DE1802768B2 - PIEZOELECTRIC CERAMIC FABRIC - Google Patents

Description

The invention relates to piezoelectric ceramics, which for certain areas of application have excellent properties.

One of the typical areas of application for piezoelectric materials is the manufacture of transducers for the sending and receiving of ultrasonic waves. In this case, the electromechanical coupling factor the most important variable for the practical evaluation of the piezoelectric materials to be used The electromechanical coupling factor is a measure of the efficiency of the conversion of electrical Vibrations into mechanical vibrations and vice versa; a greater value of the electromechanical Coupling factor corresponds to a better conversion efficiency, what with piezoelectric Substances for transducers is desirable. Piezoelectric substances have other parameters, e.g. B. the dielectric loss, the dielectric constant and the mechanical quality value that are used to evaluate them can be used. Piezoelectric materials for converters should have a dielectric that is as small as possible Loss and, depending on the electrical load, a large or a small value of the dielectric constant to have. The mechanical quality value, which is the reciprocal measure of the in the substance during the Energy conversion represents energy consumed, is not so significant in this case.

The relationships mentioned are z. B. described in the following works: D. B er 1 i η c ο urt et al., "Transducer Properties of Lead Titanate Zirconate Ceramics", in Ire Transactions on Ultrasonic Engineering, February 1960, pp. 1 to 6, and RCV M acari ο , "Design Data for Band-Pass Ladder Filters Employing Ceramic Resonators," Electronic Engineering, Vol. 33, No. 3 (1916), pp. 171-177. It has often been found that conventional piezoelectric ceramics, e.g. B. barium titanate (BaTiO ₃ ) and lead titanate zirconate Pb (Ti ■ Zr) O ₃ , have a small electromechanical coupling factor and are unsuitable for practical use. Improvements in the parameters have only been made by incorporating various additives.

The invention is therefore based on the object to provide a piezoelectric ceramic material that has a large electromechanical coupling factor.

This new substance is intended for special applications such as the manufacture of transducers for ultrasonic transmitters and receivers are particularly suitable.

The piezoelectric ceramic according to the invention consists essentially of a solid solution of the quaternary

(A _{g | / 2} Bi _1/2 ) TiO ₃ - (A _{gl / 2} Bi _1/2 ) ZrO ₃ -PbTiO ₃ -

PbZrO ₃ system

it contains up to 25 atomic percent lead through at least one element from the group barium, strontium and calcium replaceable or replaced.

This substance contains lead (Pb) as a divalent metallic element, titanium (Ti) and zirconium (Zr) as a tetravalent metallic elements and also silver (Ag) and bismuth (Bi) in such proportions that it, as a whole, as can be regarded as equivalent to a divalent metallic element.

In a further development of the invention, the piezoelectric ceramic material identified above is essentially according to the formula

[(Ag ₁ Z ₂ Bi ₁ Z ₂ ) TiO ₃ ], [(Ag ₁ Z ₂ Bi ₁ Z ₂ ) ZrO ₃ ] ,, [PbTiO ₃ ], [PbZrO ₃ ] _M

in which t, u, ν and w indicate the molar ratios and the condition

t + u + υ + w = 1.00

suffice, composed, and its specific coordinates are in a diagram with the Coordinates

α = t / (t + v) = ul (u + w) β = t / {t + u) = v / (v + w),

which represent the ratio of (Ag _1/2 Bi _1/2 ) to (Ag _1/2 Bi _1/2 ) + Pb or from Ti to Ti + Zr, within a polygon

The excellent piezoelectric properties of the composite ceramic according to the invention proceed from the following, more detailed description of preferred exemplary embodiments for a ceramic material according to the invention, which is supported by the drawings.

F i g. 1 is a composition diagram showing the total effective range of compositions for the ceramic according to the invention and the range of particular compositions according to shows the examples;

F i g. Fig. 2 is a graph showing the electromechanical coupling factor of the conventional lead-titanate-zirconate ceramic and the ceramic of the invention as a function of β ;

F i g. Figure 3 is a phase diagram of compositions for a ceramic according to the invention.

