Lead-free potassium sodium niobate-based textured piezoelectric ceramics with high-voltage electric energy harvesting performance and preparation method thereof

Abstract

The present invention relates to a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance and a preparation method thereof. The chemical general formula of the lead-free potassium sodium niobate-based textured piezoelectric ceramic is 97 wt.% (K 0.505 Na 0.5(0.99‑x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99‑x%) Sb 0.035(0.99‑x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 + 3 wt.% NaNbO3, where 1 ≤ x ≤ 5. Compared with the prior art, the lead-free potassium sodium niobate-based textured piezoelectric ceramic prepared by the present invention through the combination of composition design, traditional textured tape casting process, and two-step sintering method has ultra-high piezoelectric coefficient and excellent electromechanical coupling coefficient, so as to generate high energy harvesting performance, which is of great significance for the development of safe, long-life, and environmentally friendly energy supply materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional ceramic materials, and relates to a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance and a preparation method thereof. Background Art

[0002] In nature, mechanical energy is ubiquitous, including vibrations generated by human motion, machine motion, sound waves, and wave energy, etc. It is inexhaustible and easy to use, and is expected to become one of the most promising energy sources to be developed and applied on a large scale. According to the conversion form, vibration energy harvesting methods can generally be divided into electromagnetic conversion, electrostatic conversion, and piezoelectric conversion. Compared with the other two forms, the piezoelectric energy harvesting technology has many advantages such as simple structure, stable output, high power density, and good integration and matching with microelectromechanical systems. It is expected to replace the traditional battery system, thereby realizing the energy self-sufficiency of microelectronic devices. Therefore, the piezoelectric energy harvesting technology can well alleviate the serious global energy crisis and environmental pollution problems, and thus become the focus of current research on environmental energy harvesting technology.

[0003] Piezoelectric materials can directly convert mechanical energy into electrical energy with high power density, so they are considered ideal candidate materials for energy harvesting applications. So far, several piezoelectric materials have been used in piezoelectric energy harvesters (PEHs) with different structures, including piezoelectric ceramics, piezoelectric polymers, and composites. Among them, perovskite-type lead-based (especially Pb(Zr,Ti)O3, PZT) piezoelectric ceramics have received extensive international attention due to their excellent electromechanical properties. However, due to the increasing attention to the health and environmental problems of lead toxicity, there is an urgent need to develop high-performance environmentally friendly piezoelectric energy harvesters.

[0004] Recently, compared with other lead-free piezoelectric materials (i.e., BaTiO3-based and ZnO), potassium sodium niobate ((K,Na)NbO3, KNN) ceramics have attracted more and more attention due to their good piezoelectricity and high Curie temperature ( T c ) and have become the most promising ceramics. However, its ferroelectric and piezoelectric properties are poor. The piezoelectric coefficient of (K,Na)NbO3 ceramics obtained by traditional solid-phase sintering method without composition modification d 33 is generally 80-120 pC / N, which is still far from the piezoelectric properties of lead-based ceramics. At present, the research on lead-free potassium sodium niobate (KNN) piezoelectric ceramics mainly focuses on the phase boundary design based on composition regulation, and good progress has been made. For example, Wu Jiagang et al. from Sichuan University can easily obtain d 33>300 pC / N KNN-based piezoelectric ceramics. However, from this method alone, a satisfactory electromechanical coupling coefficient ( k p ) cannot be obtained simultaneously, and its k p value is usually less than 0.5, thus unable to exhibit excellent energy harvesting performance. SUMMARY OF THE INVENTION

[0005] The purpose of the present invention is to provide a lead-free sodium potassium niobate-based textured piezoelectric ceramic material with high piezoelectric energy harvesting performance and its preparation method to overcome the above defects.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The first purpose of the present invention is to provide a lead-free sodium potassium niobate-based textured piezoelectric ceramic with high piezoelectric energy harvesting performance. The chemical general formula of the lead-free sodium potassium niobate-based textured piezoelectric ceramic is 97 wt.% (K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 + 3 wt.% NaNbO3, where 1 ≤ x ≤ 5.

[0008] Furthermore, the room temperature phase structure of the lead-free sodium potassium niobate-based textured piezoelectric ceramic is a coexistence of (rhombohedral - orthorhombic - tetragonal) three phases and the grain orientation is <001> C >90%.

