Porous lead-free piezoelectric material, preparation method thereof and piezoelectric energy collector

Abstract

The invention relates to a porous lead-free piezoelectric material, a preparation method thereof and a piezoelectric energy collector, and relates to the field of lead-free piezoelectric materials. The preparation method of the porous lead-free piezoelectric material comprises the following steps: preparing a ceramic substrate into a first piezoelectric film; preparing a second piezoelectric film from the ceramic matrix and a pore forming agent; a plurality of first piezoelectric films and a plurality of second piezoelectric films are stacked according to the sequence of the first piezoelectric films, the second piezoelectric films and the first piezoelectric films, and a multi-layer ceramic body is obtained. Compared with the prior art, the preparation method has the advantages that the addition amount of the pore-forming agent in the prepared porous ceramic layer and the thickness ratio are limited to be simultaneously within a specific range, so that the coupling relationship between the piezoelectric constant and the dielectric constant is effectively broken, and the piezoelectric voltage constant and the energy acquisition quality factor of the lead-free piezoelectric material are synergistically improved; therefore, the use requirements in the fields of piezoelectric energy collectors and the like are met, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of lead-free piezoelectric materials, and more particularly to a porous lead-free piezoelectric material, its preparation method, and a piezoelectric energy harvester. Background Technology

[0002] With the rapid development of wearable and implantable medical electronic devices and the Internet of Things (IoT) in healthcare, the demand for flexible, biosafety, and self-powered devices is increasing. Piezoelectric energy harvesters can convert mechanical energy, such as ultrasound waves, into electrical energy, providing a promising solution for wireless power supply systems. However, existing piezoelectric bioelectronic devices typically face the following limitations:

[0003] 1) Piezoelectric energy harvesters mostly use lead-based materials (such as lead zirconate titanate ceramics - PZT ceramics, etc.). Although they have good piezoelectric properties, they rely on toxic lead-containing materials, which are not good for human health and environmental protection, and face strict restrictions on their use in electronic applications.

[0004] 2) Although lead-free piezoelectric materials (such as potassium sodium niobate-based ceramics and KNN-based ceramics) are environmentally friendly, their piezoelectric constant ( ) and dielectric constant ( There is a strong coupling relationship between them. In existing technologies, to improve the piezoelectric constant ( ), often leading to a decrease in dielectric constant ( The piezoelectric voltage constant increases synchronously, thus limiting the piezoelectric voltage constant. ) and energy harvesting quality factor (FOM = The improvement of these two values ​​is significant. These two values ​​are two important parameters for evaluating the receiving sensitivity and energy harvesting capability of piezoelectric ceramics.

[0005] 3) Traditionally, pores are considered defects in ceramics, but the porous structure can be used to reduce the dielectric constant of the material. However, traditional porous ceramic preparation methods struggle to achieve pore gradient distribution and cannot effectively decouple pores. and This results in limited improvement in energy harvesting performance. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a porous lead-free piezoelectric material, its preparation method, and a piezoelectric energy harvester.

[0007] The technical solution provided by this invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a porous lead-free piezoelectric material, the method comprising the following steps:

[0009] The ceramic substrate is used to form the first piezoelectric film;

[0010] A second piezoelectric film is made by combining a ceramic matrix and a pore-forming agent;

[0011] A number of first piezoelectric films and a number of second piezoelectric films are stacked in the order of first piezoelectric film, second piezoelectric film and first piezoelectric film to obtain a multilayer ceramic blank;

[0012] The multilayer ceramic preform is subjected to pressing, debinding, and sintering to obtain the porous lead-free piezoelectric material.

[0013] In the preparation of the second piezoelectric film, the weight of the pore-forming agent added accounts for 12-14 wt% of the weight of the ceramic matrix; the total stacked thickness of the second piezoelectric film accounts for 70%-80% of the thickness of the multilayer ceramic preform.

[0014] Furthermore, the ceramic matrix comprises potassium sodium niobate-based ceramic as shown in Chemical Formula 1, which is as follows: .

[0015] Furthermore, the step of forming the first piezoelectric film from the ceramic substrate includes the following processes:

[0016] The raw materials were weighed and mixed according to the stoichiometric ratio of the ceramic matrix, and then the ceramic matrix was prepared by solid-state sintering.

[0017] The binder, the first dispersant, and the solvent are mixed to obtain a colloidal solution;

[0018] The ceramic matrix, the colloidal solution, and the second dispersant are mixed, and then the first piezoelectric film is formed by casting.

[0019] Furthermore, the step of forming a second piezoelectric film from a ceramic substrate and a pore-forming agent includes the following processes:

[0020] The raw materials were weighed and mixed according to the stoichiometric ratio of the ceramic matrix, and then the ceramic matrix was prepared by solid-state sintering.

[0021] The ceramic matrix and the pore-forming agent are mixed to obtain a mixture;

[0022] The binder, the first dispersant, and the solvent are mixed to obtain a colloidal solution;

[0023] The mixture, the colloidal solution, and the second dispersant are mixed, and then the second piezoelectric film is formed by casting.

