Piezoelectric material with perovskite structure for high operating temperatures and production method for same

Abstract

The invention relates to a compound with a perovskite structure, which has the following basic composition: AgxBiyMzFevNwO3 where x + y + z = 0.9 to 1.1 and v + w = 0.9 to 1.1, wherein M is selected from Pb and / or Ba, and wherein N is selected from Ti and / or Zr, and which can be used as the basis for the production of perovskite materials and functional ceramics with piezoelectrical properties at high temperatures. The invention also relates to a method for producing a material with piezoelectrical functionality, which guarantees consistent and high product quality and simultaneously offers advantages in terms of safety or allows for production without the use of organic solvents. The invention further relates to a piezoelectric device comprising the above-mentioned perovskite material or the compound with the perovskite structure.

Description

Piezoelectric material with perovskite structure for high operating temperatures and its manufacturing process DESCRIPTION Technical area

[0001] The present invention relates to a composition with a perovskite structure which can be used as a starting material for the production of perovskite functional ceramics with piezoelectric properties at high temperatures.

[0002] Furthermore, a method for producing a material comprising the specified composition and a piezoelectric device comprising the material are described. State of the art

[0003] Piezoelectric materials have the property that their electrical polarization changes as a result of mechanical action (piezoelectric effect), or the application of an electrical voltage causes a change in the material's dimensions or its mechanical movement (inverse piezoelectric effect). Based on these functions, piezoelectric elements are widely used in numerous technical fields, both as sensors and actuators, for example in medical technology, sonar applications, ultrasound technology, consumer electronics, mechanical engineering, the automotive industry, and aerospace.

[0004] The state of the art describes numerous materials that are suitable as a basis for piezoelectrically active components.

[0005] For example, document DE 10 2019 135 245 B9 discloses a piezoelectric composition comprising silver and an oxide, wherein the oxide has a perovskite structure and is at least partially represented by the formula x[Bi m FeO3]- y[Ba n TiO3] is represented.

[0006] The most common piezoelectric materials today are based on the ferroelectric crystal lead zirconate titanate Pb(Zr x Ti(i. X ))O3 (PZT), which, like its similar counterpart, barium titanate, usually has a perovskite structure. Perovskite refers to the general structural type of the close-packed ionic structure ABX3, where A and B are cations and X is the anion. Distortions in the perovskite structure can cause polarization and thus dipole formation in the crystal lattice, which is responsible for the piezoelectric properties of many perovskites. For example, in lead zirconate titanate (PZT), below the Curie temperature (T c ) the titanium ions in the ion lattice move from their central position, creating a dipole lattice with piezoelectric properties.

[0007] However, the temperature range for the use of PZT is severely limited. The maximum temperature at which PZT can be used continuously while maintaining a sufficient piezoelectric coefficient (d33) of over 50 pC / N (with a field and a length change along the poling axis (longitudinal effect)) is typically around 250°C.

[0008] To solve this problem, WO 2019 / 243778 A1 , US 2013 / 0207020 A1 and US 2018 / 0315916 A1 describe a material with improved piezoelectric functionality at high temperatures, wherein the perovskite material (Bi a Ki- a )TiO3- yBiFeOs-PbTiOs (or in alternative formula notation K x BiyPb z Fe v Ti w O3 with x + y + z = 1 ,0 and v + w = ​​1 ,0) serves as the material basis.

[0009] As part of the production of the (Bi a Ki- a )TiO3- y In WO 2019 / 243778 A1, US 2013 / 0207020 A1 and US 2018 / 0315916 A1, BiFeO3-PbTiO3 are weighed and mixed alongside Bi2O3, Fe2O3 and TiO2, as well as PbO as lead component and K2COs as potassium component.

[0010] Potassium carbonate (K2CO3) is highly hygroscopic and has a water solubility of L=1120 g / l at 25°C, while alternative potassium compounds are typically also hygroscopic and water-soluble (e.g., KOH: L=1130 g / l; KNO3: L=316 g / l; K2C2O4: L=360 g / l; K2CO3: L=1120 g / l; KCl: L=347 g / l, all at 25°C). These properties pose major challenges for the manufacturing process of the piezoceramic material under the following aspects:

[0011] The pronounced hygroscopy of potassium compounds leads to the constant absorption of atmospheric moisture and makes it difficult to weigh the reactant quantity accurately and consistently, which can have a negative impact on the quality of the products and the reproducibility of the manufacturing process, unless controlled environmental conditions are ensured at considerable expense and effort.

