Composite medium for cable insulating material and preparation method thereof

Abstract

The invention discloses a composite medium for a cable insulating material and a preparation method of the composite medium. The composite medium comprises a gradient layer, an interface passivation layer and a substrate layer which are sequentially connected from top to bottom, the gradient layer is a gradient layer, the interface passivation layer is an aluminum oxide layer, and the substrate layer is a high dielectric constant ceramic layer. Through the composite medium composed of the substrate layer, the interface passivation layer and the gradient layer, the problems of high dielectric constant temperature sensitivity, leakage conductance caused by interface defects and insufficient breakdown field strength of the composite medium are effectively solved, the condition of insulation failure of a cable insulation material is avoided, the substrate layer provides thermal stability support for the composite medium, and the service life of the cable is prolonged. The interface passivation layer blocks oxygen vacancy migration, so that the leakage current of the composite medium is reduced, the gradient layer reduces the dielectric constant wide-temperature fluctuation rate of the composite medium, the breakdown field strength is improved, and the condition of insulation failure of a cable insulation material is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of composite medium preparation, and particularly to a composite medium for cable insulation materials and a preparation method thereof. Background Art

[0002] Composite media play an increasingly important role in the field of cable insulation materials. By combining the characteristics of multiple materials, they aim to improve insulation performance, heat resistance, and mechanical strength. Composite media are usually composed of polymers, ceramics, and other functional materials, which can provide more excellent physical and chemical stability while meeting the electrical insulation requirements. As cable insulation materials, composite media can not only significantly improve their dielectric properties but also enhance their reliability and durability under harsh conditions.

[0003] When existing composite media are used as cable insulation materials, there are problems such as high temperature sensitivity of the dielectric constant, leakage conduction caused by interface defects, and insufficient breakdown field strength, resulting in insulation failure of the cable insulation materials. For example, due to the single coefficient of thermal expansion of the constituent materials of the composite medium, the dielectric constant fluctuates violently in a wide temperature range. At high temperatures, lattice mismatch causes interface microcracks, which exacerbates the migration of oxygen vacancies and forms leakage conduction channels. The disordered domain structure and interface defects of the composite medium lead to uneven electric field distribution, and local electric field concentration significantly reduces the breakdown strength. At the same time, space charges accumulate at grain boundaries, further amplifying the high-frequency attenuation of the dielectric constant. The above problems result in interface defects induced by temperature fluctuations in the composite medium, and the interface defects exacerbate leakage conduction and electric field distortion, ultimately leading to insulation failure of the cable insulation materials.

[0004] Therefore, a composite medium for cable insulation materials and a preparation method thereof are proposed to solve the problems of high temperature sensitivity of the dielectric constant, leakage conduction caused by interface defects, and insufficient breakdown field strength in the composite medium, resulting in insulation failure of the cable insulation materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite medium for cable insulation materials and a preparation method thereof, to solve the problems of high temperature sensitivity of the dielectric constant, leakage conduction caused by interface defects, and insufficient breakdown field strength in the composite medium, resulting in insulation failure of the cable insulation materials.

[0006] To achieve this purpose, the present invention adopts the following technical solutions: A composite medium for cable insulation materials, the composite medium includes a gradient layer, an interface passivation layer, and a base layer connected in sequence from top to bottom; the gradient layer is a gradient layer, the interface passivation layer is an alumina layer, and the base layer is a high-dielectric-constant ceramic layer.

[0007] The base is any one of alumina, hafnium dioxide, and strontium titanate.

[0008] A preparation method of a composite medium for cable insulation materials, which is applied to the composite medium as described above. The preparation method includes: Step S1: Pretreat the substrate to obtain a substrate with a dense polycrystalline structure and a surface roughness ≤ 1 nm; Step S2: Treat the surface of the substrate through a plasma-enhanced atomic layer deposition device to form a passivation layer, and then chemically modify the passivation layer with a modification solution to form an interfacial passivation layer on the surface of the substrate; Step S3: After alternately depositing a number of preliminary layers on the interfacial passivation layer, perform pulse electric field induction treatment to obtain a gradient layer; 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 the composite medium.

