High-entropy relaxation type lead-free perovskite ceramic and preparation method thereof

Abstract

The invention discloses a high-entropy relaxation type lead-free perovskite ceramic and a preparation method thereof. The high-entropy relaxation type lead-free perovskite ceramic is a solid solution of Na < 0.2 > Bi < 0.2 > Ba < 0.2 > Sr < 0.2 > Ca < 0.2 >) TiO3 and (K < 0.5 > Na < 0.5 >) NbO3; the content of the (K0. 5Na0. 5) NbO3 accounts for 5 to 15 mol percent of the high-entropy relaxation type lead-free perovskite ceramic. By introducing (K0. 5Na0. 5) NbO3, energy band regulation and relaxation behavior adjustment are effectively realized, the breakdown electric field intensity is remarkably improved, the energy storage performance is improved, good stability is kept under the conditions of temperature, frequency and a circulating electric field, and the actual requirements of a pulse power capacitor on a high-performance and long-life energy storage dielectric material are met.

Description

Technical Field

[0001] The present invention relates to the field of energy storage ceramics, and in particular to a high-entropy relaxation type lead-free perovskite ceramic and a preparation method thereof. Background Art

[0002] Pulse power systems are widely used in defense, biotechnology, and medical fields, placing higher demands on the performance of energy storage components. Capacitors are currently the most commonly used form of energy storage due to their high power density, fast charge and discharge speeds, and flexible configurations. Ceramic materials, as capacitor dielectrics, offer advantages such as high temperature resistance, low loss, and high dielectric strength, making them an ideal choice for high-performance pulse capacitors.

[0003] Currently used ferroelectric ceramics are mostly lead-based. While they offer excellent performance, the environmental hazards of lead present in them limit their further development. Lead-free ceramics, such as sodium bismuth titanate, exhibit excellent polarization properties but suffer from large remanent polarization, high coercive field, low energy storage efficiency, and insufficient breakdown electric field, making it difficult to achieve both high energy density and reliability. Furthermore, the limited design freedom of traditional materials makes it difficult to overcome energy storage performance bottlenecks. Therefore, the development of new, high-performance, lead-free energy storage ceramic materials is urgently needed to meet the application requirements of advanced pulse systems. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a high entropy relaxor lead-free perovskite ceramic, 0.5 Na 0.5 The introduction of )NbO3(KNN) effectively realizes the band regulation and relaxation behavior adjustment, significantly improves the breakdown electric field strength, improves the energy storage performance, and maintains good stability under temperature, frequency and cyclic electric field, meeting the actual needs of pulse power capacitors for high-performance and long-life energy storage dielectric materials.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a high entropy relaxation type lead-free perovskite ceramic, which is Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 and (K 0.5 Na 0.5 )NbO3 solid solution; the (K 0.5 Na 0.5 )NbO3 content is 5 to 15 mol% of the high entropy relaxor lead-free perovskite ceramic; Specifically, the high entropy relaxor lead-free perovskite ceramic has the following chemical composition: (1-x)(Na 0.2 Bi 0.2 Ba 0.2Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3, wherein x (by mole) is 0.05 to 0.15.

[0007] Preferably, the (K 0.5 Na 0.5 ) The content of NbO3 is 10 mol% of the high entropy relaxor lead-free perovskite ceramic.

[0008] Preferably, the high entropy relaxor lead-free perovskite ceramic has a breakdown electric field strength of 420 kV / cm and a recoverable energy storage density of 6.16 J / cm 3 , the energy storage efficiency is 82.7%.

[0009] The present invention also provides a method for preparing the high-entropy relaxor lead-free perovskite ceramic, comprising the following steps:

[0010] (1) Weighing raw materials: weighing Na-containing compound, Bi-containing compound, Ba-containing compound, Sr-containing compound, Ca-containing compound, K-containing compound, Nb-containing compound and Ti-containing compound according to the target stoichiometric ratio;

[0011] (2) First ball milling: The raw materials weighed in step (1) are dried and then placed in a planetary ball mill for the first ball milling;

[0012] (3) Pre-calcination treatment: After the ball-milled powder in step (2) is dried, it is placed in a crucible, compacted and covered, and heated to 850-870°C at a heating rate of 5-6°C / min and kept at this temperature for 1.8-2.2h for pre-calcination;

[0013] (4) Second ball milling: The product obtained by pre-calcining in step (3) is subjected to a second ball milling;

[0014] (5) Granulation and tableting: Grinding, granulating, and tableting the powder obtained by the second ball milling in step (4) to obtain a green body;

[0015] (6) Debinding and sintering: The green body obtained in step (5) is kept at 530-550°C for 2.5-3 hours, then heated to 1150-1250°C at a heating rate of 5-6°C / min and kept at this temperature for 1.8-2 hours to obtain a high-entropy relaxor lead-free perovskite ceramic.