[0012] The high water solubility of potassium compounds also requires mixing in organic, liquid, anhydrous media. Solvents such as isopropyl alcohol, which is used in US 2013 / 0207020 A1 and US 2018 / 0315916 A1, are flammable. This requires complex safety precautions, particularly with regard to upscaling the manufacturing process. Irrespective of this, it is desirable, not least for environmental reasons, to minimize the use of organic solvents in the manufacturing process.

[0013] Publication EP 3 331 840 A1 describes a process in which the starting material is homogenized in an aqueous suspension and subsequently subjected to spray-freeze granulation to prevent water-soluble components such as alkalis from being dissolved out during subsequent processing and segregating during drying. In addition to requiring additional process steps, however, the process is unable to minimize inaccuracies in the weighing of the starting materials.

[0014] WO 2019 / 243778 A1 describes dry mixing without a liquid medium. However, this process is associated with significant disadvantages, as the hygroscopic properties of the potassium compounds during feeding and the actual dry mixing can lead to clumping and consequently unfavorable heterogeneous mixture distributions, which can reduce the quality of the resulting materials.

[0015] From the above, it is therefore an object of the invention to provide a compound and a material which are characterized by excellent piezoelectric functionality at high temperatures and at the same time can be provided in high quality and quantity using a simple, cost-effective and environmentally friendly process. Description of the invention

[0016] Therefore, as a solution to the above-mentioned problems, the present invention provides a compound with perovskite structure, characterized in that it has the basic composition Ag x BiyM z Fe v N w O3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1, wherein M is selected from Pb and / or Ba, and wherein N is selected from Ti and / or Zr.

[0017] Furthermore, a material with piezoelectric functionality is provided, which is characterized in that it comprises perovskite material containing the above-mentioned compound.

[0018] Furthermore, the present invention provides a method for producing the above-mentioned material with piezoelectric functionality.

[0019] Furthermore, a piezoelectric device is described, preferably comprising a piezoceramic body with at least two electrodes, which comprises the above compound with perovskite structure or the above material with piezoelectric functionality.

[0020] Advantageous embodiments of the invention can be found in the dependent claims and the following explanations.

[0021] The invention is described in more detail with reference to the accompanying drawings.

[0022] Fig. 1 shows an exemplary process for the production of piezoceramic materials according to the invention, and

[0023] Fig. 2A and 2B are ceramographic images of exemplary sintered compositions. Best way of carrying out the invention

[0024] The invention and its advantages are explained in more detail below using preferred embodiments.

[0025] In one embodiment, the present invention relates to a compound with a perovskite structure, which is characterized in that the compound has the basic composition Ag x BiyM z Fe v N w O3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1, wherein M is selected from Pb and / or Ba, preferably Pb or Ba, and wherein N is selected from Ti and / or Zr, preferably Ti or Zr.

[0026] In a preferred embodiment, M comprises both Pb and Ba, so that the compound has the basic composition Ag x Biy(Pb,Ba) z Fe v N w O3 and z represents the mass fraction of the sum of both metals in the basic composition.

[0027] In a further preferred embodiment, M represents Pb, so that the compound has the basic composition Ag x Bi y Pb z Fe v N w O3.

[0028] Preferably, the sum of x, y, and z is 0.95 to 1.05, and the sum of v and w is 0.95 to 1.05. Particularly preferably, x + y + z = 1 and v + w = ​​1. Generally, for x, y, z, v, and w, independently of one another, 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < v < 1, and 0 < w < 1.

[0029] It has been found that silver compounds, which are characterized by relatively low water solubility and non-hygroscopic properties In addition to being easy to handle, they enable the production of materials that have excellent piezoelectric properties at high temperatures.

[0030] In a preferred embodiment, the following applies to x, y, z, v and w: 0.005 < x < 0.30 0.40 < y < 0.90 0.01 < z < 0.70 0.40 < v < 0.80 0.20 < w < 0.60.

[0031] In a further preferred embodiment, the following applies to x, y, z, v and w: 0.01 < x < 0.20 0.50 < y < 0.80 0.05 < z < 0.50 0.50 < v < 0.70 0.30 < w < 0.50.

[0032] In a particularly preferred embodiment with regard to the piezoelectric properties (e.g. determined by T c and d3s) in the high temperature range applies to x, y, z, v and w: 0.02 < x < 0.14 0.56 < y < 0.76 0.10 < z < 0.42 0.54 < v < 0.62 0.38 < w < 0.46.

[0033] Perovskites are characterized by the general structural type of the close-packed ionic structure ABX3, where A and B represent cations and X the anion. In this regard, it is preferred that Ag and Bi (or Ag + and Bi 3+ ) occupy position A in the underlying perovskite basic structure ABO3. Furthermore or alternatively, it is preferred that in the compound according to the invention Fe and Ti or Zr (or Fe 3+ and Ti 4+ or Zr 4 *) occupy position B in the underlying perovskite structure ABO3.

