CN101269962B - Niobate base leadless piezoelectric ceramic with high tension electricity coefficient and preparation method thereof - Google Patents

Abstract

The present invention provides niobate-based lead-free piezoelectric ceramics of high piezoelectric coefficient, which is shown in the general formula (1-z)(Nav-tKu-x-wLixHwAgt)(Nb1-x-y-wTaxSbyTiw)O3.zM Alpha O Beta; wherein, v is more than 0,5 and less than 0.6; w is more than or equal to 0 and less than 0.02; v plus u is 1; t is more than or equal to 0 and less than 0.03; x is more than 0.02 and less than 0.07; y is more than 0.03 and less than 0.08; z is more than or equal to 0 and less than 5; x, y, u, v, w and t stand for atomic percent of each element in the ingredients; z stands for the weight percent of oxides in the ingredients; H is selected from at least one of Ba, Mg, Sr and Ca; M Alpha O Beta is one oxide or a plurality of mixed oxides; the value of M is 1 to 6, and M is an element that can form a solid oxide with oxygen. The preparation method comprises mixing raw materials, presintering, granulation, preparing bisque, dumping, sintering, silver coating, and polarization. In the lead-free piezoelectric ceramics, the d33 can reach 350pC/N; the kp can reach 50 percent; the dielectric constant Epsilon r is 1550; the tangent tan Delta of the loss angle is less than 0.03;the Tc can reach 310 DEG C; the time stability is excellent; and the process is simple. And the lead-free piezoelectric ceramics can be used for preparing drives, sound generators, ultrasonic transducer, resonator and other devices.

Description

A niobate-based lead-free piezoelectric ceramic with high piezoelectric coefficient and preparation method thereof

1. Technical field

The invention relates to a functional ceramic material and a preparation method thereof, in particular to a niobate-based lead-free piezoelectric ceramic with high piezoelectric coefficient and a preparation method thereof.

2. Background technology

The piezoelectric ceramic material that has been widely used for many years is mainly composed of lead zirconate titanate (Pb(Zr,Ti)O ₃ ), wherein the content of lead oxide or trilead tetroxide accounts for more than 60% of the raw material. These lead-containing piezoelectric ceramics will bring serious harm to human health and the living environment during use and disposal.

Lead-free piezoelectric ceramics usually mainly include barium titanate base (BaTiO ₃ , referred to as BT), bismuth sodium titanate base ((Bi _0.5 Na _0.5 )TiO ₃ , referred to as BNT), potassium sodium niobate base ((K, Na) NbO ₃ , referred to as KNN), a ferroelectric material with a tungsten bronze structure and a bismuth layer structure. Among them, BT is a piezoelectric ceramic that was used earlier, but its use is greatly limited due to its low piezoelectric performance, especially its low Curie temperature. BNT is an A-site complex lead-free piezoelectric material with a perovskite structure. It is an earlier researched lead-free ferroelectric ceramic. It forms a quasi-isomorphic phase boundary composition with BT and has good piezoelectricity. Electrical and electromechanical coupling properties (T.Takenaka, K.Maruyama, and K.Sakata, Jpn.J.Appl.Phys., 30(1991) 2236), however, a very high coercive field (E _c =7.3 kV/ mm), making it quite difficult to polarize, and the depolarization temperature is low, which limits its practical application.

In recent years, ceramics with alkali metal niobate as the main component have received extensive attention and research. The ceramics of this system usually have large piezoelectric and electromechanical coupling properties and high Curie temperature, showing great application potential. However, this kind of ceramic is difficult to sinter under the conventional preparation process, and is easy to be hydrolyzed, so that its electrical properties cannot be fully utilized. Although the piezoelectric properties have been effectively improved through various doping modifications, the current process repeatability of this type of ceramics is poor, and potassium and sodium are easily volatile, resulting in stoichiometric deviations, low mechanical strength, and poor piezoelectric and electromechanical properties. Insufficient temperature stability. At present, a lot of research work has been carried out for this material system, including finding new potassium-sodium niobate-based compositions with quasi-isomorphic phase boundaries; A-site stoichiometry and K/Na Ratio adjustment; adjust the relative content of lithium, tantalum and antimony; improve the thermal stability of its electrical properties; optimize the sintering process, powder preparation process and electrode polarization process; texturing process, etc. Although these research works have improved the electrical properties and performance stability of this lead-free piezoelectric ceramic material to a certain extent, compared with the PZT-based composition, its piezoelectric properties still need to be further improved, such as low d ₃₃ and electromechanical coupling coefficient. Insufficient etc. All of these greatly limit the practical application of this lead-free piezoelectric material in devices.

