DE2423970A1 - PIEZOELECTRIC CERAMIC COMPOUNDS - Google Patents

Description

PATENT LAWYERS

Dr.-Ing. HAKS RUSCHKE Dipl. - Ing.OLAF RU3CHKE Dipl.-Ing. HANS E. RUSCHKE 1 BERLIN 33

tyihiQftefiSneft

M 34-27

Matsushita Electric Industrial Go., Ltd., 1006 Kadoma, Osaka, Japan

Piezoelectric ceramic masses

Summary of the description:

It is a piezoelectric ceramic mass made of a solid solution of a material Pb (Sn ^,., Nb ₂ / ^) Ti Zr 0 ,, where 0.01 <x- i 0.25, O < y < 0.75 and O £ ζ < 0.375 and χ + y + ζ = 1, which also contains an amount of cobalt that is 0.1 to 3% by weight & equivalent to cobalt oxide (GoO). This ceramic has a high mechanical quality factor, a high constancy of the resonance frequency within a wide temperature range and a high constancy of the capacitance ratio within a wide temperature range.

The invention relates to piezoelectric ceramic compositions and articles made therefrom. More specifically, the invention relates to new ferroelectric ceramic compositions, the polycrystalline Are aggregates of certain components. Liese

A09849 / 1039

piezoelectric masses become ceramic materials according to sintered techniques common in the field of ceramics, and the ceramic materials thus produced are applied by applying a DC voltage polarized between the electrodes to give the ceramic materials electromechanical ^ transducer properties, according to the known piezoelectric effect to give. The invention also encompasses the calcined product the raw ingredients and items such as electromechanical transducers made from the sintered ceramic have been.

The proposed according to the invention ceramic body are generally present in solid solution systems \ Pb (Sn ₁ ^ ₅ Nb ₂ Z _{5) 5} O ₃ -PbZrO -PbOIiO _5, Pb (Sn _1/5 Nb _2/5) 0 ₅ -PbTi0 ₅ \ or ()

^ z-JNTb ₀ ZZ) OJ-PbZrO,;, modified with a GoG addition of V3 <V3 3 3 '

0.1 to 3 wt.

The application of piezoelectric materials on various Converter application areas in manufacture, measurement and .Determination of the sense of direction of sound, shock, vibration, pressure, etc. has increased significantly in recent years. Both Kristalials Ceramic types of transducers have also been used extensively. Because of the possibly lesser Kosuen and the Ease of manufacture of ceramic materials of various shapes and sizes, as well as greater resistance to high "temperature and / or .humidity than Crystalline substances such as Rochelle's salt have recently been used in the piezoelectric ceramic materials in various ways converter application areas gained importance.

The required piezoelectric properties of ceramic materials obviously vary with the type of application. E.g. require electromechanical converters, e.g. for xon consumers and microphones, piezoelectric ceramic materials characterized by a substantially high electromechanical coupling coefficient and has a high dielectric constant

409849/1039

are. In contrast, it is when using piezoelectric ceramic materials desirable in the field of ceramic filters, that the hater.ialien have a high value for the mechanical Show quality factor. The ceramic materials must also have a high constancy of the resonance frequency and others electrical properties with the (temperature and time.

As quite promising ceramic materials that meet these requirements, lead titanate-lead zirconate is widely available Extensions have been used so far. However, it is very difficult to get one with the lead titanate-lead zirconate ceramic materials To obtain small temperature coefficients of the resonance frequency, also change the dielectric and piezoelectric Properties of the lead titanate-lead zirconate ceramic materials are strongly related to the firing technique, resulting in the evaporation of PbO ζ related

The main object of the invention is therefore to find new and improved piezoelectric To propose ceramic materials that solve at least one of the problems identified above.

A more specific object of the invention is to provide improved ones polycrystalline ceramic materials, which have a high mechanical quality factor together with a high degree of constancy the resonance frequency within a wide temperature range and a high constancy of the capacitance ratio within are excellent over a wide temperature range. '

Another object of the invention is to provide new piezoelectric Ceramic masses are proposed in which certain properties can be set, uiü they different Customize applications.

Another object of the invention is to provide an improvement eiektromecheiiischer converter are created, namely

409849/1039

using an electrostatically polarized body made of the new ceramic masses as active elements.

These objects of the invention and the manner in which these objects are achieved are set out in the following description Connection with the associated drawing is easy to find. In the drawing, figure 1 (the only figure) gives one Cross-section of an electromechanical transducer according to the invention again.

Before the proposed according to the invention piezoelectric materials are explained in detail, their piezoelectric Application in electromechanical converters will be described with reference to FIG. 1, in which the reference number 7 denotes an electromechanical transducer as a whole, the active element being a preferably disk-shaped Includes body 1 made of a piezoelectric ceramic material of the invention.

