阅读说明：本技术 一种铁酸铋/聚偏二氟乙烯-三氟乙烯多层复合薄膜及其制备方法 (Bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film and preparation method thereof ) 是由 徐玲芳 桂迟 张雨 肖海波 王瑞龙 杨昌平 于 2020-04-23 设计创作，主要内容包括：本发明属于多铁性薄膜技术领域,具体涉及一种铁酸铋/聚偏二氟乙烯-三氟乙烯多层复合薄膜,包括包括PVDF-TrFE薄膜和至少一层BFO/PVDF-TrFE复合薄膜,最上面的BFO/PVDF-TrFE复合薄膜上贴附有PVDF-TrFE薄膜；其制备方法为：将PVDF-TrFE粉末溶解得到溶液A,再向溶液A中加入BFO纳米级粉末得到混合溶液B；然后以FTO导电玻璃为衬底,将混合溶液B在FTO导电玻璃上进行旋转涂膜,制备BFO/PVDF-TrFE复合薄膜,烘干后,再将溶液A在BFO/PVDF-TrFE复合薄膜上进行旋转涂膜,制备PVDF-TrFE薄膜；之后将湿膜置进行退火处理,得到铁酸钴/聚偏二氟乙烯-三氟乙烯多层复合薄膜,最后在其上镀铂点电极。本发明的铁酸铋/聚偏二氟乙烯-三氟乙烯多层复合薄膜不仅漏电流低,且有较高的剩余极化强度,其工艺设备成本低、过程简单且可控性强。(The invention belongs to the technical field of multiferroic films, and particularly relates to a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film which comprises a PVDF-TrFE film and at least one layer of BFO/PVDF-TrFE composite film, wherein the PVDF-TrFE film is attached to the uppermost BFO/PVDF-TrFE composite film; the preparation method comprises the following steps: dissolving PVDF-TrFE powder to obtain a solution A, and adding BFO nano-scale powder into the solution A to obtain a mixed solution B; then, using FTO conductive glass as a substrate, carrying out rotary coating on the mixed solution B on the FTO conductive glass to prepare a BFO/PVDF-TrFE composite film, drying, and carrying out rotary coating on the solution A on the BFO/PVDF-TrFE composite film to prepare the PVDF-TrFE film; and then annealing the wet film to obtain the cobalt ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film, and finally plating a platinum point electrode on the cobalt ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film. The bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film disclosed by the invention is low in leakage current, higher in residual polarization strength, low in cost of process equipment, simple in process and strong in controllability.)

1. A bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film is characterized in that: the composite film comprises a PVDF-TrFE film and at least one layer of BFO/PVDF-TrFE composite film; when the BFO/PVDF-TrFE composite film is a layer, the PVDF-TrFE film is attached to the BFO/PVDF-TrFE composite film; when the BFO/PVDF-TrFE composite film is two or more than two layers, the multiple layers of BFO/PVDF-TrFE composite films are overlapped in sequence, and the PVDF-TrFE film is attached to the BFO/PVDF-TrFE composite film positioned at the uppermost layer.

2. A preparation method of a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film is characterized by comprising the following steps:

s1, preparing BFO nano-scale powder;

s2, preparing the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film:

s2.1, dissolving PVDF-TrFE powder in a diethyl carbonate solvent, and fully stirring to obtain a solution A;

s2.2, adding BFO nano-scale powder into the continuously stirred solution A, and fully stirring to obtain a mixed solution B;

s2.3, using FTO conductive glass as a substrate, and performing rotary coating on the prepared mixed solution B on the FTO conductive glass by using a spin coater to prepare a BFO/PVDF-TrFE composite film;

s2.4, placing the spin-coated wet film in a drying oven for drying;

s2.5, performing rotary coating on the prepared solution A on the dried BFO/PVDF-TrFE composite film by using a spin coater to prepare the PVDF-TrFE film;

s2.6, placing the spin-coated wet film in a heat treatment furnace for annealing treatment to obtain a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film;

s2.7, manufacturing an electrode, and plating a platinum point electrode on the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film manufactured in the step S2.6.

3. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: the following steps are also included between step S2.4 and step S2.5: and (3) carrying out rotary coating on the prepared mixed solution B on the dried BFO/PVDF-TrFE composite film by using a spin coater, preparing a layer of BFO/PVDF-TrFE composite film, and drying the spin-coated wet film in a drying box.

4. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: the mass fraction of PVDF-TrFE in the solution A is 3-5%.

5. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: the mass ratio of BFO to PVDF-TrFE in the mixed solution B is 1: 1 to 3.

6. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: and S2.4, drying the wet film in a drying oven at 80-100 ℃ for 3-5 min.

7. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: in the step S2.6, the annealing treatment temperature is 135-145 ℃, and the treatment time is 1.5-2 h.

8. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: the preparation of the BFO nanoscale powder in step S1 includes the steps of:

s1.1, mixing bismuth nitrate pentahydrate and ferric nitrate nonahydrate according to a molar ratio of 1.05: 1 is dissolved in ethylene glycol monomethyl ether solvent to obtain solution C, and the concentration of the solution C is 0.5 mol/L; dissolving citric acid monohydrate and polyethylene glycol in a continuously stirred solution C, wherein the molar ratio of the citric acid monohydrate to the metal cations in the solution is 1: 1, the mass ratio of polyethylene glycol to citric acid monohydrate is 1: 8, obtaining a bismuth ferrite precursor solution;

s1.2, continuously stirring the obtained bismuth ferrite precursor solution in a water bath at 50 ℃ for 30 min to obtain stable bismuth ferrite sol, and then drying the stable bismuth ferrite sol in a drying box at 80 ℃ for 48 h to obtain bismuth ferrite xerogel;

s1.3, placing the obtained bismuth ferrite xerogel in a heat treatment furnace to carry out two-step annealing, wherein the annealing temperature of the first step is 350 ℃, and the heat preservation time is 2 hours; secondly, annealing at 500 ℃ for 2 h to obtain bismuth ferrite powder;

s1.4, placing the obtained bismuth ferrite powder in a mortar for grinding for 1-2 hours to obtain BFO nano-scale powder.

9. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: the particle size of the BFO nano-scale powder prepared in the step S1 is 100-300 nm.

10. The method for preparing a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film according to claim 2, wherein: and step S2.2, adding the BFO nano-scale powder into the solution A, stirring by using a magneton, then performing ultrasonic dispersion, and repeating for 2-3 times to ensure that the BFO nano-scale powder is uniformly dispersed.

Technical Field

The invention relates to a multiferroic composite film and a preparation method thereof, in particular to a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film and a preparation method thereof, belonging to the technical field of multiferroic films.

Background

In recent years, multiferroic composites formed of ceramics and polymers have received extensive attention and research due to the great potential for applications in multiferroic devices, such as sensors, actuators, and energy collectors. The composition of the polymer and the ceramic particles can be used for preparing a body and a film by adopting the traditional process, and the process stability is good and easy to realize. For example, the traditional lead zirconate titanate, lead titanate or ferromagnetic materials such as cobalt ferrite and the like are compounded with the copolymer PVDF-TrFE, so that the ceramic powder is easily dispersed in the copolymer to form various composite structures.

Bismuth ferrite (BiFeO)₃BFO) is of perovskite structure and has a high denier temperature (T _N643K) and Curie temperature (T _C1103K) which is a typical room-temperature single-phase ferroelectric and ferromagnetic coexisting material, and has good application prospects in the aspects of nonvolatile memories, spin electronic devices, magnetoelectric sensors and the like. However, BFO ceramics have large leakage currents due to defects caused by impurities, non-stoichiometric ratios, and oxygen vacancies, which limits their achievement of good ferroelectric properties and saturated hysteresis loops.

In order to obtain high magnetoelectric coupling performance, one effective approach is to compound BFO with a polymer to improve the characteristics thereof. Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) is the best choice for compounding with BFO due to its high sensitivity, high energy density and high insulating properties. PVDF-TrFE has high elasticity and excellent piezoelectric ferroelectric property, and has wide application prospect in the fields of elastic organic electronic devices, such as organic solar cells, lithium ion batteries, nonvolatile memories, piezoelectric sensors and the like; however, the organic ferroelectric material has the disadvantage of high coercive field, which is generally about 10 times that of the ceramic material, and this will prevent the organic ferroelectric material from obtaining high remanent polarization at low field. Experiments show that the composite film of pure BFO and PVDF-TrFE still has the defect of large leakage current.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film and the preparation method thereof, so that the multilayer composite film with small leakage current and excellent ferroelectric property can be prepared, and the preparation method has low process equipment cost, simple process and strong controllability.

In order to realize the purpose, the technical scheme of the invention is a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film, which comprises a PVDF-TrFE film and a BFO/PVDF-TrFE composite film; when the BFO/PVDF-TrFE composite film is a layer, the PVDF-TrFE film is attached to the BFO/PVDF-TrFE composite film; when the BFO/PVDF-TrFE composite film is two or more than two layers, the multiple layers of BFO/PVDF-TrFE composite films are overlapped in sequence, and the PVDF-TrFE film is attached to the BFO/PVDF-TrFE composite film positioned at the uppermost layer.