3. Contents of the invention

The present invention aims to provide a niobate-based lead-free piezoelectric ceramic with high piezoelectric coefficient in order to avoid the disadvantages of the above-mentioned prior art. The technical problems to be solved are the design of the ceramic composition and structure, and Optimization of the preparation process.

The technical scheme that the present invention adopts for solving technical problems is:

A niobate-based lead-free piezoelectric ceramic with a high piezoelectric coefficient as claimed in the present invention is characterized in that its composition is expressed by the following general formula:

(1-z)(Na _vt K _uxw Li _x H _w Ag _t )(Nb _{1-xyw Tax} Sb _y Ti _w )O ₃ zM _α O _β …………………(1)

In the general formula (1), x, y, u, v, w, t are the atomic percentages of each element in the material components, and z is the mass percentage of the oxide weight in the total amount of raw materials; 0.5<v<0.6, 0≤w<0.02, v+u=1, 0≤t<0.03, 0.02<x<0.07, 0.03<y<0.08, 0≤z<5%.

Among them, H is at least one selected from the following metal elements: Ba (barium), Mg (magnesium), Sr (strontium), Ca (calcium); the added M _α O _β is one or more doping oxides M is an element with a valence of +1 to +6 and can form a solid oxide with oxygen, at least one element selected from the following elements: Na (sodium), K (potassium), Li (lithium), Ag (silver) , Al (aluminum), Cu (copper), Fe (iron), Mn (manganese), Zn (zinc), Pr (praseodymium), Nd (neodymium), Si (silicon), Sm (samarium), Gd (gadolinium) , La (lanthanum), Bi (bismuth), Dy (dysprosium), Er (erbium), Yb (ytterbium), Sc (scandium), Sb (antimony), Nb (niobium), V (vanadium), Ta (tantalum) and W (tungsten). α and β denote the atomic numbers of the corresponding elements M and O, respectively, in the relevant oxide.

The preparation method of the niobate-based lead-free piezoelectric ceramics with high piezoelectric coefficient according to the present invention includes the steps of mixing raw materials, pre-firing, granulating, making green body, debinding, sintering, silvering, and polarization, The difference from the prior art is that a certain amount of anhydrous sodium carbonate (Na ₂ CO ₃ ), anhydrous potassium carbonate (K ₂ CO ₃ ), lithium carbonate (Li ₂ CO ₃ ), niobium pentoxide (Nb ₂ O ₅ ), tantalum pentoxide (Ta ₂ O ₅ ), antimony trioxide (Sb ₂ O ₃ ), ball milled with absolute ethanol for 4 to 18 hours to obtain a mixture; after drying the mixture, dry it at 800 to 950 Calcining at ℃ for 2 to 6 hours, and then ball milling, drying, and calcination at least once to complete the synthesis to obtain the synthetic material; add an appropriate amount of binder to the synthetic material for granulation; Sintering at lower temperature for 1-4 hours to obtain a porcelain body; polishing the porcelain body with a silver electrode, and then polarizing it in silicone oil for 10-30 minutes, with a polarization voltage of 2-4kv/mm, and a polarization temperature of 20-150°C.

The "certain amount" (each raw material) is the amount weighed after measuring according to the composition shown in the general formula (1) and the defined ratio thereof.

A certain amount of titanium dioxide (TiO ₂ ) and alkaline earth metal carbonate such as barium carbonate (BaCO ₃ ) or/and strontium carbonate (SrCO ₃ ) or/and calcium carbonate (CaCO ₃ ) or/and carbonate can also be added when the raw materials are mixed Magnesium (MgCO ₃ ) is mixed and ball milled together, and the meaning of the so-called "certain amount" is the same as above.

