DE1802768A1 - Piezoelectric ceramic material - Google Patents

Abstract

Piezoelectric ceramic material.. G7-. Consists of a quaternary solid solution of: (Ag1/2Bi1/2)TiO3-(Ag1/2Bi1)SrO3-PbToO3-PbZrO3 with up to 25 atom percent of lead through at least one element of the barium, strontium group and replaceable or replaced by calcium. Used in the manufacture of converters for the transmission and reception of ultrasonic waves where the electro-mechanical coupling factor is the most important constant for the practical utilisation of the piezoelectric material and is a measure of the effectiveness in transforming electrical oscillations into mechanical oscillations and vice-versa.

Description

Piezoelectric Ceramic The invention relates to piezoelectric Ceramic materials that have excellent properties for certain areas of application.

One of the typical areas of application for piezoelectric materials is the manufacture of transducers for the transmission and reception of ultrasonic waves. In this case, the electromechanical coupling factor is the most important variable for the practical evaluation of the piezoelectric materials to be used electromechanical coupling factor is a measure of the conversion efficiency electrical oscillation into mechanical oscillations and vice versa; a larger to larger value of the electromechanical coupling factor corresponds to one better conversion efficiency, which is desirable for piezoelectric materials for transducers.

Piezoelectric materials have other parameters, such as the dielectric Loss, the dielectric constant and the mechanical Q factor contributing to their Evaluation can be used. Piezoelectric materials for converters are supposed to be one the smallest possible dielectric loss and depending on the electrical load have a large or a small value of the dielectric constant. The olfactory one Quality value, the reciprocal measure for that in the substance during energy conversion represents consumed energy is not so meaningful in this case.

The relationships mentioned are z.3. described in the following works: D Berlincourt et al., "Trnsducer Properties of Lead Titanate Zirconate Ceramics", in IRE TRANSACTIONS ON ULTRASONIC ENGINEERING, February 1960, pp. 1-6 and R.C.V. Maeario, Design Data for Band-Pass Ladder Filters Employing Ceramic Resonators', ELECTRONIC ENGINEERING, Vol. 33, No. 5 (1961) pp. 171-177.

It has often been found that conventional piezoelectric ceramics e.g. barium titanate (BaTiO3) and lead titanate zirconate Pb (Ti.Zr) 03, a small one have electromechanical coupling factor and are unsuitable for practical use are. Improvements in the parameters are only possible through the incorporation of various additives been made.

The invention is therefore based on the object of a piesoelectriochen To create ceramic material that has a large electromechanical coupling factor.

this new substance is intended for special applications such as manufacturing of transducers for ultrasonic transmitters and receivers are particularly suitable.

The piezoelectric ceramic according to the invention consists essentially from a solid solution of the quaternary (Ag1 / 2Bi1 / 2) TiO3- (Ag1 / 2Bi1 / 2) ZrO3-PbTiO3-PbZrO3 -Systems; it contains up to 25 atomic percent lead due to at least one element the group berium, strontium and calcium can be replaced. replaced.

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

In a further development of the invention, the piezoelectric ceramic microfiber identified above is essentially according to the formula in which t, u, v and w indicate the pick-up ratios and satisfy the condition t + u + v + w = 1.00, combined, and its specific coordinates are in a diagram with the coordinates α = t / (t + v) = u / (u + w) and # = t / (t + u) = v / (v + w), which is the ratio of (Ag1 / 2Bi1 / 2) to (Ag1 / 2Bi1 / 2) + Pb or

represent from i to to 'Zr, within a polygon A - B - C - D - E - F - G - H with the corner point coordinates A ..... 0.01 0.55 5 ..... 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 ..... -.05 -.70 The excellent piezoelectric properties of the ceramic material composed according to the invention go from the following, detailed description of preferred embodiments for a ceramic material according to the invention which is supported by the accompanying drawings.

Fig. 1 is a composition diagram showing the total effective area of compositions for the ceramic according to of the invention and shows the range of particular compositions according to the examples.

Fig. 2 is a graph showing the electrical machine coupling factor the usual lead-titanate-zirconate ceramic material and the ceramic material after Invention as a function of ß shows.

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

Unless otherwise specified, examples were used as starting materials For the ceramic material according to the invention powdered silver oxide (Ag2O), bismuth sesquidoxide (Bi2O3), lead monoxide (PbO), titanium dioxide (TiO2) and zirconium dioxide (ZrO2). These powdered Materials were absorbed in such a way that the resulting fabric samples the have compositions listed in Table 1. Furthermore, lead monoxide powder, Titanium dioxide powder and zirconium dioxide powder weighed in so that the usual lead-titanium-zirconium ceramics are used of compositions shown in Table 2.