[0034] Typically, the compound of the invention has an orthorhombic / rhombohedral Krista II structure.

[0035] The Goldschmidt tolerance factor t defines a lower tolerance limit depending on the ionic radii for the formation of the perovskite structure (see VM Goldschmidt: The Laws of Crystallography. In: Die Naturwissenschaften. Volume 14, No. 21, 1926, pp. 477-485). This also allows estimates of the degree of distortion, as well as statements about the ratio of bond lengths. The compounds according to the invention preferably have a perovskite structure tolerance factor according to Goldschmidt t in the range from 0.820 to 0.880, more preferably in the range from 0.840 to 0.860. For the calculation of the Goldschmidt tolerance factor t according to the present invention, effective ionic radii according to RD Shannon; "Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides"; Acta Crystallography; A32; 1976; 751-767 are used.

[0036] In a further embodiment, the present invention provides a material with piezoelectric functionality, characterized in that the material comprises perovskite material containing the compound with perovskite structure described above.

[0037] Preferably, the total amount of non-perovskite phases present in the material is less than 10 wt.%, more preferably less than 8 wt.%, more preferably less than 5 wt.%, even more preferably less than 2 wt.%, even more preferably less than 1 wt.%, most preferably less than 0.1 wt.%. The amount of non-perovskite phases present in the ceramic may be a trace amount.

[0038] It is particularly preferred that the material consists of X-ray pure perovskite material without X-ray detectable non-perovskite foreign phases.

[0039] The perovskite material may also contain one or more perovskite phases in addition to the basic composition Ag x BiyM z Fe v N w O3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1. Additional perovskite phases may have rhombohedral or tetragonal crystal structures. It is preferred that the perovskite material does not contain a perovskite phase with the formula (Bi a Ki. a )TiO3 with 0.4 < a < 0.6. In further preferred embodiments, the perovskite material does not comprise potassium ions.

[0040] In the perovskite material contained in the material, one or more of Ag, Bi, M, Fe and N can be replaced by a dopant in order to, for example, modify the Curie temperature and / or the piezoelectric activity.

[0041] Dopants can be added in a suitable amount, for example in an amount of up to 2 wt.%, preferably up to 1 wt.%, in embodiments up to 50 atomic%, or up to 20 atomic%. It is further preferred that dopants be added in an amount of at least 0.001 wt.%, further preferably at least 0.005 wt.%. The wt.% values ​​refer to the total weight of the perovskite material.

[0042] Metal dopants are preferred dopants.

[0043] For example, a metal dopant can act as a substituent for the A-position in the underlying perovskite ABO3 structure, replacing, for example, Ag and / or Bi. Preferably, the metal dopant for the A-position is selected from the group consisting of Li, Na, Ca, Sr, Ba, and a rare earth metal. Doping with Li, Na, Ca, Sr, or Ba at the A-position can reduce dielectric loss, modify (e.g., increase) the Curie point, and / or favorably influence the phase composition, while substitution with rare earth metals (such as La or Nd) can improve piezoelectric activity.

[0044] The metal dopant can be a metal dopant for the B-position in the underlying perovskite structure ABO3 and replace, for example, Fe and / or Ti.

[0045] Preferred dopants for the B-position can be selected, for example, from the group consisting of Ti, Zr, W, Nb, V, Ta, Mo, and Mn. Preferred metal dopants for the B-position can have a higher valence than the valence of the substituted metal, thereby increasing the resistivity of the material and reducing its electrical conductivity. In a further preferred embodiment with regard to an improved reduction in insulation resistance and dielectric losses, the metal dopant for the B-position is Mn.

[0046] As mentioned above, the material according to the present invention is characterized by advantageous piezoelectric functionality in the high temperature range (ie at working temperatures above 250°C and typically up to at least 500°C).

[0047] Preferably, the material according to the invention has a piezo constant d33 (in a field and a change in length along the poling axis (longitudinal effect)) of greater than 50 pC / N, further preferably greater than 60 pC / N, and particularly preferably greater than 70 pC / N, each determined according to EN 50324. Typically, the piezo constant d33 is 50 pC / N to 110 pC / N, for example 60 to 100 pC / N.

[0048] Furthermore, the material is preferably suitable for permanent use at maximum working temperatures of at least 450°C, further preferably at least 500°C, and particularly preferably at least 550°C.

[0049] The Curie temperature T c of the functional ceramics, determinable according to EN 50324, is preferably at least 500°C, further preferably 550°C to 640°C.

