Method for preparing high-performance PMN-PT piezoelectric film through sol-gel method

Abstract

The invention relates to a PMN-PT thin film preparation method and a thin film, and the method comprises the following steps: mixing a cosolvent and a catalyst to obtain a mixed solution; adding a lead compound, a magnesium compound, a niobium compound and a titanium compound into the mixed solution according to a predetermined mass ratio of Pb, Mg, Nb and Ti elements, mixing and stirring, and adding a stabilizer and a film-forming agent to prepare PMN-PT precursor sol; and depositing the PMN-PT precursor sol on a substrate to prepare the PMN-PT thin film.

Description

Technical Field

[0001] The present invention relates to the technical field of PMN-PT piezoelectric films, and in particular to a PMN-PT film preparation method and the film. Background Art

[0002] Piezoelectric materials can convert tiny mechanical deformations into electrical signals, thereby realizing the conversion between force signals and electrical signals, and have received widespread attention in the fields of materials science and engineering. Among these piezoelectric materials, lead zirconate titanate (PMN-PT) has been widely used in various fields including sensors, actuators, energy harvesting devices, etc. due to its outstanding piezoelectric properties. Therefore, it has attracted widespread attention in the research of piezoelectric materials in recent years. Among the various properties of PMN-PT films, its piezoelectric properties are particularly important in its practical applications. Among the various properties of PMN-PT films, the preparation method of the film, especially how to prepare high-quality films and avoid the formation of pyrochlore phase, has become the focus of research. In recent years, researchers have been continuously exploring methods for preparing high-performance PMN-PT piezoelectric films.

[0003] Compared with traditional PMN-PT single crystals or ceramic materials, PMN-PT thin film materials are more suitable for making miniaturized sensors due to their smaller size and higher piezoelectric properties. Therefore, the research on their thin film preparation methods has always attracted widespread attention from scholars from all walks of life.

[0004] However, the PMN-PT films currently prepared by the sol-gel method cannot use the two-step sintering method of ceramics. As a result, the lead, magnesium, and niobium react quickly first to produce the pyrochlore phase, resulting in poor quality of the prepared films. Secondly, since the MPB phase boundary of the film is different from that of ceramics and the film preparation method is very different from that of ceramics, the piezoelectric properties of the PMN-PT films currently prepared are very poor, and the piezoelectric coefficient is very low, which is not conducive to the use of this material. At the same time, since the prepared solution is unstable, complexation reactions are prone to occur, leading to precipitation. Therefore, the prepared film has many impurities and poor crystal state, resulting in very poor performance.

[0005] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0006] The present invention provides a PMN-PT film preparation method and film, which improves the film quality and piezoelectric properties of the PMN-PT film by regulating the proportion of drugs added to the sol, adding a stabilizer, and improving the film preparation process, so that a high-performance PMN-PT film material can be prepared by a sol-gel method.

[0007] A method for preparing a PMN-PT film comprises:

[0008] mixing the co-solvent and the catalyst to obtain a mixed solution;

[0009] Adding lead compound, magnesium compound, niobium compound and titanium compound in a predetermined mass ratio of Pb, Mg, Nb and Ti elements to the mixed solution and stirring, and adding a stabilizer and a film-forming agent to prepare a PMN-PT precursor sol;

[0010] The PMN-PT precursor sol is deposited on a substrate to prepare a PMN-PT film.

[0011] In the PMN-PT film preparation method, the lead compound is selected from any one of lead acetate trihydrate, lead oxide, and lead acetate trihydrate; the magnesium compound is selected from any one of magnesium nitrate and magnesium acetate; the niobium compound is selected from any one of niobium ethanol and niobium oxalate; and the titanium compound is selected from any one of tetrabutyl titanate, titanium oxide, and titanium isopropionate. The predetermined mass ratio of the lead compound, magnesium compound, niobium compound, and titanium compound is 1:(0.5-0.8):(0.2-0.5):1.

[0012] In the PMN-PT film preparation method, the lead compound is lead acetate trihydrate [Pb(CH3COO)2·3H2O], the magnesium compound is magnesium acetate [Mg(CH3COO)2], the niobium compound is niobium ethoxide (Nb(C2H4)4), and the titanium compound is tetrabutyl titanate [Ti(OC3H9)4]. The predetermined mass ratio of the lead compound, magnesium compound, niobium compound, and titanium compound is 1:0.56:0.3:1.

[0013] In the PMN-PT film preparation method, the co-solvent is selected from one or more of ethanol, ethylene glycol, and ethylene glycol methyl ether; the catalyst is selected from one or more of acetic acid, nitric acid, and hydrochloric acid; the stabilizer is selected from one or more of acetylacetone, water, and ethanol; the film-forming agent is selected from one or more of polyethylene glycol 200, ethylene glycol, and polyethylene glycol 800; the mass ratio of the co-solvent to the catalyst is (2-8):1, and the mixing time is 1-3 h.

[0014] In the PMN-PT film preparation method, the co-solvent is ethylene glycol methyl ether, the catalyst is acetic acid, the stabilizer is acetylacetone, the film-forming agent is alcohol 800, the mass ratio of the co-solvent and the catalyst is (4~5):1, and the mixing time is 1~2h.