[0009] Sinter the substrate at 1280 - 1320 °C for 1.5 - 3.5 h to make the substrate have a dense polycrystalline structure, and the grain size of the dense polycrystalline structure is 50 - 100 nm.

[0010] The specific steps of Step S2 include: Step S21: The plasma-enhanced atomic layer deposition device uses TMA pulses and O 2 plasma pulses to treat the surface of the substrate in an alternating pulse manner, and perform the first nitrogen purge on the surface of the substrate during the alternating pulse process; Step S22: Immerse the passivation layer on the substrate in the modification solution, and perform the second nitrogen purge on the passivation layer after the immersion is completed.

[0011] In Step S21, the plasma power is 50 - 100 W, the TMA pulse time is 0.1 - 0.3 s, and the O 2 plasma pulse time is 0.1 - 0.3 s, the nitrogen purge time is 3 - 5 s, the number of alternating pulses is 80 - 100 times, the temperature is 100 - 110 °C, and the thickness of the passivation layer is 4 - 6 nm; 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 immersion time is 20 - 30 min, the time of the second nitrogen purge is 4.5 - 6 min, the flow rate is 4.5 - 6 L / min, and the angle is 45 - 60 °.

[0012] The solvent is ethanol and the solute is APTES.

[0013] The specific steps of Step S3 include: Step S31: First, deposit a ferroelectric layer on the interface passivation layer through a radio frequency magnetron sputtering system. Then, spin-coat a paraelectric on the ferroelectric layer using a spin coater, and perform annealing treatment on the paraelectric to form a paraelectric layer, so as to obtain a preliminary layer; After placing the substrate in the radio frequency magnetron sputtering system, raise the temperature to 280 - 300 °C, and evacuate to 5×10 - 4 Pa, then introduce an Ar / O2 mixed gas to 0.5 Pa, adjust the power to 130 - 150 W, and deposit the ferroelectric on the interface passivation layer to form a ferroelectric layer. Then, spin-coat the paraelectric on the ferroelectric layer at 2800 - 3000 rpm for 30 - 35 s using a spin coater. After coating, dry the paraelectric at a temperature of 150 - 170 °C for 7 - 10 min. After drying, anneal at a temperature of 380 - 450 °C for 1.5 - 2.5 h to form a paraelectric layer on the ferroelectric layer, so as to obtain a preliminary layer; Step S32: Repeat Step S31 to form a number of 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 during the repeated Step S31; In Step S33: Place the substrate on the pulsed electric field device, and make the gradient layer located between the two poles of the pulsed electric field device. Then, introduce nitrogen and raise the temperature to 50 - 80 °C, apply a pulsed electric field of 300 - 400 kV / cm, and last for 30 - 40 minutes.

[0014] In Step S31, the ferroelectric layer is a barium strontium titanate ceramic target layer, and the paraelectric is a precursor solution layer. The solvent of the precursor solution is ethylene glycol monomethyl ether, and the solutes are tetrabutyl titanate and strontium acetate, and the molar ratio of tetrabutyl titanate to strontium acetate is (1 - 2):(1 - 2).