A-B-C-D-E-F-G-H 0.55 len Corner point coordinates 0.10 A. ... 0.01 0.05 B. ... 0.01 0.05 C. ... 0.05 0.30 D. ... 0.10 0.48 E. ... 0.20 0.70 F. ... 0.20 0.70 G ... 0.10 H ... 0.05

Examples

Unless otherwise stated, the starting materials used for the ceramic according to the invention were powdered silver oxide (Ag ₂ O), bismuth sesquioxide (Bi ₂ O ₃ ), lead monoxide (PbO), titanium dioxide (TiO ₂ ) and zirconium dioxide (ZrO ₂ ). These powdered materials were weighed in such that the fabric samples obtained therefrom have the compositions listed in Table 1. Farther

lead monoxide powder, titanium dioxide powder and zirconium dioxide powder were weighed in so that the usual Lead-Titanium-Zirconia Ceramics of Compositions resulted, which emerge from Table 2.

The powders were mixed with distilled water in a ball mill. The powder mixture was filtered, dried, ground, then presintered for 1 hour at 900 ° C and finally ground again. Subsequently, the mixtures were the addition of a small amount of distilled water at a pressure of 700 kg / cm ² pressed into disks of 20 mm in diameter and sintered at temperatures from 1.250 to 1.300 ⁰ C in an atmosphere of lead oxide (PbO) for 1 hour.

The ceramic disks produced in this way were ground to a thickness of 1 mm on both sides, on both Surfaces provided with silver electrodes and then polarized for 1 hour at 100 ° C or at room temperature with the application of an electrical equilibrium of 40 to 30 kV / cm piezoelectric activated.

After a standing time of 24 hours, the electromechanical coupling factor ^,) for the radial vibration mode and the mechanical quality factor (Q _m ) to determine the piezoelectric activity were measured. These piezoelectric parameters were measured in the Ire standard circuit. The fc _r value was determined on the basis of the resonance-antiresonance frequency method. At a frequency of 1 KHz, the dielectric constant (ή and the dielectric losses (tan Λ) were also measured.

Tables 1 and 2 show typical results. The samples are arranged in the tables according to decreasing values for β . In some cases the Curie temperature is given, which was determined by measuring the temperature profile of the dielectric constant (/). The new compositions according to Table 1 are shown in FIG. 1 marked by dots, the usual compositions according to Table 2 by crosses.

A comparison of the measured values for samples 5 and 6 in Table 1 with those for sample 4 in Table 2 shows that the largest / c _r values of the new ceramic materials according to this invention are well above the maximum / c _r values for the usual Blci-titanium-zirconium ceramics, which were previously considered to be the best piezoelectric ceramics. A comparison of the measured values for the samples in Table 1 with those for the samples in Table 2, in particular between the new and the known ceramic materials in which the // values are the same or similar to one another, shows that the ceramic materials according to the Invention have a significant improvement in the / c _r value. This is even clearer from FIG. 2, where the bold curve _{indicates the / c r} values of the ceramic materials according to the invention with a fixed α value of 0.05 as a function of the // value, whereas the thin curve indicates the k _r values more known Lead titanate zirconate ceramic materials depending on the // values.

The invention thus provides extremely useful piezoelectric ceramics with high piezoelectric activity. According to the invention, the high piezoelectric activity is present when the compositions g within the area marked by points A, B, C, D, E, F, G, H polygonal surface area of F i. 1 lie.

The above-mentioned corner points of the polygon have the following pairs for and :

A ... 0.01 0.55 B ... 0.01 0.10 C ... 0.05 0.05 D ... 0.10 0.05 E ... 0.20 0.30 F ... 0.20 0.48 G ... 0.10 0.70 H ... 0.05 0.70

If α is smaller than it corresponds to the specified range, the piezoelectric properties of the ceramic materials obtained are less pronounced or only almost the same as those of conventional BIci-titanium-zirconium ceramic materials. If α is larger than the specified range, the sintering is difficult to carry out and the piezoelectric activity of the ceramic plug is so disturbed that practical use is almost impossible. If the β value is not within the stated range, then ceramic materials result which have a considerably lower piezoelectric activity.

