BaZrO3-doped KNN-based leadless piezoelectric ceramic and preparation method thereof

Abstract

The invention relates to the field of functional ceramic materials, and provides BaZrO3 doped KNN-based leadless piezoelectric ceramic and a preparation method thereof in order to solve the problem that the piezoelectric property of the leadless piezoelectric ceramic is poor. The general formula of the piezoelectric ceramic is (100-x) (K < 0.49 > Na < 0.49 > Li < 0.02 >) (Nb < 0.8 > Ta < 0.2 >) O < 3-x > BaZrO < 3 + y > wt% MnO, x is greater than or equal to 2 and less than or equal to 5, and y is greater than 1 and less than 3. The invention also provides a preparation method of the piezoelectric ceramic, which comprises the following steps: carrying out primary ball milling, pre-sintering, secondary ball milling and calcining on the raw materials, and adding MnO to carry out third ball milling; pressing the obtained mixed powder into a ceramic rough blank, and sequentially carrying out primary sintering, grinding, polishing, silver electrode coating and secondary sintering; and carrying out polarization treatment on the obtained ceramic wafer. The inverse piezoelectric constant of the piezoelectric ceramic can reach 476 pm / V at room temperature, and the piezoelectric ceramic also has excellent temperature stability and fatigue resistance.

Description

Technical Field

[0001] The present invention relates to the field of functional ceramic materials, and particularly to BaZrO3-doped KNN-based lead-free piezoelectric ceramics and a preparation method thereof. Background Art

[0002] Piezoelectric ceramics can directly convert electrical energy and mechanical energy, and thus are widely used in many scenarios such as power electronics, information automation, biomedicine, and intelligent transportation. Among many piezoelectric materials, Pb(Zr 1-x Ti x )O3 (PZT) systems with ABO3 perovskite structure have become the preferred materials for practical tools due to their excellent piezoelectric properties. However, with the increasing concern about environmental issues, the use of harmful lead-containing materials has been strictly restricted, which has directly led to the booming research on lead-free piezoelectric materials in the past few decades. Many lead-free piezoelectric systems have been discovered, such as BaTiO3 (BT), (Bi,Na)TiO3 (BNT), and (K,Na)NbO3 (KNN)-based ceramics. The main problem is that the piezoelectric properties of lead-free ceramic materials are not as good as those of lead-based materials. Several strategies for improving the piezoelectric properties of lead-free ceramics have been drawn from the development experience of lead-based materials such as chemical doping, domain engineering, and phase modulation. Recent studies have shown that through composition modulation, the electric-field-induced strain of BNT can reach 1%, and 2.3% can be achieved through atomic-scale defect engineering at high temperatures.

[0003] Nevertheless, high coercive fields, large hysteresis, and low depolarization temperatures are still huge challenges, hindering the practical applications of BNT-based ceramics. KNN-based ceramics are considered to be one of the most promising lead-free systems and can replace lead-based ceramics. Since 2000, the research interest in lead-free (K,Na)NbO3 (KNN)-based ferroelectrics has increased rapidly. After years of efforts by researchers, piezoelectric properties comparable to those of PZT have been obtained in KNN-based ceramics. Patent CN115286384A discloses a KNN-based lead-free piezoelectric ceramic and a preparation method thereof. The KNN-based lead-free piezoelectric ceramic includes the following components: carbonate, niobium pentoxide, nickel-zinc ferrite, and kaolin. Currently, the research focus on KNN-based lead-free piezoelectric ceramics is mainly on the replacement and doping modification of traditional processes. For example, doping barium zirconate in KNN-BLT-BZ ceramics can improve the temperature stability, but the Bi ions in the ceramics are incompatible with sintering in a reducing atmosphere, which will affect the piezoelectric properties of the ceramics. Accordingly, an ideal solution is needed. Summary of the Invention

[0004] In order to overcome the problem of poor piezoelectric properties of lead-free piezoelectric ceramics, the present invention provides BaZrO3-doped KNN-based lead-free piezoelectric ceramics and a preparation method thereof. The inverse piezoelectric constant (d *33 ) It can reach 476 pm / V at room temperature, and also has excellent temperature stability and fatigue resistance.

[0005] To achieve the above object, the present invention adopts the following technical solutions: BaZrO3-doped KNN-based lead-free piezoelectric ceramics, with the general formula (100 - x)(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - xBaZrO3 + ywt%MnO, where 2 ≤ x ≤ 5 and 1 < y < 3; x represents the stoichiometric ratio of BaZrO3 in the KNN-based lead-free piezoelectric ceramics, and y represents the mass percentage of MnO in the KNN-based lead-free piezoelectric ceramics. MnO refers to manganese oxide.