The powders were mixed with distilled water in a ball mill. The powder mixture was filtered, dried, ground, then for an hour Pre-sintered at 9000 C and finally ground again. flar were thereupon Mixtures with the addition of a small amount of distilled water at one pressure of 700 kg / cm2 pressed into disks of 20 mm in diameter and added for one hour Temperatures from 1.2500 C to 1.3000 C in an atmosphere of lead oxide (PbO) sintered.

The resulting ceramic disks were cut to a thickness on both sides sanded off 1 mm, provided with silver electrodes on both surfaces and then by polarization treatment for one hour at 100 ° C or at room temperature with the application of a constant electric field of 40 to 30 kV / cm piezo-electric activated. After a stana time of 24 hours, the electromechanical Coupling factor (kr) for the radial oscillation mode and the mechanical good factor (@m) for determination the piezoelectric activity measured. The measurement of these piezoelectric parameters took place in the IRE standard circuit. The kr value was obtained due to the resonance anti-resonance frequency method determined.

At a frequency of 1 kHz, the dielectric constant also became (£) and the dielectric losses (tan #) gemes-00n.

Tables 1 and 2 show typical measurement results. Dic samples are sorted in the tables according to falling inertia for ß.

In some cases the Curie temperature is indicated by measurement the temperature response of the dielectric constant (#) was determined. The new Compositions according to Table 1 are marked in FIG. 1 by dots, the usual ones Compositions according to Table 2 by crosses.

A comparison of the measured values for samples 5 and: 6 of table 1, with those for sample 4 according to Table 2 shows that the largest kr values of the new Ceramic materials according to this invention far exceed the maximum kr values for the usual ones Lead-titanium-zirconium ceramics lie so far considered to be the best piezoelectric Ceramic fabrics were viewed. Also a comparison of the measured values for the samples of Table 1 with those for the samples of Table 2, in particular between the new and the well-known ceramic materials, for which the # -values are the same or at least are similar to each other shows that the ceramic materials of the invention have a significant Improve the kr value. This can be seen even more clearly from FIG. 2, where the bold curve shows the kr values of the ceramic materials according to the invention with a fixed α value of 0.05 depending on the # value, whereas the thin, drawn-out curve shows the kr values of known lead-titanate-zirconate ceramic material as a function of the # values.

The invention thus provides extremely useful piezoelectric ache. Ceramic materials with high piezoelectric activity. According to the invention, the high piezoelectric activity present when the compositions are within the polygonal area marked by points A, B, C, D, E, F, G, H of Fig. 1 lie. The mentioned corner points of the polygon have the following Pairs of values for α 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, then the piezoelectric properties of the ceramic materials obtained are less pronounced or only almost the same as those of conventional lead-titanate-zirconate ceramics. If α is greater than the specified range, then the execution is sintering becomes difficult and the piezoelectric activity of the ceramics becomes difficult so disturbed that practical use is almost impossible. If the R value is not within the specified range, then ceramic materials result that a have significantly lower piezoelectric activity.

Thus, the compositions of the Keramil substances according to the invention, if they are to be useful for practical use, in the area A, B, C, D, E, F, G, H, H fall according to Fig. 1. Ceramics of these compositions have excellent piezoelectric properties and a high Curie temperature, see.

Table 1, so that the piezoelectric activity even with increased The quaternary system (Ag1 / 2Bi1 / 2) TiO3 - (Ag1 / 2Bi1 / 2) ZrO3 - PbTiO3 -? BZrü3 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. FIG. 3 shows the crystalline phases of the compositions of the ceramic materials which lie within the area A - B - C - D - E - F - G - H of FIG. The phases are determined at room temperature using the X-ray powder technique. These compositions have a Perowski t-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 by a cint, thick line. X) the value for kr is generally very large in the vicinity of this phase boundary.

It is clear that the manufacture of ceramics according to the invention starting materials to be used are not limited to those specified in don examples discussed above are used. In particular it should be said that those Oxides can be used in place of starting materials according to the above examples that easily disintegrate at elevated temperature and the required compositions form, as evidenced by Pb3O4 in Examples Nos. 11 and 15 for PbO. Also salts such as oil or carbonates, which easily convert into their oxides at elevated temperatures disintegrate can be used instead of the oxides used in the examples. Hydroxides of the same character can also be used instead of the oxides.

