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Definitions

• a common problem in the manufacture of piezoelectric ceramic materials is to fabricate the material so as to obtain desired piezoelectric parameters as desired.
• sintering aids such as silicates or borates were added to the ceramic material.
• This approach has the disadvantage that the sintering aids were incorporated into the ceramic material.
• Another disadvantage is the undesirable reaction of the sintering aid with the electrode material in the case where the ceramic material is sintered together with the internal electrodes.
• An object of embodiments of the invention is to provide a ceramic material having improved piezoelectric properties.
• the piezoelectric properties may, for example, be the dielectric constant ⁇ r , the piezoelectric charge constant d33 or the coupling factor k.
• the relative dielectric constant ⁇ r is the ratio of the absolute permittivity of the ceramic material and the permittivity in a vacuum, the absolute permittivity being a measure of the polarizability in the electric field.
• the effectiveness of the piezoelectric effect is characterized by the piezoelectric charge constant d 1D , which represents the ratio of the generated charge density to the mechanical deformation.
• the directionality of the parameter is indicated by the corresponding indexes.
• the index i of the piezoelectric charge constant indicates the direction of the electric field, the index j the direction of the deformation with which the crystal responds to the field.
• a 1 stands for the x direction, 2 for the y direction and 3 for the z direction.
• the piezoelectric charge constant d33 thus denotes the longitudinal elongation behavior in the direction of the z-axis.
• the coupling factor k is a measure of the degree of the piezoelectric effect. It describes the ability of a piezoelectric material to convert absorbed electrical energy into mechanical energy and vice versa. in this connection k 33 stands for the coupling factor of the longitudinal vibration. In the longitudinal effect, the polar axis of the crystal is collinear to the direction of deformation.
• the ceramic material may be described by the following general formula:
• M is at least one element selected from: Nd, La, Ba, Sr, Sb, Bi, K, Na, and where: 0 ⁇ x ⁇ 0.1; 0.3 ⁇ y ⁇ 0.7; 0 ⁇ z ⁇ y; 0 ⁇ (a-z) ⁇ 0.03 and m has the value +1, +2 or +3 corresponding to the valence of the respective metal M
• the ceramic material is a single-phase or two-phase system. Both in the single-phase system and in the two-phase system, the one or both phases are each in a perovskite structure.
• the perovskite lattice can be described by the general formula ABO 3.
• the Pb ions and, if present, also the M ions are arranged on the A sites of the lattice.
• the Zr ions and the Ti ions occupy the B sites of the ion lattice.
• m assumes a value of +3 for the elements Nd, La, Sb and Bi, +2 for the elements Ba and Sr, and +1 for the two elements K and Na.
• a ceramic material of this composition whose parameters are within the limits given above, has very good piezoelectric properties.
• the good piezoelectric properties can be achieved here, without the inclusion of foreign ions, or that the ceramic material had to be heated to very high temperatures.
• M is Nd.
• M is La.
• the parameter a is greater than the parameter z. In this case, there is a two-phase system.
• the formula gives: PBI (m / 2) x z + z M x m (Zri_ y Ti y _ z + z) O3.
• there is a single-phase system which has particularly good piezoelectric properties.
• the parameter z is 0.01 ⁇ z ⁇ 0.1.
• this has an average particle size in the range of 1 .mu.m to 3 .mu.m.
• the grain size can be determined here from microscopic photographs, such as a scanning electron microscope, of a cut.
• Parameters of the average grain size has a strong influence on the piezoelectric properties of the ceramic material.
• this has a density in the range of 7.6 to 8.1 g / cm 3 .
• this does not comprise any additional sintering aids.
• the ceramic material does not comprise any further sintering aids, thus the ceramic material is free of interfering foreign ions which are either incorporated into the crystal lattice Such foreign ions would have a negative effect on the piezoelectric properties of the ceramic material, and by adding PbTiO 3, which can also be incorporated into the PZT grid, the Sintering process, such as grain growth, positively influenced without the addition of ions, which are not already present in ceramic material itself.
• a ceramic material as described above may be used for multilayer devices such as a piezoelectric actuator.
• this comprises the method steps: providing the starting materials comprising Pb to a stoichiometric proportion of 1-xz, M to a stoichiometric proportion of x, Zr to a stoichiometric proportion of 1-y and Ti a stoichiometric proportion of yz as process step A), mixing and premilling the starting materials as process step B), calcining the mixture of B) as process step C), adding PbTi ⁇ 3 to a stoichiometric amount of a as process step D), mixing and post-milling the mixture from D) as process step E) and sintering of the mixture from E) to a ceramic material according to the general formula:
• M is an element selected from: Nd, La, Ba, Sr, Sb, Bi, K, Na, and where: 0 ⁇ x ⁇ 0.1; 0.3 ⁇ y ⁇ 0.7; 0 ⁇ z ⁇ y; 0 ⁇ (az) ⁇ 0.03 and m corresponding to the valency of the respective metal M has the value +1, +2 or +3 as process step F).
• process step A the two elements Pb and Ti are deliberately introduced in a stoichiometric amount, which is the proportion z below the amount in which these two elements should be present in the finished ceramic material.
• the other two elements M and Zr are presented in that stoichiometric amount, in which they should then be present in the finished ceramic material.
• step B) the starting materials are mixed and pre-ground.
• the grinding can be carried out, for example, using a stirred ball mill comprising zirconium oxide grinding balls.
• the premilling can be done, for example, to a particle size of 1 micron.
• the pre-milled starting materials are calcined in the subsequent process step C).
• the PbTi ⁇ 3 promotes grain growth during the sintering step.