[0006] Preferably, x is 2 or 4 or 5. When x = 4, the converse piezoelectric constant d can reach 476 pm / V under an electric field of 1.5 kV / mm. * 33 .

[0007] The present invention also provides a preparation method of the piezoelectric ceramics, including the following steps: (1) After mixing the raw materials according to the stoichiometric ratio, perform the first ball milling, pre-sintering, second ball milling, and calcination in sequence, and then add MnO for the third ball milling to obtain a mixed powder; (2) Press the mixed powder into a ceramic green body, and the ceramic green body is sintered for the first time, ground, polished, coated with silver electrodes, and sintered for the second time in sequence to obtain a ceramic wafer; (3) Perform polarization treatment on the ceramic wafer to obtain BaZrO3-doped KNN-based lead-free piezoelectric ceramics.

[0008] Different materials have different pre-sintering temperatures. By adopting the method of separate calcination, it can ensure more sufficient calcination. Two ball millings and sinterings can make the reaction of each material more sufficient, thereby improving the uniformity of material mixing.

[0009] Preferably, the raw materials in step (1) are analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3, and Ta2O5.

[0010] Preferably, the first ball milling in step (1) is carried out in a planetary ball mill, using absolute ethanol as the medium, and ball milling for 20 - 24 h. The operations of the second ball milling and the third ball milling are the same as those of the first ball milling.

[0011] Preferably, the pre-sintering in step (1) is carried out at 700 - 750 °C in air for 3 - 5 h; the calcination is carried out at 900 - 950 °C in air for 3 - 5 h.

[0012] Preferably, the pressing in step (2) is cold pressing and forming under 150 - 250 MPa.

[0013] Preferably, the ceramic green body in step (2) is a disc-shaped ceramic green body with a diameter of 10 mm and a thickness of 1.5 mm.

[0014] Preferably, the first sintering in step (2) is carried out at 1100 - 1110 °C in air for 2 - 4 h, and the second sintering is carried out at 500 - 700 °C for 20 - 40 min.

[0015] Preferably, the polarization treatment in step (3) is: placing the ceramic wafer in silicone oil at 110 - 130 °C and polarizing it for 20 - 30 min with a DC electric field strength of 2 - 4 kV / mm.

[0016] Therefore, the beneficial effects of the present invention are as follows: (1) The addition of BaZrO3 generates finer ferroelectric domains, thus effectively improving the piezoelectric and dielectric properties of the ceramic.

[0017] (2) As a sintering aid, MnO reduces the volatilization of alkaline elements by lowering the sintering temperature. The reduction of the volatilization of alkaline elements can significantly reduce the concentration of oxygen vacancies, thus contributing to enhancing the piezoelectric properties.

[0018] (3) The inverse piezoelectric constant (d * 33 ) of the piezoelectric ceramic is as high as 476 pm / V at room temperature. At a low driving electric field of E = 1.5 kV / mm, the ceramic exhibits excellent temperature stability between room temperature and 160 °C, and also exhibits excellent anti-fatigue performance after 10 6 unipolar fatigue cycles. Description of the Drawings

[0019] Figure 1 It is a diagram of the small-signal characteristics and large-signal parameters of the ceramic wafers prepared in Examples 1 - 4. In the figure, (a) is a curve diagram of the large-signal parameter polarization P (μC / m 2 ), (b) is a curve diagram of the small-signal characteristic dielectric constant ε 33 , (c) is a curve diagram of the large-signal parameter strain S (%), and (d) is a curve diagram of the small-signal characteristic inverse piezoelectric constant d* 33 (pm / V). Detailed Embodiments

[0020] The technical solution of the present invention will be further described below through specific embodiments.

[0021] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the examples are conventional methods in the art unless otherwise specified.

[0022] Example A BaZrO3-doped potassium sodium niobate-based lead-free piezoelectric ceramic, whose general formula is (100 - x)(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - xBaZrO3 + ywt%MnO, where 2 ≤ x ≤ 5 and 1 < y < 3. In the formula, x represents the stoichiometric ratio of BaZrO3 in the KNN-based lead-free piezoelectric ceramic, and y represents the mass percentage of MnO in the KNN-based lead-free piezoelectric ceramic. MnO refers to manganese oxide.