[0015] In the PMN-PT film preparation method, after adding the lead compound and the magnesium compound, the mixture is stirred for 10 to 20 minutes in a water bath, niobium ethanol is added to the solution, 2 mL of acetylacetone is added, and then the titanium compound is added and mixed at room temperature for 5 minutes, and then refluxed at 90 degrees with stirring for 30 minutes.

[0016] In the PMN-PT thin film preparation method, the PMN-PT precursor sol is evenly spin-coated, followed by thermal processing according to the following procedure. After the thermal processing is completed, the PMN-PT precursor sol is again dripped for spin coating and thermal processing, that is, this operation is repeated until the desired PMN-PT thin film thickness is achieved. The thermal processing includes:

[0017] Stage I: heating from room temperature to 300-400℃ at a heating rate of 80-120℃ / min, and keeping warm for 1-3 minutes;

[0018] Stage II: Continue heating from the first stage holding temperature to 450~550℃ at a heating rate of 30~70℃ / min, and keep warm for 1~3min.

[0019] In the PMN-PT film preparation method, the mass ratio of the sum of the lead compound, the magnesium compound, the niobium compound and the titanium compound to the co-solvent is 1:(2-6).

[0020] In the PMN-PT thin film preparation method, a PMN-PT precursor sol is deposited on a Pt / Si substrate, and the deposition is any one of atomic deposition, magnetron sputtering, and spin coating.

[0021] A PMN-PT film is prepared by the method.

[0022] Compared with existing technologies, the present invention has the following advantages: By adjusting the ratio of added chemicals and modifying the ratio of lead, magnesium, niobium, and titanium in the sol, the performance of PMN-PT films is improved, preventing the formation of a pyrochlore phase. The addition of a stabilizer and improvements in the film preparation process enhance the film quality and piezoelectric properties of PMN-PT films, enabling the preparation of high-performance PMN-PT thin films via a sol-gel process. The addition of acetylacetone as a stabilizer prevents complexation and precipitation in the sol, ensuring the preparation of high-performance PMN-PT films. The addition of polyethylene glycol 800 as a film-forming agent improves the quality of the PMN-PT films and reduces leakage current. Optimizing the spin coating time and heat treatment temperature during PMN-PT film preparation improves film quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are intended only to illustrate preferred embodiments and are not to be construed as limiting the present invention. It should be understood that the drawings described below are merely examples of the present invention, and that those skilled in the art will be able to derive other drawings from these drawings without inventive effort. Throughout the drawings, identical reference numerals are used to denote identical components.

[0024] In the attached figure:

[0025] Figure 1 Shown are SEM characterization images of PMN-PT films prepared in Examples 1-3 and Comparative Example 1;

[0026] Figure 2 The SEM characterization image of the PMN-PT film prepared in Comparative Example 1 is shown;

[0027] Figure 3 Showing the X-ray diffraction (XRD) comparison diagram of the PMN-PT thin films prepared in Examples 1-3 and the PMN-PT thin film prepared in Comparative Example 1;

[0028] Figure 4 Schematic diagram showing the state of the PMN-PT film precursor sol prepared in Examples 1-3 and Comparative Example 1;

[0029] Figure 5 Schematic diagram showing the sol state of the PMN-PT film precursor prepared in Comparative Example 1;

[0030] Figure 6 A comparison of leakage currents of PMN-PT films prepared in Examples 1-3 and Comparative Example 1 is shown;

[0031] Figure 7 The hysteresis loop diagrams of the PMN-PT films obtained in Examples 1-3 and Comparative Example 1 are shown;

[0032] Figure 8 A schematic diagram of the configuration process for preparing PMN-PT precursor sol in Example 1 is shown.

[0033] The present invention will be further explained below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0034] Specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0035] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the present invention shall be as defined in the attached claims.

[0036] To facilitate understanding of the embodiments of the present invention, further explanation will be given below using specific embodiments as examples in conjunction with the accompanying drawings, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0037] like Figures 1 to 8 As shown, the PMN-PT film preparation method includes the following steps:

[0038] mixing the co-solvent and the catalyst to obtain a mixed solution;

[0039] Lead compounds, magnesium compounds, niobium compounds and titanium compounds are added to the mixed solution according to a predetermined mass ratio of Pb, Mg, Nb and Ti elements, and the mixture is stirred. A stabilizer and a film-forming agent are added to obtain a PMN-PT precursor sol. The PMN-PT precursor sol is colloidally clear and transparent, and its properties can be maintained unchanged for three months without generating complexes.

[0040] The PMN-PT precursor sol is deposited on a substrate to produce a PMN-PT thin film having a uniform microstructure, good film condition, compact crystal arrangement, greatly reduced leakage current, and greatly improved piezoelectric performance.

