CN111525021B - Bismuth sodium titanate-based film with positive and negative electric clamping effect and preparation method thereof - Google Patents

Bismuth sodium titanate-based film with positive and negative electric clamping effect and preparation method thereof Download PDF

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CN111525021B
CN111525021B CN202010320707.6A CN202010320707A CN111525021B CN 111525021 B CN111525021 B CN 111525021B CN 202010320707 A CN202010320707 A CN 202010320707A CN 111525021 B CN111525021 B CN 111525021B
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film
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bismuth
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杨长红
冯超
钱进
林秀娟
程振祥
黄世峰
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University of Jinan
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Abstract

The invention belongs to the field of electronic functional materials and devices, and particularly relates to a sodium bismuth titanate-based film with positive and negative electric clamping effects and a preparation method thereof. The sodium bismuth titanate-based film consists of a substrate, a bottom electrode, a ferroelectric film layer and a top electrode, wherein the composition general formula of the film is Na 0.5×a Bi 0.5×b (Ti 1‑x‑y W x Fe y )O 3 Wherein a is more than or equal to 1.01 and less than or equal to 1.02,1.01, b is more than or equal to 1.04,0.01 and less than or equal to x is more than or equal to 0.02, and y is more than or equal to 0.01 and less than or equal to 0.02. The peak values of positive adiabatic temperature change and isothermal entropy change around 143 ℃ are the maximum values in the current report: go (L)T~55 K，∆S~64 J K ‑1 kg ‑1 The method comprises the steps of carrying out a first treatment on the surface of the Within the same refrigeration cycle, around 54 ℃, the peaks of negative adiabatic temperature change and isothermal entropy change are: go (L)T~‑17 K，∆S~‑26 J K ‑1 kg ‑1 . The bismuth sodium titanate-based film prepared by a chemical solution method has the advantages of excellent electric card performance, environmental friendliness, simple process, low cost and the like, and can be used for chip refrigeration, sensors and electronic devicesThe isothermal control field of the parts has wide application prospect.

Description

Bismuth sodium titanate-based film with positive and negative electric clamping effect and preparation method thereof
Technical Field
The invention belongs to the field of electronic functional materials and devices, and particularly relates to a sodium bismuth titanate-based film with positive and negative electric clamping effects and a preparation method thereof.
Background
The application of the refrigeration technology is penetrated into the aspects of life and production of people, and has urgent demands in the fields of industrial and agricultural production, biomedical treatment, national defense industry, advanced science and technology and the like. At present, refrigeration still almost completely depends on the traditional compressor technology, and the compressor refrigeration has the problems of high energy consumption, low working efficiency, large volume, heavy weight, environmental pollution and the like. Therefore, it has become urgent to develop a novel refrigeration technology which has high energy conversion efficiency, is miniaturized, and is environmentally friendly.
The electrocaloric effect is a phenomenon that the polarization state of a polar material changes due to the change of an applied external electric field, and the change of the order degree of a polar dipole causes the change of the entropy of the material, so that the adiabatic temperature change or isothermal entropy change is generated. The electric card effect is classified into a positive electric card effect, which completes the refrigerating process due to the decrease in temperature of the electric card material in the case of removing the external electric field, and a negative electric card effect, which completes the refrigerating process under the condition of applying the electric field. The key to the practical use of electric card refrigeration is the preparation of high-performance electric card materials. From 2006, mischenko et al found a Giant electro-clamping effect in lead zirconate titanate films (reference: giant electro-caloric effect in thin-film PbZr) 0.95 Ti 0.05 O 3 Science, 2006, 3 (5765): 1270-1271) the study of thin film electrocaloric effect continues to heat. In 2009, coreia et al found a high-temperature heat treatment in Pb (Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 Obtaining large positive card effect near depolarization temperatureT=25°C, ∆T9K) (reference: investigation of the electrocaloric effect in a PbMg 2/3 Nb 1/3 O 3 -PbTiO 3 relaxor thin film, appl. Phys. Lett., 2009 95: 182904). Peng Biaolin et al used phase transition to induce lead-free relaxor ferroelectric thin films 0.5 (Ba 0.8 Ca 0.2 )TiO 3 -0.5Bi(Mg 0.5 Ti 0.5 )O 3 The generation of huge negative electricity card effectT=163°C, ∆T-42.5K) (reference: phase-Transition Induced Giant Negative Electrocaloric Effect in a Lead-Free Relaxor Ferroelectric Thin film, energy environment, sci., 2019 12:1708-1717). In order to improve the refrigeration efficiency and meet the requirements of the electric card refrigeration device, a large adiabatic temperature change value is obtainedTClearly, an effective method is provided, and if the positive and negative electricity card refrigeration exists in the same material, different electric card effects can be adopted to continuously refrigerate by adjusting the direction of an electric field.
