High-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramics, their preparation methods and applications

Abstract

This invention provides a high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic, its preparation method, and its applications. Its general chemical formula is (1-α-β)·KNNM-α·A HE B HE O3-β·NdFeO3, where KNNM is the perovskite main phase, A HE B HE O3 is a high-entropy perovskite phase composed of multiple elements at both A and B sites, while NdFeO3 is a neodymium-iron ore phase. This invention achieves a piezoelectric ceramic with simultaneously high piezoelectric constant, high mechanical quality factor, high Curie temperature, and high electromechanical coupling coefficient through the synergistic effect of diffusion phase transformation of the high-entropy phase and defect dipole modulation of the neodymium-iron ore phase, under optimized composition. This ceramic is prepared using a solid-state method including two-step sintering and is suitable for piezoelectric devices such as sensors, transducers, actuators, and energy harvesters.

Description

Technical Field

[0001] This invention belongs to the field of lead-free piezoelectric ceramic materials technology, specifically relating to a high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic, its preparation method and application. Background Technology

[0002] Piezoelectric ceramics are key functional materials capable of converting mechanical energy into electrical energy, and are widely used in electronic devices such as sensors, transducers, actuators, and energy harvesters. For a long time, lead-based piezoelectric ceramics, represented by lead zirconate titanate (PZT), have dominated the market due to their excellent piezoelectric properties and high Curie temperature. However, lead poses serious threats to the ecological environment and human health during its production, use, and disposal, leading to increasingly stringent regulations restricting its use globally. Therefore, developing high-performance, high-stability lead-free piezoelectric ceramics has become an urgent need and a research hotspot in the field of functional materials.

[0003] Among numerous lead-free candidate materials, potassium sodium niobate (KNN)-based ceramics are considered one of the most promising alternatives due to their high Curie temperature, tunable piezoelectric properties, and environmentally friendly characteristics. However, pure KNN ceramics suffer from difficulties in densification, a narrow sintering temperature range, poor temperature stability, and electromechanical properties that still lag behind lead-based materials, limiting their practical applications. To improve their performance, researchers typically employ strategies such as ion doping, phase boundary engineering, or the introduction of a second phase. For example, introducing Li at the A-site... + Rare earth elements or the introduction of Sb at the B site 5+ Ta 5+ Equivalents can adjust the phase transition temperature and promote densification; constructing orthogonal-tetragonal phase boundaries (PPB) or trigonal-orthogonal phase boundaries (RO) can significantly improve the piezoelectric response; and composite Bi 0.5 Na 0.5 TiO3, Bi 0.5 K 0.5 Ferroelectric phases such as TiO3 can also improve performance to some extent.

[0004] Nevertheless, traditional modification methods still face the following challenges:

[0005] First, most doped or composite systems have insufficient performance stability over a wide temperature range, and their dielectric and piezoelectric properties are highly temperature-dependent.

[0006] Secondly, under cyclic electric fields or mechanical loads, domain walls are easily pinned by defects, leading to a decrease in fatigue performance;

[0007] Third, it is difficult to simultaneously achieve the high voltage coefficient (d) 33 High mechanical quality factor (Q) m ) and high Curie temperature (T cCollaborative optimization of ).

[0008] In recent years, high-entropy perovskite materials have shown unique advantages in improving thermal stability, relaxation properties, and fatigue resistance due to lattice distortion caused by multi-component solid solution, high configurational entropy effect, and diffusion-type phase transition characteristics. On the other hand, NdFeO3, a neodymium-iron perovskite with antiferromagnetic order, can enhance the reversibility of domain structure by introducing controllable oxygen vacancies and defect dipoles to regulate domain wall dynamics, and is expected to further optimize the piezoelectric response and stability of KNN-based ceramics.

[0009] Therefore, how to combine the entropy stabilization effect of high-entropy perovskites with the defect engineering of NdFeO3, and synergize with the intrinsic Ho / Mo co-doped KNN matrix, to construct a novel lead-free piezoelectric ceramic that combines high voltage conductivity, high temperature stability and excellent reliability remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing KNN-based lead-free piezoelectric ceramics in terms of temperature stability, fatigue resistance, and the difficulty in synergistically improving high piezoelectric constant and high mechanical quality factor. The invention provides a high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic with excellent comprehensive performance, especially with high stability in a wide temperature range, as well as its preparation method and application.

