KR101091192B1 - Composition and fabrication method of lead-free piezoelectric ceramics for low temperature firing - Google Patents

Abstract

The present invention relates to sensors and actuators in a manner that the composition and the production of lead-free piezoelectric ceramics for lead-free piezoelectric ceramic composition (K _{0 .52 0 .48} Na) Li _0.95 Nb _{0 .05 0 .95 0 .05} Sb

O ₃ + x mol% FeO, CoO, CuO, Mn, Mo composition (0 <x ≤ 7), and the addition of a metal and metal oxide in particular excellent piezoelectric charge coefficient (d33 = 311 pC / N) Genie has developed lead-free piezoceramic compositions for low temperature firing. In addition, since Na ₂ CO ₃ , K ₂ CO ₃ , and Nb ₂ O ₅ are used as raw material powders, which are relatively inexpensive compared to conventional PZT piezoceramic materials, they are advantageous in reducing the cost of materials and components, and do not use PbO, which is an environmental regulation material. It's environmentally friendly.

Lead-free piezoceramic composition, electromechanical coupling factor, mechanical quality factor, piezoelectric charge factor, piezoelectric actuator

Description

Composition and fabrication method of lead-free piezoelectric ceramics for low temperature firing

The present invention relates to a lead-free (Pb-free) piezoelectric ceramic, to a lead-free piezoelectric ceramic composition for low-temperature firing having excellent piezoelectric properties and to a method of manufacturing the same.

A piezoelectric material is a material that converts mechanical energy into electrical energy and electrical energy into mechanical energy. The representative material is Pb (Zr, Ti) O ₃ (so-called PZT ceramic) piezoelectric ceramic, which is currently used as the most excellent piezoelectric material. In the solid solution of PbTiO ₃ and PbZrO ₃ , PZT solid solution with Curie temperature of 390 ^o C and strong piezoelectricity was found in Morphotropic Phase Boundary (MPB) of tetragonal and trigonal systems. Actuators, piezoelectric transducers, sensors, and resonators using piezoelectric effects have been actively studied.

Piezoceramic mainly used at present is generally manufactured using PZT powder composed of Pb (Zr, Ti) O ₃ based composition. The PZT powder uses a solid-phase synthesis method obtained by mixing PbO, ZrO ₂ and TiO ₂ as main constituents with raw materials such as impurities such as Nb ₂ O ₅ , Ta ₂ O ₅ , Fe ₂ O ₃ and MnO and firing at high temperature. Are synthesized. PZT powder thus synthesized is somewhat different depending on its composition, but should be sintered at a relatively high temperature of 1200 ^o C ~ 1350 ^o C, and a large amount of PbO is volatilized during sintering, making it difficult to control the microstructure and physical properties. In order to do this, excess PbO is added to the composition to produce the composition. This is a cause of acid rain and other pollution when released into the air, and not only environmental pollution, but also has a problem in terms of price competitiveness, and is currently actively researching the development of Pb-free ceramics.

In particular, lead-free piezoelectric ceramic during niobate (Niobium) potassium sodium (Kalium Natrium) ANbO formula _3, such as _{((K, Na) NbO 3} ) Lead-free piezoelectric ceramic represented by (A is the alkali metal) (Na _{0 .5 0 .5} K) NbO ₃ is a high phase transition temperature (420 ^o C), a low coercive field (5kV), high remnant polarization (930 uC / cm ² ) It is considered to be one of the representative materials that can replace piezoelectric ceramics with lead as a basic composition. However, due to the high degradability of raw materials such as Na ₂ CO ₃ and K ₂ CO ₃ and volatilization during sintering, it is known that it is difficult to produce alkaline niobate-based sintered bodies having high characteristics by general sintering methods. Until now, sintering has been carried out using expensive manufacturing processes such as hot press and spark plasma sintering, but there is a reason to find a more economical sintering method. In addition, even in the manufactured niobate piezoelectric ceramics, piezoelectric properties are significantly lower than those of conventional PZT ceramics, and thus, it is necessary to develop lead-free ceramics having high piezoelectric properties in order to replace PbO-based ceramics.

The present invention will be designed to solve the problems described _{above, (K 0 .52 Na 0 .48} ) 0.95 Li 0 .05 (Nb 0 .95 Sb 0 .05) O 3 ( hereinafter NKN- It is an object of the present invention to provide a lead-free piezoelectric ceramic composition for low-temperature firing and a method of manufacturing the same, wherein the lead-free piezoelectric ceramic composition comprising LS) is added with a metal and a metal oxide to increase the sintering characteristics and has excellent piezoelectric properties. In addition, it is intended to lower the firing temperature of NKN-LS lead-free ceramics by adding metals such as FeO, CoO, CuO, Mn, Mo, and metal oxides.