One can use piezoelectric ceramics with the same properties as in the examples mentioned? ch obtained by beforehand (Ag1 / 2Bi1 / 2) TiO3, (Ag1 / 2Bi1 / 2) ZrO3, PbTiO3 and PbZrO3 powdered separately, and these Powder samples are used as starting materials to be mixed subsequently.

Example 8 of Table 1 shows that the good piezoelectric Activity of this composition is retained when part of it leads through Strontium has been replaced. In general, the piezoelectric activity goes on of the compositions in which lead titanate or lead zirconate is included also d. ". nn not lost if up to 25 atomic percent lead of the composition by at least an element from the series of barium, strontium and calcium is replaced. This goes out a number of studies, of which, for example, in U.S. Pat ntschrift 2 906 710 is reported. The substitution mentioned is also applicable to ceramic compositions permissible according to the invention. 3ns contains commercially available zirconium dioxide (ZrO2) for usually a few percent of hafnium dioxide (HfO2). The ceramic compositions can also do the same according to this invention contain small admixtures of such oxides or elements as they occur in commercially available substances. In addition, adding one little amount of any additional agent to the ceramic compositions after the invention, the piezoelectric properties continue to improve, such as this is known for the usual lead-titanate-zirconate ceramics. So it is it is clear that the ceramic compositions according to the invention contain suitable additives can.

Table 1 composition Curie- kr tan # No. Qm # temperature α ß (%) (%) (° C) 1 0.05 0.70 11 260 310 2.1 2 0.10 0.70 15 800 280 1.2 3 0.01 0.55 21 90 420 2.9 4 | 0.05 | 0.55 | 42 | 130 | 440 | 2.1 5 0.01 0.48 44 1.001110 2.1 6 | 0.02 | 0.48 | 59 | 80 | 1180 | 2.3 | 385 7 0.05 0.48 .61 1051580 2.4 8i * 0.05 0.48 58 1201600 2.1 9 0.10 0.48 42 140 | 1120 2.5 10 0.20 0.48 .14 170 620 2.3 350 11 * 0.05 0.40 47 120 410 2.5 12 0.05 0.30 33 310 360 2.2 13 0.10 0.30 24 280 330 2.1 14 0.20 0.30 7 120 270 2.0 15 * 0.05 0.20 21 37 290 2.6 16 0.01 0.10 16 480 250 4.1 17 0.10 0.10 18 260 330 1.8 18 0.05 0.05 11 290 180 4.9 19 0.10 0.05 8 190 160 2.5 Note: For the production of the samples, the numbers of which are provided with a simple asterisk (. *), PbO was used as one of the starting materials instead of Pb3O4.

When making the sample, its number with a double star (**), strontium carbonate (SrCO3) was measured on the basis of strontium monoxide (SrO) is used to replace 5 atomic percent lead (Pb) with strontium (Sr).

Table 2 No. Composition kr m # tan α ß (%) (% 1 0.00 0.70 - - 340 5.7 2 0.00 0.60 - - 300 2.4 3 0.00 0.55 8 30 350 1.3 4 0.00 0.48 42 250 1.060 1.6 5 0.00 0.45 38 290 640 3.0 6 0.00 0.40 30 320 460 3.1 7 7 0.00 0.30 24 380 380 3.3. 8 0.00 0.20 15 470 350 3.3 9 9 0.00 0.10 10 580 280 3.4 Note: For samples 1 and 2 / it was not possible to record the piezoelectric activity.

Claims (2)

Claims 1. Piezoelectric ceramic material, which essentially consists of a solid Solution of the quaternary (Ag1 / 2Bi1 / 2) Ti) 3- (Ag1 / 2Bi1 / 2) ZrO3-PbTiO3-PbZrO3 - system and in which up to 25 percent lead is replaced by at least one element from the Group barium, utrontium and potassium-replaceable or replaced. 2. Piezoelectric ceramic according to claim 1, which is essentially according to the formula in which t, u, v and w indicate the molar ratios and satisfy the condition t + u + vtw = 1.00, is composed and its specific coordinates in a diagram with the coordinates = = t / (tfv) = u / (u + w ) and ß = t / (t + u) = v / (v + w) which represent the ratio of (Ag1 / 2Bi1 / 2) to (Ag1 / 2Bi1 / 2) + Pb or of Ti to Ti + Zr , within a polygon - - BB - C - D - E - F - G - H 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.