CN1810711A - Lead-less lithium sodium potassium niobate piezoelectric ceramic with high curie point and its prepn - Google Patents

Abstract

A lead-free piezoelectric ceramic with a high Curie point potassium-sodium-lithium niobate series and a preparation process thereof, relating to a formulation and a preparation process of a lead-free piezoelectric ceramic composition with excellent performance. The lead-free piezoelectric ceramic composition of the present invention comprises the general formula (1-u)[(1-z)(Li _x Na _y K _1-x-y )NbO ₃ +zMTiO ₃ ]+uMnO ₂ , the formula x, y, and z in represent the number of atoms (ie atomic percentage) of the corresponding element material in each component in the compound ion, and the sum of the number of atoms of all elements should be 1, where 0.01≤x≤0.2, 0.2≤ y≤0.7, 0.01≤z≤0.25, 0≤u≤0.05, M represents at least one divalent metal ion selected from the following: Ca, Mg, Ba and (or) Sr. The preparation process of the present invention can sinter the lead-free piezoelectric ceramic composition at a lower temperature, such as 1190°C or lower, so that the prepared lead-free piezoelectric ceramic has good piezoelectricity and practical planar electromechanical coupling Coefficient kp and high Curie temperature, no lead or lead compounds in the preparation process.

Description

A kind of high Curie point potassium sodium lithium niobate series lead-free piezoelectric ceramics and preparation method thereof

1. Technical field

The invention relates to a formulation and preparation process of a lead-free piezoelectric ceramic composition with excellent performance

2. Background technology

Since the 1960s, piezoelectric ceramic materials mainly composed of PT(PbTiO ₃ ) or PZT(Pb(Zr,Ti)O ₃ ) have been widely used in electronics, communications, aerospace, military and other fields. At present, this type of material is still the main material for the preparation of various piezoelectric ceramic filters, oscillators, resonators, frequency discriminators, traps and other electronic components. Although this type of material occupies a dominant position in the field of electronic component manufacturing because of its excellent dielectric and piezoelectric properties. However, there are still many disadvantages in the preparation and use of such materials: (1), the firing temperature of PT-based or PZT-based piezoelectric ceramic materials is relatively high, generally 1200 ° C or higher, so the energy consumption is large, It is not conducive to reducing production costs; (2), PT-based or PZT-based piezoelectric ceramic materials are accompanied by volatilization of lead during the firing process, and with the increase of sintering temperature, the volatilization of lead is also intensified, thus affecting the overall performance of the material , further affecting the performance of the device; (3), the lead component (PbO or Pb ₃ O ₄ ) contained in the PT-based or PZT-based material accounts for about 70%, and the lead cannot be obtained during the raw material preparation process and after the device is discarded. Proper disposal will bring heavy pollution to the environment.

Lead-free piezoelectric ceramics mainly include barium titanate base (BaTiO ₃ ), bismuth sodium titanate base ((Bi.Na)TiO ₃ ), potassium sodium niobate base ((Na, K)NbO) and bismuth layered perovskites. Bone-structured ferroelectrics (BLSF). Barium titanate ceramics are the earliest practical piezoelectric ceramics. Although they were successfully used in hydroacoustic electromechanical transducers and communication filters in the early days, due to their weak piezoelectricity and low Curie temperature (Tc=120 ℃) to limit its scope of use, and it consumes a lot of energy, and the sintering temperature is high (1200°-1400°C), which is not conducive to the requirement of reducing costs. Now people use barium titanate ceramics mainly to dope and modify them to make them semiconducting, and to obtain barium titanate semiconductor ceramics with PTC characteristics, which are used to make various heating elements or switching devices, sensors, and automatic degaussing of color TVs. Devices, etc., such as patents CN1214328A, CN1237149A and CN1228397A respectively describe the preparation of barium titanate semiconductor ceramics with PTC characteristics and corresponding devices. Bismuth layer-structured ferroelectrics are a class of piezoelectric materials with great potential. They have the advantages of high Curie temperature, not easy to age, and good stability. They are suitable for the preparation of devices working in high-temperature and high-frequency environments. However, this kind of material also has the disadvantages of poor piezoelectricity and harsh sintering process; in addition, its high coercive field makes it difficult to polarize, which limits its application. The piezoelectric performance of BNT ((Bi _0.5 Na _0.5 )TiO ₃ ) piezoelectric ceramic composition is good, which has aroused the general attention of material scientists from various countries in recent years. Such as: patents CN85100426, JP11-217262, JP2000-22235, etc. describe the ABO ₃ type [Bi _0.5 (Na _1-x K _x ) _0.5 ]TiO ₃ series lead-free piezoelectric ceramic composition, the literature "NBT-based lead-free piezoelectric ceramic composition Electric Ceramic Filters" (Piezoelectricity and Acousto-optic Vol.25 No.5) reported the use of modified BNT-based lead-free piezoelectric ceramics to make piezoelectric ceramic filters, but compared with PZT-based materials, BNT-based lead-free piezoelectric The Curie point T _c and phase transition point T _r of lead piezoelectric ceramics are relatively low (T _r ~ 200 ℃), and the piezoelectric performance needs to be further improved.