[0011] In a first aspect, the present invention provides a KNN-based lead-free piezoelectric ceramic composed of high-entropy perovskite and neodymium iron ore, the chemical composition of which is represented by the following general formula:

[0012] (1-α-β)·KNNM - α·A HE B HE O3 - β·NdFeO3

[0013] Among them, KNNM is a potassium sodium niobate-based perovskite main phase containing K, Na, Li and Ho at the A site and Nb, Sb and Mo at the B site;

[0014] A HE B HE O3 is a high-entropy perovskite phase composed of multiple high-entropy components at both the A and B sites;

[0015] NdFeO3 is a neodymium-iron ore phase;

[0016] α and β are mole fractions, and satisfy: 0.04 < α ≤ 0.06, 0.01 < β ≤ 0.06.

[0017] This invention constructs a ternary composite lead-free piezoelectric ceramic through the above technical solution. The KNNM phase serves as the piezoelectric active matrix, and its specific ion doping (Li, Ho, Sb, Mo) is used to synergistically optimize the lattice, reduce the sintering temperature, induce polymorphic phase boundaries, and regulate defect types. The introduction of A... HE B HE The O3 high-entropy perovskite phase utilizes its high configurational entropy to induce an "entropy stabilization" effect, strong lattice distortion, and diffusion-type phase transition behavior, thereby effectively widening the ferroelectric-paraelectric phase transition range and significantly improving the material's temperature stability and fatigue resistance under alternating fields. The introduction of the NdFeO3 neodymium iron ore phase aims to leverage its ability as an antiferromagnetic perovskite to easily form controllable defect dipoles and oxygen vacancies, utilizing superexchange interactions to regulate domain wall motion, reduce the driving field, and improve strain linearity, while simultaneously improving sintering density and conductivity window. The diffusion-type phase transition effect of the high-entropy phase and the defect dipole coupling of NdFeO3 work together on the domain structure to achieve a triple synergy of "diffusion-type phase transition, flexible pinning, and reversible domain rotation," taking into account both high d... 33 High Q m It offers wide temperature range stability and low dielectric loss.

[0018] In the general formula, limiting the range of α to 0.04 < α ≤ 0.06 ensures a sufficient content of the high-entropy phase to produce significant entropy stability and phase transition diffusion effects, while avoiding excessive addition that could lead to excessive disruption of the long-range ferroelectric order of the matrix phase. Limiting the range of β to 0.01 < β ≤ 0.06 allows the NdFeO3 phase to effectively exert its defect engineering and domain structure regulation functions, while preventing excessive introduction that could cause unfavorable second-phase aggregation or deterioration of electrical properties. Through the above design of this invention, a synergistic effect can be achieved among the three phases: "matrix piezoelectric activity provides the foundation - high-entropy phase enhances stability - NdFeO phase optimizes domain dynamics," thereby achieving a breakthrough in comprehensive performance.

[0019] In some preferred embodiments of the present invention, the chemical composition of the KNNM is as follows:

[0020] (K 0.52 Na 0.46 Li 0.02 ) 0.99 Ho 0.01 )][(Nb 0.95 Sb 0.05 ) 0.98 Mo 0.02 ]O 3。

[0021] The K / Na ratio was 0.52 / 0.46, which modulated the orthorhombic-tetragonal polymorphic phase boundary (PPB) to near room temperature. At the A-site, 2 mol% Li was introduced. +Utilizing its small ionic radius, it can shrink the unit cell and lower the sintering temperature, introducing 1 mol% Ho. 3+ Grain refinement is achieved using rare earth ions, and weak pinning points conducive to domain rotation are introduced through valence state differences; at the B site, 5 mol% Sb is introduced. 5+ Used to move the orthogonal-tetragonal phase transition temperature, synergistically optimizing PPB with the K / Na ratio; 2 mol% Mo is introduced. 6+ As a high-valence dopant, it can modulate conductivity and domain wall dynamics by affecting oxygen vacancy concentration.