The technical problem is achieved by providing a composition represented by the following formula (1).

Formula 1

(K _{0 .52} Na _{0 .48} ) _0.95 Li _{0 .05} (Nb _{0 .95} Sb _{0 .05} ) O + x mol% y ------------ (1)

    Where x is 0 <x ≦ 7 and y is metal and metal oxide.

As a feature of the present invention for achieving the above object, the lead-free piezoceramic composition according to the present invention is a piezoelectric having excellent piezoelectric properties by producing a dense piezoelectric material to improve the sinterability by adding metal and metal oxide to the NKN-LS composition It is characterized by providing a method for producing a ceramic.

As described above, in the present invention, a lead-free piezoelectric ceramic having excellent piezoelectric properties was developed by adding a metal and a metal oxide to the NKN-LS composition. Low temperature firing was also possible by adding metals and metal oxides. The composition provides an environmentally friendly piezoceramic composition that can replace the lead-based piezoceramic composition that is an existing environmental regulation material.

In addition, low temperature sintering is realized, contributing to the economic production of lead-free piezoelectric ceramics.

Hereinafter, the configuration and effects of the present invention will be described in detail with reference to the accompanying drawings. However, the present embodiment is only an example for explaining the present invention, which does not limit the scope of the present invention.

The present invention provides a lead-free piezoceramic composition composed of NKN-LS, wherein the metal and the metal oxide formed by selecting at least one of FeO, CoO, CuO, Mn, and Mo are contained as additives. It provides a piezoceramic composition.

NKN-LS is a material showing the possibility of replacing lead-based piezoelectric ceramics, which is Na ₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O _{5 ,} Li ₂ CO _{3 ,} Sb ₂ O ₅ Powder is prepared as starting material.

The metals and metal oxides of FeO, CoO, CuO, Mn, and Mo are used as sintering additives. Generally, sintering additives are used to improve the sintering characteristics in the production of piezoelectric materials. When the additive mixture is properly adjusted, better electrical and mechanical properties can be obtained, and in particular, piezoelectric materials having excellent piezoelectric properties can be manufactured. Research into the mixed addition of additives is actively underway. The present inventors have studied the effects of physical properties on the addition of various metals and metal oxides, and it was found that the improvement of physical properties is large when FeO is added among the five metal oxides.

The metal oxide sintering additive described above is an important variable. This is because the improvement of physical properties such as piezoelectric constant is significantly changed depending on the amount of addition, and deterioration of the physical properties appears when excessive addition is made. As for the said FeO addition amount, 0.05-7 mol% is preferable. If the added amount is less than 0.05 mol%, the effect of improving the mechanical quality factor is small, so that piezoelectric elements suitable for vibrators and the like cannot be produced, and addition of more than 7 mol% does not increase the mechanical quality coefficient at most sintering temperatures. On the contrary, it is because the insulation of the ceramic is weakened, which makes it difficult to perform polarization treatment.

The sintering temperature of the lead-free piezoceramic composition composed of NKN-LS is preferably 1000 to 1100 ° C. This is a temperature significantly lower than the sintering temperature of the general PZT powder, 1200 ~ 1350 ℃.

As a result of the experiment, when the sintering temperature is 1050 ° C, the improvement of the piezoelectric charge coefficient value is greatest when 1 mol% of FeO is added.

In the present invention, the production method is as follows.

In addition, according to another aspect of the present invention, there is provided a method for producing a lead-free piezoelectric ceramic composition, which is a sample of Na ₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O _{5 ,} Li ₂ CO ₃ , Sb ₂ O ₅ After mixing, pulverizing and drying and calcining, 0.05 to 7 mol% of the metal and metal oxide are added to the ceramic powder of the NKN-LS composition prepared above to obtain the final powder after crushing and drying. The powder thus prepared is obtained by forming a lead-free piezoelectric body through molding and sintering. In the above production method, the sintering temperature is preferably 1000 ~ 1100 ^° C.

Example  One

       In the present invention, while varying the addition amount of the metal oxide FeO to the NKN-LS ceramic composition was prepared according to the specimen and the structural properties and piezoelectric properties were investigated. This Example was prepared by the oxide mixing method on the basis of the formula of formula (1).