Thus, if the compositions of the ceramics according to the invention are to be useful for practical use, they must be classified in the area A, B, C, D, £, F, G, H of FIG. 1 fall. Ceramic materials of these compositions have excellent piezoelectric properties and a high Curie temperature (see Table 1), so that the piezoelectric activity is not lost even at an elevated temperature.

The quaternary system

(Ag _1/2 Bi, _{/ 2} ) TiO ₃ - (Ag _{l / 2} Bi _1/2 )

ZrO ₃ - PbTiO ₃ - PbZrO ₃

according to the invention is in the form of a solid solution in larger components. Such a solid solution has a perovskite-like crystal structure. F i g. FIG. 3 shows the crystalline phases of the compositions of the ceramic materials which are contained within the area ABCDE-FGH of FIG. 1 lie. The phases are determined at room temperature using the X-ray powder technique. These compositions have a perovskite-like crystal structure and belong either to the tetragonal phase ( denoted by T in FIG. 3) or to the rhombohedral phase ( denoted by R ). The morphotropic phase boundary is shown in FIG. 3 entered by a thick line. The value for k _r is generally very large in the vicinity of this phase boundary.

It will be understood that the starting materials to be used in the manufacture of ceramics according to the invention are not limited to those used in the examples discussed above. Specifically, it should be said that those oxides can be used instead of starting materials according to the above examples which decompose easily at elevated temperature and form the required compositions, as is demonstrated in Examples U and 15 for PbO by Pb ₃ O ₄ . Salts such as oxalates or carbonates, which easily break down into their oxides at elevated temperature, can also be used in place of the oxides used in the examples. Hydroxides of the same character can also be used in place of the oxides. One can

Piezoelectric ceramics with the same properties as in the examples mentioned are also obtained, by getting in advance

(A _{gl / 2} Bi _1/2 ) TiO ₃ , (A _{gl / 2} Bi _{l / 2} ) ZrO ₃ ,

PbTiO ₃ and PbZrO ₃

pulverized provides separately and these powder samples as starting materials to be mixed subsequently used.

Example 8 of Table 1 shows that the good piezoelectric activity of this composition is retained when some of the lead has been replaced by strontium. In general, the piezoelectric activity of the compositions in which lead titanate or lead zirconate is contained is not lost even if up to 25 atomic percent lead of the composition is replaced by at least one element from the group consisting of barium, strontium and calcium. This is evident from a number of studies reported, for example, in U.S. Patent 2,906,710. The mentioned substitution is therefore also permissible in the case of ceramic compositions according to the invention. Commercially available zirconium dioxide (ZrO ₂ ) usually contains a few percent hafnium dioxide (HfO ₂ ). Likewise, the ceramic compositions according to this invention can also contain small admixtures of such oxides or elements as occur in commercially available substances. In addition, adding a small amount of any additional agent to the ceramic compositions of the invention can further improve the piezoelectric properties, as is known for common lead-titanate-zirconate ceramics. The ceramic compositions according to the invention can thus contain such additives.

Finally, a comparison should be made between the piezoelectric ceramic material according to the invention and the above-mentioned conventional ceramic materials based on lead-titanate-zirconate be drawn with built-in additives, as they are in the "Journal of The American Society", Vol. 42, No. 7 (July 1959), in the article by Frank K ulcsar, “Electromechanical Properties of Lead Titanate Zirconate Ceramics Modified with Certain Three- or Five-Valent Additions «on pages 343 to 349 are given.

Tables I and II on p. 344 show the highest coupling factor 0.57 or 57% for the Swatch B-12.

The maximum coupling factor, which can only be understood theoretically, is 100%. It is extraordinary difficult to create a ceramic that achieves a coupling factor above 60%. With the Ceramic material according to the invention can exceed this limit. Table 1 of the present Documentation shows under no. 7 the coupling factor 61%. This alone is opposite to the coupling factor 57% a considerable step forward.

