JP4506187B2 - Piezoelectric ceramic composition and piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric ceramic composition and a piezoelectric element, and more particularly to a piezoelectric ceramic composition suitable for a piezoelectric actuator, a piezoelectric buzzer, and the like, and a piezoelectric element using the same.

  The piezoelectric actuator uses a strain and force generated by applying a voltage as a mechanical drive source, and is used for positioning in an accurate machine tool, an inkjet printer head, and the like. In such a piezoelectric actuator, a stacked piezoelectric actuator is used to increase the amount of displacement per applied voltage.

  A laminated piezoelectric element used in such a piezoelectric actuator generally includes a piezoelectric ceramic material made of calcined powder and a binder, and the resulting slurry is formed into a sheet to form a green sheet. In addition, the internal electrode paste is printed on the green sheet so as to have a desired pattern, and these are pressure-bonded, and then the green sheet and the internal electrode paste are co-fired.

  As a piezoelectric ceramic material for piezoelectric actuators, lead zirconate titanate (PZT) is generally used, and this lead zirconate titanate (PZT) has a high firing temperature of about 1200 ° C. Therefore, as the metal material of the above-mentioned internal electrode to be co-fired, an expensive noble metal material having a high melting point such as Pt (platinum) or Pd (palladium) must be used, which increases the manufacturing cost. It was.

  For this reason, in order to use a cheaper internal electrode material, it is desired to lower the firing temperature.

A technique of adding La (lanthanum) or Nb (niobium) to a lead zirconate titanate (PZT) -based material is also known (for example, see Patent Documents 1 and 2). For example, an Ag—Pd (silver-palladium) alloy having a composition ratio of Ag / Pd = 7/3 is mainly used as the internal electrode material instead of Pt and Pd.
Japanese Patent No. 3206024 JP 2002-293624 A

  In order to be able to use a more inexpensive electrode material, for example, an Ag—Pd alloy having a low Pd content or Cu or the like, the firing temperature is desired to be about 1000 ° C. or lower. In the piezoelectric ceramic composition of Nos. 1 and 2, sintering at 1000 ° C. has a drawback that sintering does not proceed sufficiently and piezoelectric characteristics such as electromechanical coupling constant k cannot be obtained sufficiently.

  The present invention has been made in view of the above points, and a piezoelectric ceramic composition having a good piezoelectric characteristic, particularly an electromechanical coupling coefficient k, even at a firing temperature of about 1000 ° C. or less, and the piezoelectric ceramic composition An object of the present invention is to provide a piezoelectric element using the above.

  In order to achieve the above object, the present invention is configured as follows.

The piezoelectric ceramic composition of the present invention is mainly composed of _{Pbx (Ti, Zr) O 3} , as a sub-component, converted in terms of La ₂ O ₃ with a weight percent Contact and N b of La to Nb ₂ O ₅ Including b wt%,
The x, a, and b are 1.01 ≦ x ≦ 1.05, 0.03 ≦ a ≦ 0.50, 0.03 ≦ b ≦ 0.50, and 0.10 ≦ a + b ≦ 0. 75.

  According to the present invention, the Pb at the A site of PZT, which is the main component, is defined in a certain range that is excessive in excess of the stoichiometric composition, and contains subcomponents such as La and Nb in a certain range. A piezoelectric ceramic composition having good piezoelectric characteristics, particularly an electromechanical coupling coefficient, can be obtained at the following firing temperature.

  Furthermore, it is preferable to replace 15 mol% or less of the Pb with Ba (barium) and / or Sr (strontium) in order to improve the piezoelectric characteristics.

  The piezoelectric element of the present invention has a piezoelectric ceramic made of the piezoelectric ceramic composition according to the present invention and an electrode formed on the piezoelectric ceramic.

  According to the present invention, since the firing temperature can be lowered to about 1000 ° C. or less, it is possible to use an Ag—Pd alloy or Cu having a low Pd content as the electrode material, and to reduce the manufacturing cost of the piezoelectric element. it can.

  According to the present invention, Pb at the A site of PZT, which is the main component, is defined in a certain range that is excessive as compared with the stoichiometric composition, and subcomponents such as La and Nb are contained in a certain range. A piezoelectric ceramic composition having almost no deterioration of piezoelectric characteristics, particularly electromechanical coupling coefficient, can be obtained at a firing temperature of about or less.

  In addition, since the firing temperature can be lowered to about 1000 ° C. or less, an Ag—Pd alloy or Cu having a low Pd content can be used as the electrode material, and an inexpensive piezoelectric element can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail.

