Rare-earth-doped high-density alumina ultrahigh-voltage insulating ceramic as well as preparation method and application thereof

Abstract

The invention discloses rare earth doped high-density alumina ultrahigh-voltage insulating ceramic as well as a preparation method and application thereof. The rare earth doped high-density alumina ultrahigh-voltage insulating ceramic is prepared from the following raw materials in percentage by mass: 92-96% of alpha-Al2O3, 3-5% of rare earth oxide, 0.5-1.2% of MgO, 0.3-0.8% of Yb2O3 and 0.5-1.5% of a sintering aid. The rare earth oxide is a compound of La2O3 and Gd2O3 according to a molar ratio of (1.2 to 1.5): 1. Crystal boundary migration is inhibited through lattice distortion energy (delta E = 0.38 eV); la2O3 and Gd2O3 are compositely doped according to the molar ratio of (1.2-1.5): 1, and a gradient chemical potential is formed at a grain boundary by utilizing the synergistic distortion effect of La < 3 + >-Gd < 3 + > to drive directional segregation of rare earth ions, so that the pinning force of the grain boundary is improved, the grain boundary energy is reduced, and high-temperature grain coarsening is inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and in particular to a rare earth-doped high-density alumina ultra-high voltage insulating ceramic, a preparation method and an application thereof. Background Art

[0002] Alumina (Al2O3) ceramics are widely used in the field of electronics and electrical appliances due to their excellent insulation, high hardness, and high temperature resistance. However, traditional preparation techniques have the following drawbacks: 1. Contradiction between densification and insulation performance: Conventional high-pressure sintering can improve density by adding sintering aids such as MgO-Y2O3, but improper doping can easily form conductive paths at grain boundaries, leading to increased high-frequency dielectric loss (tanδ) (>10 -3 ), it is difficult to take into account the high-frequency insulation performance requirements and cannot meet the requirements of the 5G millimeter wave band (28GHz).

[0003] 2. Insufficient control of abnormal grain boundary growth: The existing two-step sintering method has limited inhibition on grain boundary migration and fails to completely inhibit grain boundary migration at high temperature, resulting in uneven grain size distribution, large fluctuations in mechanical properties, and poor mechanical uniformity.

[0004] 3. Residual stress and structural defects: Although ultra-high pressure sintering can refine grains and increase dislocation density, no stress release mechanism is designed, resulting in residual stress at the grain boundary exceeding 1.2 GPa, which can easily cause microcracks to expand during long-term service.

[0005] 4. Limitations in the selection of sintering aids: Traditional single additives such as B2O3 or SiO2 form a high-viscosity liquid phase under high pressure, which cannot achieve full rearrangement of particles and the density is only 95-97%.

[0006] Therefore, there is an urgent need to develop an alumina insulating ceramic that has high density, nano-grains, low dielectric loss and excellent high-temperature stability, and to develop a supporting efficient and controllable preparation process. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a rare earth-doped, high-density alumina ultra-high voltage insulating ceramic, as well as a preparation method and application thereof. This invention addresses the technical problems existing in the prior art through multi-component collaborative design, ultra-high pressure gradient sintering, and grain boundary structure optimization.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a rare earth-doped high-density alumina ultra-high voltage insulating ceramic, wherein the raw materials for preparation include, by mass percentage, 92-96% of α-Al2O3, 3-5% of rare earth oxide, 0.5-1.2% of MgO, 0.3-0.8% of Yb2O3, and 0.5-1.5% of sintering aid; The rare earth oxide is a composite of La2O3 and Gd2O3 in a molar ratio of (1.2-1.5):1.

[0009] Rare earth La 3+ With Gd 3+ The difference in ionic radius (Δr = 23%) produces an asymmetric distortion stress field in the Al2O3 lattice. 3+ (1.16Å) preferentially occupies Al 3+ octahedral sites, inducing lattice tensile strain; Gd 3+ (0.94Å) forms interstitial solid solution due to its small radius, generating compressive strain. A three-dimensional pinning network is formed by superposition of two strain fields of the double rare earth system, and grain boundary migration is suppressed by lattice distortion energy (ΔE=0.38eV); La2O3 and Gd2O3 are co-doped at a molar ratio of 1.2-1.5:1, and La 3+ -Gd 3+ The synergistic distortion effect forms a gradient chemical potential at the grain boundary, driving the directional segregation of rare earth ions, thereby improving the grain boundary pinning force, reducing the grain boundary energy, and inhibiting high-temperature grain coarsening.

[0010] In some embodiments, the sintering aid is a B2O3-SiO2-LiF ternary system with a mass ratio of (0.3-0.5): (0.2-0.4): (0.1-0.3), forming a low-viscosity transient liquid phase under ultra-high pressure.

[0011] The eutectic point of the B2O3-SiO2-LiF ternary system (Te=480℃) matches the ultra-high pressure sintering temperature range (500-800℃). + The strong polarization ability can reduce the BO bond binding energy and form a low viscosity (η≤10 3 The transient liquid phase (1000 Pa·s) with a liquid contact angle θ≤15° wets the surface of Al2O3 particles. At a mass ratio of (0.3-0.5):(0.2-0.4):(0.1-0.3), LiF reacts with B2O3 at 10 GPa / 500°C to form a LiBO2 transition phase, which reduces the activation energy of liquid phase formation. By spreading the liquid phase to fill the grain boundary pores, the density is significantly improved, while avoiding grain boundary embrittlement caused by excessive liquid phase.

[0012] In some embodiments, a rare earth segregation layer with a thickness of 1-3 nm is formed at the grain boundary. 3+The concentration gradient is ≥15at% / nm, and the segregated layer comprises periodically arranged [La-O-Gd] structural units with a spacing of 0.5-0.8nm.

[0013] La 3+ With Gd 3+ The segregation at the grain boundaries forms [La-O-Gd] structural units, whose periodic arrangement (spacing 0.5-0.8 nm) is due to the ionic charge compensation effect (La 3+ +Gd 3+ →2Al 3+ This ordered structure creates a steric hindrance, hindering grain boundary migration. During the 15 GPa / 600°C holding stage, the chemical potential gradient at the grain boundaries drives the diffusion of La / Gd ions, forming a segregated layer 1-3 nm thick. This increases the activation energy for grain boundary migration and improves the material's high-temperature stability.

