CN114477787B - Composite KTN film and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of functional film materials, and particularly relates to a composite KTN film and a preparation method thereof. The invention adopts a sol-gel method to prepare, and by adding the bismuth ferrite seed layer and co-doping lanthanum and iron, the film performance is effectively optimized, and in addition, the raw material proportion and the technological parameters are designed and optimized, so that the production cost is reduced, and the invention is beneficial to the industrialized application thereof.

Description

A kind of composite KTN thin film and preparation method thereof

technical field

The invention belongs to the technical field of functional film materials, and in particular relates to a composite KTN film and a preparation method thereof.

Background technique

Potassium tantalum niobate (KTN) is a material with pyroelectric and nonlinear optical properties, and has excellent electro-optic effect and photorefractive effect. Pyroelectric devices based on KTN thin films have more advantages in reducing the driving voltage and device size, and can better meet the needs of future miniaturization and integration of laser devices.

The sol-gel method is popular because of its simplicity. As we all know, with the development trend of miniaturization and miniaturization of thin film devices, strict requirements are put forward for the integration of thin films. In general, the performance of thin films prepared by sol-gel method has limitations.

Therefore, in order to meet the industrial development needs of KTN thin films, it is the most important to choose a preparation method that is low-cost, high-performance, and conforms to the development of KTN integration.

Contents of the invention

For the above-mentioned deficiency of prior art, the present invention provides a kind of composite KTN thin film and preparation method thereof, the present invention adopts sol-gel method to prepare the KTN composite thin film with high performance, the present invention passes the addition of bismuth ferrite seed layer, and The co-doping of lanthanum and iron effectively optimizes the performance of the film. In addition, the ratio of raw materials and process parameters are designed and optimized to reduce production costs and facilitate its industrial application.

On the one hand, the present invention provides a kind of composite KTN film, comprises KTN film layer and seed layer; The molecular formula of KTN film layer material is K _1+Z Ta _1-XY Nb _Y M _X O ₃ , the ratio of each element is K:Ta :Nb:M:O＝(1+Z):(1–XY):Y:X:3, M element is Fe.

The seed layer is a lanthanum-doped bismuth ferrite film Bi _1-n+m LanFeO ₃ , that is, the ratio of each element is Bi:La:Fe:O=1-n+m:n:1:3.

Where X is the molar equivalent of M element, 0.06≤X≤0.10, Y is the molar equivalent of Nb element, 0.48≤Y≤0.66, element K is added in excess, and Z is 8%-10%; where n is the molar equivalent of La element , 0.05≤n≤0.15, where 0.05≤n≤0.10, 0.05≤m≤0.08; where 0.10<n≤0.15, 0.02≤m<0.05.

Further, the KTN thin film layer includes N thin film sublayers, 8≤N≤17, when 8≤N≤12, the number of seed layers is 2; when 13≤N≤17, the number of seed layers is 3.

Further, the potassium source, tantalum source, and niobium source are potassium carbonate, tantalum oxide, and niobium oxide respectively; the lanthanum source, bismuth source, and iron source are respectively lanthanum nitrate, bismuth nitrate, and iron nitrate.

On the other hand, the present invention provides a kind of method for preparing above-mentioned composite KTN film, comprises the following steps:

1. Preparation of precursor solution:

(1) Preparation of potassium tantalum niobate-based precursor solution: by sol-gel method, potassium carbonate, tantalum oxide, niobium oxide, and ferric nitrate were weighed according to the stoichiometric ratio and dissolved in isopropanol. Mix solution A, stir the mixed solution A for 40 minutes, add ethanol to it to prepare a precursor solution, place the prepared precursor solution in an environment with a temperature of 19-22°C and let it stand for 6-8 hours for later use. The concentration is 0.39mol/L～0.45mol/L, and the volume ratio of isopropanol and ethanol is 6:5.