Bismuth sodium titanate (Na) 0.5 Bi 0.5 TiO 3 ) The ferroelectric with the A-site composite leadless perovskite structure has a complex phase change process from room temperature to 520 ℃, and creates potential possibility for obtaining a large electric clamping effect. In addition, the breakdown strength of the bismuth sodium titanate film can be improved through component design, which is an effective means for improving the electric card effect. In view of the above, the bismuth sodium titanate-based film is an electric card refrigerating material with high potential application value.
Disclosure of Invention
The invention aims to provide the sodium bismuth titanate-based film with the positive and negative electric card effect and the preparation method thereof, and the film is prepared by a chemical solution method, has the advantages of high electric card performance, environmental friendliness, simple process, low cost and the like, and has wide application prospects in the fields of chip refrigeration, temperature control of sensors and electronic devices and the like.
The invention is realized by the following technical scheme:
a sodium bismuth titanate based film with positive and negative electric card effect is composed of substrate, bottom electrode, ferroelectric film layer and top electrode. The composition general formula of the film isNa 0.5×a Bi 0.5×b (Ti 1-x-y W x Fe y )O 3 Wherein a is more than or equal to 1.01 and less than or equal to 1.02,1.01, b is more than or equal to 1.04,0.01 and less than or equal to x is more than or equal to 0.02, and y is more than or equal to 0.01 and less than or equal to 0.02.
The preparation method comprises the following steps:
(1) Preparation of substrate and bottom electrode
(a) Pt/Ti/SiO 2 Sequentially placing Si in a mixed solution of anhydrous ethanol and acetone, and deionized water, respectively carrying out ultrasonic treatment for 20 min, and drying by using an infrared lamp for standby. Selecting fluoromica (Mica) with the thickness less than 50 mu m as a substrate, sequentially placing the fluoromica (Mica) into a mixed solution of absolute ethyl alcohol and acetone and deionized water, respectively carrying out ultrasonic treatment for 10-30min, and drying by an infrared lamp for later use;
(b) Preparation of TiO 2 Precursor solution: adding acetylacetone and tetraisopropyl titanate into ethylene glycol methyl ether sequentially, and stirring for 1-5 hr to obtain TiO 2 Precursor solution for standby;
(c) Uniformly coating the precursor solution on the bottom electrode by adopting a spin coating method, then drying, carrying out annealing treatment, and repeating the spin coating-drying-annealing process for 4 times to obtain TiO 2 Mica, for use;
(d) TiO is prepared by direct current magnetron sputtering method 2 Depositing Pt film on Mica to obtain Pt/TiO 2 Mica is ready for use.
（2）Na 0.5×a Bi 0.5×b (Ti 1-x-y W x Fe y )O 3 Precursor solution preparation
(a) Sodium acetate, bismuth acetate or bismuth nitrate, ferric nitrate, sodium tungstate and tetraisopropyl titanate are selected as raw materials according to Na 0.5×a Bi 0.5×b (Ti 1-x-y W x Fe y )O 3 Accurately weighing the raw materials;
(b) Firstly, a certain amount of acetylacetone and ethylene glycol methyl ether are measured in a beaker, then tetraisopropyl titanate is added dropwise into the beaker, and magnetic stirring is carried out for 3-5 hours at room temperature, so that a solution 1 is defined; dissolving the weighed bismuth acetate or bismuth nitrate, sodium acetate and ferric nitrate in ethylene glycol methyl ether, and heating and stirring at 40-70 ℃; dissolving the weighed sodium tungstate into ethylene glycol, and heating and stirring at 40-70 ℃; the two solutions are mixed after being completely dissolved, and are defined as solution 2; weighing ethylene glycol 600 or polyethylene glycol 20000 accounting for 10-30% of the total mass of the raw materials, dissolving in acetic acid, stirring at room temperature until the ethylene glycol 600 or the polyethylene glycol 20000 is completely dissolved, and defining a solution 3;
(c) After all the solutions are cooled, sequentially adding the solution 2 and the solution 3 into the solution 1, magnetically stirring at room temperature for 10-15 hours to obtain a precursor solution with the concentration of 0.3 mol/L for later use.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The precursor solution is uniformly coated on the bottom electrode by adopting a spin coating method, then the precursor solution is dried on a hot plate, and then the annealing process is carried out in a rapid annealing furnace, and the spin coating-drying-annealing process is repeated.
