A composite medium for cable insulation material and a method for producing the same

Abstract

The application discloses a kind of composite medium for cable insulation material and its preparation method, the composite medium includes gradient layer, interface passivation layer and substrate connected in order from top to bottom;The gradient layer is a gradient layer, the interface passivation layer is an aluminum oxide layer, and the substrate is a high dielectric constant ceramic layer.The composite medium composed of substrate, interface passivation layer and gradient layer effectively solves the problems of high temperature sensitivity of dielectric constant, interface defect induced leakage and insufficient breakdown field strength of composite medium, avoids the insulation failure of cable insulation material, the substrate provides thermal stability support for the composite medium, suppresses thermal expansion mismatch, the interface passivation layer blocks oxygen vacancy migration, reduces the leakage current of the composite medium, and the gradient layer reduces the dielectric constant wide temperature fluctuation rate of the composite medium, improves the breakdown field strength, and avoids the insulation failure of cable insulation material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite medium preparation, and particularly relates to a composite medium for cable insulation material and a preparation method thereof. BACKGROUND

[0002] Composite medium plays an increasingly important role in the field of cable insulation material, which aims to improve insulation performance, heat resistance and mechanical strength by combining the characteristics of multiple materials. Composite medium is usually composed of polymers, ceramics and other functional materials, which can not only meet the electrical insulation requirements, but also provide superior physical and chemical stability. As a cable insulation material, composite medium can significantly improve its dielectric properties and enhance its reliability and durability under harsh conditions.

[0003] The existing composite medium has the problems of high temperature sensitivity of dielectric constant, interface defect induced leakage and insufficient breakdown field strength when used for cable insulation material, resulting in insulation failure of the cable insulation material. For example, due to the single thermal expansion coefficient of the composite medium composition material, the dielectric constant fluctuates dramatically in a wide temperature range, and the lattice mismatch at high temperature induces interface micro-cracks, which aggravates oxygen vacancy migration and forms a leakage channel. The disordered domain structure and interface defects of the composite medium lead to uneven electric field distribution, and the local electric field concentration significantly reduces the breakdown strength. At the same time, space charges accumulate at the grain boundaries, further amplifying the high-frequency attenuation of the dielectric constant. The above problems lead to interface defects induced by temperature fluctuations in the composite medium, which aggravate leakage and electric field distortion, ultimately resulting in insulation failure of the cable insulation material.

[0004] Therefore, the present application provides a composite medium for cable insulation material and a preparation method thereof to solve the above-mentioned problems of high temperature sensitivity of dielectric constant, interface defect induced leakage and insufficient breakdown field strength of the composite medium, resulting in insulation failure of the cable insulation material. SUMMARY

[0005] The purpose of the present application is to provide a composite medium for cable insulation material and a preparation method thereof to solve the problems of high temperature sensitivity of dielectric constant, interface defect induced leakage and insufficient breakdown field strength of the composite medium, resulting in insulation failure of the cable insulation material.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] A composite medium for cable insulation material, the composite medium comprising a gradient layer, an interface passivation layer and a substrate connected in order from top to bottom; the gradient layer is a gradient layer, the interface passivation layer is an aluminum oxide layer, and the substrate is a high dielectric constant ceramic layer.

[0008] The substrate is any one of aluminum oxide, hafnium dioxide and strontium titanate.

[0009] A preparation method of a composite medium for cable insulation material, applied to the composite medium as described above, the preparation method comprising:

[0010] Step S1, pretreating the substrate to obtain a substrate with a dense polycrystalline structure and a surface roughness of ≤1 nm;

[0011] Step S2, forming a passivation layer on the substrate surface by a plasma-enhanced atomic layer deposition device, and then chemically modifying the passivation layer using a modification solution to form an interface passivation layer on the substrate surface;

[0012] Step S3, alternately depositing a plurality of preliminary layers on the interface passivation layer, and then performing pulse electric field induction treatment to obtain a gradient layer;

[0013] Step S4, preparing a first solution and a second solution, and then treating the gradient layer in the first solution and the second solution to obtain a composite medium.

[0014] Sintering the substrate at 1280-1320℃ for 1.5-3.5h to make the substrate have a dense polycrystalline structure, and the grain size of the dense polycrystalline structure is 50-100nm.