To sum up, the overall performance of lead-free piezoelectric ceramics is far behind that of lead-based piezoelectric ceramics. Therefore, lead-free piezoelectric ceramics can only partially replace lead-containing materials in some application fields according to their own characteristics. Through people's efforts, lead-free materials that can completely replace lead-containing materials may be found in the near future.

For the preparation process, the current sintering temperature of lead-containing ceramic materials is generally higher than 1200°C. Although the method of sealing and sintering with a cover is adopted, the crucible used for sintering generally needs to be pre-absorbed at high temperature (greater than 800°C). deal with. And lead starts to volatilize at 800°C, which will also cause serious pollution to the surrounding environment and damage to the health of the staff. The piezoelectric properties of ceramics are mainly obtained through the polarization of piezoelectric ceramics. Therefore, the quality or perfection of the polarization process is one of the keys to whether the potential of the material performance can be fully realized. The polarization temperature, polarization time and polarization voltage are closely related to the polarization of materials. For the existing lead-based piezoelectric ceramic materials, the general polarization process is: the sample is polarized in a silicone oil bath at about 120°C for 15-60 minutes, and the polarization voltage is slightly different depending on the specific components.

3. Contents of the invention

Therefore, the object of the present invention is to obtain a lead-free piezoelectric ceramic composition that can be sintered at a lower sintering temperature, such as below 1200 ° C or lower, and has good piezoelectricity and practical Planar electromechanical coupling coefficient kp and high Curie point.

To achieve the purpose of the present invention, the present invention proposes a lead-free piezoelectric ceramic composition, which is composed of the general formula (1-u) [(1-z) (Li _x Na _y K _1-xy ) NbO ₃ +zMTiO ₃ ]+ _uMnO2 represents the main component composition, x, y, z, u in the formula represent the number of atoms (ie atomic percentage) that the corresponding elements in the compound ion occupy in each component of the material, and the number of atoms of all elements The sum should be 1. In the formula: 0.01≤x≤0.2, 0.2≤y≤0.7, 0.01≤z≤0.25, 0≤u≤0.05, M represents at least one divalent metal ion selected from the following: Ca, Mg, Ba and (or ) Sr.

The piezoelectric ceramic composition proposed by the present invention, especially when z=0, u=0, can be composed of the main component represented by the general formula (Li _x Na _y K _1-xy ) NbO ₃ , where x , y represent the number of atoms of the corresponding element in the compound ion in each component of the material (ie atomic percentage), the sum of the number of atoms of all elements should be 1. Where: 0.01≤x≤0.2, 0.2≤y≤0.7.

The piezoelectric ceramic composition proposed by the present invention, when u=0, can be composed of main components represented by the general formula (1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ , where x, y, z represent the number of atoms of the corresponding elements in the compound ion in each component of the material (that is, the atomic percentage), and the sum of the number of atoms of all elements should be 1. In the formula: 0.01≤x≤0.2, 0.2≤y≤0.7, 0.01≤z≤0.25, M represents at least one divalent metal ion selected from the following: Ca, Mg, Ba and (or) Sr.