The NKN-LS was prepared (K _{0 .52} Na _{0 .48)} of the ceramic powder _{0.95 Li 0 .05 (Nb 0 .95} Sb 0 .05) O 3 composition as a starting material. After mixing for 24 hours using ethanol and zirconia ball and drying, it was calcined for 1 to 7 hours at 800 ~ 900 ^o C using an alumina crucible. Further, the final powder was obtained by pulverizing and drying as it is without adding an additive to the prepared NKN-LS powder. The final composition was obtained by varying the amount of metal oxide FeO added with the prepared sintering aid. After the PVA was added to the final composition to form a disk, it was heat-treated for 2 to 5 hours at 1000 ~ 1100 ^o C using an alumina crucible. Since the deliquescent property of the raw material powder was high, the contact with moisture was suppressed as much as possible in all processes.

The final composition and the sintered specimens were identified by XRD analysis, and the microstructure was observed using SEM. In order to measure the piezoelectric properties, an Ag electrode was applied to the specimen by 0.1 mm to 1 mm thickness, heat treated at 700 ^° C. for 30 minutes, and polarized at 3.5 kV / cm DC for 30 minutes at 120 ^° C. Piezoelectric properties were measured by d ₃₃ / d ₃₁ METER (ZJ-6B PIEZO) measuring instrument, and electromechanical coupling coefficient was measured by Impedance analyzer.

(Agilent 4294) was used to measure the resonance and anti-resonant frequencies and the resonance resistance to calculate the electromechanical coupling coefficient.

Tables below show the piezoelectric properties of lead-free piezoelectric ceramics according to each component content, calcining temperature, sintering temperature, and holding time by preparing the lead-free piezoelectric ceramic composition in the same manner as in the above example.

Table 1 shows NKN-LS The additives were not added to the powder, and the calcination temperature was changed to show piezoelectric properties according to the sintering temperature.

When the calcining temperature was 850 ℃, the piezoelectric charge coefficient was 282, the highest value.

sample
number
calcination
Temperature
(℃) / 3h
Sintered
Temperature
(℃) / 3h
Lead Free Piezo
Composition of the material d ₃₃ (pC / N)
k _p (%)
Q _m
Shrinkage
(%)
density
(g / cm ³⁾
Basic composition
x (mol ratio) *One 820 1030 0 132 0.298 53 11.3 4.14 2 One 205 0.331 46 12.7 4.25 * 3 1050
0 142 0.256 35 13.8 4.11 4 One 212 0.306 38 14.02 4.28 * 5 1070
0 222 0.352 44 16.7 4.23 6 One 223 0.365 37 16.9 4.25 * 7 1090
0 137 0.333 42 17.6 4.28 8 One 243 0.471 44 18.2 4.28 * 9 850 1030
0 138 0.371 42 11.2 4.22 10 One 232 0.484 45 12.3 4.12 * 11 1050
0 176 0.343 59 16.2 4.32 12 One 277 0.490 46 17.5 4.30 * 13 1070
0 243 0.428 39 16.0 4.24 14 One 282 0.489 44 17.1 4.19 * 15 1090
0 155 0.371 99 17.8 4.25 16 One 256 0.484 41 18.9 4.26 * 17 880 1030
0 123 0.311 34 10.3 4.24 18 One 215 0.325 39 13.1 4.25 * 19 1050
0 179 0.315 49 16.4 4.25 20 One 268 0.398 46 16.8 4.24 * 21 1070
0 212 0.369 42 16.8 4.28 22 One 228 0.400 67 16.7 4.31 * 23 1090
0 133 0.361 53 18.2 4.11 24 One 225 0.398 41 18.6 4.06

*: Comparative Example

Example  2

       Example 2 was carried out in the same manner as in Example 1 except for changing the holding time of the calcination temperature.

Tables 2 and 3 show NKN-LS In case of maintaining calcination temperature without adding additive in powder

The piezoelectric charge coefficient according to the sintering temperature was shown by changing the liver.

       Table 2 shows the highest piezoelectric charge coefficient of 297 when the calcination temperature holding time is 2 hours.

Represents the value.