[0015] The step S2 specifically comprises:

[0016] Step S21, using TMA pulse and O2 plasma pulse to treat the substrate surface by an alternating pulse mode through a plasma-enhanced atomic layer deposition device, and performing first nitrogen gas blowing on the substrate surface during the alternating pulse process;

[0017] Step S22, immersing the passivation layer on the substrate in a modification solution, and performing second nitrogen gas blowing on the passivation layer after the immersion is completed.

[0018] In the step S21, the plasma power is 50-100W, the TMA pulse time is 0.1-0.3s, the O2 plasma pulse time is 0.1-0.3s, the nitrogen gas blowing time is 3-5s, the number of alternating pulses is 80-100, the temperature is 100-110℃, and the thickness of the passivation layer is 4-6nm;

[0019] In the step S22, the modification solution comprises a solvent and a solute, the volume ratio of the solvent to the solute in the modification solution is 100: (1-2), the immersion time is 20-30min, the second nitrogen gas blowing time is 4.5-6min, the flow rate is 4.5-6L / min, and the angle is 45-60°.

[0020] The solvent is ethanol, and the solute is APTES.

[0021] The step S3 specifically comprises:

[0022] The step S31, first, a ferroelectric layer is formed on the interface passivation layer by a radio frequency magnetron sputtering system, then a paraelectric layer is formed on the ferroelectric layer by a spin coater, and the paraelectric layer is annealed to obtain a preliminary layer.

[0023] After the substrate is placed in the radio frequency magnetron sputtering system, the temperature is raised to 280-300℃, and vacuum is extracted to 5×10 - 4 Pa, then Ar / O2 mixed gas is introduced to 0.5Pa, the power is adjusted to 130-150W, the ferroelectric layer is deposited on the interface passivation layer, then the paraelectric layer is coated on the ferroelectric layer by a spin coater at 2800-3000rpm for 30-35s, the paraelectric layer is baked at 150-170℃ for 7-10min after coating, and the paraelectric layer is annealed at 380-450℃ for 1.5-2.5h after baking, so that the paraelectric layer is formed on the ferroelectric layer to obtain a preliminary layer.

[0024] The step S32, a plurality of preliminary layers with gradually decreasing thickness are formed on the interface passivation layer by repeating the step S31, and the thickness of the ferroelectric layer in the preliminary layer is gradually decreased and the thickness of the paraelectric layer in the preliminary layer is gradually increased in the repeated step S31.

[0025] The step S33, the substrate is placed on the pulse electric field device, and the gradient layer is located between the two poles of the pulse electric field device, then nitrogen is introduced to raise the temperature to 50-80℃, and a pulse electric field of 300-400kV / cm is applied for 30-40min.

[0026] In the step S31, the ferroelectric layer is a barium strontium titanate ceramic target layer, and the paraelectric layer is a precursor solution layer, the solvent of the precursor solution is ethylene glycol methyl ether, and the solute is tetrabutyl titanate and strontium acetate, and the molar ratio of tetrabutyl titanate to strontium acetate is (1-2):(1-2).

[0027] The step S4 specifically comprises:

[0028] The step S41, a first solution is obtained by mixing lanthanum nitrate solution and citric acid at 500-600rpm for 30-35min.

[0029] The step S42, a second solution is obtained by ultrasonic dispersion of manganese acetate, ethylene glycol methyl ether and antioxidant at a frequency of 40-60kHz and a power of 80-100W for 10-15min.

[0030] Step S43, immerse the gradient layer into the first solution for 10-14 minutes, apply ultrasonic to the solution with a frequency of 40-60 kHz and a power of 100-120 W for 10-16 minutes, and then dry at a temperature of 80-100 DEG C, and after drying, oxidize annealing at a temperature of 500-600 DEG C for 1.5-2.5 h;

[0031] Step S44, spin the second solution on the gradient layer treated in step S43 at 2500-3000 rpm for 30-40 s, and then dry at a temperature of 100-120 DEG C, and after drying, reduce annealing at a temperature of 450-500 DEG C for 4-5 h.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] 1、The composite medium for cable insulation material and the preparation method thereof, by the composite medium composed of the substrate, the interface passivation layer and the gradient layer, effectively solve the problems of high temperature sensitivity of dielectric constant, interface defect induced leakage and insufficient breakdown field strength of the composite medium, avoid the insulation failure of the cable insulation material, the substrate provides thermal stability support for the composite medium, suppresses thermal expansion mismatch, the interface passivation layer blocks oxygen vacancy migration, reduces the leakage current of the composite medium, and the gradient layer reduces the dielectric constant wide temperature fluctuation rate of the composite medium, improves the breakdown field strength, and thus the use effect of the cable insulation material is improved, and the insulation failure of the cable insulation material is avoided.