The body 1 is electrostatically polarized in the following manner and with a pair of electrodes 2 and 5 provided in a suitable manner on the two opposite Surfaces of the body are attached. Lead wires 5 and 6 are 4-conductive to electrodes 2 and 3 by solder tied together. If the ceramic is exposed to impact, vibration or other mechanical stress, can an electrical output power the lead wires ί? and 6 can be removed. Conversely, as with other piezoelectric transducers, the application of an electrical voltage leads the electrodes 2 and 3 to a mechanical deformation of the Ceramic body. The term electromechanical 'converter is intended to as used here to be understood in its broadest sense and piezoelectric ceramic filters, frequency control devices and the like, and the invention can also be used in many other fields of application and those fields of application be adapted, the materials with dielectric,

409849/1039

require piezoelectric and / or electrostrictive properties.

According to the invention, the ceramic body 1 has been manufactured in the Ii ¹ IgUr 1 from a new piezoelectric mass, which is a polycrystalline ceramic and from Pb (Sn ₁ / τ ^ ο / ⁷ ? ® ⁷ ) " -PbZrCU, Pb (Sn ^ ₅ Ub ₂ , ^) O ₃ -PbTiO ₅ or Pb (Sn ₁ , JJF, modified with an addition of CoO.

The invention is based on the finding that within particular Areas of these systems modified with a GoOy addition Samples having a relatively high mechanical quality factor along with a high constancy of the resonance frequency the 'temperature and a high constancy of the capacity ratio. show over time.

The invention has many advantages in manufacture and use in the ceramic transducer field. It is known that the evaporation of PbO during firing is a problem in the sintering of lead compounds such as lead titanate zirconate. However, the composition according to the invention shows a lower proportion of evaporated PbO than conventional lead titanate zirconate. The system according to the invention can be fired without any particular adjustment of the PbO atmosphere. A well-sintered body from the hasse according to the invention is obtained by firing in a ceramic crucible with a ceramic lid made of an Al ^ O ₅ ceramic. A high sintered density is desirable for moisture resistance and high piezoelectric sensitivity when the sintered body is attached to a resonator or the like.

Some hate falling under the system Pb (Sn ₁ , -, Hb-Z ₇ ) O ^ -PbTiO, -PbZrO, do not show a high level of piezoelectricity, and many are electromechanically active only to a small extent. The invention relates to the masses represented by the formula Pb (Sn ₁ Ti Zr O ₇ -, where x, y and ζ are like

409849/1039

0.01 <χ £ 0.25, 0 <ji 0.75, 0 4 ζ <0.875 and χ + y + ζ = 1, and which exhibit a piezoelectric sensitivity of considerable magnitude. The hats of the invention contain the basic composition given above and an addition of CoO.

The compositions described herein can be made by various known methods of making ceramic materials. A preferred method, which is described in more detail below, suggests the use of PbO or Pb ^ O ^ ,, SnO or SnO ₂ , Nb ₂ O, -, TiO ₂ , ZrO ₂ and. CoO, Go ₂ O ₅ or Co ^ O ^. However, the process given below does not represent any limitation for the production of the hats according to the invention.

The starting materials, namely lead oxide (PbO), tin oxide (SnO ₂ ), Kiob pentoxide (Wb ₂ O _n .), Titanium dioxide (TiO ₂ ), zirconium dioxide (ZrO ₂ ) and cobalt oxide (CoO), all of a relatively pure nature (e.g. from the Degree "chemically pure"), are intimately mixed with distilled water in a rubber-lined ball mill. When grinding the mixture, care must be taken to avoid contamination from abrasion of the hollow balls or stones (or the proportions of the ingredients must be varied to compensate for such contamination).

After the hate grinding, the mixture is dried. Then it will The mixture is subjected to a preliminary reaction by calcining at a temperature of around 850 C for 2 hours.

After the calcination, the reacted material is cooled and then wet milled to a small particle size. The CoO addition can be added to the reacted material after calcining the starting materials, which contain no üoO, are added, and the reacted haterial with the CoG addition can lead to a .Kleinen Particle size can be determined, "again must be responded to that contamination by abrasion of the hollow balls or stones is avoided (or such contamination kociperi-

409849/1039

is adjusted by varying the proportions of the components accordingly). Depending on the choice and the desired shapes, a mixture or slurry can be formed from the de-haterial, which is suitable for pressing, slide casting or extrusion, depending on the individual case according to conventional procedures in the field of ceramics. The samples, for which the fourth is given below, were prepared by mixing 100 g of the ground, pre-sintered mixture with 5 cm ^{5 of} distilled water. The mixture then became disks with a diameter of 20 mm and a dicice of 2 mm at a

K of 700 kg / cm pressed. The pressed discs were

Fired at 110 - 1 ^ 90 ⁰ O for a heating period of about 4-5 minutes. According to the invention, it is not necessary to burn the hasse in a PbO atmosphere and no special care must be taken with regard to the temperature drop in a furnace, in contrast to the known processes. Thus, according to the present invention, uniform and excellent ceramic piezoelectric products can be easily obtained by simply covering the samples with an alumina crucible during firing.

