JP2567914B2 - Ferroelectric ceramics - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ -PbZrO ₃ -based ferroelectric ceramics, and more specifically, a piezoelectric constant d and a mechanical constant. Pb (Mg _1/3 Nb _2/3 ) O ₃ −PbTiO ₃ −PbZrO ₃ based ferroelectric ceramics with large dynamic quality factor Qm.

Technical Background of the Invention and Problems Thereof Conventionally, piezoelectric materials made of ferroelectric ceramics have been used for various applications such as a piezoelectric filter, a piezoelectric transformer, an ultrasonic vibrator, and a piezoelectric buzzer. As the most typical ferroelectric ceramics used for these applications, a PbTiO ₃ -PbZrO ₃ -based solid solution is known. Pb (Mg _1/3 Nb _2/3 ) O ₃ -Pb with further improved piezoelectric properties
TiO ₃ -PbZrO ₃ -based solid solutions (JP-B-42-9716 and the like) and ferroelectric ceramics in which these solid solutions contain BaTiO ₃ , SrTiO ₃ or CaTiO ₃ are also known.

By the way, although the use of a piezoelectric material as an actuator has been studied, in this case, since it is necessary to convert electric energy into mechanical energy by the piezoelectric ceramic and the piezoelectric ceramic itself is displaced by this mechanical energy, the piezoelectric ceramic It is necessary to increase the piezoelectric constant d.

Generally, between the piezoelectric constant d and the electromechanical coupling coefficient K and the relative permittivity ε, In order to increase the piezoelectric constant d, the electromechanical coupling coefficient K and / or the relative dielectric constant ε must be increased.

Further, in applications such as an actuator utilizing mechanical resonance of piezoelectric ceramics, such as an ultrasonic motor, it is necessary that both the piezoelectric constant d and the mechanical quality factor Qm are large. When piezoelectric ceramics are used in applications such as ultrasonic motors, since the driving frequency is high, heat is generated when the mechanical quality factor Qm is small, spontaneous polarization decreases, and piezoelectric constants change. Therefore, a large mechanical quality factor Qm of the piezoelectric ceramic is important when the piezoelectric ceramic is used for an application such as an ultrasonic motor.

PbTiO ₃ -PbZrO ₃ based solid solution or Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTi
Against O ₃ -PbZrO ₃ solid solution, but it is possible to increase the mechanical quality factor Qm the inclusion of MnO _2, is a problem that the piezoelectric constant d is greatly reduced with increasing the content of MnO ₂ there were. Therefore, it is desirable that the base solid solution before containing MnO ₂ has a sufficiently large piezoelectric constant d.

Until now, for example, Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ -Pb
ZrO ₃ -based solid solutions and these solid solutions with BaTiO ₃ and SrTiO ₃
Alternatively, some materials have been proposed in which a solid solution containing CaTiO ₃ further contains various oxides for the purpose of increasing the piezoelectric constant d by increasing the electromechanical coupling coefficient K and / or the non-dielectric constant ε. However, the piezoelectric constant d
The size of is not always at a satisfactory level.

For example, when NiO is further contained in these solid solutions, the piezoelectric constant d improves as the NiO content increases, but when NiO is contained beyond the limit, the piezoelectric constant d decreases. This is because, in these solid solution, since the Ni ion enters the selective to B site of the perovskite type crystal represented by ABO _3, the inclusion of NiO past the limit, insufficient ions at the A site, a part finally It is considered that NiO in the perovskite crystal is not taken into the perovskite crystal.

Based on such knowledge, the present inventors have added all of these oxides in a perovskite crystal by incorporating a metal ion such as Ni ion that enters the B site and a metal ion that enters the A site together. It has been found that, when incorporated into, the ferroelectric ceramics having a large piezoelectric constant d can be obtained as compared with the case where only metal ions that enter the B site are contained. Further, it was found that when MnO ₂ was contained in the solid solution providing the ferroelectric ceramics having the large piezoelectric constant d as described above, the ferroelectric ceramics having both the large piezoelectric constant d and the mechanical quality factor Qm were obtained. The present invention has been completed.

The present invention has been completed in view of the above points, and an object of the present invention is to provide a ferroelectric ceramic having a large piezoelectric constant d and a mechanical quality factor Qm and excellent piezoelectric characteristics. I am trying.

SUMMARY OF THE INVENTION In order to achieve such an object, a ferroelectric ceramic according to the present invention comprises Pb _1-a M _a (Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z O ₃
[Wherein M is Ba or Sr and represented by x + y + z = 1], and a = 0 to 0.10 x = 0.05 to 0.70 y = 0.25 to 0.50 z = 0.05 to 0.70 For the perovskite type solid solution, At least one or more oxides selected from Group A and at least one or more oxides selected from Group B below (provided that NiO, Fe ₂ O ₃ or Ta ₂ O ₅ is always contained): Is a perovskite type solid solution in which MnO ₂ is further contained.