When the raw materials are mixed, a certain amount of silver carbonate (Ag ₂ CO ₃ ) can also be added together for ball milling. The so-called "a certain amount" has the same meaning as above.

When the raw materials are mixed, a certain amount of oxides or carbonates of the doping element M can be added together for ball milling. The so-called "certain amount" (doping material) has the same meaning as above.

Concrete preparation process is as follows:

a. Anhydrous sodium carbonate, anhydrous potassium carbonate, lithium carbonate, barium carbonate (or strontium carbonate, calcium carbonate, magnesium carbonate), titanium dioxide, silver carbonate, niobium pentoxide, tantalum pentoxide, antimony trioxide And raw materials such as oxides or carbonates used for doping element M, according to the composition of the general formula (1) and the ratio of the limits, the ingredients are measured and weighed;

b. The prepared raw materials use absolute ethanol as the medium, and after ball milling for 4 to 18 hours to obtain the ball milling mixture, after drying, calcinate in an alumina crucible at a temperature of 800 to 950°C for 2 to 6 hours; repeat ball milling and dry powder Calcining once to complete the pre-composition of calcination to obtain the synthetic material;

c. After the synthetic material is finely ground by ball milling process again, adding binder to granulate, then molding and debinding, and finally sintering at 1000-1100°C for 1-4 hours to obtain porcelain body;

d. After polishing the ceramic body, it is polarized by a silver electrode, and then applied a voltage in silicone oil. The polarization voltage is 2-4kV/mm, the polarization temperature is 25-150°C, and the polarization time is 10-30 minutes;

e. According to the standard of IRE, the piezoelectric ceramic samples are made to test the piezoelectric and electromechanical coupling performance.

A niobate-based lead-free piezoelectric ceramic with a high piezoelectric coefficient and a preparation method thereof proposed by the present invention have beneficial effects as follows:

1. The ceramic composition of the present invention is a lead-free piezoelectric ceramic with high piezoelectric coefficient and environmental coordination. Its preparation process is stable, and it can be obtained by using traditional piezoelectric ceramic preparation technology and industrial raw materials. It has practicability .

2. The present invention can obtain a ceramic composition located near the quasi-isomorphic phase boundary by adjusting the ratio of potassium/sodium, the content of silver, antimony, tantalum, and alkaline earth metal titanate, and the doping modification of an appropriate amount of oxides, so as to achieve excellent Piezoelectric coefficient and practical planar electromechanical coupling performance, good mechanical strength and temperature stability.

3. The d ₃₃ of the lead-free piezoelectric ceramic can reach 350pC/N, the k _p can reach 50%, the dielectric constant _εr is 1550, the loss tangent tanδ<0.03, and the _Tc can be as high as 310℃; and the time stability Well, the process is simple, and it can be used to make materials for drivers, sound generators, ultrasonic transducers, resonators and other devices.

4. Description of drawings

Fig. 1 is a scanning electron micrograph of a sample with the composition (Na _0.518 K _0.432 Li _0.045 Ag _0.005 )(Nb _0.90 Ta _0.045 Sb _0.55 )O ₃ in Example 1 of the present invention after sintering at 1090°C for 3 hours.

Figure 2 shows the dielectric properties of ceramic samples with the composition (Na _0.510 K _0.44 Li _0.04 Ag _0.005 Ba _0.005 )(Nb _0.895 Ta _0.04 Sb _0.06 Ti _0.005 )O ₃ +0.2wt%CuO at different frequencies in Example 2 of the present invention Constant-temperature curve.

5. Specific implementation

According to formula (1-z)( _Navt K _uxw Li _x H _w Ag _t )(Nb _{1-xyw Tax} Sb _y Ti _w )O ₃ ·zM _α O _β to calculate the amount of each component, raw materials by weight Percentage weighing.