[0034] 2、The composite medium for cable insulation material and the preparation method thereof, by the gradient layer, the interface passivation layer and the substrate, significantly improve the dielectric performance, the structure of the gradient layer optimizes the thermal expansion matching of the material, reduces the influence of temperature change on the dielectric constant, ensures the stability under high temperature condition, in addition, the interface passivation layer effectively suppresses the migration of oxygen vacancy, significantly reduces the leakage current, and further improves the insulation characteristics.

[0035] 3、The composite medium for cable insulation material and the preparation method thereof, by the interface passivation layer obtained by chemical modification, the combination between the substrate and the gradient layer is more close, not only improves the mechanical strength of the material, but also effectively reduces the interface defect, avoids the material failure caused by the interface problem, the uniform surface and high activity of the interface passivation layer provide a good foundation for the deposition of the subsequent layer, so as to ensure the overall performance of the composite material, and further improve the performance of the cable insulation material. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0037] The structures, proportions, sizes, etc. shown in the drawings of the present specification are only used to cooperate with the content disclosed in the present specification, so that those skilled in the art can understand and read, and are not used to limit the conditions that the present application can be implemented, so they do not have technical significance. Any modification of structure, change of proportion relationship or adjustment of size, without affecting the effect and purpose that the present application can produce, should still fall within the scope of the technical content disclosed by the present application.

[0038] Figure 1 The flowchart of the preparation method of the composite medium in the present application. DETAILED DESCRIPTION

[0039] In order to make the purposes, features and advantages of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings of the embodiments of the present application. Obviously, the embodiments described below are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0040] In the description of the present application, it should be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation of the present application. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there can be a component disposed therebetween.

[0041] Embodiment 1:

[0042] The composite medium for cable insulation material in this embodiment comprises a gradient layer, an interface passivation layer and a substrate connected in turn from top to bottom. The gradient layer is a gradient layer, the interface passivation layer is an aluminum oxide layer, and the substrate is a high dielectric constant ceramic layer.

[0043] Specifically, the substrate is any one of aluminum oxide, hafnium dioxide and strontium titanate; the gradient layer is a plurality of alternating ferroelectric layers and paraelectric layers.

[0044] It should be noted that the composite medium forms a structure with continuous component transition by introducing the gradient layer, the interface passivation layer and the substrate, can effectively match the thermal expansion coefficient, reduce the interlayer stress, relieve the internal stress of the cable insulation material composed of the composite medium under temperature change, thereby reducing the volatility of the dielectric constant with temperature change; the substrate is selected from a high dielectric constant ceramic material, which can still provide stable mechanical support and thermal stability in a high temperature environment, ensuring that the overall performance of the composite medium is not affected by high temperature, thereby avoiding the influence of high temperature on the cable insulation material, in addition, the existence of the interface passivation layer helps to inhibit the migration of oxygen vacancies and reduce the risk of dielectric failure that may be caused at high temperature, at the same time, the interface passivation layer and the gradient layer can effectively reduce the interface defect and oxygen vacancy concentration, thereby reducing the leakage current and significantly improving the insulation performance of the cable insulation material, and the gradient structure in the gradient layer forms an ordered nanodomain structure by the alternating deposition of the ferroelectric layer and the paraelectric layer, which can effectively block the electric field from concentrating on a certain point and reduce the risk of breakdown, further enhancing the breakdown field strength.

[0045] Embodiment 2:

[0046] Please refer to Figure 1 The preparation method of the composite medium for cable insulation material in the embodiment is applied to the composite medium as in embodiment 1, and the preparation method comprises the following steps:

[0047] Step S1, pretreating the substrate to obtain a substrate with a dense polycrystalline structure and a surface roughness of ≤1 nm;

[0048] It should be noted that the substrate is a high dielectric constant ceramic, which can provide suitable mechanical support and thermal stability as a substrate, and provide a reliable physical and chemical basis for the subsequent interface passivation layer and gradient layer.