(4) Deposition of top electrode on bismuth sodium titanate based film
And depositing a top electrode on the sodium bismuth titanate based film by adopting a metal Pt or Au target and adopting a direct current magnetron sputtering method.
Preferably, in the step (1) (b), 0.30 ml acetylacetone and 0.89 ml tetraisopropyl titanate are added into 28.81 ml ethylene glycol methyl ether in sequence, and stirred for 4 h to obtain TiO with the concentration of 0.1 mol/L 2 A precursor solution; in the step (1) (c), the rotating speed is 3000 rpm, and the time is 30 s; the drying temperature is 250 ℃, and the drying time is 3 min; the annealing temperature was 450℃and the annealing time was 8 min.
Preferably, in the step (1) (d), the atmosphere is Ar, the vacuum degree is 0.05 mbar, the current is 30 mA, and the thickness of the bottom electrode is 80 nm when the bottom electrode is deposited by direct current magnetron sputtering; the atmosphere is N during the pretreatment of the bottom electrode 2 The temperature was 500℃and the time was 8 min.
Preferably, in the step (3), the rotation speed during spin coating is 3000 rpm, and the time is 30 seconds; the drying temperature is 200 ℃, and the drying time is 3 min; the pretreatment temperature is 350 ℃, the pretreatment time is 2 min, and the annealing atmosphere is air or O 2 The annealing temperature is 500-550 ℃, and the annealing time is 6-10 min。
Preferably, the atmosphere in the step (4) is Ar, the vacuum degree is 0.05 mbar, the current is 30 mA, and the diameter of the top electrode is 200 μm.
The invention has the beneficial effects that
The invention prepares the bismuth sodium titanate based film with the positive negative electric blocking effect, and the peak value of positive adiabatic temperature change and isothermal entropy change is the maximum value in the current report at the temperature of about 143 ℃: go (L)T~55 K，∆S~64 J K -1 kg -1 In the same refrigeration cycle, around 54 ℃, peaks of negative adiabatic temperature change and isothermal entropy change are obtained: go (L)T~-17 K，∆S~-26 J K -1 kg -1 . The method has the advantages of high performance of the electric card, environmental friendliness, simple process, low cost and the like, and has wide application prospects in the fields of chip refrigeration, temperature control of sensors and electronic devices and the like.
Drawings
FIG. 1 is a schematic diagram of the structure of a sodium bismuth titanate-based film prepared by the present invention.
FIG. 2 is a view of Na in example 1 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 X-ray diffraction pattern of the film.
FIG. 3 is Na in example 1 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Dielectric thermogram of the film.
FIG. 4 is a view of Na in example 1 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Hysteresis loop plot at different temperatures of the film.
FIG. 5 is Na in example 1 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Film (d): (a) Adiabatic temperature dependence versus temperature, (b) isothermal entropy dependence versus temperature dependence.
FIG. 6 is Na in example 2 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 X-ray diffraction pattern of the film.
FIG. 7 is a view of Na in example 2 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Hysteresis loop diagram of the film.
FIG. 8 is Na in example 3 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 Scanning electron microscope image of the film.
FIG. 9 is a view of Na in example 4 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 Hysteresis loop diagrams of films at different temperatures.
FIG. 10 is a view of Na in example 4 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 Film (d): (a) Adiabatic temperature dependence versus temperature, (b) isothermal entropy dependence versus temperature dependence.
FIG. 11 is Na in example 5 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 Dielectric constant versus electric field strength of the film.
FIG. 12 is Na in example 5 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 Hysteresis loop diagram of the film.
FIG. 13 is a view of Na in example 6 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 Dielectric spectrogram of the film.
FIG. 14 is a view of Na in example 7 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 Hysteresis loop plot at different temperatures of the film.
FIG. 15 is a view of Na in example 7 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 Film (d): (a) Adiabatic temperature dependence versus temperature, (b) isothermal entropy dependence versus temperature dependence.
Detailed Description
The invention will be further illustrated by the following examples, which are given by way of illustration only and are not to be construed as limiting the invention.
Example 1
(1) Preparation of substrate and bottom electrode
Pt/Ti/SiO 2 Sequentially placing Si in a mixed solution of anhydrous ethanol and acetone, and deionized water, respectively carrying out ultrasonic treatment for 20 min, and drying by using an infrared lamp for standby.
（2）Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Is used for accurately weighing the CH of 0.3617 g 3 COONa, 1.8072 g (CH) 3 CO 2 ) 3 Bi. Na of 0.0300 g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0728 g 3 ) 3 ·9H 2 O and 0.6815 g.