In the formula, x, y, u, v, w, t are the atomic percentages of each element in the material components, and z is the mass percentage of the oxide weight in the total amount of raw materials; 0.5<v<0.6, 0≤w< 0.02, v+u=1, 0≤t<0.03, 0.02<x<0.07, 0.03<y<0.08, 0≤z<5%.

Wherein, H is at least one selected from the following metal elements: Ba, Mg, Sr, Ca; the added M _α O _β is one or more doped oxides, M is +1 to +6 valence and can Elements that form solid oxides with oxygen are selected from at least one of the following elements: Na, K, Li, Ag, Al, Cu, Fe, Mn, Zn, Pr, Nd, Si, Sm, Gd, La, Bi, Dy, Er, Yb, Sc, Sb, Nb, V, Ta and W. α and β denote the atomic numbers of the corresponding elements M and O, respectively, in the relevant oxide. In the preparation process, M is added in the form of its oxide or carbonate raw material.

The concrete steps of preparation technology are as follows:

1. Anhydrous sodium carbonate, anhydrous potassium carbonate, lithium carbonate, barium carbonate (or strontium carbonate, calcium carbonate, magnesium carbonate), titanium dioxide, silver carbonate, niobium pentoxide, tantalum pentoxide, antimony trioxide And raw materials such as oxides or carbonates used for doping element M, according to the composition of the general formula (1) and the ratio of the limits, the ingredients are measured and weighed;

2. The prepared raw materials use absolute ethanol as the medium, and after ball milling for 4 to 18 hours to obtain the ball milling mixture, after drying, calcinate in an alumina crucible at a temperature of 800 to 950°C for 2 to 6 hours; repeat ball milling and dry powder Calcining once to complete the pre-composition of calcination to obtain the synthetic material;

3. After the synthetic material is ground again by ball milling process, adding binder to granulate, then molding and debinding, and finally sintering at 1000-1100°C for 1-4 hours to obtain porcelain blank;

4. Polish the ceramic body and then apply a voltage to the silicon oil to polarize it with a silver electrode. The polarization voltage is 2-4kV/mm, the polarization temperature is 25-150°C, and the polarization time is 10-30 minutes;

5. According to the standard of IRE, the piezoelectric ceramic samples are made to test the piezoelectric and electromechanical coupling performance.

Embodiment 1: Carry out each step successively according to above-mentioned embodiment mode, wherein

In step 1, values are selected according to v=0.523, t=0.005, x=0.045, y=0.055, and z=0. The expression of the composition is: (Na _0.518 K _0.432 Li _0.045 Ag _0.005 )(Nb _0.90 Ta _0.045 Sb _0.055 )O ₃ ;

In step 2, the calcination temperature is 900°C, and the calcination time is 5h;

In step 3, the sintering temperature is 1080°C, and the sintering time is 3h;

The scanning electron micrograph of the natural surface of the sample obtained is shown in Figure 1, and other relevant properties are shown in Table 1:

Table 1

Density (g/cm²) T_c(°C) d₃₃(pC/N) k_p(%) 4.32 315 351 50

Embodiment 2: Carry out each step successively according to above-mentioned embodiment mode, wherein

In step 1, values are selected according to v=0.515, t=0.005, w=0.005, x=0.04, y=0.06, z=0.2%. The expression of the composition is: (Na _0.510 K _0.44 Li _0.04 Ag _0.005 Ba _0.005 )(Nb _0.895 Ta _0.04 Sb _0.06 Ti _0.005 )O ₃ ·0.2wt% CuO;

In step 2, the calcination temperature is 860°C, and the calcination time is 5h;

In step 3, the sintering temperature is 1070°C, and the sintering time is 3h;

The variation curves of the dielectric constant versus temperature of the prepared lead-free piezoelectric ceramic samples at different frequencies are shown in Figure 2, and other related properties are shown in Table 2:

Table 2

Density (g/cm²) T_c(℃) d₃₃(pC/N) k_p(%) 4.39 310 348 49

Embodiment 3: Carry out each step successively according to above-mentioned embodiment mode, wherein

