layered calcium titanium Mineral structure ceramics.

In order to clearly illustrate the present invention, the experimental processes of step A and step B are described in detail below respectively.

The step A is specifically: the bismuth source compound, the lanthanum source compound, the iron source compound, the cobalt source compound and the titanate compound according to the metal ion Bi:La:Fe:Co:Ti=7-x:x:1.5: Dissolve in a solvent with a ratio of 1.5:3, add a complexing agent and mix and stir, adjust the pH value to 5~7, preferably 6~7, obtain a clear solution, heat, evaporate to dryness, burn it into powder, and put it in a muffle furnace 700°C~800°C, preferably 720°C~780°C, pre-fired for 2~4h, preferably 3~4h, to obtain powder, wherein 0.2≤x≤1.5, preferably 0.4≤x≤1.3, more preferably 0.6 ≤x≤1.2. Wherein, the order of adding the bismuth source compound, lanthanum source compound, iron source compound, cobalt source compound, titanate compound and complexing agent is not particularly limited.

Wherein, the titanate compound is a titanate compound well known to those skilled in the art, preferably n-butyl titanate. The bismuth source compound, lanthanum source compound, iron source compound and cobalt source compound are selected according to the principle of not introducing other impurities, and the compounds whose impurities are easily removed by combustion are selected.

In the present invention, the bismuth source compound is selected from one of bismuth nitrate, bismuth subnitrate, bismuth oxide, bismuth subcarbonate and bismuth oxalate, preferably bismuth nitrate; the lanthanum source compound is selected from lanthanum nitrate, lanthanum carbonate, One of lanthanum oxide, lanthanum oxalate and lanthanum acetate, preferably lanthanum nitrate; the iron source compound is selected from one of ferric nitrate, ferric oxide, ferric oxide and ferric oxalate, preferably ferric nitrate; The cobalt source compound is selected from cobalt nitrate, cobalt oxide, cobalt oxalate and cobalt acetate, preferably cobalt nitrate.

The solvent in step A can be selected according to the bismuth source compound, lanthanum source compound, iron source compound and cobalt source compound, preferably nitric acid, oxalic acid or acetic acid, more preferably nitric acid.

The complexing agent is selected from one or more of ethylenediaminetetraacetic acid, citric acid and glycine, and the molar ratio of the complexing agent to all metal ions in the solution is 1~2.5:1, preferably 1.4~ 2:1, more preferably 1.5~1.9:1, the complexing agent is preferably ethylenediaminetetraacetic acid and citric acid, and its molar ratio to all metal ions in the solution is 0.5~1.5:1:1, preferably 0.7~1.2:1:1.

The pH regulator is preferably ethylenediamine or ammonia water, which can remove corresponding elements through combustion without introducing other impurities.

In the present invention, the organic phase can be preliminarily removed by burning into powder; the pre-calcination step can further remove residual carbon and nitrogen elements, and is also a step for pre-phase formation of materials.

According to the present invention, the selected compounds of the raw material titanate compounds, bismuth source compounds, lanthanum source compounds, iron source compounds and cobalt source compounds must be chemically pure. Ceramics perform better.

The preparation of the powder in the step A adopts the improved Pechini method carried out in the solution. Compared with the solid phase reaction method, the method of the present invention makes the raw materials titanate compound, bismuth source compound, lanthanum source compound, iron source compound and cobalt The source compound is fully dispersed and uniform, the particles of the obtained powder are finer and more uniform, and it is easy to obtain single-phase layered perovskite structure ceramics; and the method of the present invention also has the advantage of reactivity, so that Fe-Co ions are fully coupled, thereby Higher ferromagnetic properties are obtained, and at the same time, lanthanum ions are also easy to enter the A site of the perovskite structure, reducing the leakage current and improving the ferroelectric properties; the powder is prepared by the solution method without ball milling, pre-synthesis, In steps such as plastic discharge, sintering is directly carried out after tableting, which shortens the preparation cycle, and the activity of the obtained powder is higher, thereby reducing the sintering temperature and reducing the volatilization of bismuth ions.

The step B is specifically: compressing the powder under the condition of a pressure of 60~150MPa, preferably 80~100MPa, to obtain a cylindrical sample with a thickness of 3~5mm, preferably 4~5mm; The above cylindrical samples were sintered. The sintering is hot-press sintering or muffle furnace sintering, preferably hot-press sintering. Using hot-press sintering can obtain high-performance ceramics with high sintering degree and high density at a relatively low temperature, and reduce the bismuth element. of volatilization.

