DE1922265C3 - Piezoelectric ceramics - Google Patents

Description

Pb (Li ₁₁₄ Nb ^) ₁ Ti ₁ -Zr ₂ O ₃
with values for χ from 0.0IO to 0.375, for y from

5 percent by weight MnO., Contains.

2. Piezoelectric ceramic, characterized in that it consists of a solid solution of the formula

solid 5 each modified with an addition of MnO ₂ between 0.1 and 5 percent by weight.

The use of piezoelectric materials for numerous transducer applications in manufacturing, Measurement and sense of direction of

O to 0.750 and for ζ from O to 0.875, where 10 tones, shocks, vibrations, pressures, etc. + y + ζ - 1, and that it is 0.1 to has increased sharply in recent years. As well as

Crystal as well as ceramic type transducers have been widely used. Due to the possible lower costs and ease of manufacture of ceramics with different shapes and dimensions and because of their greater resistance to high temperature and / or moisture compared to crystalline substances, such as. B. Rochelle salt, but have the piezowith x + y-rz- = I, and that it contains 0.2 20 electrical ceramic materials recently for up to 3 weight percent MnO ₂ . numerous converter applications gained importance.

The required piezoelectric properties of the ceramics obviously vary with the species the application. For electromechanical converters, 25 such. B. gramophone pickups and microphones, for example piezoelectric ceramics needed by a very high electromechanical coupling coefficient and a very high dielectric constant are characterized. 30 On the other hand, it is with Iranian filters and piezoelectric filters Transformer applications of piezoelectric ceramics are desirable for the materials a higher value of the mechanical quality factor and a high electromechanical coupling indicates that it has a ceramic according to application coefficients · .n. Furthermore, the spoke 2. Ceramic materials have a high degree of stability

Temperature and time in terms of resonance frequency and other electrical properties exhibit.

Lead titanate-lead zirconate has so far been widespread as a ceramic that is quite suitable in terms of these requirements been used. However, it is difficult to achieve a very high level with the Bieititanai-Bieizirkonai-Kerafniken mechanical quality factor / usammim with one

with values i for χ from 0.010 to 0.350, for y from 0.250 to 0.650 and for ζ from 0.250 to 0.650,

3. Piezoelectric ceramic, characterized in that it consists of a solid solution of the formula

Pb (Li ₁₄ Nb ^) _x Ti ₁ Zr ₂ O ₃

with values for χ from 0.030 to 0.250, for y from 0.375 to 0.490 and for ζ from 0.375 to 0.540, where χ + y + ζ = 1, and that it contains 0.2 to 3 per cent of MnO.

4. Electromechanical \ Vandlerelernent, thereby marked, you <i it's a ceramic according to Claim 2 has.

5. Piezoelectric transformer, thereby

6. Piezoelectric ceramic material, characterized in that it consists of a solid solution with the following formula:

Pb (Li ₁₄ Nb _3/4 ) ₀ , _I25 Ti ₀ ^ ₅ Zr ₀₄₄₀ O ₃

and that it further contains 1.0 weight percent manganese oxide (MnO ₂ ).

7. Piezoelectric ceramic material, thereby
characterized in that it consists of a solid solution 45 to achieve high planar coupling coefficients, with the following formula: In addition, the dielectric and change

Pb (Li ₁₄ Nb ₃ , ₄ ) _{or similar 0G ()} Ti ₀ . _4eo :

and that it further contains 0.5 weight percent manganese oxide (MnO ₂ ).

Piezoelectric properties of the Titanate-Bieizirconate ceramics largely with the combustion technology, which can be attributed to the evaporation of PbO is.

Modified by various additives such as MnO _J

Ceramics of the learning system Pb (Mg ₁₃ Nb ^ ₃ ) O, -

PbTiO.-PbZrO. are in J. Am. Ceram. Soc, 49 (11),

The invention relates to a piezoelectric Kera 577 (1966), described. These MnO ₂ modifiers and articles made from them. In particular, the invention relates to piezoelectric ceramics of the composition. Novel ferroelectric tongues Pb (Mg ₁₃ Nb ₂₃ ) O ₃ -PbTiO ₃ -PbZrO ₃ show ceramics which are polycrystalline aggregates of certain components. These piezoelectric
Masses are sintered into ceramics according to standard ceramic procedures, and then 60
the ceramics are polarized by applying a GHc <m voltage between the electrodes to them
electromechanical converter properties similar
to give to the well-known piezoelectric Fffeki.