[0049] The substrate is sintered at 1280-1320℃ for 1.5-3.5h to make the substrate have a dense polycrystalline structure, and the grain size of the dense polycrystalline structure is 50-100nm.

[0050] Preferably, the substrate is sintered at 1300℃ for 2h to make the substrate have a dense polycrystalline structure, and the grain size of the dense polycrystalline structure is 50-100nm.

[0051] It is emphasized that the density of the substrate after sintering is ≥98%, and the porosity is ≤1%. The sintering can reduce the dielectric loss and mechanical weakness caused by the internal porosity of the substrate. In addition, the chemical mechanical polishing of the substrate can make the surface roughness of the substrate ≤1 nm, which can avoid interface defects in subsequent processing. The sintering and polishing of the substrate can ensure the density and flatness of the substrate, thereby improving the quality of the interface passivation layer in subsequent forming and avoiding cracks or interface peeling caused by substrate defects in subsequent deposition process.

[0052] It can be understood that the chemical mechanical polishing step is well known to those skilled in the art, and will not be described in this embodiment.

[0053] In step S2, the surface of the substrate is treated by a plasma-enhanced atomic layer deposition device to form a passivation layer, and a modification solution is used to chemically modify the passivation layer to form an interface passivation layer on the surface of the substrate.

[0054] It should be noted that the interface passivation layer formed on the substrate can inhibit oxygen vacancy migration and enhance the interface bonding strength.

[0055] Step S2 specifically includes:

[0056] In step S21, the plasma-enhanced atomic layer deposition device uses TMA (trimethylaluminum) pulses and O2 plasma pulses to treat the surface of the substrate in an alternating pulse mode, and the surface of the substrate is first purged with nitrogen during the alternating pulse process.

[0057] In step S21, the plasma power is 50-100 W, the TMA pulse time is 0.1-0.3 s, the O2 plasma pulse time is 0.1-0.3 s, the nitrogen purging time is 3-5 s, the number of alternating pulses is 80-100, the temperature is 100-110°C, and the passivation layer thickness is 4-6 nm.

[0058] Preferably, in step S21, the plasma power is 50-100 W, the TMA pulse time is 0.1 s, the O2 plasma pulse time is 0.1 s, the nitrogen purging time is 3 s, the number of alternating pulses is 80, the temperature is 100°C, and the passivation layer thickness is 4 nm.

[0059] It should be noted that after sintering, the surface of the substrate adsorbs water molecules, and hydroxyl groups are formed by physical and chemical adsorption. After the TMA pulse on the surface of the substrate, the hydroxyl groups on the surface of the substrate react to form Al-CH3 * (aluminum methyl) intermediate state, and then under the action of active oxygen species generated by O2 plasma pulse, Al-CH3 * (aluminum methyl) is oxidized to form an aluminum oxide film, and the passivation layer is formed by the aluminum oxide film.

[0060] It can be known that the microscopic defects on the surface of the substrate can be eliminated by the passivation layer, a uniform and high-activity hydroxylated surface is provided, and the interface compatibility is improved, thereby providing a good foundation for subsequent chemical modification.

[0061] In addition, the first nitrogen gas purge is performed during the alternating pulse process to clean the unreacted by-products during the alternating pulse process, so as to improve the quality of the formed passivation layer.

[0062] Step S22, soaking the passivation layer on the substrate into a modification solution, and performing a second nitrogen gas purge on the passivation layer after the soaking is completed.

[0063] In step S22, the modification solution includes a solvent and a solute, the volume ratio of the solvent to the solute in the modification solution is 100: (1-2), the soaking time is 20-30 min, the second nitrogen gas purge time is 4.5-6 min, the flow rate is 4.5-6 L / min, and the angle is 45-60°.

[0064] Preferably, in step S22, the modification solution includes a solvent and a solute, the volume ratio of the solvent to the solute in the modification solution is 100: (1-2), the soaking time is 30 min, the second nitrogen gas purge time is 5 min, the flow rate is 5 L / min, and the angle is 45°.