[0024] Furthermore, the working conditions parameters of the solid-state sintering method include: temperature of 800~900℃ and time of 5~8h;

[0025] And / or, the working condition parameters of the casting method include: controlling the scraper height to be 12~16μm.

[0026] Furthermore, in preparing the first piezoelectric film, the amount of the binder added is 5-10 wt% of the weight of the ceramic matrix, the amount of the first dispersant added is 0.5-2 wt% of the weight of the ceramic matrix, the amount of the solvent added is 86 wt%-93 wt% of the weight of the ceramic matrix, and the amount of the second dispersant added is 0.5-2 wt% of the weight of the ceramic matrix.

[0027] And / or, when preparing the second piezoelectric film, the amount of the binder added is 5-10 wt% of the weight of the ceramic matrix, the amount of the first dispersant added is 0.5-2 wt% of the weight of the ceramic matrix, the amount of the solvent added is 86 wt%-93 wt% of the weight of the ceramic matrix, and the amount of the second dispersant added is 0.5-2 wt% of the weight of the ceramic matrix;

[0028] And / or, the pore-forming agent comprises polystyrene, the binder comprises polyvinyl alcohol, the first dispersant comprises triethanolamine, the second dispersant comprises polyethylene glycol, and the solvent comprises ethanol.

[0029] Furthermore, the working conditions parameters for the pressing process include: temperature of 55~60℃, pressure of 2~10Mpa, and time of 5~20min;

[0030] And / or, the working conditions parameters for the glue removal process include: heat preservation at 800~900℃ for 5~10 hours;

[0031] And / or, the working conditions parameters of the sintering treatment include: maintaining at a temperature of 1000~1100℃ for 2~5 hours.

[0032] Furthermore, the thickness of the porous lead-free piezoelectric material is 0.8~1.2mm;

[0033] And / or, the porous lead-free piezoelectric material has a sandwich gradient porous structure, the sandwich gradient porous structure comprising a first dense ceramic layer, a porous ceramic layer and a second dense ceramic layer.

[0034] Secondly, the present invention provides a porous lead-free piezoelectric material, wherein the porous lead-free piezoelectric material is prepared by the method for preparing porous lead-free piezoelectric material as described in any one of the first aspects.

[0035] Thirdly, the present invention provides a piezoelectric energy harvester, comprising the porous lead-free piezoelectric material described in the second aspect.

[0036] The technical solutions provided in the embodiments of the present invention have at least the following advantages compared with the prior art:

[0037] This invention provides a porous lead-free piezoelectric material, its preparation method, and a piezoelectric energy harvester. Compared to existing technologies, the porous lead-free piezoelectric material provided by this invention has a dense-porous-dense sandwich gradient porous structure. Furthermore, by limiting the content of the pore-forming agent and the thickness ratio during pore formation in the porous ceramic layer, this effectively breaks the coupling relationship between the piezoelectric constant and the dielectric constant, achieving a synergistic improvement in the piezoelectric voltage constant and energy harvesting quality factor of the lead-free piezoelectric material. This meets the application requirements in fields such as piezoelectric energy harvesters and has broad application prospects. Specifically:

[0038] 1) The porous lead-free piezoelectric material provided by this invention has a sandwich-gradient porous structure of dense-porous-dense. The dense ceramic layers on both sides primarily function to withstand and transmit mechanical stress / acoustic pressure, providing mechanical support for the entire structure. They also utilize their high-voltage constant to achieve efficient energy conversion, ensuring the overall high-voltage output of the material. The porous ceramic layer in the middle primarily functions to introduce a low-dielectric-constant pore phase (or gas phase), achieving low-node characteristics for the entire material. Simultaneously, the precisely controlled pore structure can optimize the internal stress distribution and promote domain wall inversion. Based on this, this invention further discovers that by limiting the content of the pore-forming agent and the thickness ratio during pore formation in the porous ceramic layer, a strong coupling relationship between the piezoelectric constant and dielectric constant in traditional porous lead-free piezoelectric materials can be effectively broken (i.e., increasing the piezoelectric constant of lead-free piezoelectric materials such as potassium sodium niobate-based ceramics also leads to a simultaneous increase in the dielectric constant, and because...). ,lead to (Difficult to significantly improve), achieving a synergistic improvement in the piezoelectric voltage constant and energy harvesting quality factor of lead-free piezoelectric materials, obtaining lead-free piezoelectric materials that balance high sensitivity and high energy harvesting efficiency, effectively solving the problem of piezoelectric voltage constant in existing lead-free piezoelectric materials ( ) and the merit value of energy harvesting ( The sensitivity is generally too low, making it difficult to balance high sensitivity and high energy harvesting efficiency.