The invention also provides a preparation method of the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film, which comprises the following steps:

s1, preparing BFO nano-scale powder;

s2, preparing the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film:

s2.1, dissolving PVDF-TrFE powder in a diethyl carbonate solvent, and fully stirring to obtain a solution A;

s2.2, adding BFO nano-scale powder into the continuously stirred solution A, and fully stirring to obtain a mixed solution B;

s2.3, using FTO conductive glass as a substrate, and performing rotary coating on the prepared mixed solution B on the FTO conductive glass by using a spin coater to prepare a BFO/PVDF-TrFE composite film;

s2.4, placing the spin-coated wet film in a drying oven for drying;

s2.5, performing rotary coating on the prepared solution A on the dried BFO/PVDF-TrFE composite film by using a spin coater to prepare the PVDF-TrFE film;

s2.6, placing the spin-coated wet film in a heat treatment furnace for annealing treatment to obtain a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film;

s2.7, manufacturing an electrode, and plating a platinum point electrode on the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film manufactured in the step S2.6.

Further, the following steps are also included between step S2.4 and step S2.5: and (3) carrying out rotary coating on the prepared mixed solution B on the dried BFO/PVDF-TrFE composite film by using a spin coater, preparing a layer of BFO/PVDF-TrFE composite film, and drying the spin-coated wet film in a drying box.

Further, the mass fraction of PVDF-TrFE in the solution A is 3-5%.

Further, the mass ratio of BFO to PVDF-TrFE in the mixed solution B is 1: 1 to 3.

Further, in step S2.4, the wet film is dried in a drying oven at 80-100 ℃ for 3-5 min.

Further, in step S2.6, the annealing treatment temperature is 135-145 ℃, and the treatment time is 1.5-2 h.

Further, the preparation of BFO nanoscale powder in step S1 includes the steps of:

s1.1, mixing bismuth nitrate pentahydrate and ferric nitrate nonahydrate according to a molar ratio of 1.05: 1 is dissolved in ethylene glycol monomethyl ether solvent to obtain solution C, and the concentration of the solution C is 0.5 mol/L; dissolving citric acid monohydrate and polyethylene glycol in a continuously stirred solution C, wherein the molar ratio of the citric acid monohydrate to the metal cations in the solution is 1: 1, the mass ratio of polyethylene glycol to citric acid monohydrate is 1: 8, obtaining a bismuth ferrite precursor solution;

s1.2, continuously stirring the obtained bismuth ferrite precursor solution in a water bath at 50 ℃ for 30 min to obtain stable bismuth ferrite sol, and then drying the stable bismuth ferrite sol in a drying box at 80 ℃ for 48 h to obtain bismuth ferrite xerogel;

s1.3, placing the obtained bismuth ferrite xerogel in a heat treatment furnace to carry out two-step annealing, wherein the annealing temperature of the first step is 350 ℃, and the heat preservation time is 2 hours; secondly, annealing at 500 ℃ for 2 h to obtain bismuth ferrite powder;

s1.4, placing the obtained bismuth ferrite powder in a mortar for grinding for 1-2 hours to obtain BFO nano-scale powder.

Further, the grain size of the BFO nano-scale powder prepared in the step S1 is 100-300 nm.

Further, in step S2.2, after the BFO nanoscale powder is added to the solution a, magneton stirring is performed, ultrasonic dispersion is performed, and the process is repeated for 2 to 3 times, so that the BFO nanoscale powder is uniformly dispersed.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, bismuth ferrite is uniformly mixed in PVDF-TrFE solution to prepare a BFO/PVDF-TrFE composite film through composite spin coating, and then a PVDF-TrFE film is spin coated on the BFO/PVDF-TrFE composite film to obtain a multilayer composite film with a compact structure, so that the defect of large leakage current of the ferroelectric polymer composite film is effectively solved; the preparation method is simple, easy to operate, mild and controllable in preparation conditions and high in efficiency.

Drawings

FIG. 1 is a schematic structural view of a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene composite film (a) prepared in examples 1 and 3 and a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film (b) prepared in examples 2 and 4 according to the present invention;

FIG. 2 is an XRD spectrum of Bismuth Ferrite (BFO), a polyvinylidene fluoride-trifluoroethylene film (PVDF-TrFE), a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene composite film prepared in example 1 (0.25 BFO (0.75PVDF-TrFE)/0.25BFO (0.75 PVDF-TrFE)), and a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film prepared in example 2 (0.25 BFO (0.75PVDF-TrFE)/0.25BFO (0.75 PVDF-TrFE)/PVDF-TrFE);

FIG. 3 is a leakage current characteristic curve of the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene composite film prepared in example 1 of the present invention;

FIG. 4 is a ferroelectric hysteresis loop of a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene composite film prepared in example 1 of the present invention;

FIG. 5 is a leakage current characteristic curve of the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film prepared in example 2 of the present invention;

FIG. 6 is a ferroelectric hysteresis loop of a bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film prepared in example 2 of the present invention;

FIG. 7 is a leakage current characteristic curve of the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene composite film prepared in example 3 of the present invention;

FIG. 8 is a leakage current characteristic curve of the bismuth ferrite/polyvinylidene fluoride-trifluoroethylene multilayer composite film prepared in example 4 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.