[0009] The second purpose of the present invention is to provide a preparation method of a lead-free sodium potassium niobate-based textured piezoelectric ceramic with high piezoelectric energy harvesting performance, including the following steps:

[0010] (1) Select Na2CO3, K2CO3, Nb2O5, CaCO3, Bi2O3, HfO2, ZrO2, TiO2, Sb2O3 with a purity greater than 99% as the raw materials of the lead-free sodium potassium niobate-based textured piezoelectric ceramic material;

[0011] (2) Weigh the materials according to the chemical composition, add ball milling media for ball milling, discharge the material, dry it, pre-burn it, and perform secondary ball milling to obtain a tape-casting powder base material;

[0012] (3) Prepare high-quality NaNbO3 flake templates with an aspect ratio of ~ 15:1 through the traditional two-step molten salt method;

[0013] (4) Add the powder base material obtained in step (2) and the NaNbO3 flake template obtained in step (3) into methyl ethyl ketone and alcohol as a mixed solvent, glyceryl trioleate as a dispersant, polyethylene glycol and dibutyl phthalate as plasticizers, and PVB (polyvinyl butyral) as a binder, and mix for 5 - 8 hours to obtain a casting slurry;

[0014] (5) Use a convenient small coating machine to cast the slurry obtained in step (4), and then dry it to form a thick film with certain toughness and plasticity;

[0015] (6) Cut the dried thick film obtained in step (5) into the required shape and stack it layer by layer, and finally hot press it into a green ceramic body with a diameter of 12 - 26 mm;

[0016] (7) Place the green ceramic body obtained in step (6) in a muffle furnace for debinding, and keep it at 500 - 600 °C for 5 - 10 h;

[0017] (8) Perform two-step sintering on the debound ceramic body to obtain a sintered ceramic sheet, which is the lead-free potassium sodium niobate-based textured piezoelectric ceramic.

[0018] Further, the first half part (K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 is prepared by solid-phase synthesis method through step (1) and step (2), and its pre-sintering temperature is 800 - 850 °C; the remaining second half part, 3 wt.% NaNbO3, is realized by adding the NaNbO3 flake template in step (4).

[0019] Further, in the process of preparing the NaNbO3 flake template by two-step molten salt method in step (3), in the first step, use Bi2O3, Na2CO3 and Nb2O5 with a molar ratio of 6.5: 7: 10 as raw materials and NaCl as the molten salt to first synthesize the flake precursor Bi 2.5 Na 3.5 Nb5O 18 and filter it. In the second step, use Bi 2.5 Na 3.5 Nb5O 18 with a molar ratio of 1: 1.75 and K2CO3 as raw materials and NaCl as the molten salt to synthesize the NaNbO3 flake template and filter it. The total mass ratio of the molten salt and raw materials in the first step and the second step is 1.1: 1.

[0020] Further, the ball milling time in step (2) is 10 to 15 h for both times.

[0021] Further, when performing the flow delay in step (5), the thickness of the doctor blade is 12 μm and the moving rate is 28 - 31 cm / min.

[0022] Further, when laminating in step (6), the green diameter of the sheet used to prepare the energy collector is cut to 26 mm.

[0023] Further, when performing the two-step sintering in step (8), the heating rate of the first-step sintering is 2 - 5 °C / min and the temperature difference between the first step and the second step is 100 - 120 °C.

[0024] Further, post-treatment is performed on the obtained sintered ceramic sheet.

[0025] Further, part of the obtained sintered ceramic sheet is polished with sandpapers of different particle sizes and polished to ~0.2 - 0.7 mm, and then silver coating and electrical property testing are carried out.

[0026] Further, the polished ceramic sheet is coated with silver paste with a diameter of 4 - 20 mm, silver firing is carried out in a muffle furnace, kept at 550 °C for 10 min, and then electrical testing is carried out. The final thickness of the sheet used to prepare the energy collector is 0.24 mm and the electrode diameter is 20 mm.

[0027] Further, after the obtained lead-free potassium sodium niobate-based textured piezoelectric ceramic is silver-coated (i.e., before testing the electrical properties), polarization treatment is also required. The ceramic coated with silver electrodes is placed in a silicone oil bath and polarized under an AC electric field of 20 - 40 kV / cm.

[0028] The obtained lead-free potassium sodium niobate-based textured piezoelectric ceramic has high piezoelectric energy harvesting performance.