(b) Accurately measuring 2.26 ml acetylacetone and 2.26 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.26 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring for 4 hours at room temperature to define a solution 1; CH to be weighed 3 COONa、(CH 3 CO 2 ) 3 Bi、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 11.61 ml ethylene glycol methyl ether, and is heated and stirred at 40 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 7.74 and ml glycol, and is heated and stirred at 40 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 3.87 ml acetic acid and stirred at room temperature until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and magnetically stirred at room temperature for 12 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 After the precursor solution is kept stand and aged 48 and h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at 200 ℃ for 3 min. Then the film is put into a rapid heating annealing furnace for annealing process, and the annealing atmosphere is O 2 The annealing procedure was 2 min at 350℃and 10 min at 500 ℃. The above process of spin-coating-baking-annealing was repeated 12 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
Adopting a metal Au target and adopting a direct current magnetron sputtering method to obtain Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 And depositing an Au top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 2 is the Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 The X-ray diffraction pattern of the film indicated that it was a single polycrystalline perovskite phase. FIG. 3 is Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Dielectric temperature spectrum of film, depolarization temperatureT d About 150 ℃, phase transition temperatureT m About 310 c. At the same timeT m The relaxation of the film is demonstrated by the broader phase transition peak and frequency dispersion phenomenon. FIG. 4 is Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Hysteresis loop plot at different temperatures of the film. FIG. 5 shows the calculated adiabatic temperature change of the filmTAnd isothermal entropy changeSA profile with temperature. The peaks of positive adiabatic temperature change and isothermal entropy change are the maximum in the current report around 143 ℃: go (L)T~55 K，∆S~64 J K -1 kg -1 . This is due to the change between dipole ordered and disordered states at the phase transition under the control of the electric field and temperature. Meanwhile, in the same refrigeration cycle, the peak value of adiabatic temperature change and isothermal entropy change is obtained near 54 ℃): go (L)T~-17 K，∆S~-26 J K -1 kg -1 。
Example 2
(1) Preparation of substrate and bottom electrode
(a) Fluorine crystal Mica (Mica) with the thickness less than 50 mu m is selected as a substrate, and is sequentially placed in a mixed solution of absolute ethyl alcohol and acetone and deionized water for 20 minutes, and is dried by an infrared lamp for standby.
(b) Preparation of TiO 2 Precursor solution: adding 0.30 ml acetylacetone and 0.89 ml tetraisopropyl titanate into 28.81 ml ethylene glycol methyl ether sequentially, and stirring 3 h to obtain TiO with concentration of 0.1 mol/L 2 Precursor solution is prepared for standby.
(c) Uniformly coating the precursor solution on the bottom electrode by adopting a spin coating method, wherein the rotating speed is 3000 r/min, the time is 30 s, then drying is carried out, the drying temperature is 250 ℃, the drying time is 3 min, then annealing treatment is carried out, the annealing temperature is 450 ℃, the annealing time is 8 min, and the spin coating-drying-annealing process is repeated for 4 times to obtain the TiO 2 Mica, for use.
(d) TiO is prepared by direct current magnetron sputtering method 2 Depositing a Pt film on Mica, wherein the atmosphere is Ar, the vacuum degree is 0.05 mbar, the current is 30 mA, and the thickness of the bottom electrode is 80 nm; the atmosphere is N during the pretreatment of the bottom electrode 2 The temperature was 500℃and the time was 8 min. Obtaining Pt/TiO 2 Mica, for use.
（2）Na 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Is used for accurately weighing the CH of 0.3617 g 3 COONa, 2.2942 g Bi (NO) 3 ) 3 ·5H 2 O, na of 0.0300 g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0728 g 3 ) 3 ·9H 2 O and 0.8276 g.
(b) Accurately measuring 2.26 ml acetylacetone and 2.26 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.26 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring for 4 hours at room temperature to define a solution 1; CH to be weighed 3 COONa、Bi(NO 3 ) 3 ·5H 2 O、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 11.26 ml glycol monomethyl ether, and is heated and stirred at 40 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 8.44 and ml glycol, and is heated and stirred at 40 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 3.52 ml acetic acid and stirred at room temperature until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and are magnetically stirred at room temperature for 10 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 After the precursor solution is kept stand and aged 48 and h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at 200 ℃ for 3 min. Then the film is put into a rapid heating annealing furnace for annealing process, and the annealing atmosphere is O 2 The annealing procedure was 2 min at 350℃and 10 min at 500 ℃. The above process of spin-coating-baking-annealing was repeated 12 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
Adopting a metal Au target and adopting a direct current magnetron sputtering method to obtain Na 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 And depositing an Au top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 6 is the Na 0.5×1.01 Bi 0.5×1.03 (Ti 0.97 W 0.01 Fe 0.02 )O 3 The X-ray diffraction pattern of the film indicated that it was a single polycrystalline perovskite phase. FIG. 7 is a graph of the hysteresis loop of the film.