[0014] In some embodiments, the B2O3-SiO2-LiF transient liquid phase has a viscosity of ≤10 under ultra-high pressure. 3 Pa·s, and a nanocrystalline wrapping structure is formed during the pressure release stage, including AlBO3 phase with a size of 5-20 nm distributed at the grain boundary triple point.

[0015] Al 3+ and BO3 3- Under ultra-high pressure (22GPa), the reaction generates metastable AlBO3 (the thermodynamically stable phase is Al2O3-B2O3), whose nanocrystals (5-20nm) are distributed at the grain boundary triple points, inhibiting grain boundary sliding through the pinning effect. At 22GPa / 800℃, the B in the transient liquid phase 3+ With Al 3+ A topological reaction occurs, causing AlBO3 to nucleate and grow along a non-classical crystallization pathway (amorphous-nanocrystalline transition). The modulus of AlBO3 (E=280GPa) is higher than that of the Al2O3 matrix (E=390GPa), resulting in a local strengthening effect and improved fracture toughness.

[0016] In some embodiments, 0.1-0.5 wt % of ZrO 2 nanoparticles are further included, wherein the ZrO 2 nanoparticles have a particle size of 10-30 nm and are uniformly dispersed in the α-Al 2 O 3 matrix.

[0017] The volume expansion of ZrO2 during the t→m phase transformation (ΔV=4.5%) offsets the sintering shrinkage stress of Al2O3 (ΔV=3.2%), hindering crack propagation through a phase transformation toughening mechanism. By adding 0.1-0.5wt% t-ZrO2 (particle size 10-30nm) and applying ultrahigh pressure (22GPa) to suppress phase transformation hysteresis, the t→m phase transformation occurs completely during the sintering stage. This increases the work of fracture by requiring additional phase transformation energy to propagate cracks.

[0018] In a second aspect, an embodiment of the present application provides a method for preparing a rare earth-doped high-density alumina ultra-high voltage insulating ceramic, comprising the following steps: (1) Mix α-Al2O3 with a particle size of 50-150 nm with rare earth oxides, MgO, Yb2O3, and sintering aids according to the proportion, and wet grind for 12-18 hours in an ethanol medium with a ball-to-material ratio of 8:1 to obtain D 90 Uniform slurry ≤200nm; (2) After vacuum drying at 60°C, the slurry was placed in a furnace containing 5 vol% HF at 400°C for 2 h to pre-react LiF with B2O3 to form a LiBO2 transition phase; (3) Gradient pressurization in a multi-anvil press after cold isostatic pressing: The powder is cold isostatically pressed and placed in a six-sided top press. The pressure is increased from 5 GPa to 22 GPa at a rate of 1-3 GPa / min, and the temperature is increased from 300 °C to 800 °C in steps, where: At 10 GPa, the temperature is maintained at 500℃±20℃ for 5 minutes, so that LiBO2-SiO2 forms a low-viscosity transient liquid phase with a viscosity of η≤10 3 Pa·s; At 15 GPa, maintain 600°C ± 20°C for grain boundary reorganization with a holding time of 30-90 seconds, so that the grain boundaries of La / Gd / Yb are segregated to form a continuous stress buffer layer; (4) During the pressure release phase, the pressure is reduced at a rate of ≤0.5 GPa / s, and field-assisted annealing is performed simultaneously, applying a DC electric field with an intensity of 500-800 V / cm to induce orderly arrangement of oxygen vacancies.

[0019] The six-sided top press is suitable for the research and development and production of high-performance ceramic materials, particularly for ceramic phases that require a high-pressure environment for stability or for applications requiring extreme densification. Furthermore, staged pressurization (5 → 10 → 15 → 22 GPa) matches the sintering shrinkage curve to avoid particle breakage caused by sudden pressure changes. Liquid phase formation occurs at 10 GPa / 500°C, grain boundary recombination is triggered at 15 GPa / 600°C, and densification is completed at 22 GPa. A pressurization rate of 1-3 GPa / min controls the grain boundary diffusion rate, allowing La / Gd / Yb segregation and densification to proceed simultaneously. This ultimately improves relative density and grain boundary structural uniformity.

[0020] In some embodiments, in step (3), during the 22 GPa ultrahigh pressure sintering process, a pulse pressure wave with a frequency of 5-10 kHz and an amplitude of 0.2-0.5 GPa is applied along the direction perpendicular to the basal plane, i.e., the main axis of the crystal, in the alumina crystal structure to induce a specific mode of directional slip deformation inside the grains. The slip deformation is manifested as: on the basal plane of the alumina, i.e., the atomic layer parallel to the bottom surface in the hexagonal crystal structure, relative sliding of the atomic layer occurs along a specific crystal direction within the basal plane, and the dislocation density is ≥5×10 14 m -2 The EBSD test showed that the deviation between the slip trace and the theoretical slip direction was ≤5°.

[0021] Applying a pulse wave (5-10kHz) perpendicular to the crystal axis can activate directional slip deformation. The critical shear stress of this slip system is exceeded at 22GPa, promoting dislocation proliferation. The pulse wave amplitude of 0.2-0.5GPa corresponds to a shear stress exceeding the dislocation nucleation threshold, inducing dislocations to multiply via the Frank-Read source mechanism, resulting in a dislocation density of ≥5×10 14 m -2 , improve hardness.

[0022] In some embodiments, the loading timing of the pulse pressure wave is coupled with the temperature-pressure curve, specifically: When the pressure increases from 15 GPa to 22 GPa, a continuous wave with a frequency of 5 kHz and an amplitude of 0.5 GPa is applied; During the 22 GPa holding stage, the pulse was switched to an intermittent wave with a frequency of 10 kHz and an amplitude of 0.2 GPa (duty cycle 1:3); By dynamically adjusting the waveform parameters, the ratio of dislocation proliferation rate to grain growth rate is made ≥2:1.

[0023] A continuous wave (5kHz / 0.5GPa) provides sustained dislocation driving force during the pressurization phase, while an intermittent wave (10kHz / 0.2GPa, duty cycle 1:3) prevents dislocation accumulation and grain boundary embrittlement during the pressure-holding phase. When the dislocation multiplication rate is ≥2 times the grain growth rate, the waveform parameters are dynamically adjusted to maintain plastic deformation dominance. This results in a narrower grain size distribution and improved mechanical property consistency.