The sintered ^ ceramic masses become on both surfaces ground to a thickness of 1 mm. The ground disc surfaces can then be coated with silver paint and fired to form silver electrodes. Eventually be the slices while immersed in a bath of silicone oil are polarized at 100 G. A stress gradient a DC voltage of 4 kV / mm is maintained for one hour, and the slices are set to room temperature within 30 limits field cooled.

The piezoelectric and dielectric properties of the polarized samples were measured ^{at 20 °} C. and a relative humidity of 50 %. Examples of special ceramic masses according to the invention and various essential electromechanical ^ and dielectric properties of the ceramic masses are in the

409849/1039

! Table 1 given.

composition Table 1 PbTiO,
3 PbZrO,
3 CoO-
additive 24 hours % P-T fr-TC 0.23 of the masses 75.0 _ Weight -γ <> the after
the Pole 510 * 0.28 at
game ¥ lo1 - / j the basic together
settlements 37.5 37.5 0.5 P. 480 1.32 0.08 Kr. JT U) OXi y \ / -? Ϊ́Λ VJ r ~ \ f ~ 7 \ -f -7 J
\ / ι rf ι Ο 43.5 44.0 0.5 39.2 170 0.98 0.17 1 25.0 43.5 44.0 0.1 4.7 390 0.59 0.25 2 25.0 43.5 44.0 1.0 2.7 230 0.55 0.2ö 3 12.5 - 87.5 3.0 3, c 620 0.38 0.09 4 · 12.5 46.0 48.0 0.5 4.5 190 1.71 0.15 5 12.5 46.0 48.0 0.1 40.9 530 1.32 0.22 6th 12.5 47.0 50.0 1.0 2.8 230 O, yi 0.17 7th 6.0 47.0 po, o 0.2 3.1 500 0.89 0.21 8th 6.0 47.0 52.0 0.5 3.3 250 1.37 9 3.0 0.2 3.4 0.70 10 3.0 3.4 11 1.0

ρ is the capacity ratio

Γ _ resonance frequency "7

2 (anti-resonance frequency - resonance frequency) - '

üjyi is the mechanical quality factor. p-T is the change the capacity ratios (p) between 24 hours after poling and 1000 hours after poling. fr-TC is the change the resonance frequency (fr) within the range of -40 ° C to ÖO ° G.

The hats of the invention modified with an addition of CoO show a relatively high mechanical quality factor (Ca,) im Compared to that of the basic masses, i.e. the basic masses without CoO a own a Q of about 100-

409849/1039

The table Λ is; It can be seen that the piezoelectric ceramic masses of the invention show a high constancy of the resonance frequency with the temperature within a wide temperature range and furthermore a high consistency of the capacitance ratio with time after the poling. The hasse according to Example 3 shows a very high constancy of the resonance frequency with the egg temperature. These properties are important when the piezoelectric ceramic compositions are used for ceramic filters, frequency control devices and so on.

Ceramic materials containing a GoO addition of less than 0.1 Gev /.- ^ show a relatively low mechanical quality factor. For ceramic masses that contain a GoO additive above 5 wt .- ^, the mechanical quality factor is relatively low. Because of this, such hates are out of the invention Area excluded.

In addition to the superior properties noted above, the properties of the invention are ceramic materials of good physical quality that can be polarized well. The above information shows that the ternary solid solution Fb (Sn./JTbp / ^) O ₃ , -jr'bi'iOv-PbZrO- ,. forms an excellent piezoelectric ceramic body.

It can be seen that those to be used in the invention Starting materials are not limited to those used in the above examples. Such oxides, hydroxides and Carbonates can be used in place of any of the starting materials in the above examples, which can readily be found under formation the required composition of the hate at increased • Decompose temperature.

Sponsorship sciences

409849/1039

Claims (3)

Claims (1.j Piezoelectric ceramic mass, characterized in that they are a solid solution of a material of the formula where the ranges for x, y and ζ are v; ie 0.01 4 χ ύ 0.25, 0 ^ yi 0.75 and 0 <ζ < 0.875 and χ + y + ζ = 1, and also one Contains amount of cobalt that is 0.1 to 3 wt .- ^ cobalt oxide (GoO) equivalent. 2. Electromechanical converter, characterized in that it contains a ceramic mass according to Example 1. 3. Piezoelectric ceramic mass, characterized in that it consists essentially of a material of the formula exists and also contains an amount of cobalt that is 0.1 wt .-?.? Cobalt Oxide (GoO) is equivalent. 4-, electromechanical transducer element, characterized that it contains a piezoelectric ceramic composition according to claim 3. 5-> method for producing the ceramic mass according to claim 1, characterized in that PbO, SnOp, Wb, Oc-, TiOp, ZrOp and GoO are thoroughly wet-milled, the semis are dried and is subjected to Yorreaction by calcination, the calcined mixture is cooled; and to a smaller particle size is ground, the finely divided üeuisch shaped and the formed mixture is fired, i / r.Ye / iie 409849/1039