The step of muffle furnace sintering is a step well known to those skilled in the art, and there is no special limitation. The sintering temperature is 600°C~1000°C, preferably 800°C~950°C, and the sintering time is 2~6h, preferably 3~5h.

The specific steps of hot pressing and sintering are: placing the cylindrical sample in a corundum mold or a silicon carbide mold protected by _ZrO2 powder or MgO powder lining, and raising the temperature to 600°C~800°C in a protective atmosphere , preferably at 650°C~750°C, pressurize to 5~20MPa, preferably 10~20MPa, reach the highest sintering temperature of 800°C~1000°C for 1~6h, and then completely release the pressure, preferably 3~5h, to obtain layered calcium Titanium structure ceramics. The protective atmosphere is a protective atmosphere well known to those skilled in the art, preferably one or more of argon, oxygen and nitrogen.

According to the present invention, the structure of the cylindrical sample is preferably a powder in which the powder obtained in the above step A is coated with an excess of 10-20% of the bismuth element. Using the outer cladding of the same element as a protective layer can provide a volatile element atmosphere for sintering, which blocks the diffusion channel of the elements in the sample to the ZrO ₂ powder or MgO powder of the non-identical outer cladding, and can protect the inner sample components. It is mainly the accuracy of the content of volatile bismuth and easily diffused cobalt. At the same time, the outer cladding of the same element also has the effect of thermal stress buffering. The preparation method of the powder with an excess of 10-20% bismuth element is the same as the preparation method of the powder obtained in the inner layer step A, the only difference lies in the content of bismuth element.

The role of ZrO ₂ powder or MgO powder in the outer cladding layer of non-identical elements is to use its high melting point and high sintering temperature to achieve the purpose of isolating the sample and the mold, and it is easy to demould after hot pressing and sintering; it also has the effect of thermal stress buffering, and at the same time achieves The purpose of protecting samples and molds.

In order to further illustrate the present invention, a layered perovskite structure ceramic provided by the present invention and a preparation method thereof are described in detail below in conjunction with examples.

The reagents used in the following examples are all commercially available, and the raw materials used are n-butyl titanate, bismuth nitrate pentahydrate, lanthanum nitrate hydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate, ethylenediaminetetraacetic acid and citric acid monohydrate are all The specifications of analytical reagents from Sinopharm Group are shown in Table 1.

The specifications of raw materials used in table 1

Example 1

1.1 Dissolve 21.0269g bismuth nitrate pentahydrate, 2.6444g hydrated lanthanum nitrate, 4.3948g nonahydrated ferric nitrate, 3.1504g hexahydrated cobalt nitrate, 7.4424g n-butyl titanate, 19.6124g citric acid and 18.9965g ethylenediaminetetraacetic acid Mix and stir in nitric acid, add ammonia water dropwise to adjust the pH value of the solution to 7, obtain a clear solution, keep it stable for 3 hours, place it in a crucible, heat and concentrate until the solution is evaporated to dryness, burn it into powder, and pre-burn it in a muffle furnace at 750°C 3h, the powder was obtained.

1.2 Dry press the powder obtained in 1.1 under the condition of a pressure of 80MPa to form a cylindrical sample, the sample size is 15mm in diameter, and the thickness is 4mm. The preparation method of the obtained powder with an excess of 10% bismuth element is the same as that of 1.1, except that the content of bismuth nitrate pentahydrate is excessively 10%.

1.3 Place the cylindrical sample obtained in 1.2 in a corundum mold lined with ZrO ₂ powder protection, in an atmosphere with a volume ratio of argon to oxygen of 80:20, raise the temperature to 650°C, start pressurizing, 830 ℃, 10MPa and pressure holding for 3 hours, then cooled to room temperature to obtain layered perovskite structure ceramics Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ .

The structure of the layered perovskite ceramic Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 1.3 was analyzed using an X-ray diffractometer (Rigaku TTR III, Rigaku Corporation, Japan), and its X-ray diffraction pattern was obtained, as shown in Fig. As shown in 1, the results show that the sample is a ceramic sample with a single Aurivillius structure, and there is no obvious second phase.

The morphology of the layered perovskite structure ceramic Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 1.3 was observed with a scanning electron microscope (JEOL JSM-6390LA type, Japan Electronics Co., Ltd.), and its scanning electron micrograph was obtained, as shown in Fig. 2, the results show that the degree of sintering is better, the shape and size of the grains are basically the same, and the pores exist, and the density of the ceramics is better.

The ferroelectric properties of the layered perovskite structure ceramics Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 1.3 were tested using a ferroelectric performance measuring instrument (P-PMF type from Radiant Technologies, USA) at room temperature, and its iron The electrical performance measurement diagram is shown in Figure 3. The results show that the remanent polarization (2P _r ) of ceramics is 7.48 μC/cm ² and the coercive field (2E _c ) is 88kV/cm.

