JP3094531B2 - Ferroelectric porcelain composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving a ferroelectric ceramic composition represented by piezoelectric ceramics.

[0002]

2. Description of the Related Art A ferroelectric porcelain composition (hereinafter referred to as "ferroelectric material") is applied to a driving portion (actuator) of a fine positioning device or the like by utilizing the property (reverse voltage effect) that a ferroelectric material is deformed by strain when a strong voltage is applied. Abbreviated as “dielectric”).

[0003]

The above ferroelectric material is applied to a phase boundary which is generally considered to have the best characteristics when a voltage of about 1 V (volt) is applied. .

However, a ferroelectric selected based on characteristics near a phase boundary is easily affected by the ambient temperature, and it is necessary to perform appropriate temperature correction.

Further, as the actuator, the larger the strain displacement, the better, and it is desirable to increase the applied voltage to, for example, 1 KV. However, the conventional actuator is too short to apply such a high voltage and is not practical.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ferroelectric material having electric field characteristics capable of withstanding a high voltage, durability and good temperature characteristics.

[0007]

To achieve the above object, according to the present invention, there is provided a ferroelectric ceramic composition Pb (Zn1 / 3Nb2 / 3) O 3
-PbTiO ₃ -PbZrO ₃ system to which additives such as Ta ₂ O ₅ , SrO, and MnO ₂ are added or Pb (Zn1 / 3Nb2 / 3) O ₃
—PbTiO ₃ —PbZrO ₃ system, the crystal system of which is a tetragonal system, and a Zr ratio represented by Zr / (Zr + Ti)
Is set at least 1.5 mol% smaller than the Zr ratio at the phase boundary .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have conducted intensive studies to improve the disadvantages of the conventional PZT-based ferroelectrics, and have found that Pb (Zn1 / 3Nb2 /
3) O ₃ —PbTiO ₃ —PbZrO ₃ -based ferroelectric material with a small amount of Ta ₂ O ₅ , SrO, MnO ₂ added or P
_{b (Zn1 / 3Nb2 / 3)} O 3 -PbTiO 3 -PbZrO 3
The system and the tetragonal ferroelectric have excellent electric field characteristics and durability, and can obtain a ferroelectric porcelain composition which has not been seen in the past and which is hardly affected by environmental temperature changes. The present invention has been found, and the details thereof are as described below.

FIG. 1 is a chart (2θ) of X-ray diffraction of a fired body of each sample in a ferroelectric including a ferroelectric according to the present invention.
= 20-70 °). Zr ratio 46.4 in order from the front
→ It has been changed to 57.6. In the figure, the unit cps of the X-ray diffraction intensity I represents the number of counts per second (count per second).

The above Zr ratio is Zr / (Zr + Ti)
And means the molar fraction of Zr contained in the composition. For notation, this is multiplied by 100 and expressed in mole percent.

As shown in the figure, when the Zr ratio is 46.4, the peak waveforms around diffraction angles 2θ = 22 °, 44 °, 50 °, 55 °, and 65 ° have two peaks or stepped peaks. . As the Zr ratio increases, the two peaks or steps collapse, and the Zr ratio = 51.2 and Zr ratio = 5 indicated by thick lines.
Between the 2.8 curves, they disappear and change into one gentle chevron. This is because the crystal system changes from tetragonal to rhombohedral with an increase in the Zr ratio, and it is considered that the Zr ratio of 51.2 to 52.8 indicates a peak near the phase boundary. From this fact, it was found that when the Zr ratio was 49.6 or less, it was tetragonal, and when the Zr ratio was 54.4 or more, it was rhombohedral.

FIG. 2 is a diagram showing the relationship between the Zr ratio and the strain of the ferroelectric including the ferroelectric according to the present invention. The sample is ground to a thickness of 1 mm, and after the silver paste electrode is baked, the sample is ground.
The figure shows the result of applying a voltage of 0 V and measuring the strain using a non-contact laser displacement meter and a strain gauge.

According to FIG. 2, the distortion becomes maximum near the Zr ratio of 51.2. This is considered to be a composition in which the composition near the phase boundary is soft and easily deformed. Conventionally, the composition in the vicinity of the phase boundary has been adopted because the strain is large.