[0039] 2) The porous lead-free piezoelectric material provided by this invention has excellent performance; specifically, its piezoelectric voltage constant ( Up to 73.04 × 10 -3 V·m·N -1 The figure of merit of energy harvesting ( Up to 17311.6 × 10 -15 m 2 ·N -1Under the same ceramic matrix composition, the porous lead-free piezoelectric material provided by this invention exhibits performance far superior to dense ceramic piezoelectric materials without porous phases, as well as most existing lead-free piezoelectric materials such as KNNS-BNZ-Fe, KNNS-BNH-Cu, BCZT, BNT-BT, PZT-4, and PZT-5H, and lead-based piezoelectric materials. This highlights the competitive advantage of the piezoelectric material provided by this invention as an environmentally friendly lead-free piezoelectric composite material in fields such as next-generation piezoelectric energy harvesters. Simultaneously, the piezoelectric material provided by this invention maintains excellent structural stability; its rhombohedral-orthorhombic-tetragonal three-phase coexistence crystal structure and high Curie temperature (~220°C) at room temperature are not significantly affected, ensuring its application potential in harsh environments.

[0040] 3) This invention provides a method for preparing porous lead-free piezoelectric materials. This method proposes for the first time to achieve precise control of the material porosity by controlling two parameter variables: the amount of pore-forming agent added and the thickness ratio of the porous ceramic layer. It also precisely controls the porosity and thickness ratio of the porous ceramic layer in the material within a specific range, thereby breaking the coupling relationship between the piezoelectric constant and the dielectric constant and achieving a synergistic improvement in the piezoelectric voltage constant and energy harvesting quality factor of the lead-free piezoelectric material.

[0041] 4) The method for preparing porous lead-free piezoelectric materials provided by this invention can precisely control the overall porosity of the material (by controlling the ratio of the total stacked thickness of the second piezoelectric film to the thickness of the multilayer ceramic preform, and by controlling the different contents of pore-forming agents such as 9-19 wt% to control the porosity of the porous ceramic layers), thereby achieving "on-demand design" of the final material properties. This method is simple, low-cost, and suitable for large-scale production, overcoming the difficulty of traditional methods in achieving controllable gradient pore structures within ceramics, and providing a universal and efficient solution for the preparation of high-performance multifunctional piezoelectric composite materials. Attached Figure Description

[0042] Figure 1 This is a schematic diagram illustrating the design strategy of the lead-free piezoelectric composite material with a gradient porous structure in this invention.

[0043] Figure 2 This is a complete process flow diagram of the preparation method of the porous lead-free piezoelectric material in this invention.

[0044] Figure 3 The X-ray diffraction patterns, refinement results, and phase content distribution diagrams of the materials with different PS contents x% (x=0, 9, 13, 17) in this invention are shown.

[0045] Figure 4This is a comparison of the dielectric properties of a material with a PS content of 13wt% and containing a pore-forming agent, where the ratio of the number of stacked layers of the second piezoelectric film to the total number of stacked layers is @x (x = 0, 0.1, 0.3, 0.5, 0.7), and dense ceramics at different temperatures.

[0046] Figure 5 The results are obtained from piezoelectric microscopy testing of the porous lead-free piezoelectric material in this invention.

[0047] Figure 6 The results are obtained from scanning electron microscopy testing of the porous lead-free piezoelectric material in this invention.

[0048] Figure 7 The piezoelectric performance test results are for the material with a fixed PS content of 13wt% and containing a pore-forming agent, where the ratio of the number of stacked layers of the second piezoelectric film to the total number of stacked layers is @x (x = 0.375 (i.e., Comparative Example 4), 0.5 (i.e., Comparative Example 5), 0.625 (i.e., Comparative Example 6), 0.75 (i.e., Example 1), 1 (i.e., Comparative Example 7)).

[0049] Figure 8 The piezoelectric constants of DPD composite materials with different PS contents (xwt%) are determined by setting the ratio of the number of stacked layers of the second piezoelectric film containing the pore-forming agent to the total number of stacked layers in this invention to 0.5. (x = 0 (Comparative Example 11), 9 (Comparative Example 10), 13 (Comparative Example 5), 17 (Comparative Example 9), 19 (Comparative Example 8)). ), dielectric constant ( ), piezoelectric voltage constant ( ), energy harvesting figure of merit ( A graph showing how the composition changes. Detailed Implementation

[0050] The present invention will be specifically described below through embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description of the present invention.

[0051] The main terms and main raw materials involved in this invention are described as follows:

[0052] In this invention, the dense ceramic layer is a ceramic layer with ceramic phase as the main body and continuous distribution, having low porosity (<1%) and high density (close to more than 95% of the theoretical density).

[0053] In this invention, potassium sodium niobate-based ceramics are based on the chemical formula K 0.5 Na 0.5Lead-free piezoelectric ceramic materials with NbO3 (KNN) as the core component can be selected in addition to potassium sodium niobate-based ceramics such as those shown in Chemical Formula 1 in this invention, or other potassium sodium niobate-based ceramics with different chemical compositions.