[0041] In a preferred embodiment of the PMN-PT film preparation method, the lead compound is selected from any one of lead acetate trihydrate, lead oxide, and lead acetate trihydrate; the magnesium compound is selected from any one of magnesium nitrate and magnesium acetate; the niobium compound is selected from any one of niobium ethanol and niobium oxalate; and the titanium compound is selected from any one of tetrabutyl titanate, titanium oxide, and titanium isopropionate. The predetermined mass ratio of the lead compound, magnesium compound, niobium compound, and titanium compound is 1:(0.5~0.8):(0.2~0.5):1.

[0042] In a preferred embodiment of the PMN-PT film preparation method, the lead compound is lead acetate trihydrate [Pb(CH3COO)2·3H2O], the magnesium compound is magnesium acetate [Mg(CH3COO)2], the niobium compound is niobium ethoxide (Nb(C2H4)4), and the titanium compound is tetrabutyl titanate [Ti(OC3H9)4]. The predetermined mass ratio of the lead compound, magnesium compound, niobium compound, and titanium compound is 1:0.56:0.3:1.

[0043] In a preferred embodiment of the PMN-PT film preparation method, the co-solvent is selected from one or more of ethanol, ethylene glycol, and ethylene glycol methyl ether, the catalyst is selected from one or more of acetic acid, nitric acid, and hydrochloric acid, the stabilizer is selected from one or more of acetylacetone, water, and ethanol, the film-forming agent is selected from one or more of polyethylene glycol 200, ethylene glycol, and polyethylene glycol 800, the mass ratio of the co-solvent and the catalyst is (2~8):1, and the mixing time is 1~3 h.

[0044] In a preferred embodiment of the PMN-PT film preparation method, the co-solvent is ethylene glycol methyl ether, the catalyst is acetic acid, the stabilizer is acetylacetone, the film-forming agent is alcohol 800, the mass ratio of the co-solvent and the catalyst is (4~5):1, and the mixing time is 1~2h.

[0045] In a preferred embodiment of the PMN-PT film preparation method, after adding the lead compound and the magnesium compound, the mixture is stirred for 10 to 20 minutes in a water bath, ethanolic niobium is added to the solution, 2 mL of acetylacetone is added, and then the titanium compound is added and mixed at room temperature for 5 minutes, and then refluxed at 90 degrees with stirring for 30 minutes.

[0046] In a preferred embodiment of the PMN-PT thin film preparation method, the PMN-PT precursor sol is uniformly spin-coated, followed by thermal processing according to the following procedure. After the thermal processing is completed, the PMN-PT precursor sol is again applied for spin coating and thermal processing, that is, this operation is repeated until the desired PMN-PT thin film thickness is achieved. The thermal processing includes:

[0047] Stage I: heating from room temperature to 300-400℃ at a heating rate of 80-120℃ / min, and keeping warm for 1-3 minutes;

[0048] Stage II: Continue heating from the first stage holding temperature to 450~550℃ at a heating rate of 30~70℃ / min, and keep warm for 1~3min.

[0049] In a preferred embodiment of the PMN-PT film preparation method, the mass ratio of the sum of the lead compound, the magnesium compound, the niobium compound and the titanium compound to the co-solvent is 1:(2-6).

[0050] In a preferred embodiment of the PMN-PT thin film preparation method, the PMN-PT precursor sol is deposited on a Pt / Si substrate, and the deposition is any one of atomic deposition, magnetron sputtering, and spin coating.

[0051] A PMN-PT film is prepared by the method described.

[0052] In one embodiment, the PMN-PT film comprises, from top to bottom, a PMN-PT film layer, a bottom electrode, and a substrate. The substrate can be a polymer substrate such as polyimide (PI) or polyethylene terephthalate (PET), a metal platinum substrate such as copper foil or aluminum foil, an inorganic flexible substrate such as silicon nitride film or aluminum oxide film, or an LNO / Mica substrate, preferably a Pt / Si substrate. In a Pt / Si substrate, Pt exhibits excellent electrical conductivity, thermal stability, and chemical stability, while Si, as a natural crystal, possesses excellent flexibility and heat resistance. Pt / Si substrates exhibit unique advantages in electrical conductivity, structural stability, interfacial properties, adhesion, lattice matching, and thermal expansion coefficient matching, making them the optimal substrate for the present invention.

[0053] In the present invention, the thickness of the PMN-PT film layer is determined according to actual needs. Typically, the thickness of the PMN-PT film layer is 500-2000 nm, preferably 1000-1500 nm, for example, 1500 nm.

[0054] Among them, the PMN-PT film is used as a piezoelectric layer. If it is too thin, the piezoelectric performance will be reduced. If it is too thick, the crystallization of the top layer will be unsatisfactory, the lead in the lower layer will volatilize severely, and the performance will be reduced.

[0055] In one embodiment, the co-solvent is used to dissolve the lead compound, magnesium compound, niobium compound and titanium compound. The co-solvent is preferably ethylene glycol methyl ether, which can not only dissolve the above compounds, but also help stabilize the sol and prevent the formation of precipitates. The catalyst is preferably acetic acid, which not only acts as a catalyst but also can better control the reaction rate. The mass ratio of the co-solvent to the catalyst is 4:1. If the proportion of the co-solvent is too low, some compounds may not be fully dissolved, forming a precipitate; if the proportion is too high, although the solubility is increased, it may have an adverse effect on subsequent reaction steps or product characteristics. The catalyst can accelerate the reaction rate, but its amount needs to be appropriate. If the proportion of the catalyst is too low, the catalytic effect is insufficient and the reaction rate is too slow; if the proportion is too high, the reaction rate may be too fast, making the reaction difficult to control, and may produce unwanted by-products or affect the structure of the final product.