In step 1, values are selected according to v=0.515, t=0.005, w=0.005, x=0.04, y=0.06, z=0.2%. The expression of the composition is: (Na _0.510 K _0.44 Li _0.04 Ag _0.005 Ba _0.005 )(Nb _0.895 Ta _0.04 Sb _0.06 Ti _0.005 )O ₃ ·0.2wt% MnO ₂ ;

In step 2, the calcination temperature is 860°C, and the calcination time is 5h;

In step 3, the sintering temperature is 1070°C, and the sintering time is 3h;

The relevant properties of the prepared lead-free piezoelectric ceramic samples are shown in Table 3:

table 3

Density (g/cm²) T_c(°C) d₃₃(pC/N) k_p(%) 4.38 308 335 48

Embodiment 4: Carry out each step successively according to above-mentioned embodiment mode, wherein

In step 1, values are selected according to v=0.523, t=0.005, x=0.045, y=0.055, z=0.25%. The expression of the composition is: (Na _0.518 K _0.432 Li _0.045 Ag _0.005 )(Nb _0.90 Ta _0.045 Sb _0.055 )O ₃ ·0.25% Fe ₂ O ₃ ;

In step 2, the calcination temperature is 900°C, and the calcination time is 5h;

In step 3, the sintering temperature is 1060°C, and the sintering time is 2h;

The relevant properties of the prepared lead-free piezoelectric ceramic samples are shown in Table 4:

Table 4

Density (g/cm²) T_c(°C) d₃₃(pC/N) k_p(%) 4.41 314 345 48

Claims (6)

1. A niobate-based lead-free piezoelectric ceramic of high piezoelectric coefficient, whose composition is expressed by the following general formula (1): (1-z)(Na _vt K _uxw Li _x H _w Ag _t )(Nb _{1-xyw Tax} Sb _y Ti _w )O ₃ zM _α O _β ……………………(1) In the general formula (1), x, y, u, v, w, t are the atomic percentages of each element in the material components, and z is the mass percentage of the oxide weight in the total amount of raw materials; 0.5<v<0.6, 0≤w<0.02, v+u=1, 0≤t<0.03, 0.02<x<0.07, 0.03<y<0.08, 0≤z<5%; Wherein, H is at least one selected from the following metal elements: Ba, Mg, Sr, Ca; M _α O _β is one or more doped oxides, M is an element with a valence of +1 to +6 and can form a solid oxide with oxygen, at least one selected from the following elements: Cu, Fe, Mn, Zn , Si, Bi, V and W, α and β denote the atomic numbers of the corresponding elements M and O in the relevant oxides, respectively. 2. by the preparation method of the niobate-based lead-free piezoelectric ceramic of high piezoelectric coefficient claimed in claim 1, comprise raw material mixing, pre-sintering, granulation, make biscuit, debinding, sintering, covered with silver, pole It is characterized in that: the mixed ball mill is based on metered anhydrous sodium carbonate, anhydrous potassium carbonate, lithium carbonate, niobium pentoxide, tantalum pentoxide, and antimony trioxide, using absolute ethanol as the medium ball mill After 4-18 hours, the mixture is obtained; the mixture is dried and calcined at 800-950°C for 2-6 hours, and then ball milled, dried, and calcined at least once to complete the synthesis to obtain the synthetic material; add an appropriate amount of binder to the synthetic material It is used for granulation; the formed sample is sintered at 1000-1100°C for 1-4 hours after degumming to obtain a porcelain body; the porcelain body is polished and silver-plated, and then polarized in silicone oil for 10-30 minutes. 2~4kv/mm, polarization temperature 20~150℃. 3. The preparation method according to claim 2, characterized in that: when the raw materials are mixed, metered titanium dioxide and barium carbonate or/and strontium carbonate or/and calcium carbonate or/and magnesium carbonate are added for ball milling together. 4. according to the described preparation method of claim 2 or 3, it is characterized in that: add the metered silver carbonate ball mill together when raw material is mixed. 5. The preparation method according to claim 4, characterized in that: when the raw materials are mixed, the oxides or carbonates of the doping element M are added for ball milling together. 6. The preparation method according to claim 2 or 5, characterized in that: ball milling and calcining at least once before the synthetic material is granulated.

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