[0016] Preferably, the Na-containing compound is Na2CO3; the Bi-containing compound is Bi2O3; the Ba-containing compound is BaCO3; the Sr-containing compound is SrCO3; the Ca-containing compound is CaCO3; the K-containing compound is K2CO3; the Nb-containing compound is Nb2O5; and the Ti-containing compound is TiO2.

[0017] Preferably, the drying in step (2) is specifically: drying at 110-120° C. for 8-9 hours.

[0018] Preferably, the first ball milling in step (2) is specifically as follows: the dried raw materials, zirconia balls and anhydrous ethanol are loaded into a ball milling jar in a mass ratio of 1: (2.5-3): (1.5-2), and the ball milling is performed alternately in forward and reverse rotation at a speed of 300-350 r / min in a planetary ball mill, with the direction being reversed every 30-40 minutes, and the ball milling is continued for 10-12 hours.

[0019] Preferably, the drying in step (3) is specifically: drying at 80-90° C. for 12-24 hours.

[0020] Preferably, the second ball milling in step (4) is specifically as follows: the dried raw materials, zirconia balls and anhydrous ethanol are loaded into a ball milling jar in a mass ratio of 1: (2.5-3): (1.5-2), and the ball milling is performed alternately in forward and reverse rotation at a speed of 300-350 r / min in a planetary ball mill, with the direction being reversed every 30-40 minutes, and the ball milling is continued for 10-12 hours.

[0021] Preferably, the tableting in step (5) is specifically performed by using a pressure of 120 to 130 MPa for tableting and holding the pressure for 30 to 40 seconds.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The high-entropy relaxor lead-free perovskite ceramics of the present invention effectively promote the formation of local polarization distortion and relaxation characteristics through the introduction of KNN, so that the material achieves a balance between structural symmetry and dielectric regulation, which is suitable for high-field and high-frequency application requirements.

[0024] (2) The high entropy relaxor lead-free perovskite ceramics of the present invention significantly reduce (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The grain size of TiO3 high-entropy ceramics makes the grain boundaries denser, reduces the formation of voids, and promotes grain refinement.

[0025] (3) The high-entropy relaxor lead-free perovskite ceramics of the present invention, through the introduction of KNN, destroy the long-range ferroelectric order of the system and increase the proportion of localized polar nanoregions (PNRs), thereby enhancing the temperature stability of the dielectric response. The dielectric temperature stability of the high-entropy ceramic samples is enhanced.

[0026] (4) The high entropy relaxor lead-free perovskite ceramic of the present invention increases the band gap width and significantly improves the breakdown electric field strength by introducing KNN.

[0027] (5) The high entropy relaxor lead-free perovskite ceramic of the present invention has the best energy storage performance in the preferred embodiment with a KNN content of 10 mol%, with a breakdown electric field strength of up to 420 kV / cm and a recoverable energy storage density of up to 6.16 J / cm 3 , the energy storage efficiency can reach 82.7%; at the same time, it has excellent anti-fatigue properties, reaching a peak current of 36.83A within 45ns under an external electric field of 200kV / cm, C D =496.2A / cm 2 ,P D =51.3MW / cm 3 ,t 0.9 =148ns, which means (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-(K 0.5 Na 0.5 )NbO3 high-entropy ceramics have broad application prospects in related fields such as energy storage electronic devices, advanced pulse power capacitors, and optoelectronic multifunctional devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )XRD diffraction spectra of NbO3 (x = 0, 0.05, 0.1, 0.15) high entropy ceramic system, where (a) corresponds to the range of 2θ = 20°-80°; (b) corresponds to 2θ≈46.5°.

[0029] Figure 2 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca0.2 )TiO3-x(K 0.5 Na 0.5 )Raman spectra of NbO3(x=0, 0.05, 0.1, 0.15).

[0030] Figure 3 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )SEM images of high-entropy ceramic samples of NbO3; (a) to (d) correspond to samples with x = 0, 0.05, 0.10, and 0.15, respectively.