[0056] In one embodiment, the longer the co-solvent and catalyst are mixed, the more uniform the resulting mixed sol. Typically, the mixing time is 1-3 hours, preferably 1-2 hours, for example, 1 hour. The lead compound is selected from any one of lead acetate trihydrate, lead oxide, and lead acetate trihydrate, preferably lead acetate trihydrate [Pb(CH3COO)2·3H2O], which has excellent solubility and stability. The magnesium compound is selected from any one of magnesium nitrate and magnesium acetate, preferably magnesium acetate [Mg(CH3COO)2], which has strong solubility and controllability. The niobium compound is selected from any one of niobium ethoxide and niobium oxalate, preferably niobium ethoxide (Nb(C2H4)4), which has excellent solubility and reactivity. The titanium compound is selected from any one of tetrabutyl titanate, titanium oxide, and titanium isopropionate, preferably tetrabutyl titanate [Ti(OC3H9)4], which has excellent solubility and reactivity. The mass ratio of the lead compound, magnesium compound, niobium compound, and titanium compound is 1:(0.5-0.8):(0.2-0.5):1; (preferably 1:(0.5-0.6):(0.2-0.3):1), for example, 1:0.56:0.3:1. The lead compound is used in excess to compensate for lead loss caused by the formation of the pyrochlore phase during crystallization. The stabilizer is preferably acetylacetone, which not only inhibits premature hydrolysis of the aforementioned compounds and slows the polycondensation rate but also ensures sol uniformity and prevents localized precipitation. The film-forming agent is preferably polyethylene glycol 800, which not only adjusts the viscosity and rheological properties of the sol and inhibits compound agglomeration, but also reduces drying stress, minimizes subsequent film cracking, and improves coating uniformity and density.

[0057] According to a preferred embodiment, a lead compound, a magnesium compound, a niobium compound, and a titanium compound are sequentially added to the mixed sol. The lead compound hydrolyzes and condenses in the mixed sol, forming a basic framework that provides a stable reaction environment for the addition of the magnesium, niobium, and titanium compounds. Acetylacetone is then added to stabilize the precursor sol, making it less susceptible to complexation and precipitation. Polyethylene glycol 800 is also added as a film-forming agent to improve film quality.

[0058] In the present invention, after the lead compound and the magnesium compound are added, the mixture is stirred for 10 to 20 minutes (e.g., 15 minutes) at a time under heating conditions in a water bath, niobium ethanol is added to the above solution, 2 mL of acetylacetone is added, and then the titanium compound is added and mixed and stirred at room temperature for 5 minutes, and then refluxed at 90 degrees with stirring for 30 minutes.

[0059] Furthermore, the water bath heating temperature is 50-90°C, preferably 60-80°C, for example 70°C.

[0060] Heating accelerates the hydrolysis of lead compounds into lead ions and acetate ions, which in turn form a metal oxide network. Heating also reduces agglomeration of the lead compounds. Within this temperature range, the reaction rate can be effectively controlled and side reactions can be minimized.

[0061] In the present invention, the mass ratio of the Pb, Mg, Nb, and Ti compounds to the cosolvent is 1:(2-6), preferably 1:(3-6), for example, 1:4. This mass ratio allows the compounds of the four elements to be completely dissolved in the cosolvent. The dissolution time is 1-10 minutes, preferably 2-6 minutes, for example, 5 minutes. After stirring, the mixture is aged for 18-48 hours, for example, 24 hours, to promote gel network formation.

[0062] The spin coating speed is 2000-4000 rps, preferably 2500-3500 rps, for example 3000 rps.

[0063] In one embodiment, 1-1.5 mL of the PMN-PT precursor sol is applied at each spin coating step. The PMN-PT precursor sol is then evenly spin-coated at the aforementioned rotation speed. Heat treatment is then performed according to the following procedure. After heat treatment, the PMN-PT precursor sol is applied again, followed by spin coating and heat treatment. This process is repeated until the desired PMN-PT film thickness is achieved. In fact, the thin film formed by depositing the PMN-PT precursor sol is referred to as the PMN-PT thin film layer.

[0064] Furthermore, the thermal processing includes:

[0065] Stage I: heating from room temperature to 300-400℃ at a heating rate of 80-120℃ / min, and keeping warm for 1-3 minutes;

[0066] Stage II: Continue heating from the first stage holding temperature to 450~550℃ at a heating rate of 30~70℃ / min, and keep warm for 1~3min.

[0067] Among them, PMN-PT is first pre-crystallized at a low temperature of 300~400℃ to reduce internal stress, and then the temperature is raised to avoid the formation of process pyrochlore phase.