(2) Preparation of the seed layer bismuth ferrite-based precursor solution: using the sol-gel method, weigh bismuth nitrate and iron nitrate according to the stoichiometric ratio and dissolve them in isopropanol. Solution A, after stirring the mixed solution A for 20 minutes, add ethylene glycol methyl ether to it to prepare a precursor solution, place the prepared precursor solution in an environment with a temperature of 19-22°C and let it stand for 5 hours for later use. The concentration of the solution is 0.43mol/L-0.5mol/L, and the volume ratio of isopropanol and ethylene glycol methyl ether is 4:3.

2. Preparation of the seed layer material: using a layer-by-layer annealing process, the seed layer precursor solution is deposited on the ITO/glass substrate material by spin coating, and then the material is placed on a hot plate to dry, and the dried film Place in a rapid annealing furnace for two-stage annealing treatment; then deposit other layer materials on the respective lower layer materials according to the same method, repeat the steps of spin coating and annealing several times until the number of seed layers meets the requirements.

3. Preparation of thin film materials: using layer-by-layer annealing process, the potassium tantalum niobate-based precursor solution is deposited on the seed layer material by spin coating, and then the material is placed on a hot plate for drying, and the dried film is placed on the Perform two-stage annealing treatment in a rapid annealing furnace; then deposit other layer materials on their respective lower layer materials in the same way, and repeat the steps of spin coating and annealing several times until the film thickness meets the requirements.

4. Annealing the thin film whose thickness meets the requirement in step 3 at 575° C. to 600° C. for 4 minutes to obtain a composite potassium tantalum niobate thin film co-doped with lanthanum and iron.

In the above preparation method, the drying temperature in step 2 is 155-180°C, and the drying time is 100s-120s; the preferred drying temperature is 162°C, and the drying time is 110s;

The two-stage annealing process in step 2 is 245-285°C, 50-80s, 485-535°C, 60-90s; the preferred annealing process is 268°C, 75s, 515°C, 75s;

In step 2, the speed of spin coating and homogenization is 3700-3900rpm, and the time is 20-40s.

In the above preparation method, the drying temperature in step 3 is 165-205°C, and the drying time is 50s-80s; the preferred drying temperature is 178°C, and the drying time is 65s;

The two-stage annealing process in step 3 is 295-315°C, 90-120s, 555-585°C, 180-220s; the preferred annealing process is 305°C, 105s, 568°C, 195s;

In step 3, the speed of spin coating and uniform glue is 4500-5000rpm, and the time is 25-35s.

The beneficial effects of the present invention are:

(1) The present invention adopts the method of sol-gel, has changed the problem that the traditional potassium tantalum niobate thin film preparation cost is high, uses this preparation method, has prepared potassium tantalum niobate with high preference on the ITO/glass substrate The thin film reduces the production cost and is beneficial to its industrial application.

(2) The present invention adopts the bismuth ferrite seed layer, realizes the doping of iron and lanthanum ions, has good film uniformity, and effectively optimizes the quality of the potassium tantalum niobate film.

(3) The present invention optimizes the annealing process, adopts the layer-by-layer annealing process, and improves the performance of the film by adjusting and controlling the annealing parameters. The composite KTN film presents a saturated hysteresis loop, low leakage current, and a polarization intensity as high as 35 μC/cm ² . It has excellent electrical properties and meets the needs of future miniaturization and integration development of laser devices.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, In other words, other drawings can also be obtained from these drawings on the premise of not paying creative work.

Fig. 1 is the XRD figure of embodiment 7 of the present invention.

Fig. 2 is a hysteresis loop diagram of Embodiment 8 of the present invention.

Detailed ways

In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described The embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

Example 1

A composite potassium tantalum niobate (KTN) film based on a bismuth ferrite seed layer, comprising a KTN film layer and a seed layer; the molecular formula of the KTN film layer material is K _1+Z Ta _1-XY Nb _Y M _X O ₃ , each The ratio of elements is K:Ta:Nb:M:O=(1+Z):(1–XY):Y:X:3, and the M element is Fe.

The seed layer is a lanthanum-doped bismuth ferrite film Bi _1-n+m LanFeO ₃ , that is, the ratio of each element is Bi:La:Fe:O=1-n+m:n:1:3.