[0023] Its preparation method is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 20 - 24 h, dry them at 80 °C, and then burn the powders in air at 700 - 750 °C for 3 - 5 h; (2) Grind the pre-burned powder again for 20 - 24 h and dry it, sieve it through a 40-mesh sieve, and calcine the powder in air at 900 - 950 °C for 3 - 5 h; (3) Add MnO for the third ball milling for 20 - 24 h. Press the obtained powder into a disk with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 150 - 250 MPa to obtain a wafer; (4) Sinter the cold isostatically pressed wafer in air at 1100 - 1110 °C for 2 - 4 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample; (6) To characterize the electrical properties, coat silver electrodes on both sides of the sample and burn them at 500 - 700 °C for 20 - 40 min to obtain a ceramic disk; (7) Place the ceramic disk in silicone oil at 110 - 130 °C and polarize it at a DC electric field strength of 2 - 4 kV / mm for 20 - 30 min to obtain the BaZrO3-doped potassium sodium niobate-based lead-free piezoelectric ceramic.

[0024] Example 1 A BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramic, with x = 2 and y = 2, and its formula is 98(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 2BaZrO3 + 2wt% MnO.

[0025] The preparation method thereof is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined proportion, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Ball mill the pre-calcined powder again for 24 h and dry it, sieve it through a 40-mesh sieve, and then calcine the powder at 930 °C for 4 h again; (3) Add MnO and conduct the third ball milling for 24 h. Press the obtained powder into a disk with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatically pressed wafer in air at 1100 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0026] (6) In order to characterize the electrical properties, coat silver electrodes on both sides of the sample and sinter it at 600 °C for 30 min to obtain a ceramic disk.

[0027] (7) Polarize the ceramic disk in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramic.

[0028] Example 2 A BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramic, with x = 3 and y = 2, and its formula is 97(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 3BaZrO3 + 2wt% MnO.

[0029] The preparation method thereof is as follows: (1) Weigh the analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined proportion, grind them for 24 h using a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol), after drying at 80 °C, calcine the powder in air at 730 °C for 4 h; (2) Ball mill the pre-calcined powder again for 24 h and dry it, sieve it through a 40-mesh sieve, and calcine the powder again at 930 °C for 4 h; (3) Add MnO for the third ball milling for 24 h. Press the obtained powder into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatic pressed wafer in air at 1102 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0030] (6) To characterize the electrical properties, coat silver electrodes on both sides of the sample and sinter at 600 °C for 30 min to obtain a ceramic disc.

[0031] (7) Polarize the ceramic disc in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the Na0.5K0.5NbO3-based lead-free piezoelectric ceramic doped with BaZrO3.

[0032] Example 3 A Na0.5K0.5NbO3-based lead-free piezoelectric ceramic doped with BaZrO3, x = 4, y = 2, with the formula 96(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 4BaZrO3 + 2 wt% MnO.

[0033] Its preparation method is as follows: (1) Weigh the analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined proportion, grind them for 24 h using a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol), after drying at 80 °C, calcine the powder in air at 730 °C for 4 h; (2) Ball mill the pre-calcined powder again for 24 h and dry it, sieve it through a 40-mesh sieve, and calcine the powder again at 930 °C for 4 h; (3) Add MnO for the third ball milling for 24 h. Press the obtained powder into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatically pressed wafers in air at 1105 °C for 3 h to obtain ceramic green compacts; (5) Grind the ceramic green compacts to a thickness of 1 mm and polish them with diamond slurry to obtain samples.

[0034] (6) To characterize the electrical properties, coat silver electrodes on both sides of the samples and sinter them at 600 °C for 30 min to obtain ceramic wafers.

[0035] (7) Polarize the ceramic wafers in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramics.

[0036] Example 4 A BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramic, x = 5, y = 2, with the formula 95(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 5BaZrO3 + 2 wt% MnO.

[0037] Its preparation method is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Grind the pre-calcined powder again for 24 h and dry it, sieve it through a 40-mesh sieve, and then calcine the powder at 930 °C for 4 h again; (3) Add MnO and conduct the third ball milling for 24 h. Press the obtained powder into a disk with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain wafers; (4) Sinter the cold isostatically pressed wafers in air at 1110 °C for 3 h to obtain ceramic green compacts; (5) Grind the ceramic green compacts to a thickness of 1 mm and polish them with diamond slurry to obtain samples.