[0054] The solid-state sintering method in this invention is a material preparation technology that achieves densification through solid-state reactions such as interparticle diffusion mass transfer, grain boundary migration, and volume diffusion under solid-state conditions without the participation of a liquid phase. In specific operation, the preparation process disclosed in the prior art can be followed.

[0055] The casting process described in this invention is a wet forming process for preparing continuous thin sheets / films by applying slurry with a doctor blade. The core technology involves controlling the rheological properties of the slurry and the drying kinetics to achieve the preparation of uniform films. In specific operations, the preparation process can be carried out according to existing technologies.

[0056] In this invention, the pore-forming agent is used to form uniformly distributed pores through pyrolysis after sintering. Polymer microspheres such as polystyrene can be selected, with a specific diameter of 50 μm.

[0057] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Furthermore, unless otherwise specified or detailed, the steps and parameters involved can be performed according to existing processing techniques or using existing equipment; these will not be elaborated upon in detail in this invention document.

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0059] Example 1

[0060] This example provides a porous lead-free piezoelectric material, such as Figure 1 As shown, the porous lead-free piezoelectric material has a sandwich gradient porous structure, which includes a first dense ceramic layer, a porous ceramic layer, and a second dense ceramic layer.

[0061] The ceramic substrates in the first dense ceramic layer, the porous ceramic layer, and the second dense ceramic layer are all potassium sodium niobate-based ceramics as shown in Chemical Formula 1, which is as follows: .

[0062] The above-mentioned methods for preparing porous lead-free piezoelectric materials, such as Figure 2 As shown, it includes the following steps:

[0063] 1) Preparation of potassium sodium niobate-based ceramics as shown in formula 1

[0064] Potassium sodium niobate-based ceramics of chemical formula 1 were prepared using a traditional solid-state sintering method: raw materials (99% purity) (Purity 99.8%) (Purity 99.5%) (Purity 99.99%) (Purity 99.999%) (99% purity) (Purity 98%) Weigh and mix according to stoichiometric ratio to obtain a powder mixture. The powder mixture is wet-ball milled in ethanol for 12 hours to ensure thorough homogenization. After the solvent evaporates, the resulting powder is heat-treated at 850°C for 6 hours to complete the pre-firing, obtaining KNNS-NS ceramic powder (i.e., ceramic matrix - potassium sodium niobate-based ceramic as shown in chemical formula 1).

[0065] 2) Preparation of piezoelectric thin films

[0066] A colloidal solution is obtained by mixing 8 wt% (specifically polyvinyl alcohol), 2 wt% (specifically triethanolamine), and 92 wt% (specifically ethanol) of the binder (specifically, polyvinyl alcohol) based on the weight of the ceramic powder. The KNNS-NS ceramic powder, colloidal solution, and second dispersant (specifically polyethylene glycol, added at 2 wt% of the weight of the ceramic powder) are then mixed (specifically, the KNNS-NS ceramic powder and colloidal solution are ball-milled for 1.5 hours, followed by the addition of the second dispersant and milling at 259 rpm for 0.5 hours) to obtain a first slurry. The first slurry is then cast onto a glass plate using a casting method (the working conditions for the casting method include controlling the doctor blade height to approximately 15 μm and maintaining a uniform casting speed, which can be adjusted according to actual conditions). The formed film is then dried in an oven at 60°C for 10 minutes. The dried film is cut into 1 mm × 1 mm squares to obtain a first piezoelectric film with a thickness of approximately 15 μm that does not contain a pore-forming agent.

[0067] KNNS-NS ceramic powder and a pore-forming agent (specifically, polystyrene (PS) microspheres, 50 μm in diameter, added at 13 wt% of the weight of the KNNS-NS ceramic powder) were mechanically stirred and then milled for 8 hours to obtain a mixture. 8 wt% of a binder (specifically, polyvinyl alcohol), 2 wt% of a first dispersant (specifically, triethanolamine), and 92 wt% of a solvent (specifically, ethanol) were mixed to obtain a colloidal solution. The mixture, the colloidal solution, and the second dispersant (specifically, polyethylene glycol, added at 2 wt% of the weight of the mixture) were then combined to obtain a colloidal solution. The mixture was prepared by first ball milling the KNNS-NS ceramic powder and colloidal solution for 1.5 hours, then adding the second dispersant and grinding for 0.5 hours at a grinding speed of 259 rpm to obtain a second slurry. The second slurry was then cast onto a glass plate using a casting method (the working conditions of the casting method include controlling the doctor blade height to about 15 μm and maintaining a uniform casting speed, which can be adjusted according to the actual situation). The cast film was then dried in an oven at 60°C for 10 minutes. The dried film was cut into 1 mm × 1 mm squares to obtain a second piezoelectric film with a thickness of about 15 μm containing a pore-forming agent.

