CN109133666B - BFO-based superlattice/LSMO composite film with resistance switching effect and preparation method thereof - Google Patents

BFO-based superlattice/LSMO composite film with resistance switching effect and preparation method thereof Download PDF

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CN109133666B
CN109133666B CN201811088056.1A CN201811088056A CN109133666B CN 109133666 B CN109133666 B CN 109133666B CN 201811088056 A CN201811088056 A CN 201811088056A CN 109133666 B CN109133666 B CN 109133666B
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谈国强
刘云
郭美佑
薛敏涛
任慧君
夏傲
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Shaanxi University of Science and Technology
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Abstract

The invention provides a BFO-based superlattice/LSMO composite film with a resistance switching effect and a preparation method thereof. Comprises a lower layer film and an upper layer film which are compounded together; the chemical formula of the lower layer film is La0.7Sr0.3MnO3The perovskite structure is adopted, and the space group is R3 c; the upper film has a chemical formula of Bi0.89Ho0.08Sr0.03Fe0.97‑ xMn0.03NixO3‑Bi0.89Ho0.08Sr0.03Fe0.97‑yMn0.03NiyO3The perovskite structure is a twisted rhombus perovskite structure, the space group is R3c, wherein x is less than or equal to 0.04, y is less than or equal to 0.04, and x is not equal to y. Obtained by spin coating using a sol-gel method. BiFeO of the invention3The base superlattice/LSMO composite film has resistance switching effect.

Description

BFO-based superlattice/LSMO composite film with resistance switching effect and preparation method thereof
Technical Field
The invention belongs to the field of functional materials, and relates to a BFO-based superlattice/LSMO composite film with a resistance switching effect and a preparation method thereof.
Background
Ferroelectric materials, and in particular ferroelectric superlattices, are generally absent in nature. Due to the progress of basic theory science and technology, the research of ferroelectric superlattice is developed vigorously. A superlattice refers to an artificial crystal of two or more materials that are periodically and alternately grown. The thicknesses of the different materials of the adjacent two layers combine to be referred to as the period length of the superlattice. BiFeO3(BFO for short) as an important room-temperature multiferroic material, a multiferroic heterojunction formed by the material is widely researched in various aspects, and BiFeO is caused3Has narrow energy gap and high remanent polarization, is widely researched as an important material of a ferroelectric resistance change device, and the origin of the resistance change behavior of the ferroelectric resistance change device is BiFeO with semiconductor properties3And the interface between the upper and lower electrodes thereof in different polarization statesA change in the potential barrier.
But BiFeO3Volatile of middle bismuth element and part of Fe3+To Fe2+The transition of (2) causes a severe leakage phenomenon in the thin film, resulting in a decrease in ferroelectric properties, and thus a switching effect of the thin film resistance is adversely affected.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a BFO-based superlattice/LSMO composite film with resistance switching effect and a preparation method thereof.
The invention is realized by the following technical scheme:
a BFO-based superlattice/LSMO composite film with resistance switching effect comprises a lower layer film and an upper layer film which are compounded together; the chemical formula of the lower layer film is La0.7Sr0.3MnO3The perovskite structure is adopted, and the space group is R3 c; the upper film has a chemical formula of Bi0.89Ho0.08Sr0.03Fe0.97-xMn0.03NixO3-Bi0.89Ho0.08Sr0.03Fe0.97-yMn0.03NiyO3The perovskite structure is a twisted rhombus perovskite structure, the space group is R3c, wherein x is less than or equal to 0.04, y is less than or equal to 0.04, and x is not equal to y.
Preferably, when x is 0.03 and y is 0.01, the switching ratio R in the high and low resistance states is highHRS/RLRSIs 14.83 to 39.02.
Preferably, the remanent polarization value P is 30VrIs 78.8 mu C/cm2The reverse current I is 0.9mA, and the electric hysteresis loop squareness RsqThe coercive field strength is 190kV/cm, 1.08.