[0029] The lead-free potassium sodium niobate-based piezoelectric ceramic (lead-free potassium sodium niobate-based textured piezoelectric ceramic) prepared by the present invention through combining component design, traditional textured tape casting process and two-step sintering method has ultra-high piezoelectric coefficient and excellent electromechanical coupling coefficient, so as to generate high energy harvesting performance, which is of great significance for the development of safe, long-life and environmentally friendly energy supply materials.

[0030] The obtained lead-free potassium sodium niobate-based textured piezoelectric ceramic can be used in device components such as piezoelectric energy harvesters and ultrasonic transducers.

[0031] The applicant's concept development process is as follows: The main idea of this work is based on the synergistic optimization of phase boundary construction and texture technology. In order to achieve the coexistence of rhombohedral - orthorhombic - tetragonal three - phases at room temperature, the applicant fully considered Ca 2+ , Bi 3+ , Hf 4+ , Zr 4+ , Ti 4+ , Sb 5+ These ions. On the one hand, these ions are effective phase boundary movers, and on the other hand, introducing as many ions as possible can increase the entropy value of the system. The multi - phase coexistence at room temperature and appropriate entropy increase can both promote polarization reversal, thereby enhancing polarization and increasing piezoelectric properties. In addition, texture technology is an advantage of the applicant's laboratory. Through the texture technology of ceramics, the component ceramics form a <001> C preferred orientation, similar to single crystals, which can further improve the polarization characteristics of piezoelectric ceramics, thereby increasing the piezoelectric and electromechanical coupling coefficients, especially the electromechanical coupling coefficient.

[0032] Compared with the prior art, the present invention has the following characteristics:

[0033] 1) The method for preparing lead - free potassium sodium niobate - based textured piezoelectric ceramics provided by the present invention can prepare lead - free potassium sodium niobate - based textured piezoelectric ceramics that simultaneously possess an ultra - high piezoelectric coefficient ( d 33 ~ 700 pC / N) and excellent electromechanical coupling coefficient ( k p ~ 0.72), thereby obtaining high - voltage piezoelectric energy harvesting performance (output power: ~ 4 mW).

[0034] 2) The method for preparing lead - free potassium sodium niobate - based textured piezoelectric ceramics provided by the present invention is simple, economical and practical, and the ceramics are lead - free materials, which will not pollute the environment during the processes of preparation, application and disposal. The prepared lead - free potassium sodium niobate - based textured piezoelectric ceramics are an environmentally friendly high - performance piezoelectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 XRD patterns of lead - free potassium sodium niobate - based textured piezoelectric ceramics prepared in Examples 1 - 4;

[0036] Figure 2 SEM photos of lead - free potassium sodium niobate - based textured piezoelectric ceramics with high - voltage piezoelectric energy harvesting performance prepared in Example 3;

[0037] Figure 3 Dielectric temperature spectra of lead - free potassium sodium niobate - based textured piezoelectric ceramics with high - voltage piezoelectric energy harvesting performance prepared in Example 3;

[0038] Figure 4For the lead-free potassium sodium niobate-based textured piezoelectric ceramics prepared in Examples 1-4 d 33 and k p figures;

[0039] Figure 5 is the piezoelectric energy harvesting performance diagram of the lead-free potassium sodium niobate-based textured piezoelectric ceramics with high piezoelectric energy harvesting performance prepared in Example 3. Detailed implementation manners

[0040] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the accompanying drawings and the following embodiments are only used to illustrate the present invention, rather than limiting the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0041] In the technical solution of the present invention, the preparation means, materials, structures or composition ratios and other features not clearly described are all regarded as common technical features disclosed in the prior art.

[0042] In the following embodiments, in the process of preparing the NaNbO3 flake template by the two-step molten salt method in step (3), in the first step, Bi2O3, Na2CO3 and Nb2O5 with a molar ratio of 6.5:7:10 are used as raw materials and NaCl is used as the molten salt to first synthesize the flake precursor Bi 2.5 Na 3.5 Nb5O 18 and filtered. In the second step, Bi 2.5 Na 3.5 Nb5O 18 and K2CO3 are used as raw materials and NaCl is used as the molten salt to synthesize the NaNbO3 flake template and filtered. The total mass ratio of the molten salt and the raw materials in the first step and the second step is both 1.1:1.

[0043] In the following embodiments, the ball milling time in step (2) is 12 h both times.

[0044] In the following embodiments, during the tape casting in step (5), the thickness of the doctor blade is 12 μm and the moving speed is 30 cm / min.