[0068] 3) Preparation of porous lead-free piezoelectric materials

[0069] A number of first piezoelectric films and a number of second piezoelectric films are stacked in the order of first piezoelectric film, second piezoelectric film, and first piezoelectric film (specifically, the stacking order is 10 layers of first piezoelectric film without pore-forming agent - 60 layers of second piezoelectric film with pore-forming agent - 10 layers of first piezoelectric film without pore-forming agent), resulting in a multilayer ceramic green body formed by a total of 80 layers of piezoelectric films (wherein, the number of stacked layers of second piezoelectric film with pore-forming agent / the total number of stacked layers = 0.75, that is, the total stacked thickness of the second piezoelectric film accounts for 75% of the thickness of the multilayer ceramic green body).

[0070] A multi-layer ceramic blank was pressed at 58°C by applying pressures of 2 MPa, 4 MPa, 6 MPa, 8 MPa and 10 MPa sequentially. The holding time under the pressures of 2 MPa, 4 MPa, 6 MPa and 8 MPa was 5 min, and the holding time under the pressure of 10 MPa was 20 min, to obtain a ceramic block.

[0071] The ceramic block was heated in a muffle furnace from room temperature to 850°C at a rate of 5°C / min and held for 6 hours for debinding. Then it was sintered in air at 1070°C for 3 hours and cooled to room temperature in the furnace to obtain the porous lead-free piezoelectric material with a total thickness of about 1 mm.

[0072] The above Figure 1The design strategy for the lead-free piezoelectric composite material with a gradient porous structure of this invention macroscopically demonstrates the concept of a "dense-porous-dense" sandwich structure. The above... Figure 2 This is a complete process flow diagram of the preparation method of the porous lead-free piezoelectric material of the present invention, which shows the entire process from powder synthesis, slurry preparation, tape casting, structural stacking, hot pressing and shaping to sintering polarization step by step.

[0073] Example 2

[0074] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0075] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 0.7, that is, the total stacked thickness of the second piezoelectric film accounts for 70% of the thickness of the multilayer ceramic blank (the specific stacking order is 12 layers of the first piezoelectric film without the pore-forming agent - 56 layers of the second piezoelectric film containing the pore-forming agent - 12 layers of the first piezoelectric film without the pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0076] Example 3

[0077] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0078] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 0.8, that is, the total stacked thickness of the second piezoelectric film accounts for 80% of the thickness of the multilayer ceramic blank (the specific stacking order is 8 layers of the first piezoelectric film without the pore-forming agent - 64 layers of the second piezoelectric film containing the pore-forming agent - 8 layers of the first piezoelectric film without the pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0079] Comparative Example 1

[0080] This example provides a lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0081] (1) When preparing lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 0, that is, the multilayer ceramic blanks are all stacked with the first piezoelectric film without the pore-forming agent (the specific stacking order is 80 layers of the first piezoelectric film without the pore-forming agent stacked in sequence), and a multilayer ceramic blank is formed by stacking a total of 80 layers of piezoelectric film. The final lead-free piezoelectric material does not contain porous ceramic layers.

[0082] Comparative Example 2

[0083] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0084] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 0.1, that is, the total stacked thickness of the second piezoelectric film accounts for 10% of the thickness of the multilayer ceramic blank (the specific stacking order is 35 layers of the first piezoelectric film without the pore-forming agent - 10 layers of the second piezoelectric film containing the pore-forming agent - 35 layers of the first piezoelectric film without the pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0085] Comparative Example 3

[0086] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0087] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 0.3, that is, the total stacked thickness of the second piezoelectric film accounts for 30% of the thickness of the multilayer ceramic blank (the specific stacking order is 28 layers of the first piezoelectric film without the pore-forming agent - 24 layers of the second piezoelectric film containing the pore-forming agent - 28 layers of the first piezoelectric film without the pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0088] Comparative Example 4

[0089] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0090] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing pore-forming agent / the total number of stacked layers = 0.375, that is, the total stacked thickness of the second piezoelectric film accounts for 37.5% of the thickness of the multilayer ceramic blank (the specific stacking order is 25 layers of the first piezoelectric film without pore-forming agent - 30 layers of the second piezoelectric film containing pore-forming agent - 25 layers of the first piezoelectric film without pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0091] Comparative Example 5

[0092] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0093] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 0.5, that is, the total stacked thickness of the second piezoelectric film accounts for 50% of the thickness of the multilayer ceramic blank (the specific stacking order is 20 layers of the first piezoelectric film without the pore-forming agent - 40 layers of the second piezoelectric film containing the pore-forming agent - 20 layers of the first piezoelectric film without the pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0094] Comparative Example 6

[0095] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0096] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing pore-forming agent / the total number of stacked layers = 0.625, that is, the total stacked thickness of the second piezoelectric film accounts for 62.5% of the thickness of the multilayer ceramic blank (the specific stacking order is 15 layers of the first piezoelectric film without pore-forming agent - 50 layers of the second piezoelectric film containing pore-forming agent - 15 layers of the first piezoelectric film without pore-forming agent), resulting in a multilayer ceramic blank formed by a total of 80 layers of piezoelectric film stacked).