Group A (La ₂ O ₃ , Bi ₂ O ₃ , Nd ₂ O ₃ ) Group B (NiO, ZnO, Fe ₂ O ₃ , SnO ₂ , Ta ₂ O ₅ ) Such a ferroelectric ceramic according to the present invention is , AB
In the perovskite-type crystal represented by O ₃ , both the A and B sites contain the metal ions of the above-described metal oxides, and since MnO ₂ is contained, the conventionally known ferroelectric Compared with the conductive ceramics, it has a larger piezoelectric constant d while having almost the same mechanical quality factor Qm. Therefore, the ferroelectric ceramics according to the present invention exhibits excellent characteristics when used for applications such as actuators utilizing mechanical resonance including ultrasonic motors and the like.

Detailed Description of the Invention The ferroelectric ceramics according to the present invention will be specifically described below.

Table ferroelectric ceramics according to the present _{invention, Pb 1-a M a (} Mg 1/3 Nb 2/3) x Ti y Zr z O 3 [ , however, M is Ba or Sr, x + y + z = 1] A, x,
y and z are in the following ranges, a = 0 to 0.10, preferably 0.01 to 0.07 x = 0.05 to 0.70, preferably 0.10 to 0.60 y = 0.25 to 0.50, preferably 0.30 to 0.45 z = 0.05 to 0.70, preferably Is 0.10 to 0.60 for this perovskite type solid solution, at least one or more oxides selected from the following Group A and at least one or more oxides selected from the following Group B (provided that NiO or Fe ₂ O ₃ or Ta ₂ O ₅ is always contained), and MnO ₂ is further contained, which is a perovskite-type solid solution.

Group A (La ₂ O ₃ , Bi ₂ O ₃ , Nd ₂ O ₃ ) Group B (NiO, ZnO, Fe ₂ O ₃ , SnO ₂ , Ta ₂ O ₅ ) Perovskite constituting the ferroelectric ceramics according to the present invention When the type crystal is represented by ABO ₃ , in the present invention, A
The site contains at least one or more metal oxides selected from Group A in the form of the following metal ions,
The B site contains at least one metal oxide selected from the group B (however, NiO, Fe ₂ O ₃ or Ta ₂ O ₅ is always contained) in the form of the following metal ions. .

Group A ^{(La 3+, Bi 3+, Nd} 3+) B group ^{(Ni 2+, Nn 2+, Fe} 3+, Sn 4+, Ta 5+) Here, the above-mentioned Pb _1-a M _a ( Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z O ₃ [where M is Ba or Sr], the metal ions of group A are Pb and M (M is Ba or Sr) in the solid solution. Is preferably present in an amount of 0.5 to 5.0 atomic equivalents relative to the total atomic equivalent of 100 atomic equivalents of the above, and the effect of improving the piezoelectric constant d is particularly remarkable in this range. The metal ions of group B are
0.5 ≦ N ≦ 5.0 (however, Represents the valencies of the metal ions of Group A and Group B, respectively, and x
_Ai and _xBj each desirably represent an atomic equivalent of the metal ions in Group A and Group B), and the effect of improving the piezoelectric constant d is particularly remarkable in this range.

Further, the amount of MnO ₂ to be contained is preferably 0.1 to 2.0% by weight. In this range, the mechanical quality factor Qm is improved and the piezoelectric constant d can be maintained at a sufficiently large value.

Such a ferroelectric ceramic having the composition of the present invention uses a metal compound such as a metal oxide or a metal salt which can provide each metal oxide component when sintered, in the form of powder. It can be manufactured by sintering. The method for producing these powdery metal compounds is not particularly limited, and various known methods such as a liquid phase method and a solid phase method can be used. For example, a precipitation method, a coprecipitation method, an alkoxide method, a sol-gel method and the like can be applied to the liquid phase method, and an oxalate decomposition method and an oxide mixing method can be applied to the solid phase method. The powder obtained by any of the above methods is calcined at 800 to 1000 ° C., and the calcined body is ball milled and then dried. 500 ~ 1500kg / cm ²
Press molding at a pressure of and firing at 1000 to 1300 ° C. yields the desired ferroelectric ceramics.

[Examples] Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

The electromechanical coupling coefficient (Kp), relative permittivity (ε), piezoelectric constant (d ₃₁ ), and mechanical quality factor (Q
The measurement of m) was performed in accordance with the method specified in the Electronic Materials Industries Association Standard (EMAS).

Examples 1-3, Comparative Examples _{1~2 PbO, ZrO 2, TiO 2} , MgCO 3, Nb 2 O 5, SrCO 3, La 2 O 3, Ni
O, SnO ₂ and MnO ₂ were weighed in such a ratio as to have the composition shown in Table 1, pulverized and mixed in a ball mill. The obtained powder was calcined at 800 to 1000 ° C. for 1 to 2 hours, and the calcined body was ball-milled and then dried. This is pressed into a disk having a diameter of 25 mm at a pressure of 1000 kg / cm ² , and is pressed at 1050 to 1250 ° C.
Fired for ~ 2 hours. The sintered body thus obtained is 0.5m thick
After polishing to m, silver electrodes were applied to both sides and baked. Furthermore, after applying a polarization treatment by applying a DC electric field of 20 to 40 KV / cm in silicon oil, the sample aged for 12 hours was subjected to measurement of electrical characteristics.