Example 3
(1) Preparation of substrate and bottom electrode
Pt/Ti/SiO 2 Sequentially placing Si in a mixed solution of anhydrous ethanol and acetone, and deionized water, respectively carrying out ultrasonic treatment for 20 min, and drying by using an infrared lamp for standby.
（2）Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 Is used for accurately weighing CH of 0.3542 g 3 COONa, 2.3165 g Bi (NO) 3 ) 3 ·5H 2 O, na of 0.0450 g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0364 g 3 ) 3 ·9H 2 O and 0.6880 g.
(b) Accurately measuring 2.27 ml acetylacetone and 2.27 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.27 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring for 4 hours at room temperature to define solution 1; CH to be weighed 3 COONa、Bi(NO 3 ) 3 ·5H 2 O、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 10.91 ml ethylene glycol methyl ether, and is heated and stirred at 50 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 8.87 ml glycol and heated and stirred at 50 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 13.41 ml acetic acid at room temperatureStirred until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and the solution is magnetically stirred at room temperature for 13 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 After the precursor solution is kept stand and aged 48 and h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at the temperature of 250 ℃ for 3 min. And then the film is put into a rapid heating annealing furnace for annealing process, the annealing atmosphere is air, the annealing process is kept at 350 ℃ for 2 min, and the annealing process is kept at 520 ℃ for 8 min. The above process of spin-coating-baking-annealing was repeated 12 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
The metal Pt target is adopted, and the obtained Na is obtained by a direct current magnetron sputtering method 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 And depositing a Pt top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 8 is the Na 0.5×1.01 Bi 0.5×1.04 (Ti 0.975 W 0.015 Fe 0.01 )O 3 Scanning electron microscope image of the film.
Example 4
(1) Preparation of substrate and bottom electrode
Pt/Ti/SiO 2 Sequentially placing Si in a mixed solution of anhydrous ethanol and acetone, and deionized water, respectively carrying out ultrasonic treatment for 20 min, and drying by using an infrared lamp for standby.
（2）Na 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 Is used for accurately weighing the CH of 0.3654 g 3 COONa, 1.8072 g (CH) 3 CO 2 ) 3 Bi. Na of 0.0300 g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0546 g 3 ) 3 ·9H 2 O and 0.4514 g.
(b) Accurately measuring 2.27 ml acetylacetone and 2.27 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.27 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring at room temperature for 3 hours to define a solution 1; CH to be weighed 3 COONa、(CH 3 CO 2 ) 3 Bi、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 10.95 ml ethylene glycol methyl ether, and is heated and stirred at 60 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 9.02 ml glycol and is heated and stirred at 60 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 3.22 ml acetic acid and stirred at room temperature until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and magnetically stirred at room temperature for 15 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 After the precursor solution is kept stand and aged for 72 h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at the temperature of 250 ℃ for 3 min. Then the film is put into a rapid heating annealing furnace for annealing process,the annealing atmosphere is O 2 The annealing procedure was 2 min at 350℃and 10 min at 500 ℃. The above process of spin-coating-baking-annealing was repeated 14 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
Adopting a metal Au target and adopting a direct current magnetron sputtering method to obtain Na 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 And depositing an Au top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 9 is a view of Na in example 4 0.5×1.02 Bi 0.5×1.04 (Ti 0.975 W 0.01 Fe 0.015 )O 3 Hysteresis loop diagrams of films at different temperatures. FIG. 10 shows the filmTAnd (2) He ZhiSA profile with temperature. At around 138 ℃, a maximum of adiabatic temperature change and isothermal entropy change is obtained: go (L)T~55 K，∆S~62 J K -1 kg -1 Within the same refrigeration cycle, around 54 ℃, the minimum values of adiabatic temperature change and isothermal entropy change are obtained: go (L)T~-17 K，∆S~-26 J K -1 kg -1 。
Example 5
(1) Preparation of substrate and bottom electrode
(a) Fluorine crystal Mica (Mica) with the thickness less than 50 mu m is selected as a substrate, and is sequentially placed in a mixed solution of absolute ethyl alcohol and acetone and deionized water for 10 minutes respectively, and is dried by an infrared lamp for standby.
(b) Preparation of TiO 2 Precursor solution: adding 0.30 ml acetylacetone and 0.89 ml tetraisopropyl titanate into 28.81 ml ethylene glycol methyl ether sequentially, and stirring 1 h to obtain TiO with concentration of 0.1 mol/L 2 Precursor solution is prepared for standby.