• the grain growth can be controlled specifically.
• the ceramic material of the composition has the advantage that, unlike other sintering aids, foreign ions are not added, which are subsequently incorporated into the ceramic material, and adversely affect the piezoelectric properties of the ceramic material.
• Another advantage is that the ceramic material does not have to be sintered at temperatures as high as would be the case if one wanted to achieve a suitable grain size for the ceramic material without adding the PbTiO 3 after calcination.
• the lowering of the sintering temperature further has the advantage of being able to use cheaper materials for, for example, internal electrodes which are sintered with the ceramic material.
• the Pd content of a Pd-Ag alloy can be reduced from 30 percent to 20 percent.
• the internal electrodes may also comprise a Cu alloy, or consist of pure Cu.
• the mixture to a ceramic material according to the general formulas: (PBI m / 2) xz + z M m x (Zri-yti y - z + z) O 3 + a-zPbTiO 3, wherein M for an element is selected from: Nd, La, Ba, Sr, Sb, Bi, K, Na, and where: 0 ⁇ x ⁇ 0.1; 0.3 ⁇ y ⁇ 0.7; O ⁇ z ⁇ y; 0 ⁇ (az) ⁇ 0.03 and m corresponding to the valency of the respective metal M has the value +1, +2 or +3 sintered.
• the ceramic material thus obtained has very good piezoelectric properties, without having to be heated to very high temperatures, or having had to add sintering aids comprising foreign ions.
• moldings are formed between process steps E) and F) as a further process step E1).
• This may be, for example, the shaping of green sheets, which, for example, can be stacked in a further additional method step before or after sintering to form a multilayer component.
• a binder may be added to the ceramic material.
• a binder which is thermally degradable is advantageous here.
• a low-melting metal such as Cu may be used for the internal electrodes of the multilayer component. Due to the reduced sintering temperature, it is now possible to sinter multilayer components together with their internal electrodes, even if the internal electrodes are made of a low-melting metal.
• the multilayer component can be sintered, for example, under an air atmosphere, but also under an N 2 atmosphere, to which H 2 is added and the oxygen partial pressure is controlled with the addition of steam. By controlling the oxygen partial pressure, for example, the oxidation of the internal electrodes can be avoided.
• the binder in the green sheets can be removed before the sintering step in a further process step.
• the two atmospheres mentioned above can also be used.
• a z.
• step D) the stoichiometric proportion of PbTiO 3 is chosen exactly to correspond to the amount in which the elements Pb and Ti in the
• Process step A) were used substoichiometrically. This means that the Pb and Ti ions added in process step D) are completely incorporated onto the lattice sites of the Pbi- ( m / 2) x - z + z M m x (Zri- y Ti y - z + z ) O 3 can be. Thus results after the sintering step F) a single-phase, homogeneous ceramic material. This has very good piezoelectric properties for the parameters lying in the given ranges.
• the average grain size of the finished ceramic material is increased by the addition of PbTiO 3 in process step D).
• grain growth or grain size is directly related to the piezoelectric Characteristics of the ceramic material, the grain size and the piezoelectric properties of the material are controlled by the addition of PbTi ⁇ 3 in process step D) in this method.
• grain growth is usually controlled either by the addition of sintering aids containing foreign ions or solely by the sintering temperature.
• Ceramic materials could be achieved for the parameters selected in this way, which have particularly good piezoelectric properties.
• the starting materials are provided in process step A) as oxides.
• the elements Zr and Ti are each independently presented as oxide Zr ⁇ 2 and Ti ⁇ 2.
• the starting materials Zr and Ti are provided in process step A) as precursors in the form of zirconium titanium oxide (ZTO) or zirconium titanium hydride (ZTH).
• the conversion can take place during calcination at lower temperatures. Furthermore, the formation of PbTi ⁇ 3 can be minimized or be excluded.
• the amount of PbTiO 3 present before the sintering step should correspond as exactly as possible to the amount added in process step D). Thus, it is possible to promote the grain growth targeted.
• the mixture is calcined in process step C) at a temperature of 850 ° C. to 950 ° C.
• the mixture is calcined in process step C) at a temperature of 600 0 C to 800 0 C.
• the calcination can be carried out, for example, under an air atmosphere over a period of 10 to 20 hours.
• the holding time at the maximum temperature can be for example 4 hours.
• the mixture is sintered in process step F) at a temperature of 900 ° C. to 1200 ° C.
• the sintering can be done for example under air atmosphere over a period of 24 hours.
• Maximum temperature can be, for example, 4 hours.
• Component are shown a possible application area for the piezoelectric ceramic material.
• Figure 1 Schematic side view of a piezoelectric actuator.
• Figure 1 shows a schematic side view of a possible embodiment, for a device for which the ceramic material can be used.
• 1 shows a piezoelectric actuator 1 is shown in a schematic side view.
• the piezoelectric actuator 1 in this case comprises ceramic layers 2 between which internal electrodes 3 are arranged.
• the internal electrodes 3 are in each case connected in an alternating manner to one of the two external electrodes 4 in an electrically conductive manner.
• the ceramic layers 2 in this case comprise a ceramic material, as described above.
• a piezoelectric actuator 1 as shown in the figure can be produced, for example, by a method in which ceramic green sheets are laminated alternately with internal electrodes.
• These green sheets may be formed in a preliminary process step, for example, by placing the ceramic material with a binder.
• the layer stack of the inner electrodes 3 and the ceramic layers 2 can then be sintered, for example, in a common sintering process.
• It may, for example, Cu in the form of an alloy or pure Cu for the

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