[0097] Comparative Example 7

[0098] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Example 1 only in that:

[0099] (1) When preparing porous lead-free piezoelectric materials, the number of stacked layers of the second piezoelectric film containing the pore-forming agent / the total number of stacked layers = 1, that is, the multi-layer ceramic blanks are all stacked with the second piezoelectric film containing the pore-forming agent (the specific stacking order is 80 layers of the second piezoelectric film containing the pore-forming agent are stacked in sequence to obtain a multi-layer ceramic blank formed by a total of 80 layers of piezoelectric film stacking). The resulting porous lead-free piezoelectric material does not contain a dense ceramic layer.

[0100] Comparative Example 8

[0101] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Comparative Example 5 only in that:

[0102] (1) When preparing porous lead-free piezoelectric materials, the weight percentage of the pore-forming agent added to the KNNS-NS ceramic powder is adjusted from 13wt% to 19wt%.

[0103] Comparative Example 9

[0104] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Comparative Example 5 only in that:

[0105] (1) When preparing porous lead-free piezoelectric materials, the weight percentage of the pore-forming agent added to the KNNS-NS ceramic powder is adjusted from 13wt% to 17wt%.

[0106] Comparative Example 10

[0107] This example provides a porous lead-free piezoelectric material and its preparation method, which differs from Comparative Example 5 only in that:

[0108] (1) When preparing porous lead-free piezoelectric materials, the weight percentage of the pore-forming agent added to the KNNS-NS ceramic powder is adjusted from 13wt% to 9wt%.

[0109] Comparative Example 11

[0110] This example provides a lead-free piezoelectric material and its preparation method, which differs from Comparative Example 5 only in that:

[0111] (1) When preparing lead-free piezoelectric materials, the percentage of the weight of the pore-forming agent added to the KNNS-NS ceramic powder is adjusted from 13wt% to 0wt% (i.e. no pore-forming agent is added), and the final lead-free piezoelectric material does not contain a porous ceramic layer.

[0112] Comparative Example 12

[0113] This example provides an existing piezoelectric material, KNNS-BNZ-Fe, whose preparation method is based on existing technology - Xue, H., Jiang, L., Lu, G. & Wu, J. Multilevel structure engineered lead-free piezoelectrics enabling breakthrough in energy harvesting performance for bioelectronics. Adv. Funct. Mater. 33, 2212110 (2023).

[0114] Comparative Example 13

[0115] This example provides an existing piezoelectric material, KNN-LN, whose preparation method is based on existing technology - Ahn, C.-W. et al. Composition design rule for high piezoelectric voltage coefficient in (K0.5Na0.5)NbO3 based pb-free ceramics. Jpn. J. Appl. Phys. 51, 09MD10 (2012).

[0116] Comparative Example 14

[0117] This example provides an existing piezoelectric material, BCZT, whose preparation method refers to existing technology - Liu, Y. et al. Significantly enhanced energy-harvesting performance and superior fatigue-resistant behavior in

[001] c -textured BaTiO3 -based lead-free piezoceramics. ACS Appl. Mater. Interfaces 10, 31488–31497 (2018).

[0118] Comparative Example 15

[0119] This example provides an existing piezoelectric material, BNT-BT, whose preparation method refers to existing technology - Liu, Y. et al. Significantly enhanced energy-harvesting performance and superior fatigue-resistant behavior in

[001] c -textured BaTiO3 -based lead-free piezoceramics. ACS Appl. Mater. Interfaces 10, 31488–31497 (2018).

[0120] Comparative Example 16

[0121] This example provides an existing piezoelectric material, PZT-4, whose preparation method is based on existing technology - Saito, Y. etal. Lead-free piezoceramics. Nature 432, 84–87 (2004), DOI:10.1038 / nature03028.

[0122] Comparative Example 17

[0123] This example provides an existing piezoelectric material, PZT-5H, whose preparation method is based on existing technology - Ahn, C.-W. et al. Composition design rule for high piezoelectric voltage coefficient in (K0.5Na0.5)NbO3 based pb-free ceramics. Jpn. J. Appl. Phys. 51, 09MD10 (2012), DOI:10.1143 / JJAP.51.09MD10.

[0124] Test Example 1

[0125] In this example, X-ray diffraction tests were performed on the lead-free piezoelectric composite material obtained in Example 1 (porogen PS content x = 13 wt%), Comparative Example 11 (porogen PS content x = 0 wt%), Comparative Example 10 (porogen PS content x = 9 wt%), and Comparative Example 9 (porogen PS content x = 17 wt%). The obtained X-ray diffraction patterns are as follows. Figure 3 As shown; Figure 3 The X-ray diffraction patterns, refinement results, and phase content distribution diagrams of materials with different PS contents of x% (x=0, 9, 13, 17) are used to jointly prove that the introduction of pores successfully preserved the key rhombohedral-orthorhombic-tetragonal three-phase coexistence crystal structure of the ceramic matrix.