Wherein X is the molar equivalent of M element 0.06≤X≤0.10, Y is the molar equivalent of Nb element, 0.48≤Y≤0.66, element K is added in excess, and Z is 8%-10%; wherein n is the molar equivalent of La element, 0.05≤n≤0.15, where 0.05≤n≤0.10, 0.05≤m≤0.08; where 0.10<n≤0.15, 0.02≤m<0.05.

Example 2

On the basis of Example 1, the KTN thin film layer includes N thin film sublayers, 8≤N≤17, when 8≤N≤12, the number of layers of the seed layer is 2; when 13≤N≤17, the number of layers of the seed layer The number is 3.

Example 3

On the basis of Example 2, the potassium source, tantalum source, and niobium source are potassium carbonate, tantalum oxide, niobium oxide, and iron nitrate; the lanthanum source, bismuth source, and iron source are respectively lanthanum nitrate, bismuth nitrate, and iron nitrate.

Example 4

The method for preparing above-mentioned embodiment 1-3 composite KTN thin film may further comprise the steps:

1. Preparation of precursor solution:

1.1 Preparation of potassium tantalum niobate-based precursor solution: by sol-gel method, potassium carbonate, tantalum oxide, niobium oxide, and ferric nitrate were weighed and dissolved in isopropanol according to the stoichiometric ratio, and a mixed solution was obtained after complete dissolution A. After stirring the mixed solution A for 40 minutes, add ethanol to it to prepare a precursor solution. Place the prepared precursor solution in an environment with a temperature of 19-22°C for 6-8 hours for later use. The concentration of the precursor solution 0.39mol/L～0.45mol/L, the volume ratio of isopropanol and ethanol is 6:5.

1.2 Preparation of the seed layer bismuth ferrite-based precursor solution: use the sol-gel method to weigh bismuth nitrate and iron nitrate according to the stoichiometric ratio and dissolve them in isopropanol. After they are completely dissolved, add lanthanum nitrate in turn to obtain a mixed solution A , after stirring the mixed solution A for 20 minutes, add ethylene glycol methyl ether to it to prepare a precursor solution, place the prepared precursor solution in an environment with a temperature of 19-22°C and let it stand for 5 hours for later use. The concentration is 0.43mol/L～0.5mol/L, and the volume ratio of isopropanol and ethylene glycol methyl ether is 4:3.

2. Preparation of the seed layer material: The layer-by-layer annealing process is used to deposit the seed layer precursor solution on the ITO/glass substrate material by spin coating, and then place the material on a hot plate to dry, and the dried film Place in a rapid annealing furnace for two-stage annealing treatment; then deposit other layer materials on the respective lower layer materials according to the same method, repeat the steps of spin coating and annealing several times until the number of seed layers meets the requirements.

3. Preparation of thin film material: using layer-by-layer annealing process, deposit potassium tantalum niobate-based precursor solution on the seed layer material by spin coating method, then place the material on a hot plate for drying, and place the dried film on Perform two-stage annealing treatment in a rapid annealing furnace; then deposit other layer materials on their respective lower layer materials in the same way, and repeat the steps of spin coating and annealing several times until the film thickness meets the requirements.

4. Annealing the thin film meeting the thickness requirement at 575° C. to 600° C. for 4 minutes to obtain a composite potassium tantalum niobate thin film co-doped with lanthanum and iron.

In the above preparation method, the drying temperature in step 2 is 155-180°C, and the drying time is 100s-120s; preferably, the drying temperature is 162°C, and the drying time is 110s.

The two-stage annealing process in step 2 is 245-285°C, 50-80s, 485-535°C, 60-90s; the preferred annealing process is 268°C, 75s, 515°C, 75s.

In step 2, the speed of spin coating and homogenization is 3700-3900rpm, and the time is 20-40s.

In the above preparation method, the drying temperature in step 3 is 165-205°C, and the drying time is 50s-80s; preferably, the drying temperature is 178°C, and the drying time is 65s.

The two-stage annealing process in step 3 is 295-315°C, 90-120s, 555-585°C, 180-220s; the preferred annealing process is 305°C, 105s, 568°C, 195s.