[0031] Figure 4 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) The ε of NbO3 high entropy ceramic samples measured in the temperature range of -50-180℃ and at different frequencies of 100-100kHz r and tanδ curves as a function of temperature, where (a) to (d) correspond to samples with x = 0, 0.05, 0.10, and 0.15, respectively.

[0032] Figure 5 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 high entropy ceramics at 100Hzε r And the comparison chart of tanδ changing with temperature.

[0033] Figure 6 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5) Dielectric temperature stability test results of NbO3 high entropy ceramic samples at 100 Hz.

[0034] Figure 7 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) Relaxation factors of NbO3 high-entropy ceramic samples, where (a) to (d) correspond to samples with x = 0, 0.05, 0.10, and 0.15, respectively.

[0035] Figure 8 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) PFM amplitude diagrams of NbO3 high-entropy ceramic samples, where (a) to (d) correspond to samples with x = 0, 0.05, 0.10, and 0.15, respectively.

[0036] Figure 9 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) PFM phase images of NbO3 high-entropy ceramic samples, where (a) to (d) correspond to samples with x = 0, 0.05, 0.10, and 0.15, respectively.

[0037] Figure 10 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )Ultraviolet absorption spectra of NbO3(x=0,0.1) high entropy ceramic samples.

[0038] Figure 11 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca0.2 )TiO3-x(K 0.5 Na 0.5 )The band gap width of NbO3 (x=0,0.1) high entropy ceramic samples.

[0039] Figure 12 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )Bipolar PE loop of NbO3 high entropy ceramics under breakdown electric field strength.

[0040] Figure 13 When the W of high entropy ceramic sample increases from x = 0 to x = 0.15, rec The relationship diagram with the change of η.

[0041] Figure 12 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )Energy storage density W of NbO3 high entropy ceramic samples rec and energy storage efficiency η as a function of KNN content.

[0042] Figure 13 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) When the NbO3 high entropy ceramic sample increases from x = 0 to x = 0.15, W rec The relationship diagram with the change of η.

[0043] Figure 14 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )P–E curves of high-entropy ceramic samples of NbO3 (x=0.1) at 200 kV / cm and 1 Hz.

[0044] Figure 15 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0.1) high entropy ceramic samples were subjected to the conditions of 200kV / cm and 1Hz at 50℃-150℃. st 、W rec And the curve of η value changing with temperature.

[0045] Figure 16 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )PE curve of high entropy ceramic sample of NbO3 (x=0.1) in 200kV / cm electric field and 1-100Hz frequency range.

[0046] Figure 17 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0.1) high entropy ceramic samples obtained at different frequencies under 200kV / cm st 、W rec and η value.

[0047] Figure 18 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0.1) high entropy ceramic samples were subjected to 1-10 6 PE curve after the second cycle.

[0048] Figure 19 (1-x)(Na 0.2 Bi0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0.1) high entropy ceramic samples under 200kV / cm and 1Hz conditions at different cycle times st 、W rec and η value.

[0049] Figure 20 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0.1) high entropy ceramic samples under different applied electric fields at room temperature.

[0050] Figure 21 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )The charge and discharge parameters C of high entropy ceramic samples of NbO3(x=0.1) D and P D The relationship with the change of external electric field.

[0051] Figure 22 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )Overdamped discharge curves of high entropy ceramic samples of NbO3 (x=0.1) under different electric fields.

[0052] Figure 23 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0.1) high entropy ceramic samples under different electric fieldsd Relationships that change over time. DETAILED DESCRIPTION

[0053] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0054] Example

[0055] This example prepares a high entropy relaxor lead-free perovskite ceramic with the following chemical composition: (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3, wherein x (by mole) is 0.05, 0.10, and 0.15. In this embodiment, a lead-free perovskite ceramic in which x is 0 is also prepared as a comparative sample.

[0056] The preparation process of the lead-free perovskite ceramic material of this embodiment is as follows:

[0057] (1) Weighing raw materials:

[0058] Weigh Na2CO3, Bi2O3, BaCO3, SrCO3, CaCO3, K2CO3, Nb2O5, and TiO2 in the target stoichiometric ratio, with the purity of each component being no less than 99%. Dry the raw materials at 120°C for 8 hours to remove adsorbed moisture.