[0015] Step S4 specifically includes: Step S41: Mix the lanthanum nitrate solution and citric acid at 500 - 600 rpm for 30 - 35 min to obtain a first solution; Step S42: Ultrasonically disperse manganese acetate, ethylene glycol monomethyl ether and antioxidant at a frequency of 40 - 60 kHz and a power of 80 - 100 W for 10 - 15 minutes to obtain a second solution; Step S43: Immerse the gradient layer in the first solution for 10 - 14 min, apply ultrasound to the solution at a frequency of 40 - 60 kHz and a power of 100 - 120 W for 10 - 16 minutes, then dry at a temperature of 80 - 100 °C. After drying, perform oxidative annealing at a temperature of 500 - 600 °C for 1.5 - 2.5 h; Step S44: Spin-coat the second solution on the gradient layer processed in step S43 at 2500 - 3000 rpm for 30 - 40 s, then dry it at a temperature of 100 - 120 °C. After drying, perform reduction annealing at a temperature of 450 - 500 °C for 4 - 5 h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. For the composite dielectric for cable insulating materials and its preparation method of the present invention, through the composite dielectric composed of a base layer, an interface passivation layer, and a gradient layer, it effectively solves the problems of high temperature sensitivity of the dielectric constant, leakage conduction caused by interface defects, and insufficient breakdown field strength in the composite dielectric, avoiding the occurrence of insulation failure in cable insulating materials. The base layer provides thermal stability support for the composite dielectric, inhibits 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 wide-temperature volatility of the dielectric constant of the composite dielectric and improves the breakdown field strength, thereby improving the use effect of cable insulating materials and avoiding the occurrence of insulation failure in cable insulating materials.

[0017] 2. For the composite dielectric for cable insulating materials and its preparation method of the present invention, through the gradient layer, the interface passivation layer, and the base layer, the dielectric performance is significantly improved. The structure of the gradient layer optimizes the thermal expansion matching of the material, reduces the influence of temperature change on the dielectric constant, and ensures stability under high-temperature conditions. In addition, the interface passivation layer effectively inhibits the migration of oxygen vacancies, significantly reduces the leakage current, and further improves the insulation characteristics.

[0018] 3. For the composite dielectric for cable insulating materials and its preparation method of the present invention, through the interface passivation layer obtained by chemical modification, the bonding between the base layer and the gradient layer is made closer, which not only improves the mechanical strength of the material but also effectively reduces interface defects, avoiding material failure caused by interface problems. The uniform surface and highly active hydroxylation treatment of the interface passivation layer provide a good foundation for the deposition of subsequent layers, thus ensuring the overall performance of the composite material and further improving the performance of cable insulating materials. Description of the Drawings

[0019] 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 required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0020] The structures, proportions, sizes, etc. shown in the accompanying drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0021] Figure 1 It is a flowchart of the preparation method of the composite medium in the present invention. Detailed implementation manners

[0022] In order to make the objectives, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0023] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be intermediate components present at the same time.

[0024] Embodiment 1: A composite medium for cable insulating materials in this embodiment, the composite medium includes a gradient layer, an interface passivation layer, and a base layer connected in sequence from top to bottom; the gradient layer is a gradient layer, the interface passivation layer is an alumina layer, and the base layer is a high dielectric constant ceramic layer.

[0025] Specifically, the base is any one of alumina, hafnium dioxide, and strontium titanate; the gradient layer is a number of alternating ferroelectric layers and paraelectric layers.

[0026] It should be noted that by introducing a gradient layer, an interface passivation layer, and a base layer, the composite medium forms a structure with continuous component transitions, which can effectively match the thermal expansion coefficients, reduce the interlayer stress, and relieve the internal stress of the cable insulation material composed of the composite medium under temperature changes, thereby reducing the volatility of the dielectric constant with temperature changes; the base layer is made of a ceramic material with a high dielectric constant, 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 temperatures, and thus avoiding the influence of high temperatures on the cable insulation material. In addition, the presence of the interface passivation layer helps to inhibit the migration of oxygen vacancies, reducing the risk of dielectric failure that may occur at high temperatures. At the same time, in combination with the interface passivation layer and the gradient layer, it can effectively reduce the interface defects and the concentration of oxygen vacancies, thereby reducing the leakage current and significantly improving the insulation performance of the cable insulation material. Moreover, the gradient structure in the gradient layer, through the alternating deposition of ferroelectric layers and paraelectric layers, forms an ordered nano-domain structure, which can effectively block the electric field from concentrating at a certain point, reduce the breakdown risk, and further enhance the breakdown field strength.