In step 3, the speed of spin coating and uniform glue is 4500-5000rpm, and the time is 25-35s.

Example 5

On the basis of Example 4, the drying temperature in step 2 is 162°C, and the drying time is 110s;

The two-stage annealing process in step 2 is 268°C, 75s, 515°C, 75s;

In step 2, the speed of spin coating and homogenization is 3700-3900rpm, and the time is 20-40s.

The drying temperature in step 3 is 178°C, and the drying time is 65s;

The two-stage annealing process in step 3 is 305°C, 105s, 568°C, 195s.

Example 6

A potassium tantalum niobate thin film based on a bismuth ferrite seed layer, including a KTN thin film layer and a seed layer; a high-performance potassium tantalum niobate thin film material K ₁₊ was prepared by using sol-gel and bonding layer annealing processes _Z Ta _1-XY Nb _Y M _X O ₃ (KTNMO), that is, the ratio of each element is K:Ta:Nb:M:O=(1+Z):(1–XY):Y:X:3, M element is Fe, and this KTN film layer has 10 layers altogether, and the number of layers of seed layer is 2; Among the present invention, potassium source, tantalum source, niobium source, iron source are potassium carbonate, tantalum oxide, niobium oxide, ferric nitrate respectively, wherein X is 0.08 molar equivalent of M element, Y is 0.5 molar equivalent of Nb element, element K is added in excess, and Z is 9%.

The seed layer is bismuth ferrite film Bi _1-n+m LanFeO ₃ (BLFO) doped with lanthanum, that is, the ratio of each element is Bi:La:Fe:O=1-n+m:n:1:3; In the invention, the lanthanum source, the bismuth source, and the iron source are respectively lanthanum nitrate, bismuth nitrate, and iron nitrate, wherein n is the molar equivalent of La element 0.1, and m is 0.08.

Preparation of potassium tantalum niobate thin film based on bismuth ferrite seed layer:

1. Preparation of precursor solution:

1.1 Preparation of potassium tantalum niobate-based precursor solution: using sol-gel method, according to potassium carbonate (K ₂ CO ₃ ): tantalum oxide (Ta ₂ O ₅ ): niobium oxide (Nb ₂ O ₅ ): iron nitrate ( Fe(NO ₃ ) ₃ ) was dissolved in isopropanol at a molar ratio of 1.09:0.21:0.25:0.08. After complete dissolution, a mixed solution A was obtained. After stirring the mixed solution A for 40 minutes, ethanol was added to it to prepare a precursor Solution, the prepared precursor solution was placed in an environment with a temperature of 20°C for 7 hours for later use. The concentration of the precursor solution was 0.40mol/L, and the volume ratio of isopropanol and ethanol was 6:5.

1.2 Preparation of the seed layer bismuth ferrite-based precursor solution: using the sol-gel method, the molar ratio of bismuth nitrate (Bi(NO ₃ ) ₃ ) to iron nitrate (Fe(NO)) was dissolved in isopropyl Alcohol, after being completely dissolved, add lanthanum nitrate La(NO ₃ ) ₃ ) sequentially (the amount added is 0.1 times the molar number of ferric nitrate (Fe(NO)), to obtain mixed solution A, after stirring mixed solution A for 20min, add Add ethylene glycol methyl ether to prepare a precursor solution. Place the prepared precursor solution in an environment with a temperature of 20°C for 5 hours for later use. The concentration of the precursor solution is 0.48mol/L, isopropanol, ethylene glycol The volume ratio of alcohol methyl ether is 4:3.

2. Preparation of the seed layer material: The layer-by-layer annealing process is used to deposit the seed layer precursor solution on the ITO/glass substrate material by spin coating, and then place the material on a hot plate to dry, and the dried film Place in a rapid annealing furnace for two-stage annealing treatment; then deposit other layer materials on the respective lower layer materials according to the same method, repeat the steps of spin coating and annealing several times until the number of seed layers meets the requirements.