(c) Uniformly coating the precursor solution on the bottom electrode by adopting a spin coating method, wherein the rotating speed is 3000 r/min, the time is 30 s, then drying is carried out, the drying temperature is 250 ℃, the drying time is 3 min, then annealing treatment is carried out, the annealing temperature is 450 ℃, the annealing time is 8 min, and the spin coating-drying-annealing process is repeatedThe total process is 4 times to obtain TiO 2 Mica, for use.
(d) TiO is prepared by direct current magnetron sputtering method 2 Depositing a Pt film on Mica, wherein the atmosphere is Ar, the vacuum degree is 0.05 mbar, the current is 30 mA, and the thickness of the bottom electrode is 80 nm; the atmosphere is N during the pretreatment of the bottom electrode 2 The temperature was 500℃and the time was 8 min. Obtaining Pt/TiO 2 Mica, for use.
（2）Na 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 Is used for accurately weighing the CH of 0.3579 g 3 COONa, 2.2719 g Bi (NO) 3 ) 3 ·5H 2 O, na of 0.0450 g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0728 g 3 ) 3 ·9H 2 O and 0.9617 g.
(b) Accurately measuring 2.25 ml acetylacetone and 2.25 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.25 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring at room temperature for 3 hours to define a solution 1; CH to be weighed 3 COONa、Bi(NO 3 ) 3 ·5H 2 O、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 10.68 ml ethylene glycol methyl ether, and is heated and stirred at 50 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 9.43 ml glycol and is heated and stirred at 50 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 3.14 ml acetic acid and stirred at room temperature until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and magnetically stirred at room temperature for 11 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 After the precursor solution is kept stand and aged for 72 h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at the temperature of 250 ℃ for 3 min. And then the film is put into a rapid heating annealing furnace for annealing process, the annealing atmosphere is air, the annealing process is kept at 350 ℃ for 2 min, and the annealing process is kept at 550 ℃ for 6 min. The above process of spin-coating-baking-annealing was repeated 14 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
The metal Pt target is adopted, and the obtained Na is obtained by a direct current magnetron sputtering method 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 And depositing a Pt top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 11 is a view of Na in this embodiment 0.5×1.02 Bi 0.5×1.02 (Ti 0.965 W 0.015 Fe 0.02 )O 3 Dielectric coefficient-electric field strength plot of the film. Fig. 12 is a graph of the hysteresis loop of the film.
Example 6
(1) Preparation of substrate and bottom electrode
Pt/Ti/SiO 2 Sequentially placing Si in a mixed solution of anhydrous ethanol and acetone, and deionized water, respectively carrying out ultrasonic treatment for 20 min, and drying by using an infrared lamp for standby.
（2）Na 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 Is used for accurately weighing the CH of 0.3617 g 3 COONa, 2.2719 g Bi (NO) 3 ) 3 ·5H 2 O、0.0300 Na of g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0364 g 3 ) 3 ·9H 2 O and 0.6750 g.
(b) Accurately measuring 2.28 ml acetylacetone and 2.28 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.28 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring at room temperature for 5 hours to define a solution 1; CH to be weighed 3 COONa、Bi(NO 3 ) 3 ·5H 2 O、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 10.69 and ml glycol methyl ether, and is heated and stirred at 60 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 9.50 ml glycol and heated and stirred at 60 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 2.97 ml acetic acid and stirred at room temperature until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and magnetically stirred at room temperature for 12 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 After the precursor solution is kept stand and aged for 72 h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at the temperature of 250 ℃ for 3 min. And then the film is put into a rapid heating annealing furnace for annealing process, the annealing atmosphere is air, the annealing process is kept at 350 ℃ for 2 min, and the annealing process is kept at 550 ℃ for 6 min. The above-described "spin-coating-bake-anneal" process was repeated 16 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
Adopting a metal Au target and adopting a direct current magnetron sputtering method to obtain Na 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 And depositing an Au top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 13 is a view of Na in the present embodiment 0.5×1.01 Bi 0.5×1.02 (Ti 0.98 W 0.01 Fe 0.01 )O 3 Dielectric spectrogram of the film.
Example 7
(1) Preparation of substrate and bottom electrode
(a) Fluorine crystal Mica (Mica) with the thickness less than 50 mu m is selected as a substrate, and is sequentially placed in a mixed solution of absolute ethyl alcohol and acetone and deionized water for 30 minutes respectively, and is dried by an infrared lamp for standby.