[0126] Test Example 2

[0127] This example compares the lead-free piezoelectric composite material obtained in Example 2 (PS content of pore-forming agent is 13wt%, number of second piezoelectric film stacks containing pore-forming agent / total number of stacks = 0.7, denoted as 13%@0.7), Comparative Example 1 (PS content of pore-forming agent is 13wt%, number of second piezoelectric film stacks containing pore-forming agent / total number of stacks = 0, denoted as 13%@0), and Comparative Example 2 (PS content of pore-forming agent is 13wt%, number of second piezoelectric film stacks containing pore-forming agent / total number of stacks = 0, denoted as 13%@0). The dielectric properties of the following piezoelectric films were tested at different temperatures: Example 3 (where the PS content of the pore-forming agent was 13wt%, and the number of stacked layers of the second piezoelectric film containing the pore-forming agent was 0.3, denoted as 13%@0.3) and Example 5 (where the PS content of the pore-forming agent was 13wt%, and the number of stacked layers of the second piezoelectric film containing the pore-forming agent was 0.5, denoted as 13%@0.5). The test results are as follows: Figure 4 As shown. Figure 4The graph compares the dielectric properties of a material with a PS content of 13wt% and containing a pore-forming agent, where the ratio of the number of stacked layers of the second piezoelectric film to the total number of stacked layers is @x (x = 0, 0.1, 0.3, 0.5, 0.7), and a dense ceramic at different temperatures. This indicates that the material possesses a high Curie temperature and excellent thermal stability.

[0128] Test Example 3

[0129] In this example, the dense layer of the porous lead-free piezoelectric material obtained in Example 1 above was subjected to piezoelectric force microscopy and scanning electron microscopy tests. The test results are as follows: Figure 5 and Figure 6 As shown. Among them, Figure 5 The results of piezoelectric microscopy (SPFM) tests, including the PFM amplitude map (left), PFM phase map (middle), and SSPFM local amplitude and phase curves (right), show that the material has a good ferroelectric domain structure and its reversibility. Figure 6 The images show scanning electron microscope (SEM) images of the cross-section of the porous lead-free piezoelectric material at different magnifications (left and middle) and the elemental distribution map of the region shown (right), demonstrating the successful construction of its dense-porous-dense gradient structure, interlayer bonding, and uniformity of chemical composition.

[0130] Test Example 4

[0131] This example focuses on the core performance parameter of the piezoelectric materials obtained in Example 1 and Comparative Examples 1-17 above: piezoelectric constant. ), dielectric constant ( ), piezoelectric voltage constant ( ), energy harvesting figure of merit ( The test was conducted, and the results are as follows: Figure 7 , Figure 8 Table 1 shows a summary of comparisons with some typical test data.

[0132] Figure 7 The piezoelectric performance test results are for the material in this invention with a fixed PS content of 13wt% and containing a pore-forming agent, where the ratio of the number of stacked layers to the total number of stacked layers is @x (x = 0.375 (Comparative Example 4), 0.5 (Comparative Example 5), 0.625 (Comparative Example 6), 0.75 (Example 1), 1 (Comparative Example 7)). Figure 8 The piezoelectric constants of DPD composite materials with different PS contents (xwt%) are determined by setting the ratio of the number of stacked layers of the second piezoelectric film containing the pore-forming agent to the total number of stacked layers in this invention to 0.5. (x = 0 (Comparative Example 11), 9 (Comparative Example 10), 13 (Comparative Example 5), 17 (Comparative Example 9), 19 (Comparative Example 8)). ), dielectric constant ( ), piezoelectric voltage constant ( ), energy harvesting figure of merit ( The curves showing the changes in composition indicate that the porous lead-free piezoelectric material provided in this embodiment of the invention, by limiting the porosity and thickness ratio of the porous ceramic layer to a specific range, breaks the coupling relationship between the piezoelectric constant and the dielectric constant, and achieves a synergistic improvement in the piezoelectric voltage constant and energy harvesting quality factor of the lead-free piezoelectric material. All performance test parameters far exceed those of the comparative examples.

[0133] Table 1

[0134]

[0135] As shown in Table 1:

[0136] 1) The porous lead-free piezoelectric material provided in this embodiment of the invention breaks the coupling relationship between piezoelectric constant and dielectric constant by limiting the porosity and thickness ratio of the porous ceramic layer within a specific range, and achieves a synergistic improvement in the piezoelectric voltage constant and energy harvesting quality factor of the lead-free piezoelectric material. All performance test parameters far exceed those of the comparative examples.