The preparation method of the BFO-based superlattice/LSMO composite film with the resistance switching effect comprises the following steps:
step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether, stirring, adding water, stirring to dissolve completely, adding acetic anhydride, stirring, adding polyethylene glycol dropwise, stirring, and adding waterStanding to obtain a lower-layer membrane precursor solution;
step 2, spin-coating the lower layer film precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160-180 ℃ after glue homogenizing to obtain a dry film, and annealing at 590-620 ℃ to obtain a crystalline LSMO film;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach a preset thickness, and obtaining a lower layer film;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride, and uniformly stirring to obtain an upper layer membrane precursor solution;
step 5, coating the upper layer membrane precursor solution on the lower layer membrane in a spinning mode to obtain BiFeO3A wet film based on superlattice is subjected to glue homogenizing, then the wet film is baked at 198-220 ℃ to obtain a dry film, and then annealing is carried out at 545-565 ℃ to obtain crystalline BiFeO3A base superlattice film;
step 6, waiting for crystalline BiFeO3After the base superlattice film is naturally cooled, the base superlattice film is subjected to BiFeO3Repeating the step 5 on the base superlattice thin film to reach the preset thickness to obtain BiFeO3A base superlattice/LSMO composite film.
Preferably, the total concentration of the metal ions in the lower layer film precursor solution is 0.2-0.3 mol/L, and the total concentration of the metal ions in the upper layer film precursor solution is 0.3-0.4 mol/L.
Preferably, the volume ratio of ethylene glycol methyl ether to acetic anhydride in the upper layer film precursor liquid is (3-3.3) to 1, and the volume ratio of ethylene glycol methyl ether to acetic anhydride in the lower layer film precursor liquid is (2.8-3) to (1.1-1.2);
preferably, the spin rate of the spin coating in the step 2 and the step 5 is 3200-3600 r/min, and the spin coating time is 11-16 s.
Preferably, the baking time after the glue homogenizing in the step 2 and the step 5 is 7-9 min.
Preferably, the annealing time in the step 2 is 26-36 min, and the annealing time in the step 5 is 10-15 min.
Preferably, the number of the crystalline LSMO thin films is 5-7, and the crystalline BiFeO is3The number of layers of the base superlattice thin film is 10-14.
Compared with the prior art, the invention has the following beneficial technical effects:
the upper layer film of the BFO-based superlattice/LSMO composite film adopts rare earth elements Ho and Sr and transition elements Mn and Ni doped BiFeO3And periodically and alternately growing the film into a superlattice film, doping can effectively reduce the content of oxygen vacancies and defects, so that the leakage current density in the film is gradually reduced, and the ferroelectricity is improved; simultaneously, Sr-doped LMO magnetic layer is selected to compound Ni-doped BiFeO3Superlattice ferroelectric layer for BiFeO3The multiferroic performance and the resistance change characteristic are improved. LSMO is a giant magnetoresistance rare earth manganese oxide, is a product obtained by doping divalent element strontium to LMO (lanthanum strontium oxide) at A position, has a perovskite structure, can be matched with a ferroelectric oxide with the perovskite structure, and is used for preparing a ferroelectric film heterojunction with high orientation and a giant magnetoresistance film. The LSMO has a room temperature Colossal Magnetoresistance (CMR) effect and higher spin polarizability, and can greatly improve the sensitivity of the device. Cell parameters of LSMO and BiFeO3The crystal cell parameters of (1) are very close, and the work function difference of the two is very small, so when the two are compounded, the interface potential barrier at the interface is negligible, but a middle transition layer rich in Bi-Ho-Sr-Mn-Ni-La is formed at the interface; along with Ni ions in BiFeO3When the film is doped, a potential barrier exists in a composite film transition region, and the potential barrier can be regulated and controlled by ferroelectric polarization charges, so that BiFeO is caused3And a change in resistance at the interface of the LSMO, which has a high-to-low resistance state switching ratio RHRS/RLRSIs 14.83 to 39.02, so the composite film has a resistance switching effect. Because of the misfit dislocation generated in the interlayer of the ferroelectric superlattice film, the superlattice film has weak interface effect, and the structures between the two layers are matched, so that the matching stress is small, the ferroelectricity is better, and the resistance change is improved. Thus further increasing iron by compounding LSMOMagnetic and resistance change properties.