[0059] (2) First ball milling:

[0060] The dried raw materials, zirconium oxide balls and anhydrous ethanol were loaded into a nylon ball mill at a mass ratio of 1: (2.5-3): (1.5-2), and the ball milling was carried out alternately in forward and reverse rotation at a speed of 300 r / min in a planetary ball mill, with the direction being reversed every 30 minutes, and the ball milling was continued for 12 hours to obtain a uniformly mixed precursor powder.

[0061] (3) Pre-burning treatment:

[0062] The ball-milled powder was dried at 80°C for 12 hours, compacted in an alumina crucible, and covered to minimize the loss of volatile components. It was then pre-sintered at a rate of 5°C / min to 850°C and held for 2 hours to promote the initial formation of the crystalline phase.

[0063] (4) Second ball milling:

[0064] The calcined product was subjected to a second ball milling under the same conditions as the first ball milling, with a ball milling speed of 300 r / min and a time of 12 h to further refine the particles.

[0065] (5) Granulation and tableting:

[0066] The powder obtained from the secondary ball milling was further ground, and a 5% (mass fraction) aqueous solution of polyvinyl alcohol (PVA) was added as a binder. Granulation was then performed, and uniformly sized particles were screened. The granulated powder was then pressed into a 10 mm diameter mold using a pressure of 120 MPa and a holding time of 30 seconds to produce disc-shaped green tablets approximately 10 mm in diameter.

[0067] (6) Debinding and sintering treatment:

[0068] The pressed green compacts were held at 550°C for 3 hours to remove the organic binder. The sample was then heated to 1220°C at a rate of 5°C / min and held for 2 hours to complete densification. A stacked firing process was used during sintering. TiO2 powder was placed on the bottom to prevent adhesion between the sample and the sintering tray. Granulated powder was added between the samples for isolation. The crucibles were covered with alumina and the atmosphere was controlled to maintain Bi- and Na-rich conditions to minimize the loss of volatile elements.

[0069] After sintering, the sample was surface polished and ultrasonically cleaned, and metal electrodes were deposited on the parallel surfaces on both sides to form a standard parallel plate capacitor structure. The dielectric properties, hysteresis loop and energy storage performance tests were then carried out.

[0070] Phase structure and configuration entropy test:

[0071] Figure 1 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 (x=0, 0.05, 0.1, 0.15) high entropy ceramic system XRD spectrum. It can be seen that all samples present a single pseudo cubic perovskite structure, and no second phase is observed, which indicates that the introduction of KNN does not destroy the Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The single-phase stability of the TiO3 high entropy matrix is ​​consistent with the phase stability caused by the entropy effect. Figure 1 As shown in (b), with the increase of KNN content, its (200) diffraction peak shifts to a lower angle and the lattice parameter increases. This is because K + and Na + Partially replace the original ions at A site (Bi 3+ Ca 2+ ) leads to an increase in the average ionic radius at the A site, which in turn causes lattice expansion. As the KNN doping level increases, the full width at half maximum (FWHM) of the diffraction peak slightly broadens, as shown in Table 1. The degree of local lattice distortion within the crystal increases, a trend consistent with the cumulative effect of chemical disorder in high-entropy systems.

[0072] Table 1 Diffraction peak position and half-height width of (200) crystal plane at different x values

[0073]

[0074] In this embodiment, (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) Tolerance factor (t), A-site ion size difference (δ(R A )) and configurational entropy (ΔS config ) is shown in Table 2. As can be seen from the table, the t values ​​of each component are very close to 1 (decreased from 0.997 to 0.993), which indicates that the system has a lattice symmetry close to the ideal cubic structure. With the increase of KNN, δ(R A ) value is slightly reduced, which indicates that despite the introduction of different ion components, the ion size difference at the A site is maintained in a small range, which is not enough to cause obvious lattice distortion or precipitation of secondary phases, thus being conducive to the formation and stability of a single-phase structure. In addition, ΔS config >1.61R is the criterion for high entropy materials. ΔS config All of them meet this condition, proving that (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 system belongs to high entropy ceramics.