Table 3 shows the highest value of piezoelectric charge coefficient of 283 at the calcination temperature holding time of 3 hours.

sample
number
calcination
Temperature
(850 ^o C) / h
Sintered
Temperature
( ^o C) / 2h
Lead Free Piezo
Composition of the material d ₃₃ (pC / N)
k _p (%)
Q _m
Shrinkage
(%)
density
(g / cm ³⁾
Basic composition
x (mol ratio) * 25 2 1030 0 182 0.287 42 11.2 4.31 26 One 258 0.398 43 11.9 4.30 * 27 1050 0 250 0.383 47 13.6 4.40 28 One 297 0.409 43 13.5 4.23 * 29 1070 0 209 0.360 83 16.1 4.34 30 One 266 0.397 90 15.8 4.27 * 31 3 1030 0 187 0.339 40 13.0 4.56 32 One 207 0.322 48 13.2 4.38 * 33 1050 0 192 0.328 46 14.7 4.19 34 One 225 0.383 27 14.8 4.25 * 35 1070 0 220 0.345 23 17.2 4.36 36 One 233 0.322 38 16.4 4.31 * 37 5 1030 0 177 0.316 139 13.2 4.29 38 One 210 0.383 467 13.3 4.25 * 39 1050 0 202 0.330 588 15.5 4.33 40 One 248 0.406 409 16.0 4.20 * 41 1070 0 162 0.346 127 15.9 4.35 42 One 242 0.385 409 17.1 4.31

*: Comparative Example

sample
number
calcination
Temperature
(850 ^o C) / h
Sintered
Temperature
( ^o C) / 3h
Lead Free Piezo
Composition of the material d ₃₃ (pC / N) k _p (%)
Q _m
Shrinkage
(%)
density
(g / cm ³⁾
Basic composition
x (mol ratio) * 43 2 1030 0 173 0.363 34 10.1 4.40 44 One 203 0.307 43 12.1 4.23 * 45 1050 0 181 0.319 167 13.2 4.41 46 One 225 0.356 99 13.4 4.34 * 47 1070 0 126 0.356 37 13.2 4.27 48 One 218 0.319 33 13.4 4.32 * 49 3 1030 0 179 0.343 42 10.4 4.28 50 One 277 0.476 46 11.3 4.34 * 51 1050 0 243 0.410 45 14.2 4.46 52 One 283 0.489 44 14.6 4.32 * 53 1070 0 155 0.371 46 17.2 3.84 54 One 256 0.484 41 16.8 4.35 * 55 5 1030 0 204 0.352 345 12.7 4.14 56 One 227 0.396 482 12.2 4.22 * 57 1050 0 237 0.412 463 14.9 4.30 58 One 244 0.430 452 14.8 4.42 * 59 1070 0 220 0.354 518 16.3 4.37 60 One 258 0.471 459 16.5 4.35

*: Comparative Example

Example  3

       Example 3 is different from Example 1 except that the amount of FeO added to NKN-LS is changed.

It was done in the same way.

       Table 4 shows the characteristics of the sintering additive FeO addition amount and the sintering temperature.

When 1 mol% FeO was added, the piezoelectric charge coefficient was 311, the highest value.

sample
number Sintered
Temperature
( ^o C) Lead Free Piezo
Composition of the material d ₃₃ (pC / N) k _p (%) Q _m Shrinkage
(%) density
(g / cm ³⁾ Basic composition
x (mol ratio) * 61 1030 0 152 0.287 162 13.1 4.45 62 1030 0.5 261 0.376 34 13.1 4.41 63 1030 One 242 0.376 38 13.6 4.41 64 1030 2 221 0.365 48 16.3 4.12 65 1030 3 107 0.280 162 16.2 4.19 * 66 1050 0 220 0.346 44 15.0 4.25 67 1050 0.5 305 0.383 32 16.5 4.12 68 1050 One 311 0.421 33 15.1 4.12 69 1050 2 297 0.423 42 17.0 4.21 70 1050 3 272 0.396 45 15.3 4.23 * 71 1070 0 209 0.360 37 17.4 4.44 72 1070 0.5 264 0.384 48 16.3 4.30 73 1070 One 280 0.388 53 16.9 4.30 74 1070 2 184 0.351 47 15.2 4.27 75 1070 3 180 0.311 54 14.9 4.42

*: Comparative Example

Example  4

       Example 4 is different from Example 1 except that Mn, CoO, FeO is added to NKN-LS.

It was done in the same way.

       Table 5 shows the characteristics of the sintering additive FeO addition amount and the sintering temperature.