(b) Preparation of TiO 2 Precursor solution: adding 0.30 ml acetylacetone and 0.89 ml tetraisopropyl titanate into 28.81 ml ethylene glycol methyl ether sequentially, and stirring for 5 h to obtain TiO with concentration of 0.1 mol/L 2 Precursor solution is prepared for standby.
(c) Uniformly coating the precursor solution on the bottom electrode by adopting a spin coating method, wherein the rotating speed is 3000 r/min, the time is 30 s, then drying is carried out, the drying temperature is 250 ℃, the drying time is 3 min, then annealing treatment is carried out, the annealing temperature is 450 ℃, the annealing time is 8 min, and the spin coating-drying-annealing process is repeated for 4 times to obtain the TiO 2 Mica, for use.
(d) TiO is prepared by direct current magnetron sputtering method 2 Depositing a Pt film on Mica, wherein the atmosphere is Ar, the vacuum degree is 0.05 mbar, the current is 30 mA, and the thickness of the bottom electrode is 80 nm; the atmosphere is N during the pretreatment of the bottom electrode 2 The temperature was 500℃and the time was 8 min. Obtaining Pt/TiO 2 Mica, for use.
（2）Na 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 Precursor solution preparation
(a) According to Na 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 Is accurately weighed by the stoichiometric ratio of (2)Taking the CH of 0.3486 g 3 COONa, 1.7550 g (CH) 3 CO 2 ) 3 Bi. Na of 0.0600 g 2 WO 4 ·2H 2 Fe (NO) of O, 0.0728 g 3 ) 3 ·9H 2 O and 0.6709 g.
(b) Accurately measuring 2.24 ml acetylacetone and 2.24 ml ethylene glycol methyl ether in a beaker, dropwise adding 2.24 ml tetraisopropyl titanate into the acetylacetone, and magnetically stirring at room temperature for 5 hours to define a solution 1; CH to be weighed 3 COONa、(CH 3 CO 2 ) 3 Bi、Fe(NO 3 ) 3 ·9H 2 O is dissolved in 10.48 and ml glycol methyl ether, and is heated and stirred at 70 ℃; na to be weighed 2 WO 4 ·2H 2 O is dissolved in 9.89 ml glycol and is heated and stirred at 70 ℃; the two solutions are mixed immediately after being completely dissolved, and are defined as solution 2; polyethylene glycol 600 was dissolved in 2.91 ml acetic acid and stirred at room temperature until completely dissolved, defined as solution 3.
(c) After all the solutions are cooled, the solution 2 and the solution 3 are added into the solution 1 in turn, and the solution is magnetically stirred at room temperature for 14 h to obtain Na with the concentration of 0.3 mol/L 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 Precursor solution is prepared for standby.
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
The obtained Na 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 After the precursor solution is kept stand and aged for 72 h, the precursor solution is uniformly coated on Pt/Ti/SiO by adopting a spin coating method 2 On Si, the rotating speed is 3000 r/min, and the spin time is 30 s. And then the film is dried on a hot plate at the temperature of 250 ℃ for 3 min. Then the film is put into a rapid heating annealing furnace for annealing process, and the annealing atmosphere is O 2 The annealing procedure was 2 min at 350℃and 8 min at 520 ℃. The above-described "spin-coating-bake-anneal" process was repeated 16 times.
(4) Deposition of top electrode on bismuth sodium titanate based film
The metal Pt target is adopted, and the obtained Na is obtained by a direct current magnetron sputtering method 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 And depositing a Pt top electrode on the film. The atmosphere during deposition was Ar, the vacuum was 0.05 mbar and the current was 30 mA. The top electrode diameter was 200 μm.
FIG. 14 is Na 0.5×1.015 Bi 0.5×1.01 (Ti 0.96 W 0.02 Fe 0.02 )O 3 Hysteresis loop plot at different temperatures of the film.
FIG. 15 shows the filmTAnd (2) He ZhiSA profile with temperature. At around 140 ℃, a maximum of adiabatic temperature change and isothermal entropy change is obtained: go (L)T~49 K，∆S~55 J K -1 kg -1 。

Claims (8)

1. The bismuth sodium titanate-based film with the positive and negative electric clamping effect is characterized in that bismuth sodium titanate is taken as a base material, and iron ions and tungsten ions are compositely introduced into the B site; the composition general formula of the film is Na 0.5×a Bi 0.5×b (Ti 1-x-y W x Fe y )O 3 Wherein a is more than or equal to 1.01 and less than or equal to 1.02,1.01, b is more than or equal to 1.04,0.01 and less than or equal to x is more than or equal to 0.02, and y is more than or equal to 0.01 and less than or equal to 0.02.