The lead-free piezoelectric ceramic composition proposed by the present invention, when z=0, can be composed of main components represented by the general formula (1-u)(Li _x Na _y K _1-xy )NbO ₃ +uMnO ₂ , the formula The x and y in represent the number of atoms (that is, the atomic percentage) that the corresponding elements in the compound ion occupy in each component of the material, and the sum of the number of atoms of all elements should be 1. In the formula: 0≤u≤0.05.

Another object of the present invention is to overcome the defect of lead pollution caused by high sintering temperature in the prior art, and propose a method for preparing lead-free piezoelectric ceramic composition, which can be sintered at a temperature lower than 1200°C. In order to improve the performance of lead-free piezoelectric ceramics, according to the characteristics of the lead-free piezoelectric ceramics of the present invention, the preparation method of the present invention also proposes a stepped polarization process, that is, gradually increase the polarization voltage to the target position several times The specific steps of the polarization process are as follows: first hold the voltage at 2.5KV/mm for 10-20 minutes, then hold the voltage at 4.0KV/mm for 10-20 minutes, and then hold the voltage at 5.0-6.0KV/mm mm under pressure for 30 minutes. The (1-u)[(1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ ]+uMnO ₂ lead-free piezoelectric ceramic obtained by polarizing the polarization process proposed by the method of the present invention has Excellent piezoelectric properties.

4. Description of drawings

Figure 1 is the relationship between the dielectric constant of (1-u)[(1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ ]+uMnO ₂ lead-free piezoelectric ceramics as a function of temperature at different frequencies . It can be seen from the figure that the lead-free piezoelectric ceramic of the present invention has excellent properties of high Curie temperature (T _c >400°C).

5. Specific implementation methods

In the specific process of preparing the lead-free piezoelectric ceramics of the present invention, according to the formula (1-u)[(1-z)(Li _x Na _y K _1-xy ) _{NbO 3} +zMTiO ₃ ]+uMnO After weighing the percentage by weight, mix the materials by ball milling or vibrating milling for 2 to 5 hours; pre-sintering conditions are sintering at 700-900°C for 2-4 hours; fine grinding is also done by ball milling or vibrating milling. About 5 to 10 hours; then add 10% to 15% PVA glue as a binder to granulate. The consumption of PVA glue is 8%～15% of powder body weight. After adding PVA glue, grind it in a ceramic mortar for 0.5-1 hour, then bake it in an oven at 100°C-150°C for 8-30 minutes, take it out and grind it again, and pass through a 60-mesh sieve to get the particle size Uniform, good fluidity powder.

The powder prepared by the invention is dry-pressed under a pressure of 15-20 tons and kept under pressure for 9-30 seconds to obtain a ceramic green body of a desired shape. After fully debinding the ceramic green body, it is sintered at 1050°C to 1190°C for 2 hours to obtain a high-quality ceramic sheet. There are two ways to sinter ceramics: the first (A) is to directly place the ceramic green body in a corundum crucible and cover it for sintering; the other (B) is different in that the ceramic green body is completely buried in the same composition Sintered in the pre-fired powder. For the sintering furnaces of the two sintering methods, the atmosphere in the furnace cavity is atmospheric atmosphere.

The sintered (1-u)[(1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ ]+uMnO ₂ lead-free piezoelectric ceramics were ground, polished and cleaned, and screen printing by silver electrodes. The electroded sample was preheated in polarized oil at 120°C to 150°C for 30 minutes, and then slowly applied a DC voltage to polarize it. The specific polarization steps are as follows: 2.5Kv/mm holding pressure for 10-20 minutes → 4.0KV/mm holding pressure for 10-20 minutes → 5.0-6.0KV/mm holding pressure for 30 minutes. After the polarized piezoelectric ceramics are cleaned, the finished piezoelectric ceramics with high piezoelectric coefficient and high Curie point can be obtained.

(1-u)[(1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ ]+uMnO ₂ After the lead-free piezoelectric ceramics were annealed at 300℃ for 1 hour, the pressure of the annealed sample The electrical properties are not lower than 80% of the piezoelectric properties of the sample before annealing.