The ferromagnetic properties of the layered perovskite structure ceramics Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 1.3 were tested at room temperature by using a vibrating sample magnetometer (EV7 type, American ADE Company), and its ferromagnetic properties were measured As shown in Figure 4, the results show that the residual magnetic susceptibility (2M _r ) of ceramics is 1.12emu/g, and the coercive field (2H _c ) is 360Oe.

Example 2

2.1 Dissolve 21.0269g bismuth nitrate pentahydrate, 2.6444g lanthanum nitrate hydrate, 4.3948g ferric nitrate nonahydrate, 3.1504g cobalt nitrate hexahydrate, 7.4424g n-butyl titanate, 19.6124g citric acid and 18.9965g ethylenediaminetetraacetic acid Mix and stir in nitric acid, add ammonia water dropwise to adjust the pH value of the solution to 7, obtain a clear solution, keep it stable for 3 hours, place it in a crucible, heat and concentrate until the solution is evaporated to dryness, burn it into powder, and pre-burn it in a muffle furnace at 750°C 3h, the powder was obtained.

2.2 Dry press the powder obtained in 2.1 under the condition of a pressure of 80MPa to form a cylindrical sample, the sample size is 15mm in diameter, and the thickness is 2mm. The preparation method of the obtained powder with an excess of 10% bismuth element is the same as that of 2.1, except that the content of bismuth nitrate pentahydrate is excessively 10%.

2.3 Place the cylindrical sample obtained in 2.2 in a muffle furnace, heat up to 950°C in an air atmosphere, and sinter for 5 hours to obtain a layered perovskite structure ceramic Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ .

The ferroelectric properties of the layered perovskite structure ceramics Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 2.3 were tested using a ferroelectric performance measuring instrument (P-PMF type, Radiant Technologies, USA) at room temperature, and its iron Electrical properties, measured at room temperature with an electric field of 150kV/cm, the remanent polarization (2P _r ) is 4.99μC/cm ² , and the coercive field (2E _c ) is 67kV/cm.

The ferromagnetic properties of the layered perovskite structure ceramics Bi ₆ LaFe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 2.3 were tested using a vibrating sample magnetometer (EV7 type, American ADE Company) at room temperature, and its ferromagnetic properties were obtained. The residual magnetic susceptibility (2M _r ) is 1.93emu/g, and the coercive field (2H _c ) is 344Oe.

Example 3

3.1 Dissolve 21.9033g of bismuth nitrate pentahydrate, 1.9846g of hydrated lanthanum nitrate, 4.3947g of nonahydrated ferric nitrate, 3.1500g of hexahydrated cobalt nitrate, 7.4423g of n-butyl titanate, 19.6325g of citric acid and 18.9988g of ethylenediaminetetraacetic acid Mix and stir in nitric acid, add ammonia water dropwise to adjust the pH value of the solution to 7, obtain a clear solution, keep it stable for 3 hours, place it in a crucible, heat and concentrate until the solution is evaporated to dryness, burn it into powder, and pre-burn it in a muffle furnace at 750°C 3h, the powder was obtained.

3.2 Dry press the powder obtained in 3.1 under the condition of a pressure of 80MPa to form a cylindrical sample, the sample size is 15mm in diameter, and the thickness is 4mm. The preparation method of the obtained powder with an excess of 10% bismuth element is the same as that of 3.1, except that the content of bismuth nitrate pentahydrate is excessively 10%.

3.3 Place the cylindrical sample obtained in 3.2 in a corundum mold lined with ZrO ₂ powder protection, in an atmosphere with a volume ratio of argon to oxygen of 80:20, raise the temperature to 650°C, start pressurizing, 830 ℃ and 10MPa for 3 hours, then cooled to room temperature to obtain layered perovskite structure ceramics Bi _6.25 La _0.75 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ .

Using a ferroelectric performance measuring instrument (P-PMF type from Radiant Technologies, USA) to test the ferroelectric performance of the layered perovskite structure ceramic Bi _6.25 La _0.75 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 3.3 at room temperature, the obtained Its ferroelectric properties, measured at room temperature under the condition that the electric field is 100kV/cm, the remanent polarization (2P _r ) is 2.61μC/cm ² , and the coercive field (2E _c ) is 40kV/cm.

The ferromagnetic performance of the layered perovskite structure ceramics Bi _6.25 La _0.75 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 3.3 was tested at room temperature by using a vibrating sample magnetometer (EV7 type, American ADE Company), and its ferromagnetic properties were obtained. energy, the remanent magnetic susceptibility (2M _r ) is 2.60emu/g, and the coercive field (2H _c ) is 344Oe.