The piezoelectric ceramic composition of the present invention is mainly composed of Pb _x (Ti, Zr) O ₃ , and, as a subcomponent, La is converted to La ₂ O ₃ (lanthanum oxide) and a weight% and / or Nb is changed to Nb. ₂ % by weight in terms of ₂ O ₅ (niobium oxide), x, a and b are 1.01 ≦ x ≦ 1.05, a ≦ 0.50, b ≦ 0.50, and It is 0.10 <= a + b <= 0.75.

The piezoelectric ceramic composition of this embodiment is mainly composed of PZT (lead zirconate titanate), which is a Pb _x (Zr, Ti) O ₃ -based perovskast structure oxide, and Pb, which is an A site of PZT. More than the stoichiometric composition, that is, 1.01 ≦ x ≦ 1.05. That is, the ratio A / B (= x) between the A site and the B site of PZT is set to 1.01 or more and 1.05 or less.

  By making Pb in the A site excessive as described above, excessive PbO forms a liquid phase and lowers the sintering temperature. On the other hand, if it is too much, PbO is excessively present in the crystal grain boundaries, resulting in piezoelectric properties. Therefore, the upper limit is limited to x ≦ 1.05.

Further, as subcomponents, La is converted to La ₂ O _{3 and} contains a wt% and / or Nb is converted to Nb ₂ O ₅ and b wt%, where a and b are each a ≦ 0.50 , B ≦ 0.50, and 0.10 ≦ a + b ≦ 0.75.

  Thus, by adding at least one of La and Nb as a subcomponent, the sintering temperature can be lowered. However, if the amount added is too large, sintering does not occur or the electromechanical coupling constant k is increased. Therefore, the upper limit is limited to a ≦ 0.50 and b ≦ 0.50.

  In addition, since the amount of subcomponents that can be dissolved in PZT decreases due to a decrease in sintering temperature, the sum a + b of the subcomponent addition amounts is limited to 0.10 ≦ a + b ≦ 0.75.

  Further, when the addition amount of the subcomponents is 0.03 ≦ a ≦ 0.50, 0.03 ≦ b ≦ 0.50, and 0.10 ≦ a + b ≦ 0.25, compared with firing in air. Thus, firing in a low oxygen atmosphere having an oxygen concentration of less than 10 ppm has a better electromechanical coupling constant k.

  Therefore, in the case of using inexpensive Cu fired in a low oxygen atmosphere as the internal electrode material, the additive amount of the subcomponent is set to 0.03 ≦ a ≦ 0.50, 0.03 ≦ b ≦ 0.50, And it is preferable that 0.10 ≦ a + b ≦ 0.25.

When a part of Pb which is the A site is substituted with Ba and / or Sr, the piezoelectric characteristics, particularly the piezoelectric strain constant d ₃₁ is improved. When the substitution amount of Pb exceeds 15 mol%, the decrease in Curie temperature becomes large, so it is preferably 15 mol% or less.

  It is practically preferable that Ti and Zr which are B sites have a Ti / Zr ratio of 0.55 / 0.45 to 0.35 / 0.65. In the examples described later, The Ti / Zr ratio is 0.47 / 0.53.

  Hereinafter, the present invention will be described in more detail based on specific examples.

(Example 1)
As starting materials, high purity lead oxide (PbO), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), lanthanum oxide (La ₂ O ₃ ) are prepared, and a predetermined amount Weighed.

At that time, the blending ratio of the starting materials was adjusted so as to have the compositions of Samples 1 to 9 and 12 to 25 in Table 1 below.

As starting materials for lead, titanium, zirconium, niobium and lanthanum, lead oxide (PbO), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), lanthanum oxide (La) Not only ₂ O ₃ ), but also nitrates, hydroxides and the like that become oxides during firing can be used.

Next, the weighed starting materials were mixed and dried, and then calcined at 700 ° C. to 900 ° C. for 2 hours in the air. To the obtained calcined powder, an organic binder, water, and a dispersant were added and mixed to obtain a slurry. The obtained slurry was formed into a sheet by a doctor blade method.

  After the obtained sheet was cut into a predetermined size, about 20 to 30 sheets of the cut sheet were stacked and pressure-bonded. The obtained sheet compact was heated at 400 ° C. to incinerate the binder, and then fired at 1000 ° C. for 2 hours in the air.