The (1-u)[(1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ ]+uMnO ₂ lead-free piezoelectric ceramics provided by the present invention can be obtained by sintering at a temperature lower than 1200°C , Its piezoelectric performance is excellent, d ₃₃ can be as high as 200pC/N, the plane mechanical coupling coefficient Kp can reach 0.36, and the Curie point can reach above 450 ° C. It is a lead-free piezoelectric ceramic with practical performance.

Embodiment one:

Formula: lead-free piezoelectric ceramics represented by the general formula (1-u)[(1-z)(Li _x Na _y K _1-xy )NbO ₃ +zMTiO ₃ ]+uMnO ₂ , when x=0.03, y= 0.15, z=0, u=0: (Li _0.03 Na _0.15 K _0.82 )NbO ₃

The preparation process is as described above, and the performance parameters of the lead-free piezoelectric ceramics obtained are as follows (for clarity, the list shows): Sintering temperature Sintering process d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1080°C A 99 106 0.32 0.26 444 429 10.74 4.83 1080°C B 114 125 0.37 0.35 421 406 11.47 3.58

Embodiment two:

Formula: (Li _0.03 Na _0.25 K _0.72 )NbO 3 when x=0.03, y=0.25, z=0, u= ₀

The preparation process is as described above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows:

Sintering temperature Sintering process d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1080°C A 109 127 0.32 0.32 478 508 10.81 5.47 1080°C B 111 135 0.33 0.31 471 539 9.34 4.46

Embodiment three:

Formula: (Li _0.02 Na _0.15 K _0.83 )NbO 3 when x=0.02, y=0.15, z=0, u= ₀

The preparation process is as described above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature Sintering process d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1070°C A 187 181 0.36 0.28 692 627 7.81 2.68 1070°C B 222 175 0.39 0.23 678 534 8.05 2.72 1075°C A 161 167 0.37 0.30 776 805 4.22 4.96 1075°C B 168 175 0.35 0.32 819 838 4.00 4.52 1080°C A 168 175 0.33 0.32 761 780 4.88 4.2 1080°C B 174 172 0.34 0.29 776 780 5.42 4.16 1090°C B 143 155 0.34 0.36 517 505 4.19 3.78

Embodiment four:

Formula: (Li _0.02 Na _0.25 K _0.73 )NbO 3 when x=0.02, y=0.25, z=0, u= ₀

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1075°C 185 194 0.36 0.32 585 567 5.46 4.57 1080°C 165 166 0.32 0.28 674 697 5.30 4.19 1120°C 125 152 0.30 0.30 497 544 6.43 5.28

Embodiment five:

Formula: (Li _0.01 Na _0.15 K _0.84 )NbO 3 when x=0.01, y=0.15, z=0, u= ₀

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1080°C 119 115 0.32 0.25 312 282 9.29 3.87

Embodiment six:

Formula: (Li _0.01 Na _0.25 K _0.74 )NbO 3 when x=0.01, y=0.25, z=0, u= ₀

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1080°C 112 112 0.31 0.31 288 262 7.72 5.61

Embodiment seven:

Formula: (Li _0.01 Na _0.35 K _0.64 )NbO 3 when x=0.01, y=0.35, z=0, u= ₀

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1080°C 110 117 0.35 0.23 334 285 10.46 4.29

Embodiment eight:

Formula: when x=0.04, y=0.25, z=0.01, u=0, it is 0.99(Li _0.04 Na _0.25 K _0.71 )NbO ₃ +0.01Ca TiO ₃

The preparation process is as described above, and the performance parameters of the obtained lead-free piezoelectric ceramics are: Sintering temperature Sintering process d ₃₃ /10 ^-12 pC/N K _p ε tanδ/% Before annealing After annealing Before annealing After annealing Before annealing After annealing Before annealing After annealing 1090°C A 123 114 0.32 0.25 382 344 9.05 4.51 1090°C B 124 115 0.33 0.30 535 446 18.52 5.48

Embodiment nine:

Formula: when x=0.03, y=0.25, z=0.05, u=0, it is 0.95(Li _0.03 Na _0.25 K _0.72 )NbO ₃ +0.05 SrTiO ₃

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N ε tanδ/% 1125°C 113 812 41.17

Embodiment ten:

Formula: when x=0.02, y=0.25, z=0.1 u=0, it is 0.9(Li _0.02 Na _0.25 K _0.73 )NbO ₃ +0.1 MgTiO ₃

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N ε tanδ/% 1120°C 50 390 16.64

Embodiment eleven:

Formula: when x=0.01, y=0.25, z=0.15, u=0, it is 0.85(Li _0.01 Na _0.25 K _0.74 )NbO ₃ +0.15BaTiO ₃

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N ε tanδ/% 1140°C 30 400 7.77

Embodiment 12:

Formula: when x=0.03, y=0.25, z=0, u=0.01, it is 0.99(Li _0.03 Na _0.25 K _0.72 )NbO ₃ +0.01MnO ₂

The preparation process is as mentioned above, and the performance parameters of the obtained lead-free piezoelectric ceramics are as follows: Sintering temperature d ₃₃ /10 ^-12 pC/N ε tanδ/% 1125°C 110 670 12.37

Claims (10)

1. A lead-free piezoelectric ceramic composition is characterized in that it is represented by general formula (1-u) [(1-z) (Li _x Na _y K _1-xy ) NbO ₃ +zMTiO ₃ ]+uMnO ₂ Main component composition, where 0.01≤x≤0.2, 0.2≤y≤0.7, 0.01≤z≤0.25, 0≤u≤0.05, M represents at least one divalent metal ion selected from the following: Ca, Mg, Ba and (or) Sr. 2. The lead-free piezoelectric ceramic composition as claimed in claim 1, characterized in that when u=0, by the general formula (1-z) (Li _x Na _y K _1-xy ) NbO ₃ +zMTiO ₃ represented mainly Component composition, where 0.01≤x≤0.2, 0.2≤y≤0.7, 0.01≤z≤0.25, M represents at least one divalent metal ion selected from the following: Ca, Mg, Ba and (or) Sr. 3. the lead-free piezoelectric ceramic composition as claimed in claim 1, it is characterized in that when z=0, u=0, by general formula (Li _x Na _y K _1-xy ) NbO ₃ represent main components to form, formula In 0.01≤x≤0.2, 0.2≤y≤0.7. 4. The lead-free piezoelectric ceramic composition according to claim 1, characterized in that when z=0, by the general formula (1-u)(Li _x Na _y K _1-xy )NbO ₃ +uMnO ₂ , 0≤ u≤0.05. 5. A method for preparing the lead-free piezoelectric ceramic composition as claimed in claims 1 to 4, characterized in that the polarization process for preparing the lead-free piezoelectric ceramic is a step type, and the polarization is first performed at a voltage of 2.5KV/ mm, keep the pressure for 10-20 minutes, then keep the pressure for 10-20 minutes at a voltage of 4.0KV/mm, and then keep the pressure for 30 minutes at a voltage of 5.0-6.0KV/mm; sintering temperature. 6. The lead-free piezoelectric ceramic composition according to claim 1, characterized by the composition of 0.99 (Li _0.04 Na _0.25 K _0.71 ) NbO ₃ +0.01CaTiO ₃ . 7. The lead-free piezoelectric ceramic composition according to claim 1, characterized by the composition of 0.95(Li _0.03 Na _0.25 K _0.72 )NbO ₃ +0.05SrTiO ₃ . 8. The lead-free piezoelectric ceramic composition according to claim 1, characterized by the composition of formula 0.9 (Li _0.02 Na _0.25 K _0.73 ) NbO ₃ +0.1MgTiO ₃ . 9. The lead-free piezoelectric ceramic composition according to claim 1, characterized by the composition of 0.85 (Li _0.01 Na _0.25 K _0.74 ) NbO ₃ +0.15 BaTiO ₃ . 10. The lead-free piezoelectric ceramic composition according to claim 3, characterized by the composition of formula 0.99(Li _0.03 Na _0.25 K _0.72 )NbO ₃ +0.01MnO ₂ .