[0027] Example 2: Please refer to Figure 1 , a preparation method of a composite medium for a cable insulation material in this embodiment, is applied to the composite medium as in Example 1, and the preparation method includes: Step S1: Pretreat the substrate to obtain a substrate with a dense polycrystalline structure and a surface roughness ≤ 1 nm; It should be noted that the substrate is a ceramic with a high dielectric constant, which can provide appropriate mechanical support and thermal stability as a substrate, providing a reliable physical and chemical basis for the subsequent interface passivation layer and gradient layer.

[0028] Sinter the substrate at 1280 - 1320 °C for 1.5 - 3.5 h to make the substrate have a dense polycrystalline structure, and the grain size of the dense polycrystalline structure is 50 - 100 nm.

[0029] Preferably, sinter the substrate at 1300 °C for 2 h to make the substrate have a dense polycrystalline structure, and the grain size of the dense polycrystalline structure is 50 - 100 nm.

[0030] It should be emphasized that after sintering, the density of the substrate ≥ 98% and the porosity ≤ 1%. By sintering, the dielectric loss and mechanical weak points caused by internal pores in the substrate can be reduced. In addition, chemically mechanical polishing the substrate to make the surface roughness ≤ 1 nm can avoid interface defects in subsequent processing. By sintering and polishing the substrate, the density and flatness of the substrate can be ensured, improving the quality of the subsequent formed interface passivation layer and avoiding cracks or interface peeling caused by substrate defects during the subsequent deposition process.

[0031] It is understandable that the chemical mechanical polishing step is well-known to those skilled in the art and will not be described in this embodiment.

[0032] Step S2: Treat the surface of the substrate with a plasma-enhanced atomic layer deposition device to form a passivation layer, and then chemically modify the passivation layer with a modification solution to form an interfacial passivation layer on the surface of the substrate; It should be noted that the interfacial passivation layer formed on the substrate can inhibit the migration of oxygen vacancies and enhance the interfacial bonding strength.

[0033] Step S2 specifically includes: Step S21: The plasma-enhanced atomic layer deposition device uses a TMA (trimethylaluminum) pulse and an O 2 plasma pulse to treat the surface of the substrate in an alternating pulse manner, and perform a first nitrogen purge on the surface of the substrate during the alternating pulse; In step S21, the plasma power is 50 - 100 W, the TMA pulse time is 0.1 - 0.3 s, and the O 2 plasma pulse time is 0.1 - 0.3 s, the nitrogen purge time is 3 - 5 s, the number of alternating pulses is 80 - 100 times, the temperature is 100 - 110 °C, and the thickness of the passivation layer is 4 - 6 nm.

[0034] Preferably, in step S21, the plasma power is 50 - 100 W, the TMA pulse time is 0.1 s, and the O 2 plasma pulse time is 0.1 s, the nitrogen purge time is 3 s, the number of alternating pulses is 80 times, the temperature is 100 °C, and the thickness of the passivation layer is 4 nm.

[0035] It should be noted that after the substrate is sintered, water molecules are adsorbed on its surface, and hydroxyl groups are formed through physical adsorption and chemical adsorption. After the surface of the substrate undergoes a TMA pulse, it reacts with the hydroxyl groups on the surface of the substrate to generate an Al-CH 3 * (aluminum methyl) intermediate state, and then under the action of active oxygen species generated by the O 2 plasma pulse, the Al-CH 3 * (aluminum methyl) is oxidized to form an aluminum oxide film, and thus a passivation layer formed by the aluminum oxide film.

[0036] It can be known that through the passivation layer, the microscopic defects on the surface of the substrate can be eliminated, a uniform and highly active hydroxylated surface can be provided, and the interfacial compatibility can be improved, providing a good basis for subsequent chemical modification.

[0037] In addition, a first nitrogen purge is performed during the alternating pulse to clean the unreacted by-products during the alternating pulse, so as to improve the quality of the formed passivation layer.