2. A method for preparing the sodium bismuth titanate-based film as claimed in claim 1, which comprises the following steps:
(1) Preparing a bottom electrode;
（2）Na 0.5×a Bi 0.5×b (Ti 1-x-y W x Fe y )O 3 precursor solution preparation:
(a) Sodium acetate, bismuth acetate or bismuth nitrate, ferric nitrate, sodium tungstate and tetraisopropyl titanate are selected as raw materials according to Na 0.5× a Bi 0.5×b (Ti 1-x-y W x Fe y )O 3 Accurately weighing the raw materials;
(b) Firstly, measuring acetylacetone and ethylene glycol methyl ether in a beaker, then adding tetraisopropyl titanate into the beaker, and stirring the mixture for 3 to 5 hours at room temperature to define solution 1;
dissolving the weighed bismuth acetate or bismuth nitrate, sodium acetate and ferric nitrate in ethylene glycol methyl ether, and heating and stirring at 40-70 ℃; dissolving the weighed sodium tungstate into ethylene glycol, and heating and stirring at 40-70 ℃; the two solutions are mixed after being completely dissolved, and are defined as solution 2;
weighing polyethylene glycol 600, dissolving in acetic acid, stirring at room temperature until the polyethylene glycol 600 is completely dissolved, and defining a solution 3;
(c) After all the solutions are cooled to room temperature, adding the solution 2 and the solution 3 into the solution 1, and stirring for 10-15 hours at room temperature to obtain a precursor solution for later use;
(3) Deposition of bismuth sodium titanate based thin films on bottom electrodes
Uniformly spin-coating the precursor solution on the bottom electrode, then placing the substrate on a hot plate for drying, and then performing an annealing process, and repeating the spin-coating-drying-annealing process;
(4) Deposition of top electrode on bismuth sodium titanate based film
A metal Pt or Au target is adopted, a direct current magnetron sputtering method is used for depositing a top electrode on the sodium bismuth titanate base film,
the bottom electrode is Pt/Ti/SiO 2 Si or Pt/TiO 2 /Mica。
3. The preparation method according to claim 2, wherein the bottom electrode is sequentially placed in a mixed solution of absolute ethyl alcohol and acetone, and deionized water before use, each ultrasonic for 10-30min, and dried by an infrared lamp.
4. The method according to claim 2, wherein the Pt/TiO 2 The preparation method of the Mica substrate comprises the following steps:
selecting fluoromica (Mica) with the thickness less than 50 and mm as a substrate;
preparation of TiO 2 Precursor solution: adding acetylacetone and tetraisopropyl titanate into ethylene glycol methyl ether successively, stirring to obtain TiO 2 Precursor solution for standby;
TiO is mixed with 2 Spin-coating the precursor solution on Mica, drying, annealing, repeating the spin-coating-drying-annealing process for 3-5 times to obtain TiO 2 Mica, for use;
TiO is prepared by direct current magnetron sputtering method 2 Depositing Pt film on Mica to obtain Pt/TiO 2 /Mica。
5. The method of claim 4, wherein TiO is prepared by 2 The precursor solution is prepared by sequentially adding 0.30 ml acetylacetone and 0.89 ml tetraisopropyl titanate into 28.81 ml ethylene glycol methyl ether, and stirring 1-5 h to obtain TiO with concentration of 0.1 mol/L 2 Precursor solution.
6. The process according to claim 4, wherein,
the spin coating rotating speed is 3000 rpm, and the time is 30 s; the drying temperature is 250 ℃, and the drying time is 3 min; the annealing temperature is 450 ℃, and the annealing time is 8 min;
the method for sputtering by direct current magnetic control is used for TiO 2 Deposition of Pt film on Mica, the operating parameters are: the atmosphere is Ar when the bottom electrode is deposited by direct current magnetron sputtering, the vacuum degree is 0.05 mbar, the current is 30 mA, and the thickness of the bottom electrode is 80 nm; the atmosphere is N during the pretreatment of the bottom electrode 2 The temperature was 500℃and the time was 8 min.
7. The method according to claim 2, wherein in the step (3), the spin-coating is performed at a spin speed of 3000 rpm for 30 seconds; the drying temperature is 200 ℃, and the drying time is 3 min; the pretreatment temperature is 350 ℃, the pretreatment time is 2 min, and the annealing atmosphere is air or O 2 The annealing temperature is 500-550 ℃, and the annealing time is 6-10 min.
8. The method according to claim 2, wherein the top electrode is deposited in the step (4) in an atmosphere of Ar, a vacuum of 0.05 mbar, a current of 30 mA and a top electrode diameter of 200 μm.
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