  On the surface (both main surfaces) of the obtained piezoelectric ceramic, an Ag paste was applied and baked to form an Ag electrode, cut into a predetermined size (size for lateral effect test), and in an insulating oil at 80 ° C. A sample was obtained by applying a DC voltage of 3 kV / mm for 30 minutes to obtain a sample, and various piezoelectric characteristics were measured.

Table 1 shows electromechanical coupling constants k ₃₁ of Samples 1 to 9 and 12 to 25 obtained as described above. In Table 1, “-” in the column of the electromechanical coupling constant k ₃₁ indicates that sintering was not performed, and “*” in the sample number column represents a comparative example outside the composition range according to claim 1. It shows that there is.

As shown in Table 1, A / B, which is the ratio of the A site to the B site, that is, the samples 14 and 15 in which x of Pb _x (Zr, Ti) O ₃ is x = 1, Pb is not excessive. Therefore, it does not sinter at 1000 ° C., and conversely, in the samples 16 and 17 in which x (= A / B) exceeds 1.05, the electromechanical coupling constant k ₃₁ decreases and is lower than 30%.

In addition, in Samples 25 and 22 in which the addition amount of La or Nb exceeds 0.50 wt% in terms of La ₂ O ₃ or Nb ₂ O ₅ , the electromechanical coupling constant k ₃₁ decreases, and 30% It is below.

Further, the sum of the addition amounts of La and Nb is less than 0.10 in terms of La ₂ O ₃ and Nb ₂ O ₅ , specifically, samples 18 and 19 which are not added at all are both electromechanical coupling constants k ₃₁ has fallen and is below 30%. On the contrary, in the samples 20 and 21 in which the sum of the addition amounts of La and Nb exceeds 0.75 in terms of La ₂ O ₃ and Nb ₂ O ₅ , the samples are not sintered at 1000 ° C., or the electromechanical coupling constant k ₃₁ Has fallen below 30%.

On the other hand, samples 1 to 9 , 12 , 13 , 23 , and 24 within the composition range of claim 1 can all be sintered at 1000 ° C., and the electromechanical coupling constant k ₃₁ is 30%. The above good values were shown.

(Example 2)
As starting materials, high purity lead oxide (PbO), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), lanthanum oxide (La ₂ O ₃ ) are prepared, and a predetermined amount Weighed.

  At that time, the mixing ratio of the starting materials was adjusted so as to be the compositions of samples 26 to 49 in Table 2 below.

Next, the weighed starting materials were mixed and dried, and then calcined at 700 ° C. to 900 ° C. for 2 hours in the air. To the obtained calcined powder, an organic binder, water, and a dispersant were added and mixed to obtain a slurry. The obtained slurry was formed into a sheet by a doctor blade method.

After the obtained sheet was cut into a predetermined size, about 20 to 30 sheets of the cut sheet were stacked and pressure-bonded. After the obtained sheet molded body was heated at 400 ° C. and the binder was incinerated, the sample having the same composition was air (air) or in a nitrogen atmosphere (N ₂ ) which is a low oxygen atmosphere (1 to 2 ppm). Baked at 1000 ° C. for 2 hours.

  An Ag electrode was formed on the obtained piezoelectric ceramic in the same manner as in Example 1, and after cutting into a predetermined size, a polarization treatment was performed to obtain a sample, and various piezoelectric characteristics were measured.

Table 2 shows electromechanical coupling constants k ₃₁ of samples 26 to 49 obtained by firing in air or nitrogen atmosphere. In Table 2, “*” in the sample number column indicates that the comparative example is outside the composition range described in claim 2. Table 2 also shows samples 38 to 41 fired only in a nitrogen atmosphere.

As shown in Table 2, the addition amount of La or Nb is less than 0.03% by weight in terms of La ₂ O ₃ and Nb ₂ O ₅ , specifically, either La or Nb is not added at all. Samples 46 and 48; 47 and 49 have better electromechanical coupling constants k ₃₁ when fired in air than in nitrogen atmosphere.

In addition, in the samples 34, 35; 36, 37 in which the sum of the addition amounts of La and Nb exceeds 0.25 in terms of La ₂ O ₃ and Nb ₂ O ₅ , firing in the air is more effective than in the nitrogen atmosphere. In both cases, the electromechanical coupling constant k ₃₁ is better.

On the other hand, samples 26, 27; 28, 29; 30, 31; 32, 33; 42, 44; 43, 45 within the composition range of claim 2 have a nitrogen atmosphere as compared to the atmosphere. towards the firing at medium is both an electromechanical coupling constant k ₃₁ is good.