[0075] Table 2 Different components (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5) Tolerance factor (t), A-site ion size difference δ(R A ) and configurational entropy (ΔS config )

[0076]

[0077] (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3(x=0,0.05,0.1,0.15) high entropy ceramic system Raman spectrum Figure 2 As shown in Figure 2, with the increase of KNN doping concentration, the 400-750cm -1 The main peak in the range shifts to low frequency, indicating that the vibration mode of BO6 octahedron softens and the bonding strength weakens. This "softening effect" can be attributed to the Nb 5+ Partial replacement of Ti 4+ This results in an increase in the average ionic radius at the B site, thereby weakening the bonding strength of the BO bond and enhancing the disorder of the local structure. Combining Tables 1 and 2, it can be seen that the ΔS of all samples after doping is config The results are significantly higher than the high entropy threshold (1.61R), and the tolerance factor t is stable in the range of 0.993-0.997, which meets the thermodynamic conditions for the formation of cubic perovskite single phase. The introduction of KNN reduces the size difference of A-site ions (δ(R A ) decreased from 6.8% to 6.4%), and components with smaller size differences are more likely to form a stable phase structure.

[0078] Micromorphology test:

[0079] Figure 3 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 Scanning electron microscope (SEM) images of NbO3 high-entropy ceramic samples. All samples exhibit a dense and regular microstructure with clear grain boundaries and low porosity. Statistical analysis using Nano Measurer software revealed that increasing KNN content significantly improved grain uniformity and decreased overall grain size. The relationship between grain size and breakdown electric field strength is as follows:

[0080]

[0081] Where G represents the average grain size of the ceramic.

[0082] From the above, we can see that with the increase of KNN doping amount, (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )The average grain size of the NbO3 high-entropy ceramic sample is reduced, and this change is conducive to obtaining a higher breakdown electric field strength in subsequent ferroelectric tests.

[0083] Dielectric performance test:

[0084] (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 high entropy ceramic samples were tested at -50-180℃ and 100-100kHz different frequencies (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-(K 0.5 Na 0.5 )ε of NbO3 high entropy ceramic samples r The curves of tanδ changing with temperature are as follows Figure 4 As shown; ε obtained at 100Hz r The comparison diagram of tanδ changing with temperature is as follows Figure 5 As shown in the figure, as the test frequency increases, all samples show typical dielectric relaxation characteristics, namely frequency dispersion and diffuse phase transition. 5+ The ionic polarizability is low, and with the increase of KNN doping level, the polarization transition temperature (T m ) moves toward low temperature, and the maximum dielectric constant (ε m ) decreased significantly. r With E b Inversely proportional, with moderate ε rDielectric materials with high KNN content can generally achieve higher energy storage density. The incorporation of KNN significantly reduces the tanδ value in the high entropy system. With the increase of KNN content, the ε-T curve gradually widens, indicating that the long-range ferroelectric order of the system is destroyed and the proportion of localized polar nano-microdomains (PNRs) increases, thereby enhancing the temperature stability of the dielectric response, reflecting that the dielectric temperature stability of the ceramic is enhanced. At 100Hz, (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) The dielectric temperature stability of NbO3 high entropy ceramic samples is as follows Figure 6 As shown in the figure, the capacitance temperature stability of the KNN-doped sample is significantly better than that of the undoped sample. At 100Hz, the 0.9NBBSCT-0.1KNN sample exhibits excellent temperature stability, fully meeting the X7R specification requirements.

[0085] To further analyze the KNN doping effect (Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )The influence of the relaxation degree of TiO3 high entropy ceramics was studied by using the modified Curie-Weiss law and characterizing the relaxation degree of the material by the relaxation factor γ, such as Figure 7 As shown in Figure 2, the relaxation factor γ increases significantly with the increase of KNN doping amount, indicating that the introduction of KNN significantly improves the (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 ceramics relaxation behavior. This is consistent with the ε r The trend of the gradual broadening of the -T curve is consistent, indicating that the introduction of KNN exacerbates the destruction of long-range ferroelectric order and promotes the dynamic random distribution of polar nanodomains (PNRs). This diffusion phase transition behavior, combined with microstructural control (grain refinement and densification) and dielectric property optimization, is conducive to achieving high energy storage density and excellent temperature stability in subsequent ferroelectric testing.

[0086] Domain structure test:

[0087] For (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 high entropy ceramic samples were subjected to PFM test, and the results were as follows Figures 8-9 As shown. Among them, Figure 8 reflects the strength of the piezoelectric response, while Figure 9 The contrast reveals the polarization direction. Figure 8-9 It can be seen that no obvious domain structure was observed in all samples, indicating that the relaxation phenomenon presented in the dielectric test originated from the generation of localized polar nanodomains (PNRs).