[0024] In some embodiments, after step (4), the annealed ceramic is immersed in an ethanol solution containing 0.1-0.5 wt% boric acid and treated with 50W ultrasonic wave for 30 min to make B 3+ Selectively bonds La-O units at grain boundaries to form [La-OB] complexes with thermal stability ≥1600°C.

[0025] B 3+It forms a [La-OB] complex with the grain boundary La-O unit, whose bond energy (E=520kJ / mol) is higher than that of the La-O-Al bond (E=480kJ / mol), which can block the grain boundary corrosion caused by water molecule adsorption. Ultrasonic assisted (50W / 40kHz) driving B 3+ Penetrate into the grain boundaries and replace weakly bound OH groups by chemical adsorption - The group can control the moisture permeability of the grain boundary to a low range, and the ability to resist surface discharge is improved.

[0026] In a third aspect, an embodiment of the present application provides an application of a rare earth-doped high-density alumina ultra-high voltage insulating ceramic as described above in the field of electronic appliances, such as in vacuum tube shells, power equipment, electronic devices and other fields.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The present invention inhibits grain boundary migration by lattice distortion energy (ΔE=0.38eV); La2O3 and Gd2O3 are composite-doped at a molar ratio of 1.2-1.5:1, and La 3+ -Gd 3+ The synergistic distortion effect forms a gradient chemical potential at the grain boundary, driving the directional segregation of rare earth ions, thereby improving the grain boundary pinning force, reducing the grain boundary energy, inhibiting high-temperature grain coarsening, effectively limiting grain boundary migration, and improving insulation performance; 2. Li + The strong polarization ability can reduce the BO bond binding energy and form a low viscosity (η≤10 3 Pa·s) transient liquid phase, where LiF reacts with B2O3 to form LiBO2 transition phase, reducing the activation energy of liquid phase formation. By spreading the liquid phase to fill the grain boundary pores, the density is significantly improved while avoiding grain boundary embrittlement caused by excessive liquid phase; 3. Through the lattice distortion field caused by the size mismatch of rare earth ions, concentrated stress is converted into distributed microscopic strain, and the high pressure-high temperature process window is used to promote the self-organization reconstruction of the defect structure, and the strain energy is converted into the energy required for the reorganization of chemical bonds. Finally, through the coordinated regulation of oxygen vacancies and grain boundaries, a multi-scale stress dissipation network is established, and the special doping strategy of rare earth elements and the dynamic regulation of process conditions are used to achieve the effective release of internal stress in the material.

[0028] The present invention will be further described in detail below with reference to specific embodiments. DETAILED DESCRIPTION

[0029] The applicant found that: In the existing technology system, the coordinated regulation of high densification and insulation performance has always been a major challenge in the field of alumina ceramics. In order to improve density, traditional sintering processes often introduce transition metal oxides or carbides as sintering aids. For example, ZrB2 is used as a toughening phase in the CN112939582B patent. Although high density is achieved through the grain boundary pinning effect, the inherent high conductivity of ZrB2 leads to the formation of electron migration channels at the grain boundaries, significantly reducing the insulation performance of the material. This contradiction stems from the limitations of the existing technology on the selection of dopants - although traditional sintering aids (such as TiO2 and Fe2O3) can promote densification through the liquid phase, the metal ions or interstitial atoms they introduce are prone to band overlap, forming low-resistance paths at the grain boundaries. More importantly, the existing process has not established a directional control mechanism for the chemical state of the grain boundaries, resulting in the uncontrollable precipitation of impurity phases (such as metal borides) during the sintering process, further exacerbating the degradation of insulation performance. For example, although the two-step sintering method in CN109400123B suppressed grain growth, it did not solve the problem of oxygen vacancy aggregation introduced by the MgO-Y2O3 sintering aid, resulting in a surge in the dielectric loss of the material under high-frequency electric fields.

[0030] The root cause of the lack of control over abnormal grain boundary growth lies in the limited understanding of grain boundary migration dynamics in existing technologies. The traditional two-step sintering method suppresses grain boundary migration by pre-sintering at low temperature. When the sintering temperature exceeds 1250℃, the grain boundary energy (about 1.0 J / m 2 ) is still sufficient to drive rapid grain coarsening. Existing grain boundary pinning strategies (such as whisker toughening and second-phase particle doping) can physically block grain boundary migration, but fail to reconstruct grain boundary characteristics from an energy perspective. For example, aluminum borate whiskers are used for toughening in CN112939582B, but the interface energy difference between them and the Al2O3 matrix (Δγ≈0.3 J / m 2 ) causes debonding at the whisker-matrix interface at high temperatures, which in turn becomes a rapid pathway for grain boundary migration. A deeper problem lies in the limited control methods currently available for grain boundary chemical bonding, making it impossible to reduce the driving force for grain boundary migration through atomic-scale design.

[0031] The essence of residual stress and structural stability defects is that existing sintering technologies lack a dynamic stress release mechanism. Although traditional hot pressing or SPS processes promote densification through external pressure, after unloading the high pressure, the dislocation pile-up and lattice distortion energy generated by plastic deformation inside the material cannot be effectively dissipated, forming residual compressive stress as high as 1.5-2.0 GPa. For example, although the hardness of Al2O3 prepared using 15GPa ultra-high pressure is increased to 26GPa, the dislocation density at its grain boundary is as high as 10 15 / m -2, which can easily lead to stress concentration at the intersection of dislocation slip bands under thermal cycling or mechanical loads, resulting in intergranular fracture. Existing technologies attempt to relieve residual stress through annealing, but high-temperature annealing (>1200°C) will reactivate grain boundary migration, resulting in a vicious cycle of grain coarsening and mechanical property degradation. A deeper technical bottleneck is that the existing process cannot simultaneously achieve densification and dynamic stress balance during the sintering process - for example, the use of LiF-SiO2 composite sintering aid in CN116283251B reduces the sintering temperature, but Li + Segregation at grain boundaries leads to localized charge imbalance, inducing electrostatically enhanced stress corrosion susceptibility, making the material susceptible to stress corrosion cracking in hot and humid environments. Existing technologies have yet to offer an effective solution to this structural instability problem caused by the coupling of multiple physical fields.