The method adopts the sol-gel method to prepare the BFO-based superlattice/LSMO composite film, the adopted sol-gel method has lower equipment and maintenance cost, uniform doping on the molecular level is easy to realize, and the thickness of the film can be effectively controlled. BiFeO is prepared by good composition of ferroelectric layer and magnetic layer3The composite film prepared by the superlattice/LSMO composite film has good uniformity, good ferroelectricity and resistance switching effect.
Drawings
FIG. 1 is an XRD pattern of a BFO-based superlattice/LSMO composite thin film prepared in accordance with the present invention;
FIG. 2 is a leakage current loop of the BFO-based superlattice/LSMO composite thin film prepared by the present invention;
FIG. 3 is a diagram showing the state change of the BFO-based superlattice/LSMO composite thin film prepared by the present invention;
FIG. 4 is a graph of the hysteresis loop and polarization current of the BFO-based superlattice/LSMO composite thin film prepared by the present invention.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
The BFO-based superlattice/LSMO composite film with the resistance switching effect comprises a lower layer film and an upper layer film which are compounded together, wherein the lower layer film is La0.7Sr0.3MnO3(abbreviated LSMO) crystalline film, perovskite structure, space group R3 c; the upper film is Bi0.89Ho0.08Sr0.03Fe0.97-xMn0.03NixO3-Bi0.89Ho0.08Sr0.03Fe0.97-yMn0.03NiyO3Superlattice (abbreviated BHSFMNi)x/yX, y is less than or equal to 0.04, x is not equal to y) crystalline film, a twisted rhombus perovskite structure and a space group R3 c.
Along with Ni ions in BiFeO3Incorporation in thin films and BiFeO3The periodic alternate growth of the superlattice film generates a Bi-Ho-S-rich material at the interface of BFO-based superlattice/LSMO due to defects and space chargesR-Mn-Ni-La intermediate transition layer to make the composite film have resistance switching effect, and when x is 0.03 and y is 0.01, its high-low resistance state switching ratio RHRS/RLRSIs 14.83 to 39.02.
The remnant polarization P of the BFO-based superlattice/LSMO thin film is at a voltage of 30VrIs 78.8(-91.7) mu C/cm2The reverse current I is 0.9mA, and the electrical hysteresis loop thereof has a rectangular degree RsqThe coercive field strength is 190(-165) kV/cm, which indicates that the film has good ferroelectricity.
The preparation method of the BFO-based superlattice/LSMO composite film comprises the following steps of:
step 1: adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring, finally dropping a certain amount of polyethylene glycol, stirring and standing to obtain an LSMO precursor solution;
step 2: spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160-180 ℃ after glue homogenizing to obtain a dry film, and annealing at 590-620 ℃ to obtain a crystalline LSMO thin film;
and step 3: after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach a preset thickness, and thus obtaining the LSMO thin film;
and 4, step 4: adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the molar ratio of 0.89:0.08:0.03:0.97-x:0.03: x/0.89:0.08:0.03:0.97-y:0.03: y, and uniformly stirring to obtain the BHSFMNix/yA precursor solution;
and 5: spin coating BHSFMNi on crystalline LSMO thin filmx/yObtaining BHSFMNi from the precursor solutionx/yWet film, wet film homogenizingThen baking at 198-220 deg.C to obtain dry film, and annealing at 545-565 deg.C to obtain crystalline BHSFMNix/yA film;
step 6: to-be-crystalline state BHSFMNix/yAfter the film is naturally cooled, the film is put in BHSFMNix/yRepeating the step 5 on the film to reach the preset thickness to obtain BiFeO3A base superlattice/LSMO composite film.
The total concentration of metal ions in the LSMO precursor solution in the step 1 is 0.2-0.3 mol/L.
BHSFMNi in the step 4x/yThe total concentration of metal ions in the precursor solution is 0.3-0.4 mol/L.
The BHSFMNix/yThe volume ratio of ethylene glycol monomethyl ether to acetic anhydride in the precursor solution and the LSMO precursor solution is (3-3.3) to 1 and (2.8-3) to (1.1-1.2), respectively; the time for uniformly stirring in the steps 2 and 4 is 2-2.5 hours and 1.5-2 hours respectively.