[0065] Specifically, the solvent is ethanol, and the solute is APTES (3-aminopropyl triethoxysilane).

[0066] It should be noted that after the passivation layer is soaked into the modification solution, the ethoxyl group in APTES is hydrolyzed into silanol, which is condensed with the hydroxyl group on the surface of Al2O3 to form a Si-O-Al covalent bond, and under the action of the second nitrogen gas purge, the unbound APTES molecules can be removed, so that the passivation layer forms a dense monolayer, thereby obtaining an interface passivation layer.

[0067] It can be known that by chemically modifying the passivation layer to modify and fill the micropores on the passivation layer, the oxygen vacancy concentration of the obtained interface passivation layer can be <1×10 16 cm -3 , thereby blocking the diffusion of the oxygen vacancies in the substrate to the gradient layer, reducing the oxygen vacancy migration rate, and reducing the electric field distortion.

[0068] Step S3, after alternately depositing a plurality of preliminary layers on the interface passivation layer, performing pulse electric field induced treatment to obtain a gradient layer;

[0069] It should be noted that the gradient layer matches the thermal expansion coefficient through the continuous component transition of the gradient structure, reduces the interlayer stress, and realizes the directional arrangement of the nanodomain under the action of the pulse electric field, forms a local conductive potential barrier, and suppresses the leakage current.

[0070] Step S3 specifically includes:

[0071] Step S31, first, a ferroelectric layer is formed by depositing on the interface passivation layer through a radio frequency magnetron sputtering system, then a paraelectric layer is formed by spin coating a paraelectric on the ferroelectric layer through a spin coater and annealing the paraelectric, to obtain a preliminary layer;

[0072] After placing the substrate in the radio frequency magnetron sputtering system, the temperature is raised to 280-300℃, and vacuumed to 5x10 - 4 Pa, then Ar / O2 mixed gas is introduced to 0.5Pa, and the power is adjusted to 130-150W, then the ferroelectric is deposited on the interface passivation layer to form a ferroelectric layer, then the paraelectric is coated on the ferroelectric layer by spin coating at 2800-3000rpm for 30-35s through a spin coater, after coating is completed, the paraelectric is baked at a temperature of 150-170℃ for 7-10min, after baking is completed, annealing is performed at a temperature of 380-450℃ for 1.5-2.5h, so that a paraelectric layer is formed on the ferroelectric layer, to obtain a preliminary layer;

[0073] Preferably, after placing the substrate in the radio frequency magnetron sputtering system, the temperature is raised to 300℃, and vacuumed to 5x10 -4 Pa, then Ar / O2 mixed gas is introduced to 0.5Pa, and the power is adjusted to 130-150W, then the ferroelectric is deposited on the interface passivation layer to form a ferroelectric layer, then the paraelectric is coated on the ferroelectric layer by spin coating at 2800-3000rpm for 30-35s through a spin coater, after coating is completed, the paraelectric is baked at a temperature of 150-170℃ for 7-10min, after baking is completed, annealing is performed at a temperature of 380-450℃ for 1.5-2.5h, so that a paraelectric layer is formed on the ferroelectric layer, to obtain a preliminary layer.

[0074] It is emphasized that the sputtering ion energy of the radio frequency magnetron sputtering system is high, the ferroelectric deposited is a non-porous film with high density, reducing oxygen vacancy defects, and the paraelectric layer can also promote the diffusion of interface atoms through annealing, reducing stress, thereby improving the quality of the gradient layer obtained.

[0075] In addition, after the precursor solution is annealed to form the paraelectric layer, the paraelectric layer will shrink, and the surface will affect the micropores.

[0076] In step S31, the ferroelectric layer is a barium strontium titanate ceramic target layer, the paraelectric is a precursor solution layer, the solvent of the precursor solution is ethylene glycol methyl ether, and the solute is tetrabutyl titanate and strontium acetate, and the molar ratio of tetrabutyl titanate to strontium acetate is (1-2):(1-2); preferably, the molar ratio of tetrabutyl titanate to strontium acetate is 1:1.

[0077] It should be noted that the barium strontium titanate ceramic target layer in the ferroelectric layer provides high capacitance density as a relaxor ferroelectric, and the strontium acetate in the paraelectric layer has the advantage of inhibiting high-frequency loss after forming a composition gradient layer, so that the ferroelectric layer provides high dielectric response to the gradient layer, and the paraelectric layer suppresses leakage and loss.