[0088] Energy storage performance test:

[0089] Figure 10 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )UV absorption spectrum of NbO3 high entropy ceramic sample. Figure 11 The band gap values ​​of the high-entropy ceramic samples were calculated to fit the band gap: when x = 0, the band gap is 3.02 eV, and it increases to 3.13 eV when x = 0.1. A larger band gap can reduce local charge accumulation and suppress interfacial polarization, thereby improving the breakdown field strength of the ceramic material. Figure 12 is (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )Bipolar PE loop of NbO3 high entropy ceramics under breakdown electric field strength. Figure 13 When the W of high entropy ceramic sample increases from x = 0 to x = 0.15, rec The relationship between P and η. It can be seen that with the increase of KNN content, P max and P r The breakdown electric field strength is significantly enhanced, and the breakdown electric field strength is 410kV / cm when x=0.10. This improvement in the breakdown electric field can be attributed to factors such as the reduction in grain size and the widening of the band gap. When x=0.10, the sample shows the best energy storage performance: W rec =6.16J / cm 3 , η = 82.7%. In addition, ΔS config >1.61R indicates that the material has high entropy properties. As shown in Table 2, with the increase of KNN content, ΔS configThe Ratio has been significantly improved (from 1.610R to 1.744R), while the energy storage efficiency has also been improved.

[0090] Energy storage temperature, frequency and anti-fatigue stability test:

[0091] Figure 14 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 ) P–E curve of NbO3 high entropy ceramic sample at 200 kV / cm and 1 Hz. It remains stable in the temperature range of 50-150 °C, but its P max It decreases slightly with increasing temperature. This is attributed to the increase in the content of weak polarization phase due to the increase in temperature. The presence of weak polarization phase will inhibit the domain reversal process under the external electric field, so P max It decreases gradually with increasing temperature. Figure 15 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 high entropy ceramic samples were subjected to W at 50℃-150℃ under the conditions of 200kV / cm and 1Hz. st 、W rec The curves of the change of η value with temperature show that all three gradually decrease with increasing temperature. This is because as the temperature increases, at high temperatures, the defects inside the high entropy ceramic are activated, resulting in a decrease in energy storage efficiency. However, the ceramic still shows excellent high temperature stability in the test range of 50-150℃: at a frequency of 1Hz and an electric field of 200kV / cm, W rec Change <8%, η fluctuation <3%, and the highest W rec Reach 2.5J / cm 3 .

[0092] Figure 16 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )PE curve of NbO3 high entropy ceramic sample in 200kV / cm electric field and 1-100Hz frequency range, its elongated shape remains stable in a wide frequency range. Figure 17 As shown, W rec It is basically unchanged at the frequency of 1-100Hz, while η shows a trend of increasing first and then decreasing with increasing frequency (maximum W rec =2.3J / cm 3 , η=86%). In the range of 1-100Hz, W rec The change is less than 1% and the η fluctuation is less than 4%. This low-frequency sensitivity may be due to the polarization response dominated by polar microdomains (PNRs).

[0093] Figure 18 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 high entropy ceramic samples were subjected to 1-10 6 The PE curve after the second cycle did not show any significant morphological distortion. Figure 19 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )W of NbO3 high entropy ceramic samples at 200 kV / cm and 1 Hz under different cycle times st 、W rec and η values, the results show that even at high cycle numbers, W rec The changes of and η are less than 1%, indicating that the ceramic has excellent fatigue resistance. These results show that (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 ceramics can still maintain stable energy storage performance under complex working conditions, providing key support for their practical application in pulse power systems.

[0094] Discharge performance test:

[0095] (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K0.5 Na 0.5 )Underdamped discharge characteristics of NbO3 high entropy ceramic samples under different applied electric fields at room temperature. Figure 20 As shown, the discharge waveform exhibits a sinusoidal decay pattern, and the peak current increases with increasing applied electric field. At 200 kV / cm, the 0.9NBBSCT-0.1KNN high-entropy ceramic reaches a peak current of 36.83 A within 45 ns. The peak current increases with increasing electric field, a typical characteristic of pulsed dielectric ceramics. Figure 21 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )Charge and discharge parameters C of NbO3 high entropy ceramic samples D and P D These parameters increase with the increase of the applied electric field and reach the maximum value at 200kV / cm, among which C D =496.2A / cm 2 , P D =51.3MW / cm 3 . Figure 22 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 Overdamped discharge curves of NbO3 high-entropy ceramic samples under different electric fields. These curves were obtained with a 100Ω load resistor connected in series with the circuit. The discharge curves exhibit a single peak rather than periodic oscillations. Figure 23 (1-x)(Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3-x(K 0.5 Na 0.5 )NbO3 high entropy ceramic samples under different electric fields d The relationship between W d From 0.01J / cm 3 Increased to 0.5J / cm 3 , while releasing 90% W d The time required t 0.9=148ns, which is in the sub-microsecond range. Therefore, the 0.9NBBSCT-0.1KNN high-entropy ceramic exhibits high power density, excellent energy storage capacity and outstanding charge-discharge performance.