[0022] According to the KNN-based lead-free piezoelectric ceramic provided by the present invention, preferably, the A HE B HE In O3, the high-entropy component A at position A HE Contains Bi, Na, K, Ba, Sr, and the high-entropy component B at the B site. HE It contains Zr, Ti, Hf, Sn, and Nb.

[0023] The A proposed in this invention HE and B HE The "dual high entropy" design can simultaneously introduce maximum chemical disorder and lattice stress at both the A-site and B-site to induce diffusion phase transitions, form nanodomain structures, and achieve entropy stability, thereby ensuring that the material has a smooth performance change curve and excellent structural stability over a wide temperature range.

[0024] According to the KNN-based lead-free piezoelectric ceramic provided by the present invention, preferably, the A HE The elements in and the B HE Each element in the mixture exists in approximately equal atomic fractions.

[0025] The term "nearly isoatomic fraction" in this invention refers to a difference in absolute value between the mole fractions of each element not exceeding 10%. For example, A HE The five elements (Bi, Na, K, Ba, Sr) each occupy approximately equal mole fractions at site A (e.g., approximately 20% ± 5% each), while B... HE The five elements (Zr, Ti, Hf, Sn, Nb) in the system are also roughly equal in number at the B site (e.g., each accounting for about 20% ± 5%). When the elements exist in nearly equal proportions, the system can achieve the highest entropy of mixing, thus thermodynamically most inclined to form a single, homogeneous solid solution phase.

[0026] In the piezoelectric ceramic provided by the present invention, preferably, the value of β is in the range of 0.02≤β≤0.04.

[0027] Within the aforementioned preferred range, the appropriate amount of defect dipoles introduced by the NdFeO3 phase can form an effective "flexible coupling" with the dispersed domain structure induced by the high-entropy phase, providing a certain degree of domain wall pinning to improve the mechanical quality factor (Q). m Furthermore, it does not hinder domain flipping during the polarization process due to excessive pinning, thus facilitating the simultaneous attainment of a higher piezoelectric constant (d). 33 ).

[0028] According to the piezoelectric ceramic provided by the present invention, preferably, the piezoelectric ceramic satisfies one or more of the following properties: piezoelectric constant d 33 410-535 pC / N; and / or mechanical quality factor Q m 150-266; and / or Curie temperature T c The temperature is 279-345℃; and / or the planar electromechanical coupling coefficient k of the piezoelectric ceramic is... p It ranges from 0.44 to 0.52.

[0029] The above preferred embodiments define the technical effects achieved by the ceramic of the present invention through a series of excellent performance parameters. Piezoelectric constant d 33 The high pC / N ratio of 410-535 is attributed to optimized PPB, lattice softening caused by the high-entropy phase, and the promotion of domain orientation by NdFeO3. Mechanical quality factor Q m Reaching 150-266°C reflects the entropy stabilization effect of the high-entropy phase and the "flexible pinning" of NdFeO3, which together suppress the irreversible motion of domain walls and reduce mechanical losses. Curie temperature T c Maintaining a relatively high temperature range of 279-345℃, it inherits the high-temperature characteristics of KNN-based materials, ensuring performance in high-temperature applications. Planar electromechanical coupling coefficient k p A value of 0.44-0.52 indicates a highly efficient coupling ability between electrical and mechanical energy. The implementation scheme possessing these performance indicators demonstrates that the piezoelectric ceramic of this invention achieves simultaneous optimization of multiple performance characteristics.

[0030] In a preferred embodiment of the present invention, when 0.02 ≤ x ≤ 0.04, the piezoelectric constant d of the piezoelectric ceramic is... 33 The coefficient of performance is 535 pC / N, the mechanical quality factor is 266, the Curie temperature is 325℃, and the planar electromechanical coupling coefficient k is... p It is 0.52.

[0031] In a second aspect, the present invention provides a method for preparing the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic of the first aspect mentioned above, comprising the following steps:

[0032] S1. Raw material mixing: Weigh each raw material oxide or carbonate according to the chemical composition, ball mill and mix them, and dry them to obtain a mixed powder;

[0033] S2. Pre-calcination synthesis: The mixed powder is pre-calcined to obtain the initial solid-phase reaction powder;

[0034] S3. Forming and sintering: The initial solid-phase reaction powder is ball-milled, granulated, pressed into shape, and then sintered to obtain a ceramic green body;

[0035] S4. Silvering and Polarization: The ceramic blank is silvered to form electrodes, and then polarized to obtain the piezoelectric ceramic.