 Table 1 shows the results.

In the table, a, x, y, and z are represented by the formula Pb _1-a Sr _a (Mg _1/3 Nb _2/3 ) _x T
i _y Zr _z O ₃ represents each coefficient of [x + y + z = 1], p,
q and r represent the atomic equivalent of each metal ion with respect to the total atomic equivalent of Pb and Sr of 100 atomic equivalents. N is Represents the valencies of the metal ions of Group A and Group B, respectively, and x
_Ai and _xBj represent the atomic equivalents of the metal ions in Group A and Group B, respectively.

From the results of Examples 1 to 3, Pb _0.95 Sr _0.05 (Mg _1/3 N
b _2/3 ) _0.375 Ti _0.375 Zr _0.250 O ₃ Ferroelectric ceramics (I) with La ³⁺ entering the A site and (Ni ²⁺ , Sn ⁴⁺ ) entering the B site together It can be seen that as the content of MnO _{2 in} the contained ferroelectric ceramics increases, the mechanical quality factor Qm increases while the piezoelectric constant d ₃₁ decreases. However, the ferroelectric ceramics of the examples are compared by adding MnO ₂ to the ferroelectric ceramic (I) or the ferroelectric ceramic (I) containing only Ni ²⁺ that enters the B site. Compared to the ceramics of Examples 1 and 2, even if the mechanical quality factor Qm is increased to almost the same value, the larger piezoelectric constant d
It was confirmed to indicate ₃₁ .

Example 4 to 10 PbO, and _{ZrO 2, TiO 2, MgCO 3} , Nb 2 O 5, SrCO 3, A group (La
₂ O ₃ , Bi ₂ O ₃ , Nd ₂ O ₃ ) and at least one oxide selected from the group B (NiO, ZnOFe ₂ O ₃ , SnO ₂ , Ta ₂ O ₅ ) At least one oxide (however, NiO
Or Fe ₂ O ₃ or Ta ₂ O ₅ is always contained) and MnO ₂ were weighed in a quantity ratio having a composition shown in Table 2 and pulverized and mixed in a ball mill. Ferroelectric ceramics were produced by the same method, and the electrical characteristics were measured.

 The results are shown in Table 2.

Also from these examples, the ferroelectric ceramics (I) containing both the metal ions of the groups A and B and further containing MnO ₂ showed a mechanical quality factor Qm. , And that the piezoelectric constant d ₃₁ is large.

Examples 11 to 13 and Comparative Examples 3 to 5 Pb _1-a Sr _a (Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z O ₃ [x + y + z =
In the same manner as in Example 1, a ferroelectric ceramic in which a predetermined amount of La ₂ O ₃ , NiO, SnO ₂ and MnO ₂ was contained in a ferroelectric ceramic having different coefficients of 1] from those in Examples 1 to 10 was used. It was produced and the electrical characteristics were measured.

 Table 3 shows the results.

Example 14, Comparative Example 6 Ferroelectric ceramics were prepared in the same manner as in Example 2 and Comparative Example 1 except that BaCO ₃ was used instead of SrCO ₃ in Example 2 and Comparative Example 1, and the electrical characteristics Was measured.

 Table 3 shows the results.

EFFECTS OF THE INVENTION As is clear from the above description, the ferroelectric ceramics according to the present invention contain metal ions that can enter both A and B sites in the perovskite type crystal represented by ABO ₃ , and these oxides are included. Since all of is incorporated into the perovskite crystal and then contains MnO ₂ , when compared with the conventionally known ferroelectric ceramics,
It has a larger piezoelectric constant d while having substantially the same mechanical quality factor Qm. Therefore, the ferroelectric ceramics according to the present invention can exhibit excellent characteristics when used in applications such as actuators utilizing mechanical resonance including ultrasonic motors and the like.

Claims (2)

(57) [Claims] 1. Pb _1-a M _a (Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z O ₃ [wherein M is Ba or Sr and x + y + z = 1], and a = 0 to 0.10 x = 0.05 to 0.70 y = 0.25 to 0.50 z = 0.05 to 0.70 For perovskite type solid solution, at least one oxide selected from the following group A and the following group B are selected: And a perovskite type solid solution containing at least one kind of oxide (however, NiO or Fe ₂ O ₃ or Ta ₂ O ₅ is always included), and further containing MnO _2. Ferroelectric ceramics. Group A (La ₂ O ₃ , Bi ₂ O ₃ , Nd ₂ O ₃ ) Group B (NiO, ZnO, Fe ₂ O ₃ , SnO ₂ , Ta ₂ O ₅ ) _2. The ferroelectric ceramic according to claim 1, wherein the content of MnO ₂ is 0.1 to 2.0% by weight.