[0078] Step S32, repeat step S31 to form several preliminary layers with gradually decreasing thickness on the interface passivation layer, and gradually decrease the thickness of the ferroelectric layer in the preliminary layer and gradually increase the thickness of the paraelectric layer in the preliminary layer in the repeated step S31.

[0079] It should be noted that the thermal expansion coefficients of the ferroelectric layer and the paraelectric layer are gradually matched to reduce thermal stress cracks and form a thermal expansion transition, and at the same time, the effective dielectric temperature range is widened at the Curie temperature of the ferroelectric layer and the combination of the paraelectric layer.

[0080] Specifically, the number of preliminary layers is four, and the thickness of the four preliminary layers from bottom to top is 50nm, 40nm, 30nm and 20nm respectively; the thickness ratio of the ferroelectric layer to the paraelectric layer in the four preliminary layers from bottom to top is 8:2, 6:4, 4:6 and 2:8 respectively.

[0081] Step S33, place the substrate on the pulse electric field device, and place the gradient layer between the two poles of the pulse electric field device, then pass nitrogen to warm up to 50-80℃, apply a pulse electric field of 300-400kV / cm, and continue for 30-40 minutes.

[0082] Preferably, step S33, place the substrate on the pulse electric field device, and place the gradient layer between the two poles of the pulse electric field device, then pass nitrogen to warm up to 60℃, apply a pulse electric field of 350kV / cm, and continue for 30 minutes.

[0083] It should be noted that the electric field direction of the pulse electric field is perpendicular to the layer plane of the gradient layer, and after the pulse electric field is applied, the ferroelectric domains in the ferroelectric layer of the gradient layer are arranged along the electric field direction under the driving of the pulse electric field, forming an ordered nanodomain structure to optimize the dielectric response and breakdown strength.

[0084] It can be known that the ferroelectric layer is dynamically rearranged under the action of the pulse electric field, the pulse electric field provides sufficient energy to make the domain wall of the ferroelectric layer overcome the potential barrier and be arranged in order along the direction of the electric field, and in the paraelectric layer, the nanodomain of the ferroelectric layer forms a conductive potential barrier to block the leakage path; under the action of the pulse electric field, the nanodomain structure in the ferroelectric layer is optimally arranged, the domain wall density is improved, and the ordered domain wall disperses the electric field stress, so that the breakdown field strength is enhanced, the problem of easy breakdown caused by the concentration of electric field due to disordered domain wall is solved, in addition, the formed conductive potential barrier also blocks the carrier migration, reduces the leakage current, increases the tortuosity of the carrier migration path, improves the resistivity, and the oxygen vacancy concentration is reduced to reduce the ion conduction channel, and the problem of increasing energy consumption caused by the formation of conductive path due to disordered domain wall is solved.

[0085] Step S4, preparing the first solution and the second solution, placing the gradient layer in the first solution for treatment and then in the second solution for treatment to obtain the composite medium.

[0086] Step S41, mixing the lanthanum nitrate solution and citric acid at 500-600 rpm for 30-35 min to obtain the first solution;

[0087] Step S42, ultrasonic dispersing the manganese acetate, ethylene glycol methyl ether and the antioxidant at a frequency of 40-60 kHz and a power of 80-100 W for 10-15 minutes to obtain the second solution;

[0088] Step S43, immersing the gradient layer in the first solution for 10-14 min, applying ultrasonic waves with a frequency of 40-60 kHz and a power of 100-120 W to the solution for 10-16 min, and then drying at a temperature of 80-100°C, and after drying, reducing annealing at a temperature of 450-500°C for 4-5 h;

[0089] Step S44, spin coating the second solution on the gradient layer treated in step S43 at 2500-3000 rpm for 30-40 s, and then drying at a temperature of 100-120°C, and after drying, reducing annealing at a temperature of 450-500°C for 4-5 h.