[0036] The preparation method of the present invention is proposed for the chemical composition described in the first aspect, wherein step S2 completes the solid-state reaction by pre-firing to generate the target crystalline phase precursor and avoids the generation of impurity phases during final sintering; step S3 achieves the final density and microstructure of the ceramic; and step S4 activates the piezoelectric properties by being silvered and polarized.

[0037] According to the preparation method provided by the present invention, preferably, the pre-firing temperature in step S2 is 700-750℃, and the holding time is 3-4 hours. In step S2, the mixed powder is pre-firing to obtain ceramic main crystalline phase powder. This step is a solid-state reaction process, the purpose of which is not final densification, but to allow the components to undergo preliminary chemical reactions at a lower temperature to generate crystal nuclei with the target perovskite structure, thus avoiding problems such as chemical composition deviation, precipitation, or uneven densification caused by different reaction rates or volatilization differences among the components during the final high-temperature sintering.

[0038] Preferably, the sintering in step S3 is a two-step sintering process, comprising: a first step of holding at 1150-1165℃ for 60-80 minutes, and a second step of holding at 1100-1150℃ for 2-3 hours. The two-step sintering process proposed in this invention is designed to address the challenges of narrow sintering temperature windows and the easy volatilization of alkali metals in KNN-based materials: the first step of high-temperature (1150-1165℃) short-time holding provides high driving force to achieve initial densification; the second step of lower temperature (1100-1150℃) long-time holding suppresses abnormal grain growth while promoting the elimination of pores, thereby achieving a high-density and uniform fine-grained structure to obtain excellent electrical properties.

[0039] According to the preparation method provided by the present invention, preferably, the polarization treatment in step S4 is oil bath polarization, the polarization field strength can be 3-5 kV / mm, the polarization temperature can be 100-120℃, and the polarization time can be 10-15 minutes.

[0040] In this preferred embodiment, oil bath polarization can prevent air breakdown and provide uniform heat dissipation. A polarization field strength of 3-5 kV / mm, a polarization temperature of 100-120°C, and a polarization time of 10-15 minutes can ensure domain orientation is completed, enhance domain wall mobility, and facilitate full polarization under a lower electric field.

[0041] In a preferred embodiment of the present invention, the raw materials mentioned in step S1 include the following compounds weighed in stoichiometric proportions: K2CO3, Na2CO3, Nb2O5, Li2CO3, Sb2O3, Bi2O3, ZrO2, HfO2, BaCO3, Ho2O, MoO3, SrCO3, TiO2, SnO2, Nd2O3, and Fe2O3. Preferably, K, Na, and Li elements are added in excess by 1-2 mol% to compensate for sintering volatilization.

[0042] In some specific embodiments of the present invention, step S3 includes the following operations: adding a binder (such as PVA) to the sieved ceramic main crystalline phase powder, grinding, granulating, and pressing into a circular sheet. The sheet is then subjected to a binder removal process at 700-750°C for 8-12 hours, followed by two-step high-temperature sintering to obtain a ceramic wafer.

[0043] According to the preparation method provided by the present invention, step S4 includes silvering treatment and polarization treatment. Silvering treatment forms a good ohmic electrode on the ceramic surface, providing a pathway for subsequent application of a high-voltage electric field. Polarization treatment is a step to activate the piezoelectric properties of the material. By applying a DC electric field exceeding the coercive field of the material, the originally randomly oriented ferroelectric domains inside the ceramic preferentially align along the direction of the electric field, thereby exhibiting a piezoelectric effect macroscopically.