Example 4

4.1 Dissolve 22.7791g of bismuth nitrate pentahydrate, 1.3225g of hydrated lanthanum nitrate, 4.3955g of nonahydrated ferric nitrate, 3.1501g of hexahydrated cobalt nitrate, 7.4428g of n-butyl titanate, 19.6091g of citric acid and 1809986g of ethylenediaminetetraacetic acid in In nitric acid, mix and stir, dropwise add ammonia water to adjust the pH value of the solution to 7, obtain a clear solution, stabilize it for 3 hours, place it in a crucible, heat and concentrate until the solution evaporates, burn it into powder, and pre-burn it in a muffle furnace at 750°C for 3 hours , to obtain powder.

4.2 Dry press the powder obtained in 4.1 under the condition of a pressure of 80MPa to form a cylindrical sample, the sample size is 15mm in diameter, and the thickness is 4mm. The preparation method of the obtained powder with an excess of 10% bismuth element is the same as that of 4.1, except that the content of bismuth nitrate pentahydrate is excessively 10%.

4.3 Place the cylindrical sample obtained in 4.2 in a corundum mold lined with ZrO ₂ powder protection, in an atmosphere with a volume ratio of argon to oxygen of 80:20, raise the temperature to 650°C, and start to pressurize, 830 ℃ and 10MPa for 3 hours, then cooled to room temperature to obtain layered perovskite structure ceramics Bi _6.5 La _0.5 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ .

Use a ferroelectric performance measuring instrument (P-PMF type from Radiant Technologies, USA) to test the ferroelectric performance of the layered perovskite structure ceramic Bi _6.5 La _0.5 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 4.3 at room temperature, and get Its ferroelectric properties, measured at room temperature under the condition that the electric field is 100kV/cm, the remanent polarization (2P _r ) is 1.53μC/cm ² , and the coercive field (2E _c ) is 32kV/cm.

The ferromagnetic performance of the layered perovskite structure ceramic Bi _6.5 La _0.5 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 4.3 was tested at room temperature by using a vibrating sample magnetometer (EV7 type, American ADE Company), and its ferromagnetic properties were obtained. energy, the remanent magnetic susceptibility (2M _r ) is 1.38emu/g, and the coercive field (2H _c ) is 257Oe.

Example 5

5.1 Dissolve 23.6287g of bismuth nitrate pentahydrate, 0.6617g of hydrated lanthanum nitrate, 4.3950g of nonahydrated ferric nitrate, 3.1507g of hexahydrated cobalt nitrate, 7.4430g of n-butyl titanate, 19.6824g of citric acid and 19.0010g of ethylenediaminetetraacetic acid Mix and stir in nitric acid, add ammonia water dropwise to adjust the pH value of the solution to 7, obtain a clear solution, keep it stable for 3 hours, place it in a crucible, heat and concentrate until the solution is evaporated to dryness, burn it into powder, and pre-burn it in a muffle furnace at 750°C 3h, the powder was obtained.

5.2 Dry press the powder obtained in 5.1 under the condition of a pressure of 80MPa to form a cylindrical sample. The sample size is 15mm in diameter and 4mm in thickness. The preparation method of the obtained powder with an excess of 10% bismuth element is the same as that of 5.1, except that the content of bismuth nitrate pentahydrate is excessively 10%.

5.3 Place the cylindrical sample obtained in 5.2 in a corundum mold lined with ZrO ₂ powder protection, in an atmosphere with a volume ratio of argon to oxygen of 80:20, raise the temperature to 650°C, start pressurizing, 830 ℃ and 10MPa for 3 hours, then cooled to room temperature to obtain layered perovskite structure ceramics Bi _6.75 La _0.25 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ .

Using a ferroelectric performance measuring instrument (Radiant Technologies, USA, P-PMF type) to test the ferroelectric performance of the layered perovskite structure ceramic Bi _6.75 La _0.25 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 5.3 at room temperature, the obtained Its ferroelectric properties, measured at room temperature with an electric field of 100kV/cm, the remanent polarization (2P _r ) is 1.89μC/cm ² , and the coercive field (2E _c ) is 40kV/cm.

The ferromagnetic performance of the layered perovskite structure ceramic Bi _6.75 La _0.25 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 5.3 was tested at room temperature by using a vibrating sample magnetometer (EV7 type of ADE Company of the United States), and its ferromagnetic properties were obtained. energy, the remanent magnetic susceptibility (2M _r ) is 1.20emu/g, and the coercive field (2H _c ) is 250Oe.