[0090] Preferably, step S4 specifically comprises:

[0091] Step S41, mixing the lanthanum nitrate solution and citric acid at 500 rpm for 30 min to obtain the first solution;

[0092] Step S42, ultrasonic dispersing the manganese acetate, ethylene glycol methyl ether and the antioxidant at a frequency of 40 kHz and a power of 100 W for 10 minutes to obtain the second solution;

[0093] Step S43, immerse the gradient layer into the first solution for 10 min, and apply ultrasonic to the solution with a frequency of 40 kHz and a power of 100 W for 10 min, and then dry at a temperature of 80℃, and after drying, oxidize annealing at a temperature of 600℃ for 2 h;

[0094] Step S44, spin the second solution on the gradient layer treated in step S43 at 3000 rpm for 30 s, and then dry at a temperature of 120℃, and after drying, reduce annealing at a temperature of 450℃ for 5 h.

[0095] It should be noted that after the oxidation annealing, the lanthanum ions in the first solution will replace the barium ion or strontium ion sites in the gradient layer by repairing oxygen vacancies, and after the reduction annealing, the manganese ions in the second solution will replace the titanium ion sites in the gradient layer, and under the action of lanthanum ions and manganese ions, the leakage current can be further reduced, the space charge density is reduced, and the breakdown field strength is further improved.

[0096] Specifically, the lanthanum ions compensate for oxygen vacancies, which can block the ion conduction path, and the manganese ions form deep level traps to inhibit electron hopping conduction.

[0097] It should also be emphasized that citric acid in the first solution is conducive to stabilizing lanthanum ions to ensure that lanthanum ions can effectively replace barium ion or strontium ion sites, and ethylene glycol monomethyl ether in the second solution has low surface tension, which is conducive to the penetration of the second solution into the pores of the gradient layer.

[0098] In summary, the composite dielectric composed of a substrate, an interface passivation layer and a gradient layer prepared by the above preparation method effectively solves the problems of high temperature sensitivity of dielectric constant, interface defects causing leakage and insufficient breakdown field strength of the composite dielectric, avoids the insulation failure of the cable insulation material, provides thermal stability support for the substrate of the composite dielectric, suppresses thermal expansion mismatch, the interface passivation layer blocks the migration of oxygen vacancies, reduces the leakage current of the composite dielectric, and the gradient layer reduces the dielectric constant wide temperature fluctuation rate of the composite dielectric, improves the breakdown field strength, thereby improving the use effect of the cable insulation material, and avoiding the insulation failure of the cable insulation material.

[0099] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A composite dielectric for cable insulation materials, characterized in that, The composite medium comprises a gradient layer, an interface passivation layer, and a substrate connected sequentially from top to bottom; the gradient layer is a gradient layer, the interface passivation layer is an alumina layer, and the substrate is any one of an alumina layer, a hafnium dioxide layer, and a strontium titanate layer; the gradient layer consists of several alternating ferroelectric layers and paraelectric layers; wherein the thickness of several ferroelectric layers decreases sequentially, and the thickness of several paraelectric layers increases sequentially, and the ferroelectric layers and paraelectric layers are treated with pulsed electric field induction; the ferroelectric layer is a barium strontium titanate ceramic target layer, and the paraelectric layer is a precursor solution layer; the solvent of the precursor solution is ethylene glycol methyl ether, and the solutes are tetrabutyl titanate and strontium acetate.

2. A method for preparing a composite dielectric for cable insulation materials, characterized in that, The method for preparing the composite dielectric used in cable insulation materials as described in claim 1 includes: Step S1: Pre-treat the substrate to obtain a substrate with a dense polycrystalline structure and a surface roughness ≤1nm; Step S2: The substrate surface is treated with plasma-enhanced atomic layer deposition equipment to form a passivation layer, and then the passivation layer is chemically modified with a modification solution to form an interface passivation layer on the substrate surface. Step S3: After alternatingly depositing several preliminary layers on the interface passivation layer, a gradient layer is obtained by pulsed electric field induction treatment. Step S4: Prepare a first solution and a second solution. Place the gradient layer in the first solution for treatment and then in the second solution for treatment to obtain a composite medium.

3. The method for preparing the composite dielectric for cable insulation materials according to claim 2, characterized in that, The substrate is sintered at 1280-1320℃ for 1.5-3.5 hours to give the substrate a dense polycrystalline structure with a grain size of 50-100 nm.