[0045] In the following embodiments, during the lamination in step (6), the green diameter of the wafers used to prepare the energy harvester is cut to 26 mm.

[0046] In the following embodiments, during the two-step sintering in step (8), the heating rate of the first step of sintering is 3 °C / min and the temperature difference between the first step and the second step is 100 °C.

[0047] In the following examples, the raw materials used are all commercially available.

[0048] Example 1

[0049] This example provides a lead-free potassium sodium niobate-based textured piezoelectric ceramic with a chemical composition of 97 wt.% (K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 +3 wt.% NaNbO3, where x = 0, including the following steps:

[0050] (1) Select Na2CO3, K2CO3, Nb2O5, CaCO3, Bi2O3, HfO2, ZrO2, TiO2, Sb2O3 with a purity greater than 99% as the raw materials for the lead-free potassium sodium niobate-based textured piezoelectric ceramic material;

[0051] (2) Weigh the materials according to the chemical composition, add ball milling media for ball milling, discharge the material, dry it, pre-burn it, and perform secondary ball milling to obtain a tape-casting powder base material;

[0052] (3) Prepare high-quality NaNbO3 flake templates with an aspect ratio of ~15:1 by the traditional two-step molten salt method;

[0053] (4) Add the powder base material obtained in step (2) and the NaNbO3 flake templates obtained in step (3) to methyl ethyl ketone and alcohol as a mixed solvent, glyceryl trioleate as a dispersant, polyethylene glycol and dibutyl phthalate as plasticizers, and PVB as a binder, and mix for 8 hours to obtain a tape-casting slurry;

[0054] (5) Use a convenient small-scale coater to tape-cast the slurry obtained in step (4), and then dry it to form a thick film with a certain toughness and plasticity;

[0055] (6) Cut the dried thick film obtained in step (5) into the required shape and stack it layer by layer, and finally hot-press it into a green ceramic body with a diameter of 12 - 26 mm;

[0056] (7) Place the green ceramic body obtained in step (6) in a muffle furnace for debinding, and keep it at 600 °C for 8 h;

[0057] (8) The debinded ceramic green bodies are sintered by a two-step method at 1190 °C for 4 h of heat preservation. After natural cooling to room temperature, part of the sintered ceramic wafers are ground and polished to ~0.2 - 0.7 mm with sandpapers of different grit sizes. The ground and polished ceramic wafers are coated with silver paste with a diameter of 4 - 20 mm, and then silver firing is carried out in a muffle furnace at 550 °C for 10 min. Subsequently, electrical property tests are conducted. The final thickness of the wafers used for fabricating the energy harvester is 0.24 mm, and the electrode diameter is 20 mm.

[0058] After silver coating (i.e., before testing the electrical properties), the prepared lead-free potassium sodium niobate-based textured piezoelectric ceramics need to be poled. The ceramics with silver electrodes are placed in a silicone oil bath and poled under an alternating electric field of 20 - 40 kV / cm.

[0059] Figure 1 XRD of the lead-free potassium sodium niobate-based textured piezoelectric ceramics prepared in Examples 1 - 4. It can be seen from the figure that the sample with x = 0 has obvious <001> C grain orientation growth, and its orientation degree f can reach 95%, and the piezoelectric coefficient is ~200 pC / N, k p ~0.44 ( Figure 4 ).

[0060] Example 2

[0061] The chemical composition of the lead-free potassium sodium niobate-based textured piezoelectric ceramics is 97 wt.% (K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 + 3 wt.% NaNbO3, where x = 1, and it includes the following steps:

[0062] (1) Select Na2CO3, K2CO3, Nb2O5, CaCO3, Bi2O3, HfO2, ZrO2, TiO2, Sb2O3 with a purity greater than 99% as the raw materials for the lead-free potassium sodium niobate-based textured piezoelectric ceramic materials;

[0063] (2) Weigh the materials according to the chemical composition, add ball-milling media for ball-milling, discharge the materials, dry them, pre-sinter them, and then conduct secondary ball-milling to obtain the tape-casting powder base material;

[0064] (3) High-quality NaNbO3 flake templates with an aspect ratio of ~15:1 were prepared by the traditional two-step molten salt method;

[0065] (4) The powder base material obtained in step (2) and the NaNbO3 flake templates obtained in step (3) were respectively added to methyl ethyl ketone and alcohol as a mixed solvent, glyceryl trioleate as a dispersant, polyethylene glycol and dibutyl phthalate as plasticizers, and PVB as a binder, and mixed for 8 hours to obtain a casting slurry;