Cleaning the FTO/glass substrate before the step 2, then irradiating under ultraviolet light, and spin-coating the LSMO precursor solution; the step 4 is to perform ultraviolet irradiation treatment on the LSMO crystalline film before the step is performed, and then spin-coat BHSFMNix/yA precursor liquid.
The spin rate of the spin coating in the step 2 and the step 5 is 3200-3600 r/min, and the spin coating time is 11-16 s.
And (3) baking time after glue homogenizing in the step (2) and the step (5) is 7-9 min.
The annealing time in the step 2 is 26-36 min, and the annealing time in the step 5 is 10-15 min.
The number of the crystalline LSMO thin films is 5-7, and the crystalline BiFeO3The number of layers of the base superlattice thin film is 10-14.
Specific examples are as follows.
Example 1
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether at a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring to dissolve completely, adding acetic anhydride, stirring for 90min, and adding dropwise a certain amount of acetic anhydrideUniformly stirring the polyethylene glycol for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160 ℃ for 8min after glue homogenizing to obtain a dry film, and annealing at 600 ℃ for 30min to obtain a crystalline LSMO thin film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film; wherein the number of the crystalline LSMO thin films is 5;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.95:0.03:0.02/0.89:0.08:0.03: 0.94:0.03:0.03, and uniformly stirring for 2 hours to obtain BHSFMNi0.02/0.03Precursor solution of BHSFMNi0.02/0.03The concentration of metal ions in the precursor liquid is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMNi0.02/0.03Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.02/0.03Obtaining BHSFMNi from the precursor solution0.02/0.03Wet film, homogenizing the wet film, baking at 200 deg.C for 8min to obtain dry film, and annealing at 550 deg.C for 10min to obtain BHSFMNi0.02/0.03A film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 6, waiting crystalline state BHSFMNi0.02/0.03After the film is naturally cooled, the film is put in BHSFMNi0.02/0.03Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.02/0.03A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.02/0.03The number of layers of the film was 10And (3) a layer.
Example 2
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160 ℃ for 8min after glue homogenizing to obtain a dry film, and annealing at 600 ℃ for 30min to obtain a crystalline LSMO thin film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film; wherein the number of the crystalline LSMO thin films is 5;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.96:0.03:0.01/0.89:0.08:0.03: 0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.01/0.04Precursor solution of BHSFMNi0.01/0.04The concentration of metal ions in the precursor liquid is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMNi0.01/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.01/0.04Obtaining BHSFMNi from the precursor solution0.01/0.04Wet film, homogenizing, baking at 200 deg.C for 8min to obtain dry film, and annealing at 550 deg.CObtaining BHSFMNi in 10min0.01/0.04A film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 6, waiting crystalline state BHSFMNi0.01/0.04After the film is naturally cooled, the film is put in BHSFMNi0.01/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.01/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.01/0.04The number of layers of the film was 10.
Example 3
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160 ℃ for 8min after glue homogenizing to obtain a dry film, and annealing at 600 ℃ for 30min to obtain a crystalline LSMO thin film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film; wherein the number of the crystalline LSMO thin films is 5;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the molar ratio of 0.89:0.08:0.03:0.94:0.03:0.03/0.89:0.08:0.03: 0.01, and uniformly stirring for 2 hours to obtain BHSFMN0.03/0.01Precursor solution of BHSFMN0.03/0.01Metal separation in precursor solutionThe concentration of the active ingredients is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMN0.03/0.01Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMN on the crystalline LSMO thin film0.03/0.01Obtaining BHSFMN from the precursor solution0.03/0.01Wet film, homogenizing the wet film, baking at 200 deg.C for 8min to obtain dry film, and annealing at 550 deg.C for 10min to obtain BHSFMN0.03/0.01A film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 6, waiting crystalline state BHSFMN0.03/0.01After the film is naturally cooled, the film is placed in BHSFMN0.03/0.01Repeating the step 5 on the film to reach the required thickness to obtain BiFeO3A base superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.03/0.01The number of layers of the film was 10.