[0038] (6) To characterize the electrical properties, coat silver electrodes on both sides of the samples and sinter them at 600 °C for 30 min to obtain ceramic wafers.

[0039] (7) Polarize the ceramic wafers in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramics.

[0040] Comparative Example Comparative Example 1 A sodium potassium niobate-based lead-free piezoelectric ceramic, with the formula 100(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3. x = 0, y = 0, that is, the matrix ceramic without doping BaZrO3 and MnO.

[0041] The preparation method is as follows: (1) Weigh the analytical pure powders of K2CO3, Na2CO3, Li2CO3, Nb2O5 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Ball mill the pre-calcined powder again for 24 h and dry it, sieve it through a 40-mesh sieve, and then calcine the powder at 930 °C for 4 h again; (3) Press the obtained powder into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatic pressed wafer in air at 1110 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0042] (6) To characterize the electrical properties, coat silver electrodes on both sides of the sample and sinter it at 600 °C for 30 min to obtain a ceramic disc.

[0043] (7) Polarize the ceramic disc in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the sodium potassium niobate-based lead-free piezoelectric ceramic without doping BaZrO3 and MnO.

[0044] Comparative Example 2 The difference from Example 1 is that MnO is not doped. x = 2, y = 0, and its formula is 98(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 2BaZrO3.

[0045] The preparation method is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Re-grind the pre-calcined powder for 24 h and dry it, sieve it through a 40-mesh sieve, and then re-calcine the powder at 930 °C for 4 h; (3) Press the obtained powder into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatic pressed wafer in air at 1110 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0046] (6) To characterize the electrical properties, coat silver electrodes on both sides of the sample and sinter it at 600 °C for 30 min to obtain a ceramic disc.

[0047] (7) Polarize the ceramic disc in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the Na0.5K0.5NbO3-based lead-free piezoelectric ceramic doped with BaZrO3.

[0048] Comparative Example 3 The difference from Example 1 is that x = 1, y = 2, and its formula is 99(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - BaZrO3 + 2 wt% MnO.

[0049] Its preparation method is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Re-grind the pre-calcined powder for 24 h and dry it, sieve it through a 40-mesh sieve, and then re-calcine the powder at 930 °C for 4 h; (3) Add MnO and perform the third grinding for 24 h. Press the obtained powder into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatic pressed wafer in air at 1110 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0050] (6) To characterize the electrical properties, silver electrodes are coated on both sides of the sample and sintered at 600 °C for 30 min to obtain a ceramic wafer.

[0051] (7) Polarize the ceramic wafer in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramic.

[0052] Comparative Example 4 The difference from Example 1 is that x = 6, y = 2, and its formula is 94(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 6BaZrO3 + 2 wt% MnO.

[0053] Its preparation method is as follows: (1) Weigh the analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Ball mill the pre-calcined powder again for 24 h and dry it, sieve it through a 40-mesh sieve, and then calcine the powder at 930 °C for 4 h again; (3) Add MnO and conduct the third ball milling for 24 h. Press the obtained powder into a disk with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold isostatically pressed wafer in air at 1110 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0054] (6) To characterize the electrical properties, silver electrodes are coated on both sides of the sample and sintered at 600 °C for 30 min to obtain a ceramic wafer.

[0055] (7) Polarize the ceramic wafer in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramic.

[0056] Comparative Example 5 The difference from Example 1 is that x = 2, y = 1, and its formula is 98(K 0.49Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 2BaZrO3 + 1 wt% MnO.

[0057] The preparation method is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) Re - grind the pre - calcined powder for 24 h and dry it, sieve it through a 40 - mesh sieve, and then calcine the powder at 930 °C for 4 h again; (3) Add MnO and conduct the third grinding for 24 h. Press the obtained powder into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then perform cold isostatic pressing at 200 MPa to obtain a wafer; (4) Sinter the cold - isostatically - pressed wafer in air at 1110 °C for 3 h to obtain a ceramic green body; (5) Grind the ceramic green body to a thickness of 1 mm and polish it with diamond slurry to obtain a sample.

[0058] (6) To characterize the electrical properties, coat silver electrodes on both sides of the sample and sinter them at 600 °C for 30 min to obtain a ceramic disc.

[0059] (7) Polarize the ceramic disc in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the lead - free piezoelectric ceramic based on sodium - potassium niobate doped with BaZrO3.

[0060] Comparative Example 6 The difference from Example 1 is that x = 2, y = 3, and its formula is 98(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 2BaZrO3 + 3 wt% MnO.