3. Preparation of thin film material: using layer-by-layer annealing process, deposit potassium tantalum niobate-based precursor solution on the seed layer material by spin coating method, then place the material on a hot plate for drying, and place the dried film on Perform two-stage annealing treatment in a rapid annealing furnace; then deposit other layer materials on their respective lower layer materials in the same way, and repeat the steps of spin coating and annealing several times until the film thickness meets the requirements.

4. Anneal the thin film that meets the thickness requirement at 580° C. for 4 minutes to obtain a composite potassium tantalum niobate thin film co-doped with lanthanum and iron.

In the above preparation method, the drying temperature in step 3 is 178°C, and the drying time is 65s;

The two-stage annealing process in step 3 is 305°C, 105s, 568°C, 195s;

In step 3, the speed of spin coating and homogenization is 5000rpm, and the time is 30s.

Example 7

Carry out XRD test to the sample of embodiment 6, see accompanying drawing 1 for the result, it can be seen that a composite KTN thin film with high preference has been formed on the ITO/glass substrate.

Example 8

The hysteresis loop test was carried out on the sample of Example 6, and the results are shown in Figure 2. The film showed a saturated hysteresis loop with low leakage current and a high polarization intensity of 35 μC/cm ² .

Example 9

A potassium tantalum niobate thin film based on a bismuth ferrite seed layer, including a KTN thin film layer and a seed layer; a high-performance potassium tantalum niobate thin film material K ₁₊ was prepared by using sol-gel and bonding layer annealing processes _Z Ta _1-XY Nb _Y M _X O ₃ (KTNMO), that is, the ratio of each element is K:Ta:Nb:M:O=(1+Z):(1–XY):Y:X:3, M element is Fe, and this KTN film layer has 10 layers altogether, and the number of layers of seed layer is 2; Among the present invention, potassium source, tantalum source, niobium source, iron source are potassium carbonate, tantalum oxide, niobium oxide, ferric nitrate respectively, wherein X is 0.06 molar equivalent of M element, Y is 0.48 molar equivalent of Nb element, element K is added in excess, and Z is 8%.

The seed layer is bismuth ferrite film Bi _1-n+m LanFeO ₃ (BLFO) doped with lanthanum, that is, the ratio of each element is Bi:La:Fe:O=1-n+m:n:1:3; In the invention, the lanthanum source, the bismuth source, and the iron source are respectively lanthanum nitrate, bismuth nitrate, and iron nitrate, wherein n is the molar equivalent of La element 0.05, and m is 0.05.

Preparation of potassium tantalum niobate thin film based on bismuth ferrite seed layer:

1. Preparation of precursor solution: 1.1 Preparation of potassium tantalum niobate-based precursor solution: using sol-gel method, according to potassium carbonate (K ₂ CO ₃ ): tantalum oxide (Ta ₂ O ₅ ): niobium oxide (Nb ₂ O ₅ ): ferric nitrate (Fe(NO ₃ ) ₃ ) molar ratio 1.08:0.23:0.24:0.06 was dissolved in isopropanol, and mixed solution A was obtained after complete dissolution. After stirring mixed solution A for 40 minutes, pour Add ethanol to prepare a precursor solution, place the prepared precursor solution in an environment with a temperature of 20°C for 7 hours for later use, the concentration of the precursor solution is 0.39mol/Lmol/L, the volume of isopropanol and ethanol The ratio is 6:5.

1.2 Preparation of the seed layer bismuth ferrite-based precursor solution: using the sol-gel method, the molar ratio of bismuth nitrate (Bi(NO ₃ ) ₃ ) and iron nitrate (Fe(NO)) was dissolved in isopropyl Alcohol, after being completely dissolved, add lanthanum nitrate La(NO ₃ ) ₃ ) sequentially (the amount added is 0.05 times the molar number of ferric nitrate (Fe(NO)) to obtain a mixed solution A. After stirring the mixed solution A for 20 min, add Add ethylene glycol methyl ether to prepare a precursor solution. Place the prepared precursor solution in an environment with a temperature of 19°C for 5 hours for later use. The concentration of the precursor solution is 0.43mol/L, isopropanol, ethylene glycol The volume ratio of alcohol methyl ether is 4:3.