[0032] In view of this, the applicant proposed a rare earth doped high-density alumina ultra-high voltage insulating ceramic, the raw materials for preparation of which include, by mass percentage, α-Al2O3 92-96%, rare earth oxide 3-5%, MgO 0.5-1.2%, Yb2O3 0.3-0.8%, and sintering aid 0.5-1.5%; The rare earth oxide is a composite of La2O3 and Gd2O3 in a molar ratio of (1.2-1.5):1.

[0033] Preferably, the sintering aid is a B2O3-SiO2-LiF ternary system with a mass ratio of (0.3-0.5): (0.2-0.4): (0.1-0.3), forming a low-viscosity transient liquid phase under ultra-high pressure.

[0034] Preferably, a rare earth segregation layer with a thickness of 1-3 nm is formed at the grain boundary. 3+ The concentration gradient is ≥15at% / nm, and the segregated layer comprises periodically arranged [La-O-Gd] structural units with a spacing of 0.5-0.8nm.

[0035] Preferably, the viscosity of the B2O3-SiO2-LiF transient liquid phase under ultrahigh pressure is ≤10 3 Pa·s, and a nanocrystalline wrapping structure is formed during the pressure release stage, including AlBO3 phase with a size of 5-20 nm distributed at the grain boundary triple point.

[0036] More specifically, the preparation process includes the following steps: (1) Mix α-Al2O3 with a particle size of 50-150 nm with rare earth oxides, MgO, Yb2O3, and sintering aids according to the proportion, and wet grind for 12-18 hours in an ethanol medium with a ball-to-material ratio of 8:1 to obtain D 90 Uniform slurry ≤200nm; (2) After vacuum drying at 60°C, the slurry was placed in a furnace containing 5 vol% HF at 400°C for 2 h to pre-react LiF with B2O3 to form a LiBO2 transition phase; (3) Gradient pressurization in a multi-anvil press after cold isostatic pressing: The powder is cold isostatically pressed and placed in a six-sided top press. The pressure is increased from 5 GPa to 22 GPa at a rate of 1-3 GPa / min, and the temperature is increased from 300 °C to 800 °C in steps, where: At 10 GPa, the temperature is maintained at 500℃±20℃ for 5 minutes, so that LiBO2-SiO2 forms a low-viscosity transient liquid phase with a viscosity of η≤10 3 Pa·s; At 15 GPa, maintain 600°C ± 20°C for grain boundary reorganization with a holding time of 30-90 seconds, so that the grain boundaries of La / Gd / Yb are segregated to form a continuous stress buffer layer; (4) During the pressure release phase, the pressure is reduced at a rate of ≤0.5 GPa / s, and field-assisted annealing is performed simultaneously, applying a DC electric field of 500-800 V / cm to induce orderly arrangement of oxygen vacancies.

[0037] Preferably, in step (3), during the 22 GPa ultrahigh pressure sintering process, a pulse pressure wave with a frequency of 5-10 kHz and an amplitude of 0.2-0.5 GPa is applied along the direction perpendicular to the basal plane, i.e., the main axis of the crystal, in the alumina crystal structure to induce a specific mode of directional slip deformation inside the grains. The slip deformation is manifested as: on the basal plane of the alumina, i.e., the atomic layer parallel to the bottom surface in the hexagonal crystal structure, relative sliding of the atomic layer occurs along a specific crystal direction within the basal plane, and the dislocation density is ≥5×10 14 m -2 The EBSD test showed that the deviation between the slip trace and the theoretical slip direction was ≤5°.

[0038] The loading timing of the pulse pressure wave is coupled with the temperature-pressure curve, specifically: When the pressure increases from 15 GPa to 22 GPa, a continuous wave with a frequency of 5 kHz and an amplitude of 0.5 GPa is applied; During the 22 GPa holding stage, the pressure was switched to an intermittent wave with a frequency of 10 kHz and an amplitude of 0.2 GPa (duty cycle 1:3); By dynamically adjusting the waveform parameters, the ratio of dislocation multiplication rate to grain growth rate is made ≥2:1.

[0039] First, in order to solve the problem of coordinated regulation of high densification and insulation performance, this solution is realized through deep coupling of rare earth doping system and ultra-high pressure process. Its core lies in utilizing the synergistic effect of high pressure thermodynamic condition reconstruction and rare earth defect chemistry to break through the bottleneck of mutual restriction between densification and insulation performance in traditional sintering.3+ / Gd 3+ Double rare earth doping as the structural framework, combined with Yb 3+ / Mg 2+ The co-doping system and 15GPa ultra-high pressure and low temperature sintering process are used to construct multi-level composite functional structures from the atomic scale to the mesoscopic scale. The specific technical paths are as follows: 1. La2O3 and Gd2O3 are co-doped at a molar ratio of 1.2-1.5:1, and the lattice distortion energy is released by the difference in ionic radius. 3+ (radius 1.16Å) preferentially occupies the octahedral sites of the Al2O3 lattice, causing local lattice expansion and forming a tensile strain field; Gd 3+ (radius 0.94Å) partially enters the interstitial sites, generating compressive strain. The alternating distribution of these two strain fields is strengthened into a periodic stress network under an ultra-high pressure of 15GPa. Through the synergistic effect of dislocation slip and grain boundary slip, the Al2O3 particles are densified under the control of plastic flow at a low temperature of 800℃. During this process, La / Gd segregates at the grain boundaries to form a [La-O-Gd] bridge structure. Its high stability inhibits grain boundary migration, and the grain size is controlled below 0.45μm. 2. Yttrium ion (Yb 3+ ) as acceptor defects, by replacing aluminum ions (Al 3+ ) sites, forming defect centers with effective negative charges; at the same time, magnesium ions (Mg 2+ ) acts as a donor defect, also occupying the aluminum ion site, forming a positively charged defect. These two defects achieve charge neutralization in a specific ratio (for example, two yttrium defects for each magnesium defect), ultimately achieving overall charge neutrality. This mutually offsetting charge compensation significantly reduces the number of oxygen vacancies that spontaneously generate in the lattice to maintain charge neutrality. It also forces the remaining oxygen vacancies to form an orderly arrangement under ultrahigh voltage, thereby blocking electron migration paths and fundamentally improving the material's insulation properties.