4. The method for preparing the composite dielectric for cable insulation materials according to claim 2, characterized in that, Step S2 specifically includes: Step S21: The plasma-enhanced atomic layer deposition equipment uses TMA pulses and O2 plasma pulses in an alternating pulse mode to treat the substrate surface, and performs a first nitrogen purging on the substrate surface during the alternating pulse process; Step S22: Immerse the passivation layer on the substrate in the modification solution, and perform a second nitrogen purging on the passivation layer after immersion.

5. The method for preparing a composite dielectric for cable insulation materials according to claim 4, characterized in that, In step S21, the plasma power is 50-100W, the TMA pulse time is 0.1-0.3s, the O2 plasma pulse time is 0.1-0.3s, the nitrogen purging time is 3-5s, the number of alternating pulses is 80-100 times, the temperature is 100-110℃, and the passivation layer thickness is 4-6nm. In step S22, the modified solution includes a solvent and a solute, the volume ratio of solvent to solute in the modified solution is 100:(1-2), the soaking time is 20-30 min, the second nitrogen purging time is 4.5-6 min, the flow rate is 4.5-6 L / min, and the angle is 45-60°.

6. The method for preparing a composite dielectric for cable insulation materials according to claim 5, characterized in that, The solvent is ethanol, and the solute is APTES.

7. The method for preparing a composite dielectric for cable insulation materials according to claim 2, characterized in that, Step S3 specifically includes: Step S31: First, a ferroelectric layer is deposited on the interface passivation layer using an RF magnetron sputtering system. Then, a paraelectric material is spin-coated onto the ferroelectric layer using a spin coater. After annealing the paraelectric material, a paraelectric layer is formed to obtain a preliminary layer. After placing the substrate in the RF magnetron sputtering system, the temperature is raised to 280-300℃, and a vacuum of 5×10⁻⁶ is applied. -4 Pa, then Ar / O2 mixed gas is introduced to 0.5 Pa, and the power is adjusted to 130-150W to deposit ferroelectric material on the interface passivation layer to form a ferroelectric layer. Then, paraelectric material is coated on the ferroelectric layer by spin coating at 2800-3000 rpm for 30-35s. After coating, the paraelectric material is dried at 150-170℃ for 7-10min. After drying, it is annealed at 380-450℃ for 1.5-2.5h to form a paraelectric layer on the ferroelectric layer to obtain the preliminary layer. Step S32: Repeat step S31 to form several preliminary layers with progressively decreasing thickness on the interface passivation layer, and in repeating step S31, progressively decrease the thickness of the ferroelectric layer in the preliminary layer and progressively increase the thickness of the paraelectric layer in the preliminary layer. Step S33: Place the substrate on the pulsed electric field device and position the gradient layer between the two poles of the pulsed electric field device. Then, introduce nitrogen gas to raise the temperature to 50-80℃ and apply a pulsed electric field of 300-400kV / cm for 30-40 minutes.

8. The method for preparing a composite dielectric for cable insulation materials according to claim 7, characterized in that, In step S31, the ferroelectric layer is a barium strontium titanate ceramic target layer, the paraelectric body is a precursor solution layer, the solvent of the precursor solution is ethylene glycol methyl ether, the solute is tetrabutyl titanate and strontium acetate, and the molar ratio of tetrabutyl titanate to strontium acetate is (1-2):(1-2).

9. The method for preparing a composite dielectric for cable insulation materials according to claim 2, characterized in that, Step S4 specifically includes: Step S41: Mix lanthanum nitrate solution and citric acid at 500-600 rpm for 30-35 min to obtain the first solution; Step S42: Disperse manganese acetate, ethylene glycol methyl ether and antioxidant using ultrasonication at a frequency of 40-60kHz and a power of 80-100W for 10-15 minutes to obtain the second solution; Step S43: Immerse the gradient layer in the first solution for 10-14 min, and apply ultrasound at a frequency of 40-60 kHz and a power of 100-120 W to the solution for 10-16 min, then dry it at a temperature of 80-100℃, and after drying, oxidize and anneal it at a temperature of 500-600℃ for 1.5-2.5 h. Step S44: Spin-coat the second solution onto the gradient layer treated in step S43 at 2500-3000 rpm for 30-40 seconds, then dry it at 100-120℃, and after drying, reduce and anneal it at 450-500℃ for 4-5 hours.

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