Example 4
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160 ℃ for 8min after glue homogenizing to obtain a dry film, and annealing at 600 ℃ for 30min to obtain a crystalline LSMO thin film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film; wherein the number of the crystalline LSMO thin films is 5;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.94:0.03:0.03/0.89:0.08:0.03: 0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.03/0.04Precursor solution of BHSFMNi0.03/0.04The concentration of metal ions in the precursor liquid is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMNi0.03/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.03/0.04Obtaining BHSFMNi from the precursor solution0.03/0.04Wet film, homogenizing the wet film, baking at 200 deg.C for 8min to obtain dry film, and annealing at 550 deg.C for 10min to obtain BHSFMNi0.03/0.04A film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 6, waiting crystalline state BHSFMNi0.03/0.04After the film is naturally cooled, the film is put in BHSFMNi0.03/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.03/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.03/0.04The number of layers of the film was 10.
Example 5
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160 ℃ for 8min after glue homogenizing to obtain a dry film, and annealing at 600 ℃ for 30min to obtain a crystalline LSMO thin film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film; wherein the number of the crystalline LSMO thin films is 5;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.96:0.03:0.01/0.89:0.08:0.03: 0.95:0.03:0.02, and uniformly stirring for 2 hours to obtain BHSFMNi0.01/0.02Precursor solution of BHSFMNi0.01/0.02The concentration of metal ions in the precursor liquid is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMNi0.01/0.02Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.01/0.02Obtaining BHSFMNi from the precursor solution0.01/0.02Wet film, homogenizing the wet film, baking at 200 deg.C for 8min to obtain dry film, and annealing at 550 deg.C for 10min to obtain BHSFMNi0.01/0.02A film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 6, waiting crystalline state BHSFMNi0.01/0.02After the film is naturally cooled, the film is put in BHSFMNi0.01/0.02Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.01/0.02A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.01/0.02The number of layers of the film was 10.
Example 6
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether at a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring to dissolve completely, adding acetic anhydride, stirring for 90min, and adding certain amount of polyethylene glycolStirring for 30min, standing to obtain LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160 ℃ for 8min after glue homogenizing to obtain a dry film, and annealing at 600 ℃ for 30min to obtain a crystalline LSMO thin film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film; wherein the number of the crystalline LSMO thin films is 5;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.95:0.03:0.02/0.89:0.08:0.03: 0.93: 0.03:0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.02/0.04Precursor solution of BHSFMNi0.02/0.04The concentration of metal ions in the precursor liquid is 0.3mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMNi0.02/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.02/0.04Obtaining BHSFMNi from the precursor solution0.02/0.04Wet film, homogenizing the wet film, baking at 200 deg.C for 8min to obtain dry film, and annealing at 550 deg.C for 10min to obtain BHSFMNi0.02/0.04A film; the glue homogenizing rotation speed is 3500r/min, and the glue homogenizing time is 15 s;
step 6, waiting crystalline state BHSFMNi0.02/0.04After the film is naturally cooled, the film is put in BHSFMNi0.02/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.02/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.02/0.04The number of layers of the film was 10.
Example 7
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.2mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 165 ℃ for 7min after glue homogenizing to obtain a dry film, and annealing at 590 ℃ for 26min to obtain a crystalline LSMO thin film; the spin rate of the spin coating is 3200r/min, and the spin coating time is 16 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.95:0.03:0.02/0.89:0.08:0.03: 0.93: 0.03:0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.02/0.04Precursor solution of BHSFMNi0.02/0.04The concentration of metal ions in the precursor liquid is 0.32mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1;
step 5, preparing BHSFMNi0.02/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.02/0.04Obtaining BHSFMNi from the precursor solution0.02/0.04Wet film, homogenizing the wet film, baking at 198 deg.C for 7min to obtain dry film, and annealing at 545 deg.C for 12min to obtain BHSFMNi0.02/0.04A film; the rotating speed of the glue homogenizing is 3200r/min, and the glue homogenizing time is 16 s;
step 6, waiting crystalline state BHSFMNi0.02/0.04After the film is naturally cooled, the film is put in BHSFMNi0.02/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.02/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.02/0.04The number of layers of the film was 11.