In the introduction, however, it was pointed out that in addition to the coupling factor k _r, depending on the application, other variables are also decisive for the quality and usability of a ceramic material, especially the dielectric constant f. Two applications are to be examined in more detail.

With mechanical filters it is important to keep the impedance Rq small for which the relationship

with W being the bandwidth of the filter and L _n being the inductance of the piezoelectric material. Since W is determined by the task assigned to the filter, in order to decrease R ₀ one must decrease the inductance L _n.

ίο From equations (1), (2) and (4) of the initially mentioned work by R. C. V. M a c a r i ο in Electronic Engineering, Vol. 33, No. 3 (1961), pp. 171 to 177, lets the relationship

1-k?

derive. It all comes down to small values of the fraction on the right hand side of this relationship.

Table 3 shows characteristic values for k _n f and the expression just mentioned for compositions according to the invention and according to the prior art, namely for sample no. 7 (Table 1) according to the invention and. for the rehearsals

A-IO and B-12 according to the essay by F. K u 1 csar, Tables I and II.
In the case of the composition according to the invention, it is around 30% lower, that is to say more favorable than in the case of the known compositions.

For use as a converter for mechanical filters, especially for broadband wave filters, piezoelectric ceramic material should combine a high coupling factor k _r with high piezoelectric stability S , so that a high level of stability is achieved

of the converter with its electromechanical coupling factor Zc ₀ results.

The characteristic values of the stability over time for the resonance frequency / _r and the dielectric constant f are denoted by k ² _r ■ (-.-) and k ² _r Y —- ^,

where the constancy indicators -τ- and -τ- for S

stand.

To determine the stability characteristics given in Table 4 for compositions No. 6, 7 and 8 of Table 1 according to the invention, the values of the resonance frequency J _r and the dielectric constant f of the samples were first repeated after various numbers of days that had passed since polarization, to be precise, on the days with 2 " (n = 0, 1, 2 ...) up to about the 150th day. Then, assuming that the aging behavior of f _r and / ■ by the aging behavior expression

Φι-Φ \

is given, a proportionality constant A / _r and A _{c are} determined. In the above expression means

01 the value of / _r or * measured 1 day after polarization,

Φί the value of / _r or f measured t days after polarization,

i, the time lapse of 1 day after polarization, ί the lapse of time in days after polarization

and
A is the constant of proportionality for f _r or f.

The time constancy Door f _r and t was determined as the reciprocal of the proportionality constants Af and A ₁ and calculated accordingly.

The above-mentioned article by F. K u 1 csar contains data on the change over time of k _r , t (denoted there by K ) and f _r for only four compositions, namely in the form of the diagrams in FIG. 9, 10 on p. 347.

The characteristic values for the stability over time of the four compositions known from this article were determined from these data, although an exact calculation was not possible due to the only roughly apparent data. The results are shown in Table 5. A (A _{r , A _c ) became

Δ Φ

8th No. Zusan
set
n imcn-
u ng
ft <%) 120 270 (at Λ
(%) Curie-
Tempe
rature
(C) 14th 0.20 0.30 7th 37 290 2.0 15 * 0.05 0.20 21 480 250 2.6 16 0.01 0.10 16 260 330 4.1 ίο ΐ7 0.10 0.10 18th 290 180 1.8 18th 0.05 0.05 11th 190 160 4.9 19th 0.10 0.05 8th 2.5

5 Note: For the production of the samples, the numbers of which are provided with a single asterisk (*), _{PbO 4 was used} as one of the starting materials _{instead of Pb 1} O 4.

When preparing the sample, its number with a double asterisk (**), strontium carbonate (SrCO,), measured on the basis of strontium monoxide (SrO), was used, 5 atomic percent Replace lead (Pb) with strondium (Sr).

Table 2

defined (with ΑΦ as the maximum deviation from j _r or f and t _max as the maximum time in days that has elapsed since polarization), because in FIGS. 9 and 10 of the article, the extent of the change over time is not related to the logarithm of the elapsed time.