[0068] In a further preferred embodiment, the thermal processing comprises:

[0069] Stage I: heating from room temperature to 330-380°C at a heating rate of 90-110°C / min, and keeping warm for 1.5-2 minutes;

[0070] Stage II: Continue heating from the first stage holding temperature to 480~520℃ at a heating rate of 40~60℃ / min, and keep warm for 2~3min.

[0071] In a further preferred embodiment, the thermal processing comprises:

[0072] Stage I: heating from room temperature to 350°C at a heating rate of 100°C / min and keeping at this temperature for 2 minutes;

[0073] Stage II: Continue heating from the first stage holding temperature to 500°C at a heating rate of 50°C / min and keep warm for 2 minutes.

[0074] In step 2, after the last deposition is completed, the thermal processing before annealing preferably includes:

[0075] The first stage: heating from room temperature to 300-400℃ at a heating rate of 80-120℃ / min, and keeping warm for 1-3 minutes;

[0076] The second stage: continue heating from the first stage holding temperature to 450~550℃ at a heating rate of 30~70℃ / min, and keep warm for 3~8min;

[0077] The third stage: continue heating from the second stage holding temperature to 600~700℃ at a heating rate of 30~70℃ / min, keep warm for 8~15min, and then cool naturally.

[0078] Among them, the generation of pyrochlore phase is avoided by heating in stages, and the internal stress of the PMN-PT film layer is optimized by the above-mentioned thermal processing before annealing.

[0079] In a further preferred embodiment, the thermal processing before annealing preferably includes:

[0080] The first stage: heating from room temperature to 330-380℃ at a heating rate of 90-110℃ / min, and keeping warm for 1.5-2min;

[0081] The second stage: continue heating from the first stage holding temperature to 480~520℃ at a heating rate of 40~60℃ / min, and keep warm for 4~6 minutes;

[0082] The third stage: continue heating from the second stage holding temperature to 620~660℃ at a heating rate of 40~60℃ / min, keep warm for 9~12min, and then cool naturally.

[0083] In a further preferred embodiment, the thermal processing before annealing preferably includes:

[0084] The first stage: heating from room temperature to 350℃ at a heating rate of 100℃ / min and keeping at this temperature for 2min;

[0085] The second stage: continue heating from the first stage holding temperature to 500℃ at a heating rate of 50℃ / min and keep warm for 5 minutes;

[0086] The third stage: continue heating from the second stage holding temperature to 650°C at a heating rate of 50°C / min, keep warm for 10 minutes, and then cool naturally.

[0087] In the present invention, the normal temperature is room temperature.

[0088] Example 1

[0089] Stir the lead and magnesium compounds at a ratio of 1:0.7 at high temperature until dissolved, then stir at room temperature for 5 minutes. Add niobium to the mixed solution at a standard ratio of 1:0.3 to the lead compound, followed by 2 mL of acetylacetone. Mix the magnesium and niobium at room temperature for 5 minutes, then reflux at 90 degrees Celsius for 30 minutes. Stir the titanium solution with 2 mL of acetylacetone at a standard ratio of 1:1 to the lead compound separately for 5 minutes. Place the magnesium and niobium in an alcohol beaker and cool to room temperature. Add 2 mL of acetylacetone and further add the titanium solution, stirring at room temperature for 5 minutes, then stir at 90 degrees Celsius for half an hour. (After heating and stirring, turbidity may occur; remove the solution and add 2 mL of water and stir at room temperature until clear, approximately five minutes). Add lead at room temperature (first add 2 mL of acetylacetone) and stir for 5 minutes. Heat and stir at 60 degrees Celsius for half an hour. After stirring, add 1 mL of formamide and 0.69 g (0.23 g / 10 mL solvent) of polyethylene glycol-800 and stir until uniform. A clear solution is obtained, which is then transferred to a vial, ultrasonically dispersed for 30 minutes, and aged for 24 hours.

[0090] 20 drops (1.5 mL) of PMN-PT precursor sol were dropped onto the Pt / Si substrate and the PMN-PT precursor sol was evenly spin-coated at 3000 rps, followed by thermal processing according to the following procedure:

[0091] Stage I: heating from room temperature to 350°C at a heating rate of 100°C / min and keeping at this temperature for 2 minutes;

[0092] Stage II: Continue heating from the first stage holding temperature to 500°C at a heating rate of 50°C / min and hold for 2 minutes;

[0093] After the heat treatment, the PMN-PT precursor sol is dripped again to perform the above spin coating and heat treatment operations until the desired PMN-PT film thickness is reached. The last heat treatment, i.e., the heat treatment before annealing, is performed according to the following procedure:

[0094] The first stage: heating from room temperature to 350℃ at a heating rate of 200℃ / min, and keeping at this temperature for 2min;

[0095] The second stage: continue heating from the first stage holding temperature to 500℃ at a heating rate of 100℃ / min and keep warm for 5 minutes;

[0096] The third stage: continue heating from the second stage holding temperature to 700℃ at a heating rate of 200℃ / min, keep at that temperature for 10min, and then cool naturally;

[0097] After the above operations are completed, a PMN-PT film is obtained, wherein the PMN-PT film layer has a thickness of 1500 nm.