[0137] 2) The porous lead-free piezoelectric material provided by this invention has excellent performance. Under the same ceramic matrix composition, the performance of the porous lead-free piezoelectric material provided by this invention far exceeds that of dense ceramic piezoelectric materials without porous phases, as well as most existing lead-free piezoelectric materials such as KNNS-BNZ-Fe, KNN-LN, BCZT, BNT-BT, PZT-4, PZT-5H and lead-based piezoelectric materials. This highlights the competitive advantage of the piezoelectric material provided by this invention as an environmentally friendly lead-free piezoelectric composite material in the field of next-generation piezoelectric energy harvesters.

[0138] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a porous lead-free piezoelectric material, characterized in that, Includes the following steps: The ceramic substrate is used to form the first piezoelectric film; A second piezoelectric film is made by combining a ceramic matrix and a pore-forming agent; A number of first piezoelectric films and a number of second piezoelectric films are stacked in the order of first piezoelectric film, second piezoelectric film and first piezoelectric film to obtain a multilayer ceramic blank; The multilayer ceramic preform is subjected to pressing, debinding, and sintering to obtain the porous lead-free piezoelectric material. In the preparation of the second piezoelectric film, the weight of the pore-forming agent added accounts for 12-14 wt% of the weight of the ceramic matrix; the total stacked thickness of the second piezoelectric film accounts for 70%-80% of the thickness of the multilayer ceramic preform.

2. The method for preparing porous lead-free piezoelectric materials according to claim 1, characterized in that, The ceramic matrix comprises potassium sodium niobate-based ceramic as shown in Chemical Formula 1, which is as follows: .

3. The method for preparing porous lead-free piezoelectric materials according to claim 2, characterized in that, The steps for forming the first piezoelectric film from the ceramic substrate include the following processes: The raw materials were weighed and mixed according to the stoichiometric ratio of the ceramic matrix, and then the ceramic matrix was prepared by solid-state sintering. The binder, the first dispersant, and the solvent are mixed to obtain a colloidal solution; The ceramic matrix, the colloidal solution, and the second dispersant are mixed, and then the first piezoelectric film is formed by casting.

4. The method for preparing porous lead-free piezoelectric materials according to claim 3, characterized in that, The steps of forming a second piezoelectric film from a ceramic substrate and a pore-forming agent include the following processes: The raw materials were weighed and mixed according to the stoichiometric ratio of the ceramic matrix, and then the ceramic matrix was prepared by solid-state sintering. The ceramic matrix and the pore-forming agent are mixed to obtain a mixture; The binder, the first dispersant, and the solvent are mixed to obtain a colloidal solution; The mixture, the colloidal solution, and the second dispersant are mixed, and then the second piezoelectric film is formed by casting.

5. The method for preparing porous lead-free piezoelectric materials according to claim 4, characterized in that, The working conditions for the solid-state sintering method include: a temperature of 800~900℃ and a time of 5~8h. And / or, the working condition parameters of the casting method include: controlling the scraper height to be 12~16μm.

6. The method for preparing porous lead-free piezoelectric materials according to claim 5, characterized in that, When preparing the first piezoelectric film, the amount of the binder added is 5-10 wt% of the weight of the ceramic matrix, the amount of the first dispersant added is 0.5-2 wt% of the weight of the ceramic matrix, the amount of the solvent added is 86 wt%-93 wt% of the weight of the ceramic matrix, and the amount of the second dispersant added is 0.5-2 wt% of the weight of the ceramic matrix. And / or, when preparing the second piezoelectric film, the amount of the binder added is 5-10 wt% of the weight of the ceramic matrix, the amount of the first dispersant added is 0.5-2 wt% of the weight of the ceramic matrix, the amount of the solvent added is 86 wt%-93 wt% of the weight of the ceramic matrix, and the amount of the second dispersant added is 0.5-2 wt% of the weight of the ceramic matrix; And / or, the pore-forming agent comprises polystyrene, the binder comprises polyvinyl alcohol, the first dispersant comprises triethanolamine, the second dispersant comprises polyethylene glycol, and the solvent comprises ethanol.

7. The method for preparing porous lead-free piezoelectric materials according to claim 6, characterized in that, The working conditions for the pressing process include: temperature of 55~60℃, pressure of 2~10Mpa, and time of 5~20min. And / or, the working conditions parameters for the glue removal process include: heat preservation at 800~900℃ for 5~10 hours; And / or, the working conditions parameters of the sintering treatment include: maintaining at a temperature of 1000~1100℃ for 2~5 hours.

8. The method for preparing porous lead-free piezoelectric materials according to claim 7, characterized in that, The thickness of the porous lead-free piezoelectric material is 0.8~1.2mm; And / or, the porous lead-free piezoelectric material has a sandwich gradient porous structure, the sandwich gradient porous structure comprising a first dense ceramic layer, a porous ceramic layer and a second dense ceramic layer.

9. A porous lead-free piezoelectric material, characterized in that, The porous lead-free piezoelectric material is prepared by the method for preparing porous lead-free piezoelectric materials according to any one of claims 1 to 8.

10. A piezoelectric energy harvester, characterized in that, Includes the porous lead-free piezoelectric material as described in claim 9.

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