Example 6

6.1 Dissolve 20.1253g of bismuth nitrate pentahydrate, 3.3055g of hydrated lanthanum nitrate, 4.3947g of nonahydrated ferric nitrate, 3.1501g of hexahydrated cobalt nitrate, 7.4424g of n-butyl titanate, 19.6424g of citric acid and 19.0040g of ethylenediaminetetraacetic acid Mix and stir in nitric acid, add ammonia water dropwise to adjust the pH value of the solution to 7, obtain a clear solution, keep it stable for 3 hours, place it in a crucible, heat and concentrate until the solution is evaporated to dryness, burn it into powder, and pre-burn it in a muffle furnace at 750°C 3h, the powder was obtained.

6.2 Dry press the powder obtained in 6.1 under the condition of a pressure of 80MPa to form a cylindrical sample. The diameter of the sample is 15mm and the thickness is 4mm. The obtained powder, the outer cladding with 10% excess bismuth element is the same as the preparation method in 6.1, the difference is that the content of bismuth nitrate pentahydrate is excessive 10%.

6.3 Place the cylindrical sample obtained in 6.2 in a corundum mold lined with ZrO ₂ powder protection, in an atmosphere with a volume ratio of argon to oxygen of 80:20, raise the temperature to 650°C, and start to pressurize, 830 ℃ and 10MPa for 3 hours, then cooled to room temperature to obtain layered perovskite structure ceramics Bi _5.75 La _1.25 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ .

Using a ferroelectric performance measuring instrument (P-PMF type of Radiant Technologies, USA) to test the ferroelectric performance of the layered perovskite structure ceramic Bi _5.75 La _1.25 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 6.3 at room temperature, the obtained Its ferroelectric properties, measured at room temperature under the condition that the electric field is 100kV/cm, the remanent polarization (2P _r ) is 1.35μC/cm ² , and the coercive field (2E _c ) is 23kV/cm.

The ferromagnetic performance of the layered perovskite structure ceramic Bi _5.75 La _1.25 Fe _1.5 Co _1.5 Ti ₃ O ₂₁ obtained in 6.3 was tested at room temperature by using a vibrating sample magnetometer (EV7 type, American ADE Company), and its ferromagnetic properties were obtained. energy, the remanent magnetic susceptibility (2M _r ) is 1.64emu/g, and the coercive field (2H _c ) is 290Oe.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. A layered perovskite structure ceramic, as shown in formula (I): Bi _7-x La _x Fe _1.5 Co _1.5 Ti ₃ O ₂₁ (I) Wherein, x is 0.25, 0.5, 0.75, 1 or 1.25. 2. A preparation method of layered perovskite structure ceramics, characterized in that, comprising the following steps: A) Bismuth source compound, lanthanum source compound, iron source compound, cobalt source compound and titanate compound according to the ratio of metal ion Bi:La:Fe:Co:Ti=7-x:x:1.5:1.5:3 Dissolve in a solvent, add a complexing agent to mix and stir, adjust the pH value to 5-7, heat, evaporate to dryness and burn into a powder, and obtain a powder after pre-calcination, wherein x is 0.25, 0.5, 0.75, 1 or 1.25; the complex The mixture is selected from ethylenediaminetetraacetic acid and citric acid; B) pressing the powder into tablets and sintering to obtain layered perovskite structure ceramics; The sintering is hot press sintering, including: placing the pressed sample in a corundum mold lined with _ZrO2 powder protection, and raising the temperature to 650°C in an atmosphere with a volume ratio of argon to oxygen of 80:20 , start to pressurize, keep the pressure at 830°C and 10MPa for 3 hours, then cool to room temperature. 3. The preparation method according to claim 2, wherein the bismuth source compound is selected from one of bismuth nitrate, bismuth hyponitrate, bismuth oxide, bismuth subcarbonate and bismuth oxalate. 4. The preparation method according to claim 2, wherein the lanthanum source compound is selected from one of lanthanum nitrate, lanthanum carbonate, lanthanum oxide, lanthanum oxalate and lanthanum acetate. 5. The preparation method according to claim 2, wherein the iron source compound is selected from one of ferric nitrate, ferric oxide, ferric oxide and ferric oxalate. 6. The preparation method according to claim 2, wherein the cobalt source compound is selected from one of cobalt nitrate, cobalt oxide, cobalt oxalate and cobalt acetate. 7. The preparation method according to claim 2, characterized in that the molar ratio of the complexing agent to the total number of metal ions is 1-2.5:1. 8. The preparation method according to claim 2, characterized in that the temperature of the pre-calcination is 700°C-800°C, and the time is 2-4h.