[0066] (5) The slurry obtained in step (4) was cast using a convenient small-scale coater, and then dried to form a thick film with a certain toughness and plasticity;

[0067] (6) The dried thick film obtained in step (5) was cut into the required shape and stacked layer by layer, and finally hot-pressed into a green ceramic body with a diameter of 12 - 26 mm;

[0068] (7) The green ceramic body obtained in step (6) was placed in a muffle furnace for debinding, and kept at 600 °C for 8 h;

[0069] (8) The debound ceramic body was sintered by a two-step method at 1190 °C, kept at temperature for 6 h, and after naturally cooling to room temperature, part of the sintered ceramic pieces were polished with sandpapers of different grits to ~0.2 - 0.7 mm, and the polished ceramic pieces were coated with silver paste with a diameter of 4 - 20 mm, and then fired in a muffle furnace, kept at 550 °C for 10 min, and then the electrical properties were tested. The final thickness of the pieces used to prepare the energy harvester is 0.24 mm, and the electrode diameter is 20 mm.

[0070] After coating with silver (i.e., before testing the electrical properties), the prepared lead-free potassium sodium niobate-based textured piezoelectric ceramics need to be poled. The ceramics coated with silver electrodes were placed in a silicone oil bath and poled under an alternating electric field of 20 - 40 kV / cm.

[0071] Figure 1 XRD of the lead-free potassium sodium niobate-based textured piezoelectric ceramics prepared in Examples 1 - 4. It can be seen from the figure that the x = 1 sample has obvious <001> C grain-oriented growth, and its orientation degree f can reach 96%, the piezoelectric coefficient is ~250 pC / N, k p ~0.47 ( Figure 4 )

[0072] Example 3

[0073] The chemical composition of the lead-free potassium sodium niobate-based textured piezoelectric ceramics is 97 wt.% (K 0.505Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 + 3 wt.% NaNbO3, where x = 3.5, comprising the following steps:

[0074] (1) Select Na2CO3, K2CO3, Nb2O5, CaCO3, Bi2O3, HfO2, ZrO2, TiO2, Sb2O3 with a purity greater than 99% as raw materials for the lead-free sodium potassium niobate-based textured piezoelectric ceramic material;

[0075] (2) Weigh materials according to the chemical composition, add ball-milling media for ball-milling, discharge, dry, pre-burn, and perform secondary ball-milling to obtain a tape-casting powder base material;

[0076] (3) Prepare high-quality NaNbO3 flake templates with an aspect ratio of ~15:1 through the traditional two-step molten salt method;

[0077] (4) Add the powder base material obtained in step (2) and the NaNbO3 flake templates obtained in step (3) to methyl ethyl ketone and alcohol as a mixed solvent, glyceryl trioleate as a dispersant, polyethylene glycol and dibutyl phthalate as plasticizers, and PVB as a binder, and mix for 8 hours to obtain a tape-casting slurry;

[0078] (5) Use a convenient small-scale coater to perform tape-casting on the slurry obtained in step (4), and then dry to form a thick film with a certain toughness and plasticity;

[0079] (6) Cut the dried thick film obtained in step (5) into the required shape and stack them layer by layer, and finally hot-press them into a green ceramic body with a diameter of 12 - 26 mm;

[0080] (7) Place the green ceramic body obtained in step (6) in a muffle furnace for debinding, and keep it at 600 °C for 8 h;

[0081] (8) The debound ceramic body is sintered by a two-step method at 1200 °C, kept warm for 8 h, and after natural cooling to room temperature, polish part of the sintered ceramic pieces with sandpapers of different particle sizes to ~0.2 - 0.7 mm, coat the polished ceramic pieces with silver paste with a diameter of 4 - 20 mm, perform silver firing in a muffle furnace, keep it at 550 °C for 10 min, and then perform electrical property tests. The final thickness of the pieces used to prepare the energy harvester is 0.24 mm, and the electrode diameter is 20 mm.

[0082] The obtained lead-free potassium sodium niobate-based textured piezoelectric ceramics need to be poled after silver coating (i.e., before testing the electrical properties). The ceramics with silver electrodes are placed in a silicone oil bath and poled under an alternating electric field of 20 - 40 kV / cm.