[0098] Example 2

[0099] A PMN-PT film was prepared in a similar manner to Example 1, except for the ratios of Pb, Mg, Nb, and Ti. The specific steps were as follows:

[0100] Stir the lead and magnesium compounds at a ratio of 1:0.5 at high temperature until dissolved, then stir at room temperature for 5 minutes. Add niobium to the mixed solution at a standard ratio of 1:0.5 to the lead compound, followed by 2 mL of acetylacetone. Stir the magnesium and niobium mixture at room temperature for 5 minutes, then reflux at 90°C for 30 minutes. Stir the titanium solution separately at a standard ratio of 1:1 to the lead compound for 5 minutes. Cool the magnesium and niobium to room temperature in an alcohol beaker, add 2 mL of acetylacetone, and then add the titanium solution to the mixture at room temperature for 5 minutes. Stir at 90°C for half an hour. (After heating and stirring, turbidity may develop; remove the solution and add 2 mL of water and stir at room temperature until clear, approximately five minutes.) Add lead at room temperature (previously add 2 mL of acetylacetone) and stir for 5 minutes. Heat and stir at 60°C for half an hour. After stirring, add 1 mL of formamide and 0.69 g (0.23 g / 10 mL solvent) of polyethylene glycol-800 and stir until uniform. A clear solution is obtained, which is then transferred to a vial, ultrasonically dispersed for 30 minutes, and aged for 24 hours.

[0101] 20 drops (1.5 mL) of PMN-PT precursor sol were dropped onto the Pt / Si substrate and the PMN-PT precursor sol was evenly spin-coated at 3000 rps, followed by thermal processing according to the following procedure:

[0102] Stage I: heating from room temperature to 350°C at a heating rate of 100°C / min and keeping at this temperature for 2 minutes;

[0103] Stage II: Continue heating from the first stage holding temperature to 500°C at a heating rate of 50°C / min and hold for 2 minutes;

[0104] After the heat treatment, the PMN-PT precursor sol is dripped again to perform the above spin coating and heat treatment operations until the desired PMN-PT film thickness is reached. The last heat treatment, i.e., the heat treatment before annealing, is performed according to the following procedure:

[0105] The first stage: heating from room temperature to 350℃ at a heating rate of 200℃ / min, and keeping at this temperature for 2min;

[0106] The second stage: continue heating from the first stage holding temperature to 500℃ at a heating rate of 100℃ / min and keep warm for 5 minutes;

[0107] The third stage: continue heating from the second stage holding temperature to 700℃ at a heating rate of 200℃ / min, keep at that temperature for 10min, and then cool naturally;

[0108] After the above operations are completed, a PMN-PT film is obtained, wherein the PMN-PT film layer has a thickness of 1500 nm.

[0109] Example 3

[0110] A PMN-PT film was prepared in a manner similar to Example 1, except that no stabilizer and film-forming agent were added. The specific steps were as follows:

[0111] Stir the lead compound and magnesium compound at a ratio of 1:0.7 at high temperature until dissolved, and then stir at room temperature for 5 minutes; add niobium to the mixed solution at a ratio of 1:0.3 of the standard lead amount, and then add 2mL of acetylacetone; mix and stir the magnesium and niobium at room temperature for 5 minutes, and then reflux and stir at 90 degrees for 30 minutes; stir the titanium separately at a ratio of 1:1 of the standard lead amount for 5 minutes; put the magnesium and niobium into an alcohol beaker and cool to room temperature, add 2mL of acetylacetone, and further add the titanium solution and mix and stir at room temperature for 5 minutes, and stir at 90 degrees for half an hour (turbidity may occur after heating and stirring, take it out and add 2mL of water and stir at room temperature until it is clear, about five minutes); add lead at room temperature (add 2mL of acetylacetone first) and stir for 5 minutes; heat and stir at 60 degrees for half an hour until it is uniform, to obtain a clear solution, put it into a small bottle, ultrasonically disperse it for 30 minutes, and age it for 24 hours.

[0112] 20 drops (1.5 mL) of PMN-PT precursor sol were dropped onto the Pt / Si substrate and the PMN-PT precursor sol was evenly spin-coated at 3000 rps, followed by thermal processing according to the following procedure:

[0113] Stage I: heating from room temperature to 350°C at a heating rate of 100°C / min and keeping at this temperature for 2 minutes;

[0114] Stage II: Continue heating from the first stage holding temperature to 500°C at a heating rate of 50°C / min and hold for 2 minutes;

[0115] After the heat treatment, the PMN-PT precursor sol is dripped again to perform the above spin coating and heat treatment operations until the desired PMN-PT film thickness is reached. The last heat treatment, i.e., the heat treatment before annealing, is performed according to the following procedure:

[0116] The first stage: heating from room temperature to 350℃ at a heating rate of 200℃ / min, and keeping at this temperature for 2min;

[0117] The second stage: continue heating from the first stage holding temperature to 500℃ at a heating rate of 100℃ / min and keep warm for 5 minutes;

[0118] The third stage: continue heating from the second stage holding temperature to 700℃ at a heating rate of 200℃ / min, keep at that temperature for 10min, and then cool naturally;

[0119] After the above operations are completed, a PMN-PT film is obtained, wherein the PMN-PT film layer has a thickness of 1500 nm.