[0038] Step S22: Immerse the passivation layer on the substrate in the modification solution, and perform a second nitrogen purge on the passivation layer after the immersion is completed.

[0039] 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 immersion time is 20 - 30 min, the time for the second nitrogen purge is 4.5 - 6 min, the flow rate is 4.5 - 6 L / min, and the angle is 45 - 60°.

[0040] 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 immersion time is 30 min, the time for the second nitrogen purge is 5 min, the flow rate is 5 L / min, and the angle is 45°.

[0041] Specifically, the solvent is ethanol and the solute is APTES (3 - aminopropyltriethoxysilane).

[0042] It should be noted that after the passivation layer is immersed in the modification solution, the ethoxy groups in APTES are hydrolyzed into silanols, which condense with the hydroxyl groups on the Al 2 O 3 surface to form Si - O - Al covalent bonds. Under the action of the second nitrogen purge, unbonded APTES molecules can be removed, enabling the passivation layer to form a dense monolayer to obtain an interfacial passivation layer.

[0043] It can be known that by chemically modifying the passivation layer to fill the micropores on the passivation layer, the oxygen vacancy concentration of the obtained interfacial passivation layer can be made < 1×10 16 cm -3 , blocking the diffusion of oxygen vacancies in the base layer to the gradient layer, thereby reducing the oxygen vacancy migration rate and reducing electric field distortion.

[0044] Step S3: After alternately depositing a number of preliminary layers on the interfacial passivation layer, perform pulsed - electric - field induction treatment to obtain a gradient layer; It should be noted that the gradient layer matches the thermal expansion coefficients through the continuous component transition of the gradient structure, reduces the inter - layer stress, and under the action of the pulsed electric field, realizes the directional alignment of nano - domains, forms a local conduction barrier, and suppresses the leakage current.

[0045] Step S3 specifically includes: Step S31: First, deposit a ferroelectric layer on the interfacial passivation layer through a radio - frequency magnetron sputtering system, then spin - coat a paraelectric on the ferroelectric layer, and perform annealing treatment on the paraelectric to form a paraelectric layer to obtain a preliminary layer; After placing the substrate in the radio - frequency magnetron sputtering system, raise the temperature to 280 - 300 °C and evacuate to 5×10 -4 Pa, then introduce an Ar / O2 mixed gas to 0.5 Pa, adjust the power to 130 - 150 W, deposit the ferroelectric on the interface passivation layer to form a ferroelectric layer, then spin-coat the paraelectric on the ferroelectric layer with a spin coater at 2800 - 3000 rpm for 30 - 35 s. After the coating is completed, dry the paraelectric at a temperature of 150 - 170 °C for 7 - 10 min. After drying, anneal it at a temperature of 380 - 450 °C for 1.5 - 2.5 h to form a paraelectric layer on the ferroelectric layer to obtain a preliminary layer; Preferably, after placing the substrate in the radio frequency magnetron sputtering system, raise the temperature to 300 °C and evacuate to 5×10 -4 Pa, then introduce an Ar / O 2 mixed gas to 0.5 Pa, adjust the power to 150 W, deposit the ferroelectric on the interface passivation layer to form a ferroelectric layer, then spin-coat the paraelectric on the ferroelectric layer with a spin coater at 3000 rpm for 30 s. After the coating is completed, dry the paraelectric at a temperature of 150 °C for 10 min. After drying, anneal it at a temperature of 450 °C for 2 h to form a paraelectric layer on the ferroelectric layer to obtain a preliminary layer.

[0046] It should be emphasized that the sputtering ions of the radio frequency magnetron sputtering system have high energy, and the deposited ferroelectric is a hole-free thin film with high density, reducing oxygen vacancy defects. The paraelectric layer can also promote the diffusion of interface atoms and reduce stress through annealing, thereby improving the quality of the obtained gradient layer.

[0047] In addition, after the precursor solution is annealed to form a paraelectric layer, the formed paraelectric layer will shrink, and its surface will affect the micropores.