[0040] 3. Under ultrahigh pressure of 15GPa, the phase equilibrium of the B2O3-SiO2-LiF sintering aid ternary system is reconstructed, and LiF dissociates to generate Li + At 800°C, a transient LiBO2 liquid phase (melting point 680°C) is formed with B2O3. This liquid phase wraps around the Al2O3 particles in the form of a nanofilm (2-5nm thick), promoting particle rearrangement through capillary action, while the high-pressure environment inhibits the volatilization of the liquid phase. The La / Gd segregation layer (1.5-2.0nm thick) at the grain boundary isolates the transient liquid phase into discrete island structures, blocking the formation of conductive paths (grain boundary resistivity ≥10 15 / Ω·cm).

[0041] The synergistic effect of ultrahigh-pressure plastic deformation and transient liquid-phase diffusion enables the material to achieve near-full densification at 800°C, resulting in high flexural strength and fracture toughness. Transmission electron microscopy reveals the coexistence of La / Gd segregated layers and oxygen vacancy corrugations (wavelength 4.5 nm) at grain boundaries, effectively pinning dislocation motion. Yb / Mg co-doping extends the cutoff length of the oxygen vacancy conduction path from 5 nm to 22 nm, maintaining a high baseline volume resistivity even at high temperatures. Low dielectric loss is attributed to the shortened polarization relaxation time caused by stress release.

[0042] Secondly, to address the problem of insufficient control over abnormal grain boundary growth, this scheme utilizes the lattice distortion field induced by rare earth doping and dynamic plastic deformation under ultra-high pressure environment to construct a "self-locking" grain boundary structure, fundamentally eliminating the thermodynamic driving force and kinetic conditions of grain growth.

[0043] When La 3+ With Gd 3+ When embedded in the alumina lattice in a specific ratio, the two form a complementary strain field due to the difference in ion size - La 3+ The large volume effect of Gd expands the lattice framework, while 3+ The compactness occupies the reverse tightening local structure. This push-pull effect forms an interlaced stress network near the grain boundary, just like laying countless micro springs on both sides of the grain boundary. Any grain boundary migration needs to overcome the collective reaction force of these springs. More importantly, under the action of 15GPa ultra-high pressure, this strain field is strengthened into a three-dimensional interlocking structure. 3+ With Gd 3+ Through chemical bond reorganization, a stable [La-O-Gd] bridging unit is formed, with a binding energy of up to 5.2eV, far exceeding the van der Waals interaction of traditional grain boundaries (approximately 0.5eV). This chemical pinning effect increases the activation energy of grain boundary migration at high temperatures to 3.0eV, equivalent to 1.5 times that of traditional Al2O3 grain boundaries, significantly raising the thermodynamic threshold for grain growth.

[0044] At the dynamic level, the ultrahigh pressure process reconstructs the densification path. When 15GPa pressure acts on Al2O3 particles, the local stress at the contact point between the particles far exceeds the yield strength of the material, triggering plastic flow dominated by dislocation slip. This deformation mechanism is like forging metal with a hydraulic press, achieving densification through plastic deformation of particles rather than high-temperature diffusion, and the time window for grain growth is compressed. At the same time, Yb 3+ With Mg 2+ The co-doping system builds an oxygen vacancy control network at the grain boundary - Yb 3+ The acceptor characteristics of Mg 2+The donor properties of the oxygen vacancies create a charge balance, forcing the oxygen vacancies to align along specific crystal planes. These ordered defects act like a rubble array at the grain boundaries, forcing the migrating grain boundaries to constantly change their paths and increase migration resistance. Transmission electron microscopy reveals this effect as a jagged morphology at the grain boundaries, rather than the straight grain boundaries of conventional materials.

[0045] This approach overturns the traditional sintering paradigm of "trading temperature for density." By coupling rare earth doping with extreme pressure, it transforms the energy barrier for grain growth from a single temperature dependency to a complex energy field regulation—much like installing a smart sensor lock on the grain boundary, allowing limited structural adjustment only under specific pressure-chemical potential conditions. When applied to 5G millimeter-wave filters, the material's uniform nanocrystalline structure significantly reduces signal transmission loss while resisting thermal breakdown even under high-power loads, shifting the paradigm from passive tolerance to active regulation.

[0046] Finally, in order to solve the problem of stress release mechanism, this solution uses the special doping strategy of rare earth elements and the dynamic regulation of process conditions to effectively release the internal stress of the material. 3+ With Gd 3+ The synergistic effect of the dual rare earth system is carried out, and an asymmetric lattice distortion stress field is constructed in the Al2O3 matrix through the composite doping of La2O3 and Gd2O3 (molar ratio 1.2-1.5:1) with a specific ratio, combined with ultra-high pressure sintering process. 3+ Because the ionic radius (1.16Å) is much larger than that of Al 3+ (0.54Å), preferentially occupying the octahedral sites in the lattice, causing the local lattice to stretch and expand; while Gd 3+ (radius 0.94Å), due to differences in size adaptability, some of them enter the interstitial sites and form compressive strain regions. This periodic alternation of tensile and compressive strains creates a dynamic stress balance network in the material at the microscale, offsetting macroscopic internal stresses through the gradient release of lattice distortion energy.

[0047] In the specific process implementation, the combination strategy of ultra-high pressure sintering and staged pressure holding plays a key role. The high pressure environment forces La 3+ With Gd 3+ Rapid diffusion to the predetermined lattice position, while the high temperature holding stage drives the rare earth ions to segregate at the grain boundary, forming a stable [La-O-Gd] bridge structure. This structure not only releases the interface stress through chemical bond reorganization, but also guides the lattice distortion energy to gradually convert into the activation energy required for atomic position adjustment during the subsequent gradient cooling (5℃ / min). At the same time, the added Yb2O3 (0.3-0.8wt%) and the Mg in the matrix 2+Through synergistic action, [Yb-Mg-Vo] (Vo is oxygen vacancy) composite defects are constructed near the grain boundaries. These oxygen vacancies form orderly arranged dissipation channels in the stress concentration area, effectively blocking the propagation path of microcracks and further dissipating the residual stress.

[0048] The underlying logic of the entire stress release system can be summarized as three levels of dynamic interactions: first, the lattice distortion field caused by the size mismatch of rare earth ions is used to convert concentrated stress into distributed microscopic strain; second, the high pressure-high temperature process window is used to promote the self-organization reconstruction of the defect structure, converting strain energy into the energy required for chemical bond reorganization; finally, through the coordinated regulation of oxygen vacancies and grain boundaries, a multi-scale stress dissipation network is established.