The invention relates to: in addition, the cal.
stands, such as electromechanical converters, which are derived from the German Auslegeschrift 11 Io 742

sintered ceramics are made. various additives modified PbTiO ₃ -PbZrO., -

strong piezoelectricity and a relatively high, mechanical one Figure of merit. The mechanical quality factor is, however, strongly dependent on temperature.

The electrochemical properties of lead titanate-lead zirconate ceramics modified by various additives are described in J. Am. Ceram. Soc, 42 (7), 344 (1959). _{The PbTiO 3} -PbZrO., - ceramics modified by various additives

pbSnO ₃ ceramics described. The ceramics according to German Auslegeschrift 11 16 742 also show a high level of piezoelectricity, but have a small mechanical quality factor.

In contrast to this, the Pb (Li ₁₁₁ Nb ₃₁₄ ) O ₃ -PbTiO _{3 -PbZrO., - ceramics according to the invention, modified with MnO 2} , show a high piezoelectricity, a large mechanical quality factor and a high temperature stability of the resonance frequencies and the mechanical quality factor.

The aim of the present invention is therefore novel and improved piezoelectric .ehe ceramic materials with which at least one of the ~ ^! u-.gskQefuzienteri characterized;> s discussed problems are eliminated ku ..... A particular object of the invention Sinii ravaged pclykristallinc ceramics high by ei cr · cir mechanical Qualitätifaktrr "ν prumdung _r with a high piezoelectric K.or-! .

Another object of the invention are novel piezoelectric ceramics, which have a very high mechanical quality factor, a high electromechanical Coupling coefficients as well as high stability with respect to temperature the resonance frequency and the mechanical quality factor.

Another object of the invention is novel piezoelectric ceramics in which certain Properties can be adapted to different applications.

Another object of the invention are improved electromechanical converters for which an electrostatic polarized body from the novel ceramics is used as the active element.

These objects of the invention, as well as how it can be practiced, will be apparent from the following description and the drawing.

The figure shows a cross-sectional view of an electromechanical transducer according to the invention shown.

Before describing the piezoelectric materials according to the invention in detail, their Application for electromechanical converters with Be7ug on the figure of the drawing explained in Jer the reference number 7 ^ inen electromechanical The transducer is referred to as a whole, the active element a preferably disk-shaped body 1 made of a piezoelectric Ktramikmaterial according to of the invention.

The body 1 is electrically polarized as described below and has been provided with a pair of electrodes 2 and 3, which are fractured in a suitable manner on the opposite surfaces. The wire lines 5 ozw. 6 are conductively connected to electrodes 2 and 3 by means of soldering points 4. If di <- ceramic to a shock, vibration or other mechanical loads subjected we "), ί; 3ππ em r / fiipler Au * - output current nittcls the wire kt.in jjen 5 and 6; il> are taken. Conversely, i; ilvi as hot-line piezoelectric transducers ci; i- applying an electrical voltage to the F-.lck '. »Nlc: i 2 lv» Λ / u of a mechanical deformation ■!. ■■. Ceramic body It is pointed out that .l, i!> Die Hc / iR-hm :: ■ »eleklromechan'scherWandler«, v.icstehier \ raimk ', in the broadest sense on / in.issen μ urut i .n: i piczocfcktris ^u e filter. pie / -> eli-kiriM ■ I rnisinrm.i toren, Frequen / Regelungseinrit'i'iingen 1 tlgl he / u I) 'and that the invention can also be used for numerous other applications and these can be adapted, for materials with dielectric, pietoelectric and / or electrostrictive properties are required.

According to the invention, the ceramic body 1 in the figure is made of novel piezoelectric masses, which bind polycrystalline ceramics, soft from Pb (Li ₁₄ Nb, JO ₃ -PbTiO ₃ -PbZrO ₃ ,

_lv Pb (Li ₁₄ Nb ₃₄ ) O ₃ -PbTiO ₃ or Pb (Li ₁ ^ Nb ₃₁₄ ) O ₃ -PbZrO. ,, jewels modified by an addition of MnO. ,,.

The present invention is based on the fact that, within certain ranges of these systems, those samples which _{have been modified by the addition of MnO 2} have a very high mechanical quality factor and a high electromechanical coupling coefficient together with a high stability with respect to temperature with regard to the resonance frequency and the mechanical quality factor (Q _M ) .

The present invention has numerous advantages in terms of the manufacturing process and application of ceramic transducers. It is already known that the evaporation of PbO during firing is a problem in sintering. B. lead titanate zirconate represents. However, the composition according to the invention shows a smaller amount of evaporated PbO than is usually the case with lead titanate zirconate. The ternary system can be fired without any special regulation of the PbO atmosphere. A well-sintered body made from the composition according to the invention is obtained by firing in a ceramic _{crucible with a ceramic lid made from Al 2} O _{3 ceramics.} A high sintered density is desirable for moisture resistance and high piezoelectric responsiveness when the sintered body is used for a resonator or other devices.