[0048] 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 monomethyl ether, 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.

[0049] It should be noted that the barium strontium titanate ceramic target layer in the ferroelectric layer, as a relaxor ferroelectric, provides a high capacitance density. After forming the gradient layer, strontium acetate in the paraelectric layer has the advantage of suppressing high-frequency loss. Therefore, the ferroelectric layer provides a high dielectric response for the gradient layer, and the paraelectric layer suppresses leakage conductance and loss.

[0050] 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 during the repeated step S31.

[0051] It should be noted that the gradual thermal expansion coefficient matching between the ferroelectric layer and the paraelectric layer reduces thermal stress cracks, forms a thermal expansion transition, and at the same time, under the combination of the Curie temperature of the ferroelectric layer and the paraelectric layer, the effective dielectric temperature range is broadened.

[0052] Specifically, the number of preliminary layers is four, and the thicknesses of the four preliminary layers from bottom to top are 50 nm, 40 nm, 30 nm, and 20 nm respectively; the thickness ratios of the ferroelectric layer to the paraelectric layer in the four preliminary layers from bottom to top are 8:2, 6:4, 4:6, and 2:8 respectively.

[0053] Step S33: Place the substrate on the pulsed electric field device, make the gradient layer located between the two poles of the pulsed electric field device, then introduce nitrogen to heat up to 50 - 80 °C, apply a pulsed electric field of 300 - 400 kV / cm, and keep it for 30 - 40 minutes.

[0054] Preferably, in step S33: Place the substrate on the pulsed electric field device, make the gradient layer located between the two poles of the pulsed electric field device, then introduce nitrogen to heat up to 60 °C, apply a pulsed electric field of 350 kV / cm, and keep it for 30 minutes.

[0055] It should be noted that the electric field direction of the pulsed electric field is perpendicular to the plane of the gradient layer. After the pulsed electric field is applied, the ferroelectric domains in the ferroelectric layer of the gradient layer are arranged along the electric field direction under the drive of the pulsed electric field, forming an ordered nano-domain structure to optimize the dielectric response and breakdown strength.

[0056] It can be known that the ferroelectric layer undergoes dynamic rearrangement under the action of the pulsed electric field. The pulsed electric field provides sufficient energy to enable the domain walls of the ferroelectric layer to overcome the potential barrier and be arranged orderly along the electric field direction. In the paraelectric layer, a conductive potential barrier is formed by the nano-domains of the ferroelectric layer to block the leakage conduction path; under the action of the pulsed electric field, the nano-domain structure in the ferroelectric layer is optimally arranged, the domain wall density is increased, and the ordered domain walls disperse the electric field stress, enhancing the breakdown field strength, solving the problem of electric field concentration caused by disordered domain walls, which is prone to cause breakdown. 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 reduces the oxygen vacancy concentration to reduce the ionic conduction channels, solving the problem of forming a conductive path due to disordered domain walls and increasing energy consumption.

[0057] Step S4: Prepare the first solution and the 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.

[0058] Step S41: Mix the lanthanum nitrate solution and citric acid at 500 - 600 rpm for 30 - 35 min to obtain the first solution; Step S42: Ultrasonically disperse manganese acetate, ethylene glycol monomethyl ether and an antioxidant at a frequency of 40 - 60 kHz and a power of 80 - 100 W for 10 - 15 minutes to obtain a second solution; Step S43: Immerse the gradient layer in the first solution for 10 - 14 min, apply ultrasound to the solution at a frequency of 40 - 60 kHz and a power of 100 - 120 W for 10 - 16 minutes, then dry at a temperature of 80 - 100 °C. After drying, perform oxidative annealing at a temperature of 500 - 600 °C for 1.5 - 2.5 h; Step S44: Spin - coat the second solution on the gradient layer treated in Step S43 at 2500 - 3000 rpm for 30 - 40 s, then dry at a temperature of 100 - 120 °C. After drying, perform reduction annealing at a temperature of 450 - 500 °C for 4 - 5 h.