[0049] As an embodiment, it further comprises 0.1-0.5 wt % of ZrO2 nanoparticles, wherein the particle size of the ZrO2 nanoparticles is 10-30 nm and the ZrO2 nanoparticles are uniformly dispersed in the α-Al2O3 matrix.

[0050] The introduction of ZrO2 nanoparticles essentially creates a multiscale toughening network within the alumina matrix. Because fracture in conventional alumina ceramics often begins due to stress concentration at grain boundaries, the introduction of a nanoscale second phase disrupts crack propagation pathways through multiple mechanisms while preserving the matrix's intrinsic properties. Zirconia exhibits unique phase transformation toughening properties. Its transition from tetragonal to monoclinic phase is accompanied by a 3-5% volume expansion, a process that effectively absorbs crack propagation energy. The process involves first blending a ZrO2 precursor (such as ZrOCl2) with Al2O3 powders via high-energy ball milling. A monolayer of ZrO2 nanocrystals is then coated onto the Al2O3 particles via mechanochemical action. Subsequently, during the initial sintering phase (300-500°C), the ZrO2 precursor is decomposed into nanoparticles that are anchored to the Al2O3 grain surfaces by a controlled heating rate. Ultrahigh pressure (UHV) plays a key role in this stage – high pressure forces ZrO2 nanoparticles to embed into Al2O3 lattice defect sites, forming a “mechanically interlocking” structure rather than a simple physical mixture. This atomic-scale embedding allows the ZrO2 particles to be encapsulated by Al2O3 grains during the subsequent densification process, preventing particle migration and aggregation.

[0051] As an embodiment, after step (4), the annealed ceramic is immersed in an ethanol solution containing 0.1-0.5 wt% boric acid and treated for 30 min under the assistance of 50W ultrasonic wave to make B 3+ Selectively bonds La-O units at grain boundaries to form [La-OB] complexes with thermal stability ≥1600°C.

[0052] Since the traditional annealing process can release some residual stress, it cannot eliminate the risk of structural degradation of grain boundaries under extreme temperatures. Therefore, in this embodiment, the technical solution of introducing boric acid solution treatment after annealing is the core of the technical solution to reconstruct the rare earth element coordination environment at the grain boundary through chemical bonding to build a high-temperature stable interface barrier. 3+ It has a unique electron-deficient property and can form a strong coordination bond with the lone pair electrons in the La-O structure at the grain boundary. 3+ There are unsaturated coordination sites in the [La-O] units formed by grain boundary segregation. Boric acid treatment is essentially the use of B 3+ The electron-deficient empty orbitals react with the oxygen ligands of La to transform the originally isolated La-O units into a three-dimensional cross-linked [La-OB] network. This chemical reconstruction transforms the grain boundary from a weakly bonded state that is easily damaged by thermal activation to a stable structure with covalent bond characteristics. In the process implementation, ethanol is used as a solvent instead of water, which can not only avoid the hydrolysis side reaction between water molecules and rare earth oxides, but also utilize its low surface tension characteristics to penetrate into the nanoscale grain boundary channels. Ultrasonic treatment (50W) produces a cavitation effect at the microscale, causing the solution to form transient microjets in the grain boundary capillaries, forcing B 3+ At the same time, the cavitation collapse of ultrasound creates a local high temperature and high pressure micro-region at the grain boundary, which instantly activates the coordination activity of La-O bonds and promotes B 3+ It preferentially reacts with high-energy grain boundary La-O units rather than being randomly adsorbed on the grain surface.

[0053] The present invention will be further described below with reference to specific embodiments.

[0054] Example 1: (1) α-Al2O3 with a particle size of 50-150 nm was mixed with rare earth oxides, MgO, Yb2O3, and sintering aids in the following ratio: α-Al2O3 93.5%, La2O3 2.5%, Gd2O3 1.8%, MgO 0.8%, Yb2O3 0.5%, and B2O3-SiO2-LiF ternary system sintering aid 0.9%; wet milling was carried out in ethanol medium at a ball-to-material ratio of 8:1 for 15 h to obtain D 90 ≤200nm uniform slurry; wherein the molar ratio of La2O3 to Gd2O3 is 1.5:1, and the mass ratio of B2O3-SiO2-LiF ternary system sintering aid is 0.4:0.3:0.2; (2) After vacuum drying at 60°C, the slurry was placed in a furnace containing 5 vol% HF at 400°C for 2 h to pre-react LiF with B2O3 to form a LiBO2 transition phase; (3) Gradient pressurization in a multi-anvil press after cold isostatic pressing: The powder is cold isostatically pressed and placed in a six-sided top press. The pressure is increased from 5 GPa to 22 GPa at a rate of 1-3 GPa / min, and the temperature is increased from 300 °C to 800 °C in steps, where: At 10 GPa, the temperature is maintained at 500℃±20℃ for 5 minutes, so that LiBO2-SiO2 forms a low-viscosity transient liquid phase with a viscosity of η≤10 3 Pa·s; At 15 GPa, maintain 600°C ± 20°C for grain boundary reorganization with a holding time of 30-90 seconds, so that the grain boundaries of La / Gd / Yb are segregated to form a continuous stress buffer layer; (4) During the pressure release phase, the pressure is reduced at a rate of ≤0.5 GPa / s, and field-assisted annealing is performed simultaneously, applying a DC electric field of 500-800 V / cm to induce orderly arrangement of oxygen vacancies.

[0055] Example 2: The difference between Example 2 and Example 1 is that α-Al2O3 with a particle size of 50-150 nm is mixed with rare earth oxides, MgO, Yb2O3, and sintering aids in the following proportions: α-Al2O3 93.8%, La2O3 2.5%, Gd2O3 1.5%, MgO 0.8%, Yb2O3 0.5%, and B2O3-SiO2-LiF ternary system sintering aid 0.9%; wherein the molar ratio of La2O3 to Gd2O3 is 1.9:1.

[0056] This embodiment 2 mainly adjusts the molar ratio of rare earth oxides La2O3 and Gd2O3.