Subsequent (2) preparation of the seed layer material, (3) preparation of the thin film material, and (4) annealing process are the same as in Example 6.

Example 10

A potassium tantalum niobate thin film based on a bismuth ferrite seed layer, including a KTN thin film layer and a seed layer; a high-performance potassium tantalum niobate thin film material K ₁₊ was prepared by using sol-gel and bonding layer annealing processes _Z Ta _1-XY Nb _Y M _X O ₃ (KTNMO), that is, the ratio of each element is K:Ta:Nb:M:O=(1+Z):(1–XY):Y:X:3, The M element is Fe, and the KTN film has 13 layers in total, and the number of layers of the seed layer is 3; among the present invention, the potassium source, tantalum source, niobium source, and iron source are potassium carbonate, tantalum oxide, niobium oxide, iron nitrate, wherein X The molar equivalent of M element is 0.10, the molar equivalent of Nb element Y is 0.66, the element K is added in excess, and Z is 10%.

The seed layer is bismuth ferrite film Bi _1-n+m LanFeO ₃ (BLFO) doped with lanthanum, that is, the ratio of each element is Bi:La:Fe:O=1-n+m:n:1:3; In the invention, the lanthanum source, the bismuth source, and the iron source are respectively lanthanum nitrate, bismuth nitrate, and iron nitrate, wherein n is the molar equivalent of La element 0.15, and m is 0.04.

Preparation of potassium tantalum niobate thin film based on bismuth ferrite seed layer:

1. Preparation of precursor solution: 1.1 Preparation of potassium tantalum niobate-based precursor solution: using sol-gel method, according to potassium carbonate (K ₂ CO ₃ ): tantalum oxide (Ta ₂ O ₅ ): niobium oxide (Nb ₂ O ₅ ): ferric nitrate (Fe(NO ₃ ) ₃ ) molar ratio 1.1:0.12:0.33:0.10 was dissolved in isopropanol, and mixed solution A was obtained after complete dissolution. After stirring mixed solution A for 40 minutes, pour It adds ethanol to prepare a precursor solution. The prepared precursor solution is placed in an environment with a temperature of 22°C for 8 hours for later use. The concentration of the precursor solution is 0.45mol/L, and the volume ratio of isopropanol and ethanol is 6:5.

1.2 Preparation of the bismuth ferrite-based precursor solution for the seed layer: using the sol-gel method, the molar ratio of bismuth nitrate (Bi(NO ₃ ) ₃ ) to iron nitrate (Fe(NO)) was dissolved in isopropyl Alcohol, after being completely dissolved, add lanthanum nitrate La(NO ₃ ) ₃ ) sequentially (the amount added is 0.04 times the molar number of ferric nitrate (Fe(NO)) to obtain a mixed solution A, after stirring the mixed solution A for 20min, add to it Add ethylene glycol methyl ether to prepare a precursor solution. Place the prepared precursor solution in an environment with a temperature of 22°C for 5 hours for later use. The concentration of the precursor solution is 0.5mol/L, isopropanol, ethylene glycol The volume ratio of alcohol methyl ether is 4:3.

Subsequent (2) preparation of the seed layer material, (3) preparation of the thin film material, and (4) annealing process are the same as in Example 6.

Although the present invention has been described in detail in conjunction with preferred embodiments with reference to the accompanying drawings, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, those skilled in the art can make various equivalent modifications or replacements to the embodiments of the present invention, and these modifications or replacements should be within the scope of the present invention/any Those skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention, and all should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (8)