Example 8
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.23mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3: 1.2;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, carrying out spin-coating on the wet film, baking the wet film at 170 ℃ for 8min to obtain a dry film, and annealing the dry film at 595 ℃ for 28min to obtain a crystalline LSMO thin film; the spin rate of the spin coating is 3300r/min, the spin coating time is 14 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.95:0.03:0.02/0.89:0.08:0.03: 0.93: 0.03:0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.02/0.04Precursor solution of BHSFMNi0.02/0.04The concentration of metal ions in the precursor liquid is 0.32mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3.1: 1;
step 5, preparing BHSFMNi0.02/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.02/0.04Obtaining BHSFMNi from the precursor solution0.02/0.04Wet film, homogenizing the wet film, baking at 205 deg.C for 8min to obtain dry film, and annealing at 555 deg.C for 13min to obtain BHSFMNi0.02/0.04A film; the spin rate of the spin coating is 3300r/min, the spin coating time is 14 s;
step 6, waiting crystalline state BHSFMNi0.02/0.04After the film is naturally cooled, the film is put in BHSFMNi0.02/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.02/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.02/0.04The number of layers of the film was 12.
Example 9
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.27mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 2.8: 1.1;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 175 ℃ for 9min after glue homogenizing to obtain a dry film, and annealing at 610 ℃ for 32min to obtain a crystalline LSMO thin film; the spin rate of the spin coating is 3400r/min, and the spin coating time is 12 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.95:0.03:0.02/0.89:0.08:0.03: 0.93: 0.03:0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.02/0.04Precursor solution of BHSFMNi0.02/0.04The concentration of metal ions in the precursor liquid is 0.35mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3.2: 1;
step 5, preparing BHSFMNi0.02/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.02/0.04Obtaining BHSFMNi from the precursor solution0.02/0.04Wet film, homogenizing the wet film, baking at 210 deg.C for 9min to obtain dry film, and annealing at 560 deg.C for 14min to obtain BHSFMNi0.02/0.04A film; the spin rate of the spin coating is 3400r/min, and the spin coating time is 12 s;
step 6, waiting crystalline state BHSFMNi0.02/0.04After the film is naturally cooled, the film is put in BHSFMNi0.02/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.02/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.02/0.04The number of layers of the film was 13.
Example 10
Step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether according to a molar ratio of 0.7:0.3:1, stirring for 30min, adding deionized water, stirring until the O is completely dissolved, adding acetic anhydride, stirring for 90min, finally, dripping a certain amount of polyethylene glycol, uniformly stirring for 30min, standing to obtain an LSMO precursor solution, wherein the concentration of metal ions in the LSMO precursor solution is 0.29mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 2.9: 1.2;
step 2, spin-coating the LSMO precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 180 ℃ for 10min after glue homogenizing to obtain a dry film, and annealing at 620 ℃ for 36min to obtain a crystalline LSMO thin film; the spin rate of spin coating is 3600r/min, and the spin coating time is 11 s;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach the required thickness, and obtaining the LSMO thin film;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride according to the mol ratio of 0.89:0.08:0.03:0.95:0.03:0.02/0.89:0.08:0.03: 0.93: 0.03:0.04, and uniformly stirring for 2 hours to obtain BHSFMNi0.02/0.04Precursor solution of BHSFMNi0.02/0.04The concentration of metal ions in the precursor liquid is 0.4mol/L, and the volume ratio of ethylene glycol monomethyl ether to acetic anhydride is 3.3: 1;
step 5, preparing BHSFMNi0.02/0.04Standing the precursor solution for 24h, irradiating the LSMO crystalline film for 40min by adopting ultraviolet, and spin-coating BHSFMNi on the crystalline LSMO thin film0.02/0.04Obtaining BHSFMNi from the precursor solution0.02/0.04Wet film, homogenizing the wet film, baking at 220 deg.C for 10min to obtain dry film, and annealing at 565 deg.C for 15min to obtain BHSFMNi0.02/0.04A film; the spin rate of spin coating is 3600r/min, and the spin coating time is 11 s;
step 6, waiting crystalline state BHSFMNi0.02/0.04After the film is naturally cooled, the film is put in BHSFMNi0.02/0.04Repeating the step 5 on the thin film to reach the required thickness to obtain the BHSFMNi0.02/0.04A superlattice/LSMO composite film; wherein, the crystalline BHSFMNi0.02/0.04The number of layers of the film was 14.