[0057] Example 3: The difference between Example 3 and Example 1 is that α-Al2O3 with a particle size of 50-150 nm is mixed with rare earth oxides, MgO, Yb2O3, a sintering aid, and ZrO2 nanoparticles in the following ratio: α-Al2O3 93.2%, La2O3 2.5%, Gd2O3 1.8%, MgO 0.8%, Yb2O3 0.5%, B2O3-SiO2-LiF ternary system sintering aid 0.9%, and ZrO2 nanoparticles 0.3%; wherein the molar ratio of La2O3 to Gd2O3 is 1.5:1, and the particle size of the ZrO2 nanoparticles is 20 nm.

[0058] This embodiment 3 mainly introduces ZrO2 nanoparticles into the alumina matrix.

[0059] Example 4: The difference between Example 4 and Example 1 is that in step (3), during the 22 GPa ultrahigh pressure sintering process, a pulse pressure wave with a frequency of 5-10 kHz and an amplitude of 0.2-0.5 GPa is applied along the direction perpendicular to the basal plane, i.e., the main axis of the crystal, in the alumina crystal structure to induce a specific mode of directional slip deformation inside the grains. The slip deformation is manifested as: on the basal plane of alumina, i.e., the atomic layer parallel to the bottom surface in the hexagonal crystal structure, relative sliding of the atomic layer occurs along a specific crystal direction within the basal plane, and the dislocation density is ≥5×10 14 m -2 The deviation between the slip trace and the theoretical slip direction is ≤5° when tested by EBSD. The loading timing of the pulse pressure wave is coupled with the temperature-pressure curve, specifically: When the pressure increases from 15 GPa to 22 GPa, a continuous wave with a frequency of 5 kHz and an amplitude of 0.5 GPa is applied; During the 22 GPa holding stage, the pressure was switched to an intermittent wave with a frequency of 10 kHz and an amplitude of 0.2 GPa (duty cycle 1:3); By dynamically adjusting the waveform parameters, the ratio of dislocation multiplication rate to grain growth rate is made ≥2:1.

[0060] This embodiment 4 mainly applies a pulse wave in the direction perpendicular to the main axis of the crystal to activate directional slip deformation during the ultra-high pressure sintering process, so as to avoid dislocation accumulation leading to grain boundary embrittlement.

[0061] Example 5: The difference between Example 5 and Example 1 is that after step (4), the annealed ceramic is immersed in an ethanol solution containing 0.3 wt% boric acid and treated for 30 min under the assistance of 50W ultrasonic wave to make B 3+ Selectively bonds La-O units at grain boundaries to form [La-OB] complexes with thermal stability ≥1600°C.

[0062] This embodiment 5 mainly uses an ethanol solution of boric acid for treatment after annealing.

[0063] Example 6: The difference between Example 6 and Example 1 is that α-Al2O3 with a particle size of 50-150 nm is mixed with rare earth oxides, MgO, Yb2O3, a sintering aid, and ZrO2 nanoparticles in the following ratio: α-Al2O3 93.2%, La2O3 2.5%, Gd2O3 1.8%, MgO 0.8%, Yb2O3 0.5%, B2O3-SiO2-LiF ternary system sintering aid 0.9%, and ZrO2 nanoparticles 0.3%; wherein the molar ratio of La2O3 to Gd2O3 is 1.5:1, and the particle size of the ZrO2 nanoparticles is 20 nm.

[0064] The high-pressure pulse pressure wave treatment in Example 4 and the annealing in Example 5 were then followed by treatment with an ethanol solution of boric acid.

[0065] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that α-Al2O3 with a particle size of 50-150 nm is mixed with rare earth oxides, MgO, Yb2O3, and sintering aids in the following ratio: α-Al2O3 95.8%, Gd2O3 2.0%, MgO 0.8%, Yb2O3 0.5%, and B2O3-SiO2-LiF ternary system sintering aid 0.9%; and wet-milled in an ethanol medium at a ball-to-material ratio of 8:1 for 15 h to obtain D 90 A uniform slurry with a particle size of ≤200 nm; wherein the molar ratio of La2O3 to Gd2O3 is 0:1.

[0066] This comparative example 1 mainly eliminates La2O3 in the selection of rare earth oxides.

[0067] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that after cold isostatic pressing, the product is directly sintered at normal pressure and 1600° C. for 2 h.

[0068] This comparative example 2 mainly adopts normal pressure high temperature sintering in the sintering process.

[0069] The main components and process parameters of Examples 1-6 and Comparative Examples 1-2 are shown in Table 1 below.

[0070] Table 1: Main components and process parameters of Examples and Comparative Examples

[0071]

[0072]

[0073] Performance tests were conducted on the examples and comparative examples. The performance test standards were based on national standards. The grain size was tested using an FE-SEM test instrument, the density was tested using GB / T 25995-2010 "Test Method for Density and Apparent Porosity of Fine Ceramics", the flexural strength was tested using GB / T 6569-2006 "Test Method for Flexural Strength of Fine Ceramics", and the fracture toughness was tested using the single-edge notched beam method. The performance test results are shown in Table 2.

[0074] Table 2: Performance test parameters

[0075]

[0076] Analysis of the above performance test results shows that the high-density alumina ultra-high voltage insulating ceramics prepared in Examples 1, 3, 4, 5, and 6 have a density greater than 98%, good density, an average grain size of no more than 1.5 μm, a small grain size, a bending strength greater than 550 MPa, a fracture toughness greater than 5.5 MPa·m½, excellent mechanical properties, and a volume resistivity greater than 5×10 14 Ω·cm, dielectric loss is not greater than 3.5×10 -4 , excellent insulation performance, suitable for vacuum tube shells, power equipment, electronic devices and other fields.

[0077] in: In terms of grain size, Example 3 further enhances the grain boundary pinning effect by introducing ZrO2 nanoparticles (approximately 20 nm in diameter), effectively suppressing the abnormal growth of α-Al2O3 grains during sintering, keeping the average grain size below 0.8 μm. This represents a 33% reduction compared to Example 1 (1.2 μm), which did not incorporate ZrO2. Examples 4 and 6 employ a dynamic plastic deformation mechanism driven by high-pressure pulse pressure waves, further refining the grain size to 0.9 μm and 0.6 μm, respectively, through mechanical energy-driven grain boundary migration. In contrast, Comparative Example 2, due to the lack of external field energy during pressureless sintering, exhibits abnormal grain growth to 5.2 μm, resulting in a distinct "double-peak" grain distribution.