1. A composite KTN film is characterized by comprising a KTN film layer and a seed layer; the molecular formula of the KTN film layer material is K _1+Z Ta _1-X-Y Nb _Y M _X O ₃ The proportion of each element is K, nb, M, O= (1+Z): (1-X-Y), Y, X and 3, and the M element is Fe;

the seed layer is lanthanum-doped bismuth ferrite film Bi _1-n+m LanFeO ₃ Namely, the proportion of each element is Bi, la, fe, O=1-n+m, n is 1:3;

wherein X is molar equivalent of M element, X is more than or equal to 0.06 and less than or equal to 0.10, Y is molar equivalent of Nb element, Y is more than or equal to 0.48 and less than or equal to 0.66, element K is excessively added, and Z is 8% -10%; wherein n is the molar equivalent of La element, n is more than or equal to 0.05 and less than or equal to 0.15, and when n is more than or equal to 0.05 and less than or equal to 0.10, m is more than or equal to 0.05 and less than or equal to 0.08; when n is more than 0.10 and less than or equal to 0.15, m is more than or equal to 0.02 and less than 0.05.

2. The composite KTN film according to claim 1, wherein the KTN film layer comprises N film sublayers, and N is more than or equal to 8 and less than or equal to 17; when N is more than or equal to 8 and less than or equal to 12, the number of layers of the seed layer is 2; when N is more than or equal to 13 and less than or equal to 17, the number of seed layers is 3.

3. The composite KTN film according to claim 1, wherein the potassium source, the tantalum source and the niobium source are potassium carbonate, tantalum oxide and niobium oxide, respectively; lanthanum source, bismuth source and iron source are lanthanum nitrate, bismuth nitrate and ferric nitrate respectively.

4. A method of making the composite KTN film of any of claims 1-3, characterized by: the method comprises the following steps:

(1) Preparing a precursor solution:

1.1 preparation of a potassium tantalate niobate-based precursor solution: the preparation method comprises the steps of adopting a sol-gel method, weighing potassium carbonate, tantalum oxide, niobium oxide and ferric nitrate according to stoichiometric ratio, dissolving in isopropanol, obtaining a mixed solution A after complete dissolution, stirring the mixed solution A, adding ethanol into the mixed solution A to prepare a precursor solution, and standing the prepared precursor solution for later use;

1.2 preparation of a bismuth ferrite-based precursor solution for a seed layer: weighing bismuth nitrate and ferric nitrate according to a stoichiometric ratio by adopting a sol-gel method, dissolving the bismuth nitrate and the ferric nitrate in isopropanol, sequentially adding lanthanum nitrate after the bismuth nitrate and the ferric nitrate are completely dissolved to obtain a mixed solution A, stirring the mixed solution A, adding ethylene glycol methyl ether into the mixed solution A to prepare a precursor solution, and standing the prepared precursor solution for later use;

(2) Preparation of seed layer material: depositing a seed layer precursor solution on an ITO/glass substrate material by a spin coating method by adopting a layer-by-layer annealing process, then placing the material on a hot plate for drying, and placing the dried film in a rapid annealing furnace for two-stage annealing treatment; then depositing other layer materials on the respective lower layer materials according to the same method, and repeating the spin coating and annealing steps for a plurality of times until the seed layer number meets the requirement;

(3) Preparation of a film material: depositing a potassium tantalate niobate-based precursor solution on a seed layer material by adopting a layer-by-layer annealing process by using a spin coating method, then placing the material on a hot plate for drying, and placing the dried film in a rapid annealing furnace for two-stage annealing treatment; then depositing other layer materials on the respective lower layer materials according to the same method, and repeating the spin coating and annealing steps for a plurality of times until the thickness of the film meets the requirement;

(4) Annealing the film with the thickness required in the step (3) for 4min at the temperature of 575-600 ℃ to obtain the lanthanum and iron co-doped composite potassium tantalate niobate film.

5. The method for preparing a composite KTN film according to claim 4, wherein: the drying temperature in the step (2) is 155-180 ℃ and the drying time is 100-120 s;

the two-stage annealing treatment process in the step (2) is 245-285 ℃,50-80s,485-535 ℃ and 60-90s; spin coating glue homogenizing speed in the step (2) is 3700-3900rpm, and time is 20-40s;

the drying temperature in the step (3) is 165-205 ℃ and the drying time is 50-80 s;

the two-stage annealing treatment process in the step (3) is 295-315 ℃,90-120s,555-585 ℃ and 180-220s;

spin coating of spin coating glue in step (3) the speed is 4500-5000rpm, the time is 25-35s.