Measurement of BiFeO by XRD3The phase composition structure of the superlattice/LSMO thin film is based; analyzing the dielectric property of the film by using an E4980 impedance analyzer; testing of BiFeO with Agilent B29003The leakage current characteristic of the superlattice/LSMO composite film is based; testing BiFeO by TF2000 ferroelectric analyzer3The ferroelectric property of the superlattice/LSMO composite film is improved.
FIG. 1 is an XRD pattern of a BFO-based superlattice/LSMO composite thin film prepared in examples 1-4 of the present invention. As can be seen from the figure, BiFeO3The phase diffraction peak is consistent with the PDF standard card 86-1518, and the LSMO phase diffraction peak is consistent with the PDF card 51-0409Are matched. BiFeO3The phase has a twisted rhombus perovskite structure, a space group R3c has obvious preferred orientation in the (110) direction, the LSMO phase is a perovskite structure, the space group R3c is BiFeO3The crystallinity of the base superlattice/LSMO composite film is good, and no impurity phase appears. BHSFMNi was also observed0.01/0.04BiFeO in LSMO thin film3The diffraction peak intensity of the crystal face of the phase (202) is obviously enhanced, and the film structure is distorted, which shows that Ni2+Doping amount variation to BiFeO3The microstructure of the base superlattice/LSMO film has an effect.
FIG. 2 shows BHSFMNi prepared in example 3 and example 40.03/0.01/LSMO composite film and BHSFMNi0.03/0.04Leakage current plot of/LSMO composite films, FIG. 3 is a plot of BHSFMNi prepared in examples 3 and 40.03/0.01/LSMO composite film and BHSFMNi0.03/0.04High and low resistance state change diagram of the/LSMO composite film. From fig. 2 and 3, it can be seen that BHSFMNi0.03/0.01the/LSMO composite film shows obvious resistance transition effect. Because the LSMO introduces BiFeO3The heterojunction structure of the metal-ferroelectric layer-semiconductor structure is prepared by the superlattice film, so that the transportation and distribution of charges in the film and at the interface are different under positive and negative electric fields, and the leakage current shows obvious asymmetry under the positive and negative electric fields. Along with Ni ions in BiFeO3Incorporation in thin films and BiFeO3Periodically and alternately growing the superlattice thin film in BiFeO3Defects and space charges at the interface of the superlattice/LSMO generate a Bi-Ho-Sr-Mn-Ni-La-rich intermediate transition layer, so that the high-low resistance state switching ratio R of the intermediate transition layer is causedHRS/RLRS14.83-39.02, and the on-off ratio of the film is maximized in the vicinity of an electric field of-70 kV/cm. The on-off ratio of the resistance transition effect in the thin film varies due to different interface effects in the thin film.
FIG. 4 is a BHSFMNi prepared in example 10.02/0.03The hysteresis loop and polarization current graph of the/LSMO composite film are shown by measuring the hysteresis loop at room temperature of 1kHz, and BHSFMNi is applied at a voltage of 30V0.02/0.03Residual polarization value P of/LSMO thin filmrIs 78.8 mu C/cm2Reversing the current I0.90mA, and the electric hysteresis loop rectangle degree RsqThe coercive field strength is 190kV/cm, and the film has good ferroelectricity.
The above-described details are further intended to describe the present invention in connection with the particular preferred embodiments thereof, and it is not intended to limit the invention to all or the only embodiments disclosed, and all equivalents and modifications which may occur to those skilled in the art upon reading the present specification are intended to be encompassed by the present claims.

Claims (10)

1. A BFO-based superlattice/LSMO composite film with resistance switching effect is characterized by comprising a lower layer film and an upper layer film which are compounded together; the chemical formula of the lower layer film is La0.7Sr0.3MnO3The perovskite structure is adopted, and the space group is R3 c; the upper film has a chemical formula of Bi0.89Ho0.08Sr0.03Fe0.97-xMn0.03NixO3-Bi0.89Ho0.08Sr0.03Fe0.97-yMn0.03NiyO3The perovskite structure is a twisted rhombus perovskite structure, the space group is R3c, wherein x is less than or equal to 0.04, y is less than or equal to 0.04, and x is not equal to y.