FIGS. 3 to 5 are diagrams showing the change in d constant when a voltage is applied to the ferroelectric material including the ferroelectric material according to the present invention. m
m is a plot of a piezoelectric d-constant (hereinafter abbreviated as “d-constant”) calculated on the basis of a DC voltage of up to m and three-dimensional distortion generated at this time.

FIG . 3 shows the results for the tetragonal samples having a Zr ratio of 49.6 or 48.0. The d constant increases as the Zr ratio increases. The d constant is almost directly proportional to the size. The Zr ratio is 49.
For No. 6, there is an increasing trend up to 1200 V / mm.

FIG . 4 is for a sample having a Zr ratio of 51.2, ie, near the phase boundary.
It tends to decrease from around V / mm.

FIG . 5 is for a sample having a Zr ratio of 56.0 or 57.6, that is, a rhombohedral system, and it cannot be said that the d constant is small and that it is proportional to the increase of the electric field.

As can be seen from FIGS. 3 to 5 , in order to obtain a relatively large d constant and to obtain a d constant proportional to the strength of the electric field, it is necessary to use a tetragonal system and a Zr ratio of 48.0 to 48.0. 4
It can be said that a sample around 9.6 is preferable.

FIG . 6 is a graph showing the rate of change in strain of the ferroelectric including the ferroelectric according to the present invention.
It shows the rate of change of strain after 1,000 times, 10,000 times and 100,000 times of application of a DC bias of HZ. Deterioration progresses at the phase boundary, and deterioration of the rhombohedral system is also recognized.

On the other hand, in the tetragonal system, the degree of deterioration is small even after 100,000 times, and the durability is large.

From the above, it is preferable that the ferroelectric ceramic composition suitable for the actuator is a tetragonal system and has a Zr ratio smaller than the Zr ratio at the phase boundary by at least 1.5 mol%.

If the Zr ratio is set too close to the phase boundary, each characteristic tends to be unstable. If the Zr ratio is set too low, the generated distortion becomes small as shown in FIGS. Therefore, in the embodiment shown in FIGS. 3 to 5 , the Zr ratio is preferably set in the range of 48.0 to 49.6.

Incidentally, Pb (Zn1 / 3Nb2 / 3) O ₃ -Pb
TiO ₃ -PbZrO additive for ₃ system Ta ₂ O _5, Sr
Not only O and MnO ₂ but also BaO, CaO, Cr ₂ O ₃ , La ₂
Oxides such as O ₃ , Fe ₂ O ₃ and NiO may be used. or,
The ferroelectric of the present invention is not limited to piezoelectric ceramics, but can be used as a ferroelectric in a broad sense.

[0024]

As described above, since the ferroelectric porcelain composition of the present invention is a tetragonal system, a large distortion is generated while maintaining a good proportional relationship with a strong electric field, and the durability is good. Therefore, according to the present invention, a high-output and highly reliable ferroelectric ceramic composition can be provided.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a ferroelectric including a ferroelectric according to the present invention.

FIG. 2 is a diagram showing a relationship between a Zr ratio and a strain of a ferroelectric including a ferroelectric according to the present invention.

FIG. 3 is a diagram showing a change in d constant when a voltage is applied to a ferroelectric including a ferroelectric according to the present invention.

FIG. 4 is a diagram showing a change in d constant when a voltage is applied to a ferroelectric including a ferroelectric according to the present invention.

FIG. 5 is a diagram showing a change in d constant when a voltage is applied to a ferroelectric including a ferroelectric according to the present invention.

FIG. 6 is a diagram showing a strain change rate of a ferroelectric including a ferroelectric according to the present invention.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenichi Kato 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu-shi, Fukuoka Tochiki Kiki Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 41/187

Claims (1)

(57) [Claims] 1. Pb (Zn1 / 3Nb2 / 3) O ₃ -PbTiO _3-
Ta ₂ O ₅ in PbZrO ₃ system, SrO, MnO ₂ and those plus additive or Pb (Zn1 / 3Nb2 / 3) O 3 -PbTiO 3
-PbZrO ₃ system, the crystal system of which is a tetragonal system, and the Zr ratio represented by Zr / (Zr + Ti) is the phase boundary.
A ferroelectric porcelain composition characterized in that it is set to be at least 1.5 mol% smaller than the Zr ratio of the above .