[0061] The preparation method is as follows: (1) Weigh analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5 in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powders in air at 730 °C for 4 h; (2) The pre-fired powder is ball milled again for 24 h and dried, sieved through a 40-mesh sieve, and the powder is calcined again at 930 °C for 4 h; (3) MnO is added for the third ball milling for 24 h. The obtained powder is pressed into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then cold isostatically pressed at 200 MPa to obtain a wafer; (4) The cold isostatically pressed wafer is sintered in air at 1110 °C for 3 h to obtain a ceramic green body; (5) The ceramic green body is ground to a thickness of 1 mm and polished with diamond slurry to obtain a sample.

[0062] (6) To characterize the electrical properties, silver electrodes are coated on both sides of the sample and sintered at 600 °C for 30 min to obtain a ceramic wafer.

[0063] (7) The ceramic wafer is polarized in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the Na0.5K0.5NbO3-based lead-free piezoelectric ceramic doped with BaZrO3.

[0064] Comparative Example 7 The difference from Example 1 is that after mixing the raw materials, it is only ball milled once.

[0065] A Na0.5K0.5NbO3-based lead-free piezoelectric ceramic doped with BaZrO3, x = 2, y = 2, and its formula is 98(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - 2BaZrO3 + 2 wt% MnO.

[0066] Its preparation method is as follows: (1) Weigh the analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3, Ta2O5 and MnO in a predetermined ratio, grind them with a planetary ball mill and zirconia balls (the grinding medium is anhydrous ethanol) for 24 h, dry them at 80 °C, and then calcine the powder in air at 730 °C for 4 h; (2) The obtained powder is pressed into a disc with a diameter of 10 mm and a thickness of 1.5 mm, and then cold isostatically pressed at 200 MPa to obtain a wafer; (3) The cold isostatically pressed wafer is sintered in air at 1110 °C for 3 h to obtain a ceramic green body; (4) The ceramic green body is ground to a thickness of 1 mm and polished with diamond slurry to obtain a sample.

[0067] (5) To characterize the electrical properties, silver electrodes are coated on both sides of the sample and sintered at 600 °C for 30 min to obtain a ceramic wafer.

[0068] (6) The ceramic wafers were polarized in silicone oil at 120 °C under an electric field of 3 kV / mm for 30 min to obtain the BaZrO3-doped sodium potassium niobate-based lead-free piezoelectric ceramics.

[0069] Performance test The sodium potassium niobate-based lead-free piezoelectric ceramics prepared in each example and comparative example were subjected to performance tests. The test methods were as follows: ① In the 2Theta range of 200 - 600, at a scanning speed of 0.05 ° / s, the crystal structure of the samples was measured using Cu Kα1 radiation (D8 Advance, Bruker, Germany). ② The small-signal characteristic permittivity ε 33 and the large-signal parameters (polarization P and strain S) were measured using a ferroelectric measurement system TF Analyzer 2000E (aixACCT Systems GmbH, Aachen, Germany). The results are as Figure 1 shown in the following table. x, y, number of ball milling times <![CDATA[Inverse piezoelectric constant (d * 33 ) pm / V]]> Example 1 x = 2, y = 2, ball milled 3 times 375 Example 2 x = 3, y = 2, ball milled 3 times 342 Example 3 x = 4, y = 2, ball milled 3 times 476 Example 4 x = 5, y = 2, ball milled 3 times 445 Comparative Example 1 x = 0, y = 0, ball milled 2 times 285 Comparative Example 2 x = 2, y = 0, ball milled 2 times 306 Comparative Example 3 x = 1, y = 2, ball milled 3 times 313 Comparative Example 4 x = 6, y = 2, ball milled 3 times 320 Comparative Example 5 x = 2, y = 1, ball milled 3 times 339 Comparative Example 6 x = 2, y = 3, ball milled 3 times 317 Comparative Example 7 x = 2, y = 2, ball milled 1 time 290

[0070] As can be seen from the above table, the ceramic shows the maximum d * 33 value of up to 476 pm / V at x = 4, indicating that the BZ4Mn2 system can generate a relatively high d * 33 value at low electric fields. This will add another candidate material for lead-free multilayer actuators that can be co-fired with nickel electrodes.