A comparison between Tables 4 and 5 shows

that the values k ² ■ (-j—) of the composition according to the invention are about twice as large or even greater than those of the known substances and that the

Values k; \ - j- ! Are three times as large or even larger. Thus, the compositions according to the invention have significantly improved characteristics of the time constancy of the resonance frequency and the dielectric constant and are therefore outstandingly suitable as materials for the converters of mechanical air filters, especially broadband filters.

Table 1

Together U Il k _r Q _n , F. tan Λ No. settlement 0.00 0.70 </ o) (/ ο) 0.00 0.60 - - 340 5.7 1 (), () () 0.55 - - 300 2.4 2 0.00 0.48 8th 30th 350 1.3 3 0.00 0.45 42 250 1060 1.6 4th 0.00 0.40 38 290 640 3.0 5 0.00 0.30 30th 320 460 3.1 6th 0.00 0.20 24 380 380 3.3 7th 0.00 0.10 15th 470 350 3.3 8th 10 580 280 3.4 9

45

No. Zusan
set
a imcn-
ung
ft * r
(%) Q, 310 At Λ
(%) Curie-
Tempe
rature
( ⁰ C) 1 0.05 0.70 11th 260 280 2.1 2 0.10 0.70 15th 8 (X) 420 1.2 3 0.01 0.55 21 90 440 2.9 4th 0.05 0.55 42 130 1110 2.1 5 0.01 0.48 44 KK) 1180 2.1 6th 0.02 0.48 59 80 1580 2.3 385 7th 0.05 0.48 61 105 1600 2.4 8th** 0.05 0.48 58 120 1120 2.1 9 0.10 0.48 42 140 620 2.5 10 0.20 0.48 14th 170 410 2.3 350 11 * 0.05 0.40 47 120 360 2.5 12th 0.05 0.30 33 310 330 2.2 13th 0.10 0.30 24 2K0 2.1

Note: For samples I and 2, it was not possible to determine the piezoelectric activity.

Table 3

invention
State of

Composition No. A _r

7 (table 1)
A-10 (Table I)

Technique \ B-12 (Table II) 0.57 1377 1.506 10

0.61 0.51

1580 1792

1.066 x 10 " ³ 1.585 x 10" ³

Table 4

composition

No according to the invention!

(Table I)

7th
8th

435
536
481

97

124 112

109 531/301

composition
No. according to status

of the technique
(Tables I and II)

A-4

A-7
B-7
B-15

Tabel

85 145 180 300

25 25 40 20

Claims (2)

Patent claims: 1. Piezoelectric ceramic material, which consists essentially of a solid solution of the quaternary (A _{gl / 2} Bi _1/2 ) TiO ₃ - (A _{gl / 2} Bi _{l / 2} ) ZrO ₃ -PbTiO ₃ -PbZrO ₃ system consists and in which up to 25 atomic percent lead by at least one element from the group Barium, strontium and calcium can be replaced or replaced. 2. Piezoelectric ceramic according to claim 1, which is essentially according to the formula [(Ag ₁ ABi ₁ A) TiO ₃ ], [(Ag ₁ Z ₂ Bi ₁ /,) ZrO ₃ L [PbTiO ₃ L [PbZrO ₃ L in which i, u, υ and w indicate the molar ratios and satisfy the condition t + u + v + w = 1.00, is composed and its specific coordinates in a diagram with the coordinates α = t / (t + v) = u / (u + w) β = t / (t + u) = v / (v + w) which represent the ratio of (Ag | _{/ 2} Bi _1/2 ) to (Ag _1/2 Bi _1/2 ) + Pb or from Ti to Ti + Zr, within a polygon ABCDEFGH with the corner point coordinates A 0.01 0.55 B 0.01 0.10 C 0.05 0.05 D 0.10 0.05 E 0.20 0.30 F 0.20 0.48 G 0.10 0.70 H 0.05 0.70 lie. 1 sheet of drawings