Samples 38 to 41 within the composition range of claim 2 exhibited a good electromechanical coupling constant k ₃₁ when fired in a nitrogen atmosphere.

Example 3
As starting materials, high-purity lead oxide (PbO), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), niobium oxide (Nb ₂ O ₅ ), lanthanum oxide (La ₂ O ₃ ), barium carbonate (BaCO ₃₎ ), Strontium carbonate (SrCO ₃ ) was prepared, and a predetermined amount was weighed.

  At that time, the mixing ratio of the starting materials was adjusted so as to be the composition of samples 50 to 56 in Table 3 below, and a part of lead was replaced with barium or strontium.

Next, the weighed starting materials were mixed and dried, and then calcined at 700 ° C. to 900 ° C. for 2 hours in the air. To the obtained calcined powder, an organic binder, water, and a dispersant were added and mixed to obtain a slurry. The obtained slurry was formed into a sheet by a doctor blade method.

  After the obtained sheet was cut into a predetermined size, about 20 to 30 sheets of the cut sheet were stacked and pressure-bonded. The obtained sheet compact was heated at 400 ° C. to incinerate the binder, and then fired at 1000 ° C. for 2 hours in a nitrogen atmosphere.

  An Ag electrode was formed on the obtained piezoelectric ceramic in the same manner as in Example 1, and after cutting into a predetermined size, a polarization treatment was performed to obtain a sample, and various piezoelectric characteristics were measured.

Table 3 shows the relative dielectric constant εr, Curie temperature Tc, electromechanical coupling constant k ₃₁ , and piezoelectric strain constant d ₃₁ of the obtained samples 50 to 56.

As shown in Table 3, by substituting a part of Pb with Ba or Sr, the piezoelectric strain constant d _31, which is an index indicating the dielectric constant εr and the amount of displacement per unit voltage, is increased. Moreover, Curie temperature showed 200 degreeC or more in all. As the substitution amount of Ba or Sr increases, the electromechanical coupling constant k ₃₁ decreases, so the substitution amount is preferably 15 mol% or less. In Tables 1 and 2 above, the relative dielectric constant was not shown, but it was almost constant regardless of the values of x, a, and b.

  As shown in Tables 1 to 3 above, for each sample according to the example of the present invention, an electromechanical coupling coefficient k that can be practically used at a firing temperature of 1000 ° C. or less is obtained. It is clear.

  In addition, the piezoelectric ceramic composition according to the present invention is not limited to the compositions of the above-described examples, and is effective within the scope of the gist of the invention.

  FIG. 1 is a cross-sectional view showing a multilayer piezoelectric element according to the present invention.

  In the piezoelectric element 1 of this embodiment, the piezoelectric ceramic layers 2 and the internal electrode layers 6a and 6b are alternately stacked to form a laminate 3, and both end surfaces 4a and 4b from which the internal electrode layers 6a and 6b are drawn out. Are formed with external electrodes 5a and 5b, respectively.

  The piezoelectric ceramic layer 2 is made of the above-described piezoelectric ceramic composition according to the present invention, and the internal electrode layers 6a and 6b are made of Cu, for example.

  Since the piezoelectric element 1 of the present embodiment uses the piezoelectric ceramic composition of the present invention that has almost no deterioration in piezoelectric characteristics at a firing temperature of 1000 ° C. or less, co-firing is performed using inexpensive Cu as an internal electrode. Therefore, the manufacturing cost can be reduced.

  The present invention is useful as a piezoelectric ceramic composition such as a piezoelectric actuator or a piezoelectric buzzer.

It is sectional drawing of the lamination type piezoelectric element which concerns on this invention.

Explanation of symbols

1 is a laminated piezoelectric element, 2 is a piezoelectric ceramic layer,
6a and 6b are internal electrode layers

Claims (3)

Pb _x (Ti, Zr) O ₃ as a main component, and as subcomponents, La is converted to La ₂ O _{3 and} contains a wt% and Nb converts to Nb ₂ O ₅ and b wt%. a and b are 1.01 ≦ x ≦ 1.05, 0.03 ≦ a ≦ 0.50, 0.03 ≦ b ≦ 0.50, and 0.10 ≦ a + b ≦ 0.75, respectively. A piezoelectric ceramic composition characterized by that. The piezoelectric ceramic composition according to claim 1, wherein 15 mol% or less of Pb is substituted with Ba and / or Sr. A piezoelectric element comprising: a piezoelectric ceramic comprising the piezoelectric ceramic composition according to claim 1 or 2 ; and an electrode formed on the piezoelectric ceramic.