[0059] Preferably, Step S4 specifically includes: Step S41: Mix the lanthanum nitrate solution and citric acid at 500 rpm for 30 min to obtain a first solution; Step S42: Ultrasonically disperse manganese acetate, ethylene glycol monomethyl ether and an antioxidant at a frequency of 40 kHz and a power of 100 W for 10 minutes to obtain a second solution; Step S43: Immerse the gradient layer in the first solution for 10 min, apply ultrasound to the solution at a frequency of 40 kHz and a power of 100 W for 10 minutes, then dry at a temperature of 80 °C. After drying, perform oxidative annealing at a temperature of 600 °C for 2 h; Step S44: Spin - coat the second solution on the gradient layer treated in Step S43 at 3000 rpm for 30 s, then dry at a temperature of 120 °C. After drying, perform reduction annealing at a temperature of 450 °C for 5 h.

[0060] It should be noted that after oxidative annealing, by repairing the oxygen vacancies, the lanthanum ions in the first solution will replace the barium ions or strontium ion sites in the gradient layer. After reduction annealing, the manganese ions in the second solution will replace the titanium ion sites in the gradient layer. Under the action of lanthanum ions and manganese ions, the leakage current can be further reduced, the space charge density can be decreased, and the breakdown field strength can be further improved.

[0061] Specifically, lanthanum ions compensate for oxygen vacancies, which can block the ionic conduction path, while manganese ions form deep - level traps to inhibit electron hopping conduction.

[0062] It should also be emphasized that citric acid in the first solution is beneficial to stabilizing lanthanum ions to ensure that lanthanum ions can effectively replace barium ions or strontium ion sites, and ethylene glycol monomethyl ether in the second solution has a low surface tension, which is beneficial to the second solution penetrating into the pores of the gradient layer.

[0063] In summary, the composite dielectric composed of a base layer, an interface passivation layer and a gradient layer prepared by the above preparation method effectively solves the problems of high temperature sensitivity of the dielectric constant, leakage conductance caused by interface defects and insufficient breakdown field strength in the composite dielectric, avoids the insulation failure of the cable insulation material, the base layer provides thermal stability support for the composite dielectric and suppresses the 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 wide-temperature volatility of the dielectric constant of the composite dielectric and 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.

[0064] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the 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 invention.

Claims

1. A composite medium for cable insulation material, characterized in that: The composite medium comprises a gradient layer, an interface passivation layer and a base layer which are sequentially connected from top to bottom; the gradient layer is a gradual change layer, the interface passivation layer is an aluminum oxide layer, and the base layer is a high dielectric constant ceramic layer.

2. The method for preparing a composite medium for cable insulation material according to claim 1, characterized in that: The substrate is any one of aluminum oxide, hafnium dioxide and strontium titanate.

3. A method for preparing a composite medium for cable insulation material, characterized in that: Applicable to the composite medium for cable insulation material as claimed in claims 1-2, the preparation method comprising: Step S1, pre-treating the substrate to obtain a substrate with a dense polycrystalline structure and a surface roughness of ≤1 nm; Step S2, treating the surface of the substrate by a plasma enhanced atomic layer deposition device to form a passivation layer, and then chemically modifying the passivation layer by using a modified solution to form an interface passivation layer on the surface of the substrate; Step S3, after alternately depositing a number of preliminary layers on the interface passivation layer, a pulse electric field induction treatment is performed to obtain a gradient layer; Step S4, preparing a first solution and a second solution, placing the gradient layer in the first solution for treatment and then in the second solution for treatment to obtain a composite medium.

4. The method for preparing a composite medium for cable insulation material according to claim 3, characterized in that: The substrate is sintered at 1280-1320° C. for 1.5-3.5 hours to make the substrate have a dense polycrystalline structure, wherein the grain size of the dense polycrystalline structure is 50-100 nm.