All possible compositions of the ternary system from the basic components according to the invention are represented by the three-component system with the vertices Pb (Li ₁ ) PbTiO- and PbZrO-. However, some of the masses represented by the diagram do not show high piezoelectricity, and many are only slightly electromechanically active. The present invention relates only to those ceramics which exhibit enhanced piezoelectric responsiveness. For convenience, the piano coupling coefficient (Kp.) Of test disks is used as a measure of piezoelectric activity.
Alir by the formula

Pb (Li ₁₄ Nb ₃ J

with values for χ from 0.010 to 0.375, for y from 0 to 0.750 and for ζ from 0 to 0.875, where x + y + 7 is 1. The ceramics reproduced and tested after polarization showed a planar coupling coefficient of approximately 0.1 and a higher planar coupling coefficient.
The by the formula

fi _r , Pb (Li ₁ , Nb ₁₁ ) JTi ₁ Zr ₂ O ₃

mn values f ^; ir χ from 0.030 to 0.25 <>. for y from 0.375 to 0.490 and for ζ from 0.375 to υ.540, where

x + y + z- 1, ceramics shown exhibited a planar coupling coefficient of approximately 0.5 or greater planar coupling coefficient.

The ceramics according to the invention contain the components specified above and an addition of MnO ₂ -

The composition described herein can be made in accordance with various known ceramic techniques. A preferred method, described in more detail below, however, consists in the use of PbO or Pb ₁ O ₄ LiCO ₁ or LiOH-H ₄ O. Nb ₂ O ₅ , TiO ₂ , ZrO ₂ and MnO ₂ .

The starting materials, i.e. lead oxide (PbO). Lithium carbonate (Li ₂ CO ₃ ), niobium pentoxide (Nb ₂ O,). Titanium dioxide (Ti0 ₂ ), zirconium dioxide (Zr0 ₂ ) and Mn0 ₂ . all of relatively high purity (e.g. chemically pure), are intimately mixed with distilled water in a rubber-clad ball mill The proportions of the constituents must be varied in order to compensate for such contamination.

Following the wet grinding, the mixture is dried and mixed again in order to ensure that the mixture is as homogeneous as possible. The mixture is then brought into the desired shape in a suitable manner at a pressure of 400 kg / cm ^2. The compacts are allowed to prereact by calcination at a temperature of about 850 ° C. for 2 hours.

After calcination, the reacted material is allowed to cool and then wet milled to a small particle size. The MnO ₂ additive can be added to the reacted material after the calcination of the raw materials _{not containing MnO 2} , and the reacted material can be ground together with the MnO ₂ to a small particle size. Again, care should be taken to avoid contamination from wear of the grinding balls or stones, or the proportions of the ingredients must be varied to compensate for such contamination. Depending on the particular preference and the desired shape, the material can be processed into a mixture or a slurry, which - depending on the case at hand - is suitable for pressing. Sludge potting or extrusion are according to

Table I.

common ceramic work methods. The samples, the values of which are given below; were by mixing prepared from 100 g of the ground presinized mixtures with 5 ml of distilled water.

S The mixture was then pressed into disks with a diameter of 8 mm and a thickness of 1 mm at a pressure of 70GiCgZCm ² . The pressed panes were fired at 1200 to 1280 ° C. for a heating time of 45 minutes.

ίο According to the present: Invention does not exist Need to put the'mass in a PbO atmosphere to burn, and c «T is contrary to the 'state of Technique does not require special care with regard to the temperature gradient in the furnace. So According to the present invention, uniform and excellent piezoelectric ceramic products can easily be obtained can be obtained by simply touching the samples with an alumina ticgel while firing covers

so The sintered ceramics were polished on both surfaces to a thickness of 0.5 mm. The polished surfaces of the disks can then be coated with silver paint and fired to form silver electrodes. Finally, the disks were polarized while immersed in a JOO C silicon solder bath. A voltage gradient of 4 kV / mm DC was maintained for one hour and the disks were placed in the field for 10 minutes at room temperature

let cool down. The piezoelectric and dielectric properties of the polarized samples were measured at 20 ° C and a relative humidity of 50 ° <ο and at a frequency of 1 kHz. Examples of specific ceramic compositions according to the invention and various associated electromechanical and dielectric properties are given in Table I. It can be seen from Table I that all of the examples given which _{have been modified with the addition of MnO 2 are} characterized by a very high mechanical quality factor and a high planar coupling coefficient, these properties for the use of piezoelectric masses in ceramic Filters, piezoelectric transformers, and ultrasonic transducers are important. It can be seen that the _{compositions modified with the addition of MnO 2 show} a considerable improvement in the mechanical quality factor (Q _M ) compared to that of the base compositions, ie the base compositions without the addition of MnO. show η a value Qm of about 200 or less.