[0083] The XRD, SEM, dielectric temperature spectrum, d 33 and k p as well as the piezoelectric energy harvesting performance of the potassium sodium niobate-based lead-free textured piezoelectric ceramics obtained in Example 3 are respectively shown in Figures 1-5 From Figure 1 and Figure 2 it can be seen that the potassium sodium niobate-based ceramics obtained in Example 3 have a high degree of texture ( C = 96%) in the <001> f direction and relatively large grain sizes. From Figure 3 it can be seen that the phase transition temperature of the lead-free potassium sodium niobate-based textured piezoelectric ceramics obtained in Example 3 is shifted to room temperature, so it belongs to the coexistence of rhombohedral - orthorhombic - tetragonal multiphases at room temperature. From Figure 4 it can be seen that the lead-free potassium sodium niobate-based textured piezoelectric ceramics obtained in Example 3 not only have a relatively high piezoelectric coefficient ( d 33 ~ 700 pC / N), but also have a high k p value (>0.7). The combination of a high Curie temperature and high piezoelectric properties greatly improves the contradiction between the high piezoelectric properties and temperature stability of potassium sodium niobate-based materials. From Figure 5 it can be seen that the power output by the vibration of the lead-free potassium sodium niobate-based textured piezoelectric ceramics obtained in Example 3 in a traditional disk-shaped piezoelectric vibration energy harvester can reach ~ 4 mW.

[0084] Example 4

[0085] The chemical composition of the lead-free potassium sodium niobate-based textured piezoelectric ceramics is 97 wt.% (K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 + 3 wt.% NaNbO3, where x = 5, and it includes the following steps:

[0086] (1)Select Na2CO3, K2CO3, Nb2O5, CaCO3, Bi2O3, HfO2, ZrO2, TiO2, Sb2O3 with a purity greater than 99% as the raw materials for the lead-free potassium sodium niobate-based textured piezoelectric ceramic material;

[0087] (2)Weigh the materials according to the chemical composition, add ball-milling media for ball-milling, discharge the material, dry it, pre-burn it, and perform secondary ball-milling to obtain the tape-casting powder base material;

[0088] (3)Prepare high-quality NaNbO3 flake templates with an aspect ratio of ~15:1 by the traditional two-step molten salt method;

[0089] (4)Add the powder base material obtained in step (2) and the NaNbO3 flake template obtained in step (3) to methyl ethyl ketone and alcohol as a mixed solvent, glyceryl trioleate as a dispersant, polyethylene glycol and dibutyl phthalate as plasticizers, and PVB as a binder, and mix for 8 hours to obtain the tape-casting slurry;

[0090] (5)Use a convenient small-scale coater to perform tape-casting on the slurry obtained in step (4), and then dry it to form a thick film with a certain toughness and plasticity;

[0091] (6)Cut the dried thick film obtained in step (5) into the required shape and stack it layer by layer, and finally hot-press it into a green ceramic body with a diameter of 12 - 26 mm;

[0092] (7)Place the green ceramic body obtained in step (6) in a muffle furnace for debinding, and keep it at 600 °C for 8 h;

[0093] (8)The debound ceramic body is sintered by a two-step method at 1200 °C for 8 h. After natural cooling to room temperature, polish some of the sintered ceramic pieces with sandpapers of different grits to ~0.2 - 0.7 mm, coat the polished ceramic pieces with silver paste with a diameter of 4 - 20 mm, perform silver firing in a muffle furnace, keep it at 550 °C for 10 min, and then perform electrical property tests. The final thickness of the piece used to prepare the energy harvester is 0.24 mm, and the electrode diameter is 20 mm.

[0094] The prepared lead-free potassium sodium niobate-based textured piezoelectric ceramic needs to be poled after silver coating (i.e., before testing the electrical properties). Place the ceramic with silver electrodes in a silicone oil bath and pole it under an alternating electric field of 20 - 40 kV / cm.

[0095] Figure 1 XRD of the lead-free potassium sodium niobate-based textured piezoelectric ceramics prepared in Examples 1 - 4. It can be seen from the figure that the x = 5 sample has obvious <001> CGrain orientation growth, with an orientation degree f up to 98%, and a piezoelectric coefficient of ~ 400 pC / N, k p ~ 0.34 ( Figure 4 ).