[0044] Thirdly, the present invention also provides the application of the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic described in the first aspect in the preparation of piezoelectric devices, wherein the piezoelectric devices are selected from sensors, transducers, actuators or energy harvesters.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] Innovative material design: By constructing a ternary composite system of "KNN-based main phase - high-entropy perovskite phase - neodymium iron ore phase", an organic combination of entropy stabilization, defect regulation, and phase boundary engineering is achieved at the material genome level. The high-entropy phase utilizes the high configurational entropy resulting from the near-equal occupancy of multiple components to induce a strong diffusion phase transition, effectively broadening the performance stability temperature range; the NdFeO3 phase introduces controlled defect dipoles, achieving flexible coupling with the dispersed domain structure of the high-entropy phase. This synergistic design overcomes the limitation of traditional modification methods in simultaneously optimizing multiple properties.

[0047] Synergistic Enhancement of Overall Electrical Performance: Under optimized composition, the ceramic of this invention achieves simultaneous optimization of high voltage constant, high mechanical quality factor, high Curie temperature, and high planar electromechanical coupling coefficient. This synergistic improvement in multiple indicators is significantly superior to most existing KNN-based lead-free piezoelectric ceramics.

[0048] Temperature stability and reliability: Benefiting from the entropy stabilization effect and diffusion phase transition characteristics of the high-entropy phase, the dielectric and piezoelectric properties of the ceramics of this invention exhibit low drift characteristics over a wide temperature range (e.g., room temperature to 250°C) and better fatigue resistance. This solves the long-standing problem of poor temperature stability faced by KNN-based ceramics, broadening their application potential in harsh environments (such as automotive, aerospace, and deep exploration).

[0049] Controllable and reproducible preparation process: The two-step sintering method and optimized polarization process parameters provided by this invention effectively suppress alkali metal volatilization, resulting in a high-density, uniform, fine-grained microstructure, ensuring high consistency of material properties and reproducibility of preparation. This process is mature and stable, easy to scale up, and provides a reliable technical path for the industrial application of high-performance lead-free piezoelectric ceramics.

[0050] The ceramic of this invention has excellent comprehensive performance, especially with high voltage electrical properties, high stability and high Curie temperature, making it very suitable for manufacturing piezoelectric devices such as high-performance sensors, ultrasonic transducers, precision actuators and wide-temperature-range energy harvesters. It is expected to achieve lead-free replacement in high-end fields such as medical imaging, industrial non-destructive testing, intelligent sensing and new energy vehicles, with significant social benefits and market prospects. Attached Figure Description

[0051] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0052] Figure 1 The XRD patterns of the lead-free piezoelectric ceramics prepared in Examples 1 to 4 of this invention are shown below.

[0053] Figure 2 SEM images of the lead-free piezoelectric ceramics prepared in Examples 1 to 4 of this invention;

[0054] Figure 3 The piezoelectric constant d of the lead-free piezoelectric ceramics prepared in Examples 1 to 4 of this invention. 33 And mechanical quality factor Q m A bar chart comparing the changes in NdFeO3 content;

[0055] Figure 4 The planar electromechanical coupling coefficient k of the lead-free piezoelectric ceramics prepared in Examples 1 to 4 of this invention is... p Trend curve of NdFeO3 content;

[0056] Figure 5 The graphs show the dielectric constant of the lead-free piezoelectric ceramics prepared in Examples 1 to 4 of this invention as a function of temperature. Detailed Implementation

[0057] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The described embodiments are only a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0058] In the following embodiments, unless otherwise specified, the experimental conditions used are conventional conditions in the art, the reagents and consumables used are commercially available unless otherwise specified, and the process methods used are conventional process methods in the art unless otherwise specified.

[0059] Example 1

[0060] This embodiment prepares the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic of the present invention, the chemical composition of which is as follows:

[0061] 0.94 KNNM - 0.05 A HE B HE O3 - 0.01 NdFeO3

[0062] The chemical composition of the potassium sodium niobate-based perovskite main phase KNNM is as follows:

[0063] (K 0.52 Na 0.46 Li 0.02 ) 0.99 Ho 0.01 )][(Nb 0.95 Sb 0.05 ) 0.98 Mo 0.02 O3

[0064] High-entropy perovskite phase A HE B HE The composition of O3 is:

[0065] (Bi 0.2 Na 0.2 K 0.2 Ba 0.2 Sr 0.2 (Zr) 0.2 Ti 0.2 Hf 0.2 Sn 0.2 Nb0.2 O3

[0066] Its preparation method includes the following steps:

[0067] S1. Raw Material Mixing: Analytical grade K₂CO₃, Na₂CO₃, Nb₂O₅, Li₂CO₃, Sb₂O₃, Bi₂O₃, ZrO₂, HfO₂, BaCO₃, Ho₂O, MoO₃, SrCO₃, TiO₂, SnO₂, Nd₂O₃, and Fe₂O₃ were used as raw materials, weighed according to the above chemical formulas. To compensate for the volatilization of K, Na, and Li elements during sintering, the K, Na, and Li raw materials were weighed at 10¹~10² mol% of their stoichiometric ratio. The raw materials were mixed with anhydrous ethanol and zirconium dioxide balls at a mass ratio of 1:1:2, placed in a ball mill jar, and ball-milled at 280~300 rpm for 12 hours to ensure thorough and uniform mixing. The ball-milled slurry was placed in an oven and dried at 100℃ for 6 hours to obtain a uniformly mixed dry powder.

[0068] S2. Pre-calcination synthesis: The dried powder is placed in an alumina crucible, placed in a muffle furnace, and pre-calcined at 750°C for 3 hours to obtain the initial solid-phase reaction powder.

[0069] S3. Forming and Sintering: The pre-fired powder is ball-milled again (under the same conditions as step S1) and dried. The powder is sieved through an 80-mesh standard sieve to obtain ceramic powder with uniform particle size. A 5% (w / w) aqueous solution of polyvinyl alcohol (PVA) is added to the sieved powder as a binder (the amount added is 10% of the powder mass), and the mixture is thoroughly ground and granulated. The granulated particles are pressed into circular green sheets with a diameter of approximately 10 mm and a thickness of approximately 1.0 mm under a pressure of 3 MPa.

[0070] The green sheet was placed in a muffle furnace and heated to 725°C at a rate of 3°C / min, held for 10 hours to remove the organic binder. Then, a two-step sintering process was performed: first, the temperature was increased to 1160°C at 5°C / min and held for 70 minutes; then, the temperature was rapidly reduced to 1120°C and held for 2.5 hours; finally, the sheet was cooled in the furnace to obtain a dense ceramic disc.

[0071] S4. Silvering and Polarization: The sintered ceramic disc is ground and polished on both sides until smooth and flat. Silver paste is uniformly coated on both sides of the ceramic disc using screen printing, and then placed in a muffle furnace and held at 550°C for 10 minutes to form silver electrodes. The ceramic disc with electrodes is placed in silicone oil and polarized for 15 minutes under an oil bath temperature of 110°C by applying a DC electric field of 4 kV / mm, thus obtaining the piezoelectric ceramic sample of this embodiment.

[0072] The ceramic samples prepared in this embodiment were characterized and their performance was tested. The results are as follows:

[0073] X-ray diffraction (XRD) analysis (see...) Figure 1 The results indicate that the sample has a pure perovskite structure without impurities. Splitting of diffraction peaks was observed in the 2θ range of 44°–46.5°, indicating the simultaneous presence of orthorhombic and tetragonal (OT) phases in the ceramic, forming a polymorphic phase boundary (PPB). Scanning electron microscopy (SEM) observations (see...) Figure 2 (a) shows that the ceramic grains are uniform in size and have a dense structure, with an average grain size of approximately 0.8 μm. Performance tests (see...) Figure 3 , Figure 4 , Figure 5 This indicates that the piezoelectric constant d of the ceramic sample is... 33 The planar electromechanical coupling coefficient is 408 pC / N. p The mechanical quality factor Q is 0.44. m The Curie temperature is 164 T. c At approximately 279°C, dielectric loss remains low over a wide temperature range.

[0074] Example 2

[0075] This embodiment prepares the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic of the present invention, the chemical composition of which is as follows:

[0076] 0.93 KNNM - 0.05 A HE B HE O3 - 0.02 NdFeO3

[0077] Among them, the potassium sodium niobate-based perovskite main phase KNNM and the high-entropy perovskite phase A HE B HE The composition of O3 is the same as in Example 1.

[0078] The preparation was carried out using a method that was basically the same as that in Example 1, except that: during the mixing of raw materials in step S1, the weighing ratio of Nd2O3 and Fe2O3 was adjusted according to the above chemical composition so that the molar fraction of NdFeO3 was 0.02.