[0071] An increase in the content of BZ (barium zirconate) tends to make the sample enter the pseudo-cubic phase, reducing the ionic displacement and resulting in a decrease in the polarization intensity. When x = 2, the irreversible electric domains of the sample are very few, indicating that the optimal positive strain value comes from the generation of intrinsic piezoelectric strain, thus indicating that the intrinsic contribution of the polycrystalline phase boundary is also very important for the piezoelectric properties of the ceramics. An increase in the BZ content is beneficial to the increase in the dielectric constant of the ceramics but has a negative effect on Tc. The incorporation of a small amount of BZ will reduce the grain size and promote densification, while the excessive incorporation of BZ will have the opposite effect.

[0072] Figure 1 are the small-signal characteristics and large-signal parameter diagrams of the ceramic wafers prepared in Examples 1 - 4; in the figure, (a) is the curve diagram of the large-signal parameter polarization P (μC / m 2 ), (b) is the curve diagram of the small-signal characteristic permittivity ε 33 , (c) is the curve diagram of the large-signal parameter strain S (%), and (d) is the small-signal characteristic inverse piezoelectric constant d* 33In the figure, x represents the coefficient of BaZrO3 in the general formula, x=2 corresponds to Example 1, x=3 corresponds to Example 2, x=4 corresponds to Example 3, and x=5 corresponds to Example 4.

[0073] like Figure 1 As shown in (a), with the increase of BaZrO3 content, the coercive field Ec and residual polarization of the sample continue to decrease. It can be clearly observed that the increase of BaZrO3 content does lead to a significant decrease in negative strain. (b) shows the dielectric constant ε 33 The change of ε 33 As the BaZrO3 content increases, d* increases. (c) shows that when x = 2, the sample has very few irreversible electric domains, which indicates that the optimal positive strain value comes from the generation of intrinsic piezoelectric strain, namely, OT phase transition, indicating that the intrinsic contribution of polycrystalline phase boundaries is also very important for the piezoelectric properties of ceramics. (d) shows that the increase of BaZrO3 content does not lead to d* 33 At zero field, it changes significantly and is approximately equal to the quasi-static d* 33 The inverse piezoelectric coefficient d* measured by the instrument 33 .

[0074] Compared with Example 1, the comparative example 1 has the following reasons: the MnO content is too low and the number of ball milling times is insufficient, resulting in the test results being d * 33 Not ideal.

[0075] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. The BaZrO3-doped KNN-based lead-free piezoelectric ceramic is characterized in that Its general formula is (100 - x )(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O3 - x BaZrO3 + y wt% MnO, where 2 ≤ x ≤ 5, 1 < y < 3; x represents the stoichiometric ratio of BaZrO3 in the piezoelectric ceramic, y represents the mass percentage of MnO in the piezoelectric ceramic.

2. The BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 1, characterized in that, x is 2 or 4 or 5.

3. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to any one of claims 1-2, characterized in that, It includes the following steps: (1) After mixing the raw materials according to the stoichiometric ratio, perform first ball milling, pre-sintering, second ball milling, calcination in sequence, and then add MnO for third ball milling to obtain mixed powder; (2) Press the mixed powder into a ceramic green body, and the ceramic green body is sintered for the first time, ground, polished, coated with silver electrodes, and sintered for the second time in sequence to obtain a ceramic wafer; (3) Perform polarization treatment on the ceramic wafer to obtain a KNN-based lead-free piezoelectric ceramic doped with BaZrO3.

4. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3, characterized in that, The raw materials in step (1) are analytical pure powders of BaCO3, Nb2O5, Na2CO3, K2CO3, ZrO2, Li2CO3 and Ta2O5.

5. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3, wherein, The first ball milling in step (1) is carried out in a planetary ball mill, using anhydrous ethanol as the medium, and ball milling for 20 - 24 h.

6. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3 or 4 or 5, characterized in that, The pre-sintering in step (1) is carried out at 700 - 750 °C in air for 3 - 5 h; the calcination is carried out at 900 - 950 °C in air for 3 - 5 h.

7. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3, characterized in that, The pressing in step (2) is cold pressing and forming under 150 - 250 MPa.

8. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3 or 7, characterized in that, The first sintering in step (2) is carried out at 1100 - 1110 °C in air for 2 - 4 h.

9. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3 or 7, characterized in that The second sintering in step (2) is carried out at 500 - 700 °C for 20 - 40 min.

10. The preparation method of the BaZrO3-doped KNN-based lead-free piezoelectric ceramic according to claim 3, characterized in that, The polarization treatment in step (3) is: place the ceramic wafer in silicone oil at 110 - 130 °C, and polarize it for 20 - 30 min with a DC electric field strength of 2 - 4 kV / mm.

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