2. The BFO-based superlattice/LSMO composite thin film with resistance switching effect as claimed in claim 1, wherein when x is 0.03 and y is 0.01, the high-low resistance state switching ratio RHRS/RLRSIs 14.83 to 39.02.
3. The BFO-based superlattice/LSMO composite thin film having resistance switching effect as claimed in claim 1, wherein at a voltage of 30V, the remanent polarization value P isrIs 78.8 mu C/cm2The reverse current I is 0.9mA, and the electric hysteresis loop squareness RsqThe coercive field strength is 190kV/cm, 1.08.
4. A method for preparing a BFO-based superlattice/LSMO composite thin film having a resistance switching effect as claimed in any one of claims 1-3, comprising the steps of:
step 1, adding La (NO)3)3·6H2O、Sr(NO3)2And C4H6MnO4·4H2Dissolving O in ethylene glycol monomethyl ether, stirring, adding water, stirring until the O is completely dissolved, adding acetic anhydride, stirring, finally dripping polyethylene glycol, stirring, and standing to obtain a lower-layer membrane precursor solution;
step 2, spin-coating the lower layer film precursor solution on an FTO/Glass substrate by adopting a spin-coating method to obtain an LSMO wet film, baking the wet film at 160-180 ℃ after glue homogenizing to obtain a dry film, and annealing at 590-620 ℃ to obtain a crystalline LSMO film;
step 3, after the crystalline LSMO thin film is naturally cooled, repeating the step 2 on the crystalline LSMO thin film to reach a preset thickness, and obtaining a lower layer film;
step 4, adding Bi (NO)3)3·5H2O、Ho(NO3)3·6H2O、Sr(NO3)2、Fe(NO3)3·9H2O、C4H6MnO4·4H2O、C4H6NiO4·4H2Dissolving O in the mixed solution of ethylene glycol monomethyl ether and acetic anhydride, and uniformly stirring to obtain an upper layer membrane precursor solution;
step 5, coating the upper layer membrane precursor solution on the lower layer membrane in a spinning mode to obtain BiFeO3A wet film based on superlattice is subjected to glue homogenizing, then the wet film is baked at 198-220 ℃ to obtain a dry film, and then annealing is carried out at 545-565 ℃ to obtain crystalline BiFeO3A base superlattice film;
step 6, waiting for crystalline BiFeO3After the base superlattice film is naturally cooled, the base superlattice film is subjected to BiFeO3Repeating the step 5 on the base superlattice thin film to reach the preset thickness to obtain BiFeO3A base superlattice/LSMO composite film.
5. The method for preparing the BFO-based superlattice/LSMO composite thin film with the resistance switching effect as claimed in claim 4, wherein the total concentration of metal ions in the lower layer film precursor liquid is 0.2-0.3 mol/L, and the total concentration of metal ions in the upper layer film precursor liquid is 0.3-0.4 mol/L.
6. The method for preparing the BFO-based superlattice/LSMO composite film with the resistance switching effect as claimed in claim 4, wherein the volume ratio of ethylene glycol methyl ether to acetic anhydride in the upper layer film precursor liquid is (3-3.3): 1, and the volume ratio of ethylene glycol methyl ether to acetic anhydride in the lower layer film precursor liquid is (2.8-3): 1.1-1.2.
7. The method for preparing the BFO-based superlattice/LSMO composite film with the resistance switching effect as claimed in claim 4, wherein the glue homogenizing rotation speed in step 2 and step 5 is 3200-3600 r/min, and the glue homogenizing time is 11-16 s.
8. The method for preparing the BFO-based superlattice/LSMO composite film with the resistance switching effect as claimed in claim 4, wherein the baking time after the glue homogenizing in the steps 2 and 5 is 7-9 min.
9. The method for preparing the BFO-based superlattice/LSMO composite thin film with the resistance switching effect as claimed in claim 4, wherein the annealing time in step 2 is 26-36 min, and the annealing time in step 5 is 10-15 min.
10. The method for preparing the BFO-based superlattice/LSMO composite thin film with resistance switching effect as claimed in claim 5, wherein the number of layers of the crystalline LSMO thin film is 5-7, and the crystalline BiFeO is3The number of layers of the base superlattice thin film is 10-14.
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