[0078] Density changes are closely related to sintering process parameters. Gradient pressure sintering (Examples 1, 3, 4, 5, and 6) achieves high densities of 98.5% to 99.5% by promoting particle rearrangement and plastic flow through staged pressure loading. Comparative Example 2, sintered at atmospheric pressure, lacks a pressure driving force, resulting in a density of only 92.3%. The influence of the La2O3 / Gd2O3 molar ratio is evident in a comparison of Example 1 (1.5:1) with Example 2 (1.9:1) and Comparative Example 1 (0:1). Adjusting the La2O3 / Gd2O3 molar ratio optimizes the rare earth oxide liquid phase distribution, increasing density from 98.1% to 98.5% while also reducing grain boundary glass phase segregation.

[0079] Changes in electrical insulation properties reveal the influence of microstructure on dielectric properties. The post-annealing boric acid treatment of Examples 5 and 6 further optimizes the volume resistivity and dielectric loss of the ceramics. After boric acid treatment, the volume resistivity of Example 5 increases by nearly 7% compared to that of Example 1, while also reducing dielectric loss. Optimizing the rare earth element ratio (comparing Example 1 with Comparative Example 1) reduces dielectric loss by 62%, confirming the irreplaceable role of La2O3 in regulating grain boundary electrical properties.

[0080] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A rare earth doped high-density alumina ultra-high voltage insulating ceramic, characterized in that: The raw materials for preparation include, by mass percentage, α-Al2O3 92-96%, rare earth oxide 3-5%, MgO 0.5-1.2%, Yb2O3 0.3-0.8%, and sintering aid 0.5-1.5%; The rare earth oxide is a composite of La2O3 and Gd2O3 in a molar ratio of (1.2-1.5):

1.

2. The rare earth doped high density alumina ultra-high voltage insulating ceramic according to claim 1, characterized in that: The sintering aid is a B2O3-SiO2-LiF ternary system with a mass ratio of (0.3-0.5): (0.2-0.4): (0.1-0.3), which forms a low-viscosity transient liquid phase under ultra-high pressure.

3. The rare earth doped high density alumina ultra-high voltage insulating ceramic according to claim 2, characterized in that: A rare earth segregation layer with a thickness of 1-3 nm is formed at the grain boundary. 3+ The concentration gradient is ≥15at% / nm, and the segregated layer comprises periodically arranged [La-O-Gd] structural units with a spacing of 0.5-0.8nm.

4. The rare earth doped high density alumina ultra-high voltage insulating ceramic according to claim 3, characterized in that: The viscosity of the B2O3-SiO2-LiF transient liquid phase under ultra-high pressure is ≤10 3 Pa·s, and a nanocrystalline wrapping structure is formed during the pressure release stage, including AlBO3 phase with a size of 5-20 nm distributed at the grain boundary triple point.

5. The rare earth doped high density alumina ultra-high voltage insulating ceramic according to claim 4, characterized in that: The invention also comprises 0.1-0.5 wt % of ZrO2 nanoparticles, wherein the ZrO2 nanoparticles have a particle size of 10-30 nm and are uniformly dispersed in the α-Al2O3 matrix.

6. A method for preparing a rare earth-doped high-density alumina ultra-high voltage insulating ceramic according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Mix α-Al2O3 with a particle size of 50-150 nm with rare earth oxides, MgO, Yb2O3, and sintering aids according to the proportion, and wet grind for 12-18 hours in an ethanol medium with a ball-to-material ratio of 8:1 to obtain D 90 Uniform slurry ≤200nm; (2) After vacuum drying at 60°C, the slurry was placed in a furnace containing 5 vol% HF at 400°C for 2 h to pre-react LiF with B2O3 to form a LiBO2 transition phase; (3) Gradient pressurization in a multi-anvil press after cold isostatic pressing: The powder is cold isostatically pressed and placed in a six-sided top press. The pressure is increased from 5 GPa to 22 GPa at a rate of 1-3 GPa / min, and the temperature is increased from 300 °C to 800 °C in steps, where: At 10 GPa, the temperature is maintained at 500℃±20℃ for 5 minutes, so that LiBO2-SiO2 forms a low-viscosity transient liquid phase with a viscosity of η≤10 3 Pa·s; At 15 GPa, maintain 600°C ± 20°C for grain boundary reorganization with a holding time of 30-90 seconds, so that the grain boundaries of La / Gd / Yb are segregated to form a continuous stress buffer layer; (4) During the pressure release phase, the pressure is reduced at a rate of ≤0.5 GPa / s, and field-assisted annealing is performed simultaneously, applying a DC electric field of 500-800 V / cm to induce orderly arrangement of oxygen vacancies.

7. The preparation method according to claim 6, wherein In step (3), during the 22 GPa ultra-high pressure sintering process, a pulse pressure wave with a frequency of 5-10 kHz and an amplitude of 0.2-0.5 GPa is applied along the direction perpendicular to the basal plane, i.e., the main axis of the crystal, in the alumina crystal structure to induce a specific mode of directional slip deformation inside the grains. The slip deformation is manifested as: on the basal plane of the alumina, i.e., the atomic layer parallel to the bottom surface in the hexagonal crystal structure, relative sliding of the atomic layer occurs along a specific crystal direction within the basal plane, and the dislocation density is ≥5×10 14 m -2 The EBSD test showed that the deviation between the slip trace and the theoretical slip direction was ≤5°.

8. The preparation method according to claim 7, wherein The loading timing of the pulse pressure wave is coupled with the temperature-pressure curve, specifically: When the pressure increases from 15 GPa to 22 GPa, a continuous wave with a frequency of 5 kHz and an amplitude of 0.5 GPa is applied; During the 22 GPa holding stage, the pressure was switched to an intermittent wave with a frequency of 10 kHz and an amplitude of 0.2 GPa (duty cycle 1:3); By dynamically adjusting the waveform parameters, the ratio of dislocation multiplication rate to grain growth rate is made ≥2:

1.

9. The preparation method according to claim 6, wherein After step (4), the annealed ceramic was immersed in an ethanol solution containing 0.1-0.5 wt% boric acid and treated with 50W ultrasonic wave for 30 min to make B 3+ Selectively bonds La-O units at grain boundaries to form [La-OB] complexes with thermal stability ≥1600°C.

10. Use of the rare earth-doped high-density alumina ultra-high voltage insulating ceramic according to any one of claims 1 to 5 in the field of electronic appliances.

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