at Mole percent of the base mass 46.0 PbZrO ^ MnO ₂ - 24 hours after polarity 752 more planar more mechanical game 46.0 51.0 Zusaiz Dielectrics 1237 Coupling Quality 50.0 48.0 constant 786 coefficient factor 43.5 37.5 Weight 1440 Kp G* 43.5 44.0 percent ε 995 0.53 564 1 43.5 44.0 0.5 576 0.60 2230 2 37.5 t4.0 0.5 743 0.37 2540 3 Pb (Li _{l / 4} Nb _{3, 4} O ₃ PbTiO ₃ 37.5 50.0 0.5 1523 0.45 1425 4th 3.0 37.5 0.2 0.55 1626 5 6.0 10 0.50 .1402 6th 12.5 3.0 0.52 1348 7th 12.5 0.5 0.52 873 S. 12.5 0.5 12.5 12.5 25.0

According to the present invention, piezoelectric and dielectric properties of the ceramics for various purposes Selection of the suitable basic composition and the amount of MnO "additive can be adjusted.

Table II shows that the piezoelectric ceramics according to the invention have a high resonance frequency stability with respect to the temperature and that these ceramics have a high stability with regard to the mechanical quality factor (Qm) with respect to the temperature within the range from 20 to 80 ° C.

Table II Betspiel Gj ₁ -TC /, - TC

to

»5

1 13.3 0.107 2 20.1 0.216 3 5.7 0.039 4th i0.3 0.095 5 15.2 0.122 6th 12.9 0.154 7th 18.8 0.205 8th 22.5 0.261

»5

Qu - T · C is the change in the mechanical quality factor (Q _w ) within the range from 20 to 80 ° C. I _r - T · C is the change in the resonance frequency (/,) within the range from 20 to 8O ⁰ C.

These properties are important for the use of piezoelectric masses in piezoelectric transformers, filter applications, etc. The term "piezoelectric transformer" is used here for passive transmission devices for electrical energy or for converters in which the piezoelectric properties of a material are used to achieve a transformation of voltage, current or impedance. In these fields of application for ceramics, it is desirable that these piezoelectric ceramics _t a high stability of resonance frequency and the mechanical quality factor compared to the temperature in connection with a very high mechanical quality factor and a high electromechanical Kopplun. Have oefitzients so that the piezoelectric transformers, if they are used for a television set or the like. Show a high stability of the output current and the output voltage with respect to temperature.

According to the present invention, the piezoelectric ceramics have high electromechanical properties Coupling coefficients. The ceramics according to the invention can therefore also be used for electromechanical transducer elements such. B. gramophone pickups, microphones and voltage generators in ignition systems.

In the case of ceramic masses which _{contain more than 5 percent by weight of MnO 2 added} , the mechanical quality factor is relatively low and their planar coupling coefficient is low. Ceramic masses which contain an addition of MnO ₈ of less than 0.1 percent by weight show a low mechanical quality factor. For these reasons, they do not fall within the scope of the invention.

In addition to the superior properties indicated above, the compositions of the invention result Ceramics with excellent physical quality that can be polarized well. From the above It appears that the solid solution

PKLi ₁ Z ₁ Nb ₃ Z ₄ ) Oj-PbTiO ₃ -PbZrO ₃

modified with an addition of MnO ₂ , forms an excellent piezoelectric ceramic body.

While the presently preferred embodiments of the invention have been described, it is It can be seen that numerous changes and modifications are possible without departing from the scope deviate from the invention; therefore, old such changes and modifications should be made in accordance with the Claims fall within the scope of the invention.

1 sheet of drawings

Claims (1)

19 2? 265 claims: 1. Piezoelectric ceramic, characterized in that it consists of a
Solution of the formula The ceramic bodies according to the invention mainly consist of a solid solution, which the systems Pb (Lv ₄ Nb ₃₇₄ ) O _{3 -PbTiO 3} -PbZrO ₃ , Pb (Li _1/4 Nb _3/4 ) O _a -PbTiO ₃ or Pb (Li ₁₄ Nb ₃ Z ₄ ) O ₃ -PbZrO ₃ , namely