5. The method for preparing a composite medium for cable insulation material according to claim 3, characterized in that: The step S2 specifically includes: Step S21, the plasma enhanced atomic layer deposition equipment uses TMA pulses and O2 plasma pulses to process the substrate surface in an alternating pulse manner, and performs a first nitrogen purge on the substrate surface during the alternating pulse process; Step S22, immersing the passivation layer on the substrate in the modified solution, and performing a second nitrogen purge on the passivation layer after the immersion is completed.

6. The method for preparing a composite medium for cable insulation material according to claim 5, characterized in that: 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 purge time is 3-5s, the number of alternating pulses is 80-100 times, the temperature is 100-110°C, and the passivation layer thickness is 4-6nm; In the step S22, the modified solution includes a solvent and a solute, the volume ratio of the solvent to the solute in the modified solution is 100: (1-2), the immersion time is 20-30 minutes, the second nitrogen purge time is 4.5-6 minutes, the flow rate is 4.5-6L / min, and the angle is 45-60°.

7. The method for preparing a composite medium for cable insulation material according to claim 6, characterized in that: The solvent is ethanol, and the solute is APTES.

8. The method for preparing a composite medium for cable insulation material according to claim 3, characterized in that: The step S3 specifically includes: Step S31, first depositing a ferroelectric layer on the interface passivation layer by a radio frequency magnetron sputtering system, then spin-coating a paraelectric on the ferroelectric layer by a spin coater, and annealing the paraelectric to form a paraelectric layer, so as to obtain a preliminary layer; After placing the substrate in the RF magnetron sputtering system, the temperature was raised to 280-300 °C and the vacuum was evacuated to 5 × 10 -4 Pa, then introduce Ar / O2 mixed gas to 0.5Pa, and adjust the power to 130-150W to deposit the ferroelectric on the interface passivation layer to form a ferroelectric layer, and then use a spin coater to spin coat at 2800-3000rpm for 30-35s to coat the paraelectric on the ferroelectric layer, and after coating, dry the paraelectric at 150-170℃ for 7-10min, and then anneal at 380-450℃ for 1.5-2.5h to form a paraelectric layer on the ferroelectric layer to obtain a preliminary layer; Step S32, repeating step S31 to form a plurality of preliminary layers with gradually decreasing thickness on the interface passivation layer, and gradually decreasing the thickness of the ferroelectric layer in the preliminary layer and gradually increasing the thickness of the paraelectric layer in the preliminary layer in the repeated step S31; In 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, and then nitrogen is introduced to raise the temperature to 50-80° C., and a pulse electric field of 300-400 kV / cm is applied for 30-40 minutes.

9. The method for preparing a composite medium for cable insulation material according to claim 8, characterized in that: 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, the solute is tetrabutyl titanate and strontium acetate, and the molar ratio of tetrabutyl titanate to strontium acetate is (1-2): (1-2).

10. The method for preparing a composite medium for cable insulation material according to claim 3, characterized in that: The step S4 specifically includes: Step S41, mixing the lanthanum nitrate solution and citric acid at 500-600 rpm for 30-35 min to obtain a first solution; Step S42, dispersing manganese acetate, ethylene glycol methyl ether and antioxidant by ultrasound at a frequency of 40-60 kHz and a power of 80-100 W for 10-15 minutes to obtain a second solution; Step S43, immersing the gradient layer in the first solution for 10-14 minutes, applying ultrasound at a frequency of 40-60kHz and a power of 100-120W to the solution for 10-16 minutes, and then drying at a temperature of 80-100°C. After drying, oxidative annealing is performed at a temperature of 500-600°C for 1.5-2.5 hours; Step S44, spin-coat the second solution on the gradient layer treated in step S43 at 2500-3000 rpm for 30-40 seconds, and then dry at a temperature of 100-120° C. After drying, perform reduction annealing at a temperature of 450-500° C. for 4-5 hours.

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