[0079] The ceramic samples prepared in this embodiment were characterized and their performance was tested. The results are as follows:

[0080] X-ray diffraction (XRD) analysis (see...) Figure 1 The results indicate that the sample has a pure perovskite structure, free of impurities, and exhibits polytype phase boundary (PPB) characteristics. Scanning electron microscopy (SEM) observations (see...) Figure 2 (b) shows that the ceramic grain size has increased, with an average grain size of approximately 1.2 μm, and the density has further improved. Performance testing (see...) Figure 3 , Figure 4 , Figure 5 This indicates that the piezoelectric constant d of the ceramic sample is... 33 Increased to 480 pC / N, planar electromechanical coupling coefficient k p Increased to 0.48, mechanical quality factor Q m The Curie temperature T increased significantly to 220. c The dielectric properties remain stable when the temperature is raised to approximately 310°C.

[0081] Example 3

[0082] This embodiment prepares the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic of the present invention, the chemical composition of which is as follows:

[0083] 0.92 KNNM - 0.05 A HE B HE O3 - 0.03 NdFeO3

[0084] Among them, the potassium sodium niobate-based perovskite main phase KNNM and the high-entropy perovskite phase A HE B HE The composition of O3 is the same as in Example 1.

[0085] The preparation was carried out using a method that was basically the same as that in Example 1, except that: during the mixing of raw materials in step S1, the weighing ratio of Nd2O3 and Fe2O3 was adjusted according to the above chemical composition so that the molar fraction of NdFeO3 was 0.03.

[0086] The ceramic samples prepared in this embodiment were characterized and their performance was tested. The results are as follows:

[0087] X-ray diffraction (XRD) analysis (see...) Figure 1 The results showed that the sample had a pure perovskite structure, was free of impurities, and exhibited distinct phase-polymorphic boundary (PPB) characteristics. Scanning electron microscopy (SEM) observations (see...) Figure 2 (c) shows that the ceramic grains are uniformly grown, with an average grain size of approximately 1.5 μm, and the ceramic body is extremely dense. Performance tests (see...) Figure 3 , Figure 4 , Figure 5 This indicates that the ceramic sample exhibits optimal overall performance: piezoelectric constant d 33 Up to 535 pC / N, planar electromechanical coupling coefficient k p The mechanical quality factor Q reaches 0.52. m Up to 266, Curie temperature T c It is further increased to about 325°C, with low dielectric loss and excellent temperature stability.

[0088] Example 4

[0089] This embodiment prepares the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic of the present invention, the chemical composition of which is as follows:

[0090] 0.91 KNNM - 0.05 A HE B HE O3 - 0.04 NdFeO3

[0091] Among them, the potassium sodium niobate-based perovskite main phase KNNM and the high-entropy perovskite phase A HE B HE The composition of O3 is the same as in Example 1.

[0092] The preparation was carried out using a method that was basically the same as that in Example 1, except that: during the mixing of raw materials in step S1, the weighing ratio of Nd2O3 and Fe2O3 was adjusted according to the above chemical composition so that the molar fraction of NdFeO3 was 0.04.

[0093] The ceramic samples prepared in this embodiment were characterized and their performance was tested. The results are as follows:

[0094] X-ray diffraction (XRD) analysis (see...) Figure 1 This indicates that the sample still retains the perovskite host phase. Scanning electron microscopy (SEM) observation (see...) Figure 2 (d) shows that the ceramic microstructure remains intact. Performance tests (see...) Figure 3 , Figure 4 , Figure 5 This indicates that the piezoelectric constant d of the ceramic sample is... 33 The planar electromechanical coupling coefficient is 475 pC / N. p The mechanical quality factor Q is 0.46. m The Curie temperature is 227°C (T). c The temperature was approximately 315°C. Compared to Example 3, all performance indicators decreased from their peak values, indicating that there is an optimization range for the NdFeO3 content.