[0120] Comparative Example 1

[0121] A PMN-PT film was prepared in a manner similar to Example 1, with the following differences: the ratio of Pb, Mg, Nb, and Ti, the omission of stabilizers and film-forming agents, and the original film heat treatment process. The specific steps were:

[0122] Stir the lead compound and magnesium compound at a ratio of 1:0.5 at high temperature until dissolved, and then stir at room temperature for 5 minutes; add niobium to the mixed solution at a standard lead ratio of 1:0.5; mix the magnesium and niobium at room temperature and stir evenly (5 minutes), then reflux and stir at 90 degrees for 30 minutes; stir the titanium solution separately at a standard lead ratio of 1:1 for 5 minutes; put the magnesium and niobium into an alcohol beaker and cool to room temperature, then add the titanium solution and mix and stir at room temperature for 5 minutes, and stir at 90 degrees for half an hour (turbidity may occur after heating and stirring, take it out and add 2mL of water and stir at room temperature until it is clear, about five minutes); add lead at room temperature (add 2mL of acetylacetone first) and stir for 5 minutes; heat and stir at 60 degrees for half an hour until it is evenly stirred to obtain a clear solution, which is placed in a small bottle, ultrasonically dispersed for 30 minutes, and aged for 24 hours;

[0123] 20 drops (1.5 mL) of PMN-PT precursor sol were dropped onto the Pt / Si substrate and the PMN-PT precursor sol was evenly spin-coated at 2000 rps, followed by thermal processing according to the following procedure:

[0124] Stage I: heating from room temperature to 350°C at a heating rate of 100°C / min and keeping at this temperature for 2 minutes;

[0125] Stage II: Continue heating from the first stage holding temperature to 500°C at a heating rate of 50°C / min and hold for 2 minutes;

[0126] After the heat treatment, the PMN-PT precursor sol is dripped again to perform the above spin coating and heat treatment operations until the desired PMN-PT film thickness is reached. The last heat treatment, i.e., the heat treatment before annealing, is performed according to the following procedure:

[0127] The first stage: heating from room temperature to 350℃ at a heating rate of 100℃ / min and keeping at this temperature for 2min;

[0128] The second stage: continue heating from the first stage holding temperature to 500℃ at a heating rate of 50℃ / min and keep warm for 5 minutes;

[0129] The third stage: continue heating from the second stage holding temperature to 650℃ at a heating rate of 50℃ / min, keep at that temperature for 10min, and then cool naturally;

[0130] After the above operations are completed, a PMN-PT film is obtained, wherein the PMN-PT film layer has a thickness of 1500 nm.

[0131] Figure 1 SEM images of the PMN-PT films prepared in Examples 1-3 and Comparative Example 1 are shown. The PMN-PT composite film prepared in Example 1 exhibits finer, denser grains, the best crystal quality, a uniform surface, and no obvious cracks, resulting in the best results. The surface condition of Example 2 is poor, with some cracks and pores present in the film, and reduced crystallinity. The surface of Example 3 exhibits good density and uniformity, but its crystallinity is inferior to that of Example 1. Comparative Example 1 exhibits the worst results, with incomplete crystallization and the presence of a noticeable amorphous phase and cracks.

[0132] Figure 2 The SEM characterization image of the PMN-PT composite film prepared in Comparative Example 1 is shown. It can be found that the PMN-PT composite film prepared in Example 1 has finer grains and is denser, which is the reason for its stronger mechanical properties. At the same time, the growth of columnar crystals causes its piezoelectric properties to be significantly stronger than that of Comparative Example 1.

[0133] Figure 3 The X-ray diffraction (XRD) comparison diagrams of the PMN-PT films prepared in Examples 1-3 and the PMN-PT film prepared in Comparative Example 1 are shown. It can be found that the PMN-PT films prepared in Example 1 have good crystallization quality and no pyrochlore phase is generated, while the PMN-PT films prepared in Examples 2 and 3 have slightly poor crystallization quality and have a weak pyrochlore phase. The PMN-PT film prepared in Comparative Example 1 has the worst crystallization quality, with a weak diffraction peak corresponding to perovskite and an obvious pyrochlore phase. Therefore, the piezoelectric properties and mechanical strength of Example 1 are much higher than those of Examples 2-3 and Comparative Example 1.

[0134] Figure 4 The sol states of the PMN-PT film precursors prepared in Examples 1-3 and Comparative Example 1 are shown. It can be found that the sol states of the PMN-PT precursors prepared in Examples 1-3 are clearer and more transparent, and easier to maintain stability, while Comparative Example 1 appears turbid, indicating that the addition of acetylacetone can greatly improve the stability of the precursor solution.

[0135] Figure 6 A comparison diagram of the leakage current of the PMN-PT films prepared in Examples 1-3 and Comparative Example 1 is shown. It can be seen that the high-performance PMN-PT film prepared in Example 1 has lower leakage current, which indicates that Example 1 has better film quality and higher performance.