Claims

1. A preparation method of lead-free potassium sodium niobate-based textured piezoelectric ceramics with high-voltage electric energy harvesting performance, characterized in that The preparation method includes the following steps: (1) Select Na2CO3, K2CO3, Nb2O5, CaCO3, Bi2O3, HfO2, ZrO2, TiO2, and Sb2O3 with a purity greater than 99% as the raw materials for the lead-free sodium potassium niobate-based textured piezoelectric ceramic material; (2) By chemical composition (K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 Weigh the materials, where 1 ≤ x ≤ 5, add ball-milling media for ball-milling, discharge the materials, dry them, pre-burn them, and perform secondary ball-milling to obtain the tape-casting powder base material; (3) Prepare high-quality NaNbO3 flake templates with an aspect ratio of 15:1 by a two-step molten salt method; (4) Add the powder base material obtained in step (2) and the NaNbO3 flake template obtained in step (3) in accordance with 97 wt.%(K 0.505 Na 0.5(0.99-x%) Ca 0.01 Bi 0.5·x% )(Nb 0.965(0.99-x%) Sb 0.035(0.99-x%) Zr 0.01 Hf 0.98·x% Ti 0.02·x% )O 3.005 + 3 wt.% NaNbO3 into methyl ethyl ketone and alcohol as a mixed solvent, glyceryl trioleate as a dispersant, polyethylene glycol and dibutyl phthalate as plasticizers, and PVB as a binder, and mix for 5 - 8 hours to obtain a casting slurry; (5) Use a convenient small-scale coater to cast the slurry obtained in step (4), and then dry it to form a thick film with a certain toughness and plasticity; (6) Cut the dried thick film obtained in step (5) into the required shape and stack the slices, and finally hot-press it into a green ceramic body with a diameter of 12-26 mm; (7) Place the green ceramic body obtained in step (6) in a muffle furnace for debinding, and keep it at 500-600 °C for 5-10 h; (8) Perform two-step sintering on the debound ceramic body to obtain a sintered ceramic sheet, which is the lead-free sodium potassium niobate-based textured piezoelectric ceramic.

2. The preparation method of a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance according to claim 1, characterized in that, In the process of preparing the NaNbO3 flake template by a two-step molten salt method in step (3), first, Bi2O3, Na2CO3, and Nb2O5 with a molar ratio of 6.5:7:10 are used as raw materials and NaCl is used as the molten salt to first synthesize the flaky precursor Bi 2.5 Na 3.5 Nb5O 18 and filtered. In the second step, Bi 2.5 Na 3.5 Nb5O 18 and K2CO3 are used as raw materials and NaCl is used as the molten salt to synthesize the NaNbO3 flake template and filtered; The total mass ratio of the molten salt to the raw materials in the first step and the second step is 1.1:

1.

3. The preparation method of a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance according to claim 1, characterized in that, In step (2), the ball milling time for both times is 10-15 h; In step (5), during casting, the thickness of the doctor blade is 12 μm, and the moving rate is 28-31 cm / min; In step (6), during stacking, the green body diameter of the sheet used to prepare the energy harvester is cut to 26 mm.

4. The preparation method of a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance according to claim 1, characterized in that, In step (8), during two-step sintering, the heating rate of the first step is 2-5 °C / min, the target temperature of the first step is 1190-1210 °C, then it cools down to the second step temperature after 10 min, the temperature difference between the first step and the second step is 100-120 °C, the second step is kept warm for 6-12 h, and then it is cooled in the furnace to complete sintering.

5. The preparation method of a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance according to claim 1, characterized in that, Polish some of the sintered ceramic sheets with sandpapers of different grits and polish them to 0.2-0.7 mm, and then perform silver coating and electrical property testing.

6. The preparation method of a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance according to claim 5, characterized in that, The process of silver coating is as follows: Coat the polished ceramic sheet with silver paste with a diameter of 4-20 mm, and perform silver firing in a muffle furnace, and keep it at 550 °C for 10 min; Electrical property testing is carried out after silver coating. Among them, the final thickness of the sheet used to prepare the energy harvester is 0.24 mm, and the electrode diameter is 20 mm.

7. The preparation method of a lead-free potassium sodium niobate-based textured piezoelectric ceramic with high-voltage electric energy harvesting performance according to claim 1, characterized in that, The prepared lead-free sodium potassium niobate-based textured piezoelectric ceramic also needs to be poled. Place the ceramic with silver electrodes coated in a silicone oil bath and pole it under an alternating electric field of 20-40 kV / cm.

Images