[0095] It should be understood that the above-described embodiments and accompanying drawings are only used to illustrate the technical solutions of the present invention, and not to limit its scope of protection. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0096] Based on the technical concept of "KNN-based lead-free piezoelectric ceramics composed of high-entropy perovskite and neodymium iron ore" disclosed in this specification, any reasonable adjustment, substitution, or combination of the specific constituent elements, proportions, and preparation process parameters of the main phase and high-entropy phase within the scope of the general formula proposed in this invention, as long as it utilizes the basic principle of the synergistic effect of "entropy stability and diffusion phase transition effect of high-entropy perovskite phase" and "defect dipole regulation effect of neodymium iron ore phase" to achieve high piezoelectricity and high stability, should be considered as not departing from the inventive essence of this invention and falling within the protection scope defined by the claims. The protection scope of this invention should be determined by the content of its claims, and the process details, performance parameters, and specific material forms described in the specification and drawings should not be construed as limiting the claims.

Claims

1. A high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic, characterized in that, Its chemical composition is represented by the following general formula: (1-a-b)·KNNM - a·A HE B HE O3 - β·NdFeO3 Among them, KNNM is a potassium sodium niobate-based perovskite main phase containing K, Na, Li and Ho at the A site and Nb, Sb and Mo at the B site; A HE B HE O3 is a high-entropy perovskite phase composed of more than one high-entropy component at both the A and B sites; NdFeO3 is a neodymium-iron ore phase; α and β are mole fractions, and satisfy: 0.04 < α ≤ 0.06, 0.01 < β ≤ 0.

06.

2. The KNN-based lead-free piezoelectric ceramic according to claim 1, wherein, The chemical composition of KNNM is as follows: (K 0.52 So 0.46 Li 0.02 ) 0.99 Ho 0.01 )][(No 0.95 Sb 0.05 ) 0.98 Mo 0.02 ]O 3。 3. The KNN-based lead-free piezoelectric ceramic according to claim 1, wherein, The A HE B HE In O3, the high-entropy component A at position A HE Contains Bi, Na, K, Ba, Sr, and the high-entropy component B at the B site. HE Contains Zr, Ti, Hf, Sn, Nb; and / or the aforementioned A HE The elements in and the B HE Each element in the mixture exists in approximately equal atomic fractions.

4. The KNN-based lead-free piezoelectric ceramic according to claim 1, wherein, The value of β is in the range of 0.02≤β≤0.

04.

5. The KNN-based lead-free piezoelectric ceramic according to claim 1, wherein, The piezoelectric ceramic satisfies one or more of the following properties: piezoelectric constant d 33 410-535 pC / N; and / or Mechanical quality factor Q m 150-266; and / or Curie temperature T c 279-345℃; and / or The planar electromechanical coupling coefficient k of the piezoelectric ceramic p It ranges from 0.44 to 0.

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6. The method for preparing the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Raw material mixing: Weigh each raw material oxide or carbonate according to the chemical composition, ball mill and mix them, and dry them to obtain a mixed powder; S2. Pre-calcination synthesis: The mixed powder is pre-calcined to obtain the initial solid-phase reaction powder; S3. Forming and sintering: The initial solid-phase reaction powder is ball-milled, granulated, pressed into shape, and then sintered to obtain a ceramic green body; S4. Silvering and Polarization: The ceramic blank is silvered to form electrodes, and then polarized to obtain the piezoelectric ceramic.

7. The preparation method according to claim 6, wherein, The pre-firing temperature in step S2 is 700-750℃, and the holding time is 3-4 hours; and / or The sintering in step S3 is a two-step sintering process, including: the first step of holding at 1150-1165℃ for 60-80 minutes, and the second step of holding at 1100-1150℃ for 2-3 hours.

8. The preparation method according to claim 6, wherein, The granulation described in step S3 includes adding a binder, and step S3 also includes debinding treatment by holding at 700-750°C for 8-12 hours before sintering.

9. The preparation method according to claim 6, wherein, The polarization treatment in step S4 is oil bath polarization, with a polarization field strength of 3-5 kV / mm, a polarization temperature of 100-120℃, and a polarization time of 10-15 minutes.

10. The application of the high-entropy perovskite and neodymium iron ore composite KNN-based lead-free piezoelectric ceramic according to any one of claims 1 to 5 in the fabrication of piezoelectric devices, wherein the piezoelectric devices are selected from sensors, transducers, actuators or energy harvesters.

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