6. The method for preparing a composite KTN film according to claim 5, wherein: the drying temperature in the step (2) is 162 ℃, and the drying time is 110s;

the two-stage annealing treatment process in the step (2) is carried out at 268 ℃,75s,515 ℃ and 75s;

spin coating glue homogenizing speed in the step (2) is 3700-3900rpm, and time is 20-40s;

the drying temperature in the step (3) is 178 ℃, and the drying time is 65s;

the two-stage annealing treatment process in the step (3) is 305 ℃,105s,568 ℃ and 195s.

7. The method for preparing a composite KTN film according to claim 4, wherein: the concentration of the potassium tantalate niobate-based precursor solution in the step (1) is 0.39 mol/L-0.45 mol/L, and the volume ratio of isopropanol to ethanol is 6:5; the concentration of the bismuth ferrite-based precursor solution of the seed layer is 0.43 mol/L-0.5 mol/L, and the volume ratio of isopropanol to ethylene glycol methyl ether is 4:3.

8. The method for preparing a composite KTN film according to claim 4, wherein: the method comprises the following steps:

(1) Preparing a precursor solution:

1.1 preparation of a potassium tantalate niobate-based precursor solution: the preparation method comprises the steps of adopting a sol-gel method, weighing potassium carbonate, tantalum oxide, niobium oxide and ferric nitrate according to stoichiometric ratio, dissolving the potassium carbonate, the tantalum oxide, the niobium oxide and the ferric nitrate in isopropanol, obtaining a mixed solution A after complete dissolution, stirring the mixed solution A for 40min, adding ethanol into the mixed solution A to prepare a precursor solution, standing the prepared precursor solution in an environment with the temperature of 19-22 ℃ for 6-8h for standby, wherein the concentration of the precursor solution is 0.39-0.45 mol/L, and the volume ratio of the isopropanol to the ethanol is 6:5;

1.2 preparation of a bismuth ferrite-based precursor solution for a seed layer: dissolving bismuth nitrate and ferric nitrate in isopropanol according to a stoichiometric ratio, sequentially adding lanthanum nitrate after complete dissolution to obtain a mixed solution A, stirring the mixed solution A for 20min, adding ethylene glycol methyl ether into the mixed solution A to prepare a precursor solution, standing the prepared precursor solution in an environment with the temperature of 19-22 ℃ for 5h for standby, wherein the concentration of the precursor solution is 0.43-0.5 mol/L, and the volume ratio of the isopropanol to the ethylene glycol methyl ether is 4:3;

(2) Preparation of seed layer material: depositing a seed layer precursor solution on an ITO/glass substrate material by adopting a layer-by-layer annealing process by using a spin coating method, wherein the spin coating speed is 3700-3900rpm, and the spin coating time is 20-40s; then placing the material on a hot plate to be dried at 155-180 ℃ for 100-120 s; placing the dried film in a rapid annealing furnace for two-stage annealing treatment, wherein the two-stage annealing treatment process is 245-285 ℃,50-80s,485-535 ℃ and 60-90s; then depositing other layer materials on the respective lower layer materials according to the same method, and repeating the spin coating and annealing steps for a plurality of times until the seed layer number meets the requirement;

(3) Preparation of a film material: adopting a layer-by-layer annealing process, depositing a potassium tantalate niobate-based precursor solution on a seed layer material by a spin coating method, and then placing the material on a hot plate for drying at 165-205 ℃ for 50-80 s; placing the dried film in a rapid annealing furnace for two-stage annealing treatment, wherein the two-stage annealing treatment process is 295-315 ℃,90-120s,555-585 ℃ and 180-220s; then depositing other layer materials on the respective lower layer materials according to the same method, and repeating the spin coating and annealing steps for a plurality of times until the thickness of the film meets the requirement;

(4) Annealing the film with the thickness required in the step (3) for 4min at the temperature of 575-600 ℃ to obtain the lanthanum and iron co-doped potassium tantalate niobate film.