[0136] Figure 7The hysteresis loop diagrams of the PMN-PT films obtained in Examples 1-3 and Comparative Example 1 are shown. It can be seen that the PMN-PT film obtained in Example 1 presents a typical relaxor ferroelectric hysteresis loop state, Examples 2-3 have fat hysteresis loops due to poor film density, and Comparative Example 1 has poor ferroelectric properties due to poor crystallinity, indicating that Example 1 has the best ferroelectric properties.

[0137] In summary, it is obvious that by improving the sol-gel method to regulate the performance of PMN-PT film, the metal ions in the solution are complexed, and the high-performance PMN-PT film precursor obtained is more stable, has better film quality, no pyrochlore phase is generated, has lower leakage current, and has better film quality.

[0138] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields. The above-mentioned specific embodiments are merely illustrative and instructive, and are not restrictive. A person skilled in the art, guided by this specification and without departing from the scope of protection of the claims of the present invention, may also devise various forms, all of which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a PMN-PT film, characterized in that: The steps include: mixing the co-solvent and the catalyst to obtain a mixed solution; Adding lead compound, magnesium compound, niobium compound and titanium compound in a predetermined mass ratio of Pb, Mg, Nb and Ti elements to the mixed solution and stirring, and adding a stabilizer and a film-forming agent to prepare a PMN-PT precursor sol; The PMN-PT precursor sol is deposited on a substrate to prepare a PMN-PT film.

2. The method for preparing a PMN-PT film according to claim 1, wherein: Preferably, the lead compound is selected from any one of lead acetate trihydrate, lead oxide, and lead acetate trihydrate; the magnesium compound is selected from any one of magnesium nitrate and magnesium acetate; the niobium compound is selected from any one of niobium ethanol and niobium oxalate; and the titanium compound is selected from any one of tetrabutyl titanate, titanium oxide, and titanium isopropionate. The predetermined mass ratio of the lead compound, magnesium compound, niobium compound, and titanium compound is 1:(0.5~0.8):(0.2~0.5):

1.

3. The method for preparing a PMN-PT film according to claim 1, wherein: The lead compound is lead acetate trihydrate [Pb(CH3COO)2·3H2O], the magnesium compound is magnesium acetate [Mg(CH3COO)2], the niobium compound is niobium ethoxide (Nb(C2H4)4), and the titanium compound is tetrabutyl titanate [Ti(OC3H9)4]. The predetermined mass ratio of the lead compound, the magnesium compound, the niobium compound, and the titanium compound is 1:0.56:0.3:

1.

4. The method for preparing a PMN-PT film according to claim 1, wherein: The co-solvent is selected from one or more of ethanol, ethylene glycol, and ethylene glycol methyl ether; the catalyst is selected from one or more of acetic acid, nitric acid, and hydrochloric acid; the stabilizer is selected from one or more of acetylacetone, water, and ethanol; the film-forming agent is selected from one or more of polyethylene glycol 200, ethylene glycol, and polyethylene glycol 800; the mass ratio of the co-solvent to the catalyst is (2-8):1, and the mixing time is 1-3 h.

5. The method for preparing a PMN-PT film according to claim 1, wherein: The co-solvent is ethylene glycol methyl ether, the catalyst is acetic acid, the stabilizer is acetylacetone, the film-forming agent is alcohol 800, the mass ratio of the co-solvent to the catalyst is (4-5):1, and the mixing time is 1-2 hours.

6. The method for preparing a PMN-PT film according to claim 1, characterized in that: After adding the lead compound and the magnesium compound, stir for 10 to 20 minutes at a time under heating conditions in a water bath, add niobium ethanol to the solution, add 2 mL of acetylacetone, and then add the titanium compound and mix and stir at room temperature for 5 minutes, then reflux at 90 degrees and stir for 30 minutes.

7. The method for preparing a PMN-PT film according to claim 1, characterized in that: The PMN-PT precursor sol is evenly spin-coated, followed by thermal processing according to the following procedure. After the thermal processing is completed, the PMN-PT precursor sol is dripped again for spin coating and thermal processing, that is, this operation is repeated until the desired PMN-PT film thickness is reached. The thermal processing includes: Stage I: heating from room temperature to 300-400℃ at a heating rate of 80-120℃ / min, and keeping warm for 1-3 minutes; Stage II: Continue heating from the first stage holding temperature to 450~550℃ at a heating rate of 30~70℃ / min, and keep warm for 1~3min.

8. The method for preparing a PMN-PT film according to claim 1, characterized in that: The mass ratio of the total of the lead compound, the magnesium compound, the niobium compound and the titanium compound to the co-solvent is 1:(2-6).

9. The method for preparing a PMN-PT film according to claim 1, characterized in that: The PMN-PT precursor sol is deposited on a Pt / Si substrate, wherein the deposition is any one of atomic deposition, magnetron sputtering, and spin coating.

10. A PMN-PT film, characterized in that: It is prepared by the method according to any one of claims 1 to 9.

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