When 1 mol% FeO was added, the piezoelectric charge coefficient was 297, the highest value.

sample
number Sintering temperature
( ^o C) Mn addition amount
(mol%) CoO addition amount
(mol%) FeO addition amount
(mol%) d ₃₃ (pC / N) k _p (%) Q _m * 76 1030 0 0 0 152 0.287 162 77 1030 0.5 0 0 256 0.39 96 78 1030 One 0 0 225 0.377 101 79 1030 0 0.5 0 215 0.4 60 80 1030 0 One 0 146 0.339 65 81 1030 0 0 0.5 197 0.352 48 82 1030 0 0 One 258 0.398 50 * 83 1050 0 0 0 220 0.346 44 84 1050 0.5 0 0 205 0.389 32 85 1050 One 0 0 180 0.326 33 86 1050 0 0.5 0 239 0.392 68 87 1050 0 One 0 147 0.324 72 88 1050 0 0 0.5 264 0.359 41 89 1050 0 0 One 297 0.409 47 * 90 1070 0 0 0 209 0.360 37 91 1070 0.5 0 0 165 0.266 57 92 1070 One 0 0 178 0.334 72 93 1070 0 0.5 0 221 0.403 73 94 1070 0 One 0 140 0.365 64 95 1070 0 0 0.5 242 0.428 48 96 1070 0 0 One 266 0.477 53

*: Comparative Example

1a and 1b show the piezoelectric charge coefficient (d ₃₃ ) and the electromechanical coupling according to the calcination temperature change.

It shows the total number (k _p ). When FeO metal oxide is added, the piezoelectric charge coefficient and electromechanical coupling coefficient are higher than those of pure NKN-LS, and the sintering is performed at below 1100 ^o C and shows a high piezoelectric charge coefficient.

2A and 2B show the piezoelectric charge coefficient (d ₃₃ ) and the electromechanical coupling coefficient (k _p ) according to the calcination temperature holding time. When FeO metal oxide was added, the piezoelectric charge coefficient and electromechanical coupling coefficient showed higher properties than pure NKN-LS, and also sintered and exhibited high piezoelectric charge coefficient below 1100 ^o C.

3A and 3B show the piezoelectric charge coefficient (d ₃₃ ) and the electromechanical coupling coefficient (k _p ) according to the calcination temperature holding time. When FeO metal oxide was added, the piezoelectric charge coefficient and electromechanical coupling coefficient showed higher properties than pure NKN-LS, and also sintered and exhibited high piezoelectric charge coefficient below 1100 ^o C.

4A, 4B, and 4C show piezoelectric charge coefficients (d ₃₃ ), electromechanical coupling coefficients (k _p ), and mechanical quality coefficients (Q _m ) according to the amount of FeO added. The piezoelectric charge coefficient (d ₃₃ ) was the highest when sintered at 1050 ^o C for 2 hours when 1 mol% was added.

5 is by X-ray diffraction analysis, the crystal structure of the specimen according to the addition amount of FeO exhibited both (002) and (200) peaks and showed a tetragonal phase, but no phase transition. However, due to the excessive addition of FeO metal oxide, the secondary phase due to the unreacted material was observed.

Figure 1a is a graph showing the piezoelectric charge coefficient change with calcination temperature in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

     Figure 1b is a graph showing the electromechanical coupling coefficient change with the calcination temperature in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

Figure 2a is a graph showing the change in the piezoelectric charge coefficient with the calcination temperature holding time in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

     Figure 2b is a graph showing the electromechanical coupling coefficient change with the calcination temperature holding time in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

Figure 3a is a graph showing the change in the piezoelectric charge coefficient with the calcination temperature holding time in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

     Figure 3b is a graph showing the electromechanical coupling coefficient change with the calcination temperature holding time in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

     Figure 4a is a graph showing the piezoelectric charge coefficient change according to the FeO metal oxide content in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

     Figure 4b is a graph showing the electromechanical coupling coefficient change according to the FeO metal oxide content in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

     Figure 4c is a graph showing the mechanical quality factor change according to the FeO metal oxide content in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

5 is a graph showing the crystal structure of the specimen sintered at 1050 ℃ according to the FeO metal oxide content in the lead-free piezoelectric ceramic composition prepared according to the embodiment of the present invention.

Claims (6)

A lead-free piezoceramic composition for low temperature firing represented by the formula (1).  [Formula 1] (K _0.52 Na _0.48 ) _0.95 Li _0.05 Nb _0.95 Sb _0.05 O ₃ + x mol% y Here, x is 0 <x≤7 and y is Mo metal. delete Mixing, grinding, and drying the samples of Na ₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O _5, Li ₂ CO ₃ , and Sb ₂ O ₅ ; Calcining the dried powder; Grinding and drying again by adding 0.05 to 7 mol% of Mo metal; Forming the sample and sintering it, The calcination temperature is 800 ~ 900 ^o C, sintering temperature is 1000 ~ 1100 ^o C, The calcining holding time is 1 to 7 hours, the sintering holding time is a manufacturing method of the lead-free piezoelectric ceramic composition, characterized in that 2 to 5 hours. delete delete delete

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