[0096] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A high entropy relaxor lead-free perovskite ceramic, characterized in that: for Na 0.2 Bi 0.2 Ba 0.2 Sr 0.2 Ca 0.2 )TiO3 and (K 0.5 Na 0.5 )NbO3 solid solution; the (K 0.5 Na 0.5 ) The content of NbO3 is 5 to 15 mol% of the high entropy relaxor lead-free perovskite ceramic.

2. The high entropy relaxor lead-free perovskite ceramic according to claim 1, characterized in that The (K 0.5 Na 0.5 ) The content of NbO3 is 10 mol% of the high entropy relaxor lead-free perovskite ceramic.

3. The high entropy relaxor lead-free perovskite ceramic according to claim 2, characterized in that Its breakdown electric field strength is 420kV / cm and its recoverable energy storage density is 6.16J / cm 3 , the energy storage efficiency is 82.7%.

4. The method for preparing the high entropy relaxor lead-free perovskite ceramic according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Weighing raw materials: weighing Na-containing compound, Bi-containing compound, Ba-containing compound, Sr-containing compound, Ca-containing compound, K-containing compound, Nb-containing compound and Ti-containing compound according to the target stoichiometric ratio; (2) First ball milling: The raw materials weighed in step (1) are dried and then placed in a planetary ball mill for the first ball milling; (3) Pre-calcination treatment: After the ball-milled powder in step (2) is dried, it is placed in a crucible, compacted and covered, and heated to 850-870°C at a heating rate of 5-6°C / min and kept at this temperature for 1.8-2.2h for pre-calcination; (4) Second ball milling: The product obtained by pre-calcining in step (3) is subjected to a second ball milling; (5) Granulation and tableting: Grinding, granulating, and tableting the powder obtained by the second ball milling in step (4) to obtain a green body; (6) Debinding and sintering: The green body obtained in step (5) is kept at 530-550°C for 2.5-3 hours, then heated to 1150-1250°C at a heating rate of 5-6°C / min and kept at this temperature for 1.8-2 hours to obtain a high-entropy relaxor lead-free perovskite ceramic.

5. The preparation method according to claim 4, characterized in that The Na-containing compound is Na2CO3; the Bi-containing compound is Bi2O3; the Ba-containing compound is BaCO3; the Sr-containing compound is SrCO3; the Ca-containing compound is CaCO3; the K-containing compound is K2CO3; the Nb-containing compound is Nb2O5; and the Ti-containing compound is TiO2.

6. The preparation method according to claim 4, characterized in that The drying in step (2) is specifically: drying at 110-120° C. for 8-9 hours.

7. The preparation method according to claim 4, characterized in that The first ball milling in step (2) is specifically as follows: the dried raw materials, zirconia balls and anhydrous ethanol are loaded into a ball milling jar in a mass ratio of 1: (2.5-3): (1.5-2), and the ball milling is performed alternately in a planetary ball mill at a speed of 300-350 r / min, with the direction being reversed every 30-40 minutes, and the ball milling is continued for 10-12 hours.

8. The preparation method according to claim 4, characterized in that The drying in step (3) is specifically: drying at 80-90° C. for 12-24 hours.

9. The preparation method according to claim 4, characterized in that The second ball milling in step (4) is specifically as follows: the dried raw materials, zirconia balls and anhydrous ethanol are loaded into a ball milling jar in a mass ratio of 1: (2.5-3): (1.5-2), and the ball milling is performed alternately in a planetary ball mill at a speed of 300-350 r / min, with the direction being reversed every 30-40 minutes, and the ball milling is continued for 10-12 hours.

10. The preparation method according to claim 4, characterized in that The tableting in step (5) is specifically performed by using a pressure of 120 to 130 MPa for tableting and holding the pressure for 30 to 40 seconds.

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