[0050] The permittivity E, defined as the ratio of the absolute permittivity of the material and the permittivity in vacuum (E0= 8.85 10' 12 F / m) is preferably 100 to 500, e.g. 180 to 340.

[0051] The dielectric loss factor tanö of the material, determinable by small-signal measurements, is preferably 0.05 or less, further preferably 0.04 or less, for example 0.01 to 0.03.

[0052] The invention also relates to a method for producing the above-described material with piezoelectric functionality, comprising: (1) mixing a raw material combination comprising Ag, Bi, Pb and / or Ba, Fe, Ti and O and optionally grinding the raw material combination; (2) heat-treating the mixed and, if necessary, ground raw material combination to provide the perovskite material with the basic composition Ag x BiyM z Fev Ti w O3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1, wherein M is selected from Pb and / or Ba.

[0053] In a preferred embodiment, the raw material combination comprises Ag, Bi, Pb, Ba, Fe, Ti, and O, so that M in the basic composition comprises both Pb and Ba. In another preferred embodiment, M represents exclusively Pb.

[0054] The manufacturing process according to the invention may comprise further process steps, as illustrated, for example, in Fig. 1.

[0055] In general, the process begins with the provision of the raw materials (with dopants if necessary) and their weighing. The starting raw materials are not particularly restricted and can be, among others, oxides, carbonates, hydroxides, halides or other salts of the metals used. Preferably, the raw material combination comprises Bi2O3, Fe2O3, TiO2 and PbTiO3 and / or BaTiO3, as well as one or more compounds selected from Ag2O3, AgF, AgCl, AgBr, AgI, AgNO3, AgCNO3, AgN3, Ag2S and AgOH. In view of the advantageously low water solubility of the individual raw materials, the raw material combination includes Bi2Os, Fe2Os, TiC>2 and PbTiCh and / or BaTiCh, as well as one or more compounds selected from Ag2 <D, AgCI, AgBr, Agl, AgCNO, AgNs, Ag2S und AgOH. In besonders bevorzugten Ausführungsformen findet Ag2<D als silberhaltiger Rohstoff Verwendung (Löslichkeit in Wasser bei 25°C L=0,025 g / l). Weitere Rohstoffe (wie etwa Metalloxide, beispielhaft WO3 oder MoOs) können bei Bedarf zugesetzt werden, sofern diese die Bildung der Perowskitstruktur mit der Zusammensetzung Ag x BiyM z Fe v N w O3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1.

[0056] In contrast to known processes that rely on the use of raw materials with pronounced hygroscopic properties (such as potassium compounds), the process according to the invention enables simple, constant and precise weighing of the raw materials and does not require any additional measures (e.g. pre-drying and / or weighing under a protective gas atmosphere).

[0057] The raw material combination is then mixed in a dry state or in a liquid medium and, if necessary, ground. Aqueous media (e.g., water) can advantageously be used as the liquid mixing and / or grinding medium. By minimizing or eliminating the use of organic solvents, the environmental friendliness of the process can be improved, particularly when scaling up the production process, and occupational and laboratory safety requirements can be reduced without compromising product quality and consistency.

[0058] Calcination of the mixed and, if necessary, ground raw material combination serves to provide the perovskite material with the composition Ag x BiyM z Fe v N wO3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1, wherein M is selected from Pb and / or Ba, and wherein N is selected from Ti and / or Zr. It should be noted that calcination can be carried out either before or after grinding, and that coarse and fine grinding steps can also be interposed. The calcination conditions are not particularly limited and can be suitably adjusted by a person skilled in the art. Calcination usually takes place at temperatures of above 600°C up to about 900°C.

[0059] The subsequent processing of the resulting calcinate can be carried out according to known methods.

[0060] For example, the calcinate can be slurried in a liquid (preferably aqueous) medium and cast into films, which are then subjected to a multilayer process (e.g., including printing, stacking, lamination, and / or separation) before sintering the material. Alternatively, the calcinate can be subjected to a co-firing process in which the films are provided with electrodes in the green state, laminated to form a piezoelectric element, and then sintered together with the internal electrodes in a single process step, as described, for example, in DE 10234787 C1. Another processing option is to slurry the calcinate in a liquid, preferably aqueous, medium or to plasticize and homogenize it with a suitable binder, and then process it by spray granulation and subsequent compression molding before sintering the molded material.Alternatively, the calcinate can be finely ground and then granulated and molded (as shown in Fig. 1).

[0061] The sintering conditions are not particularly limited and can be selected as appropriate by the skilled person. Sintering typically takes place at temperatures of at least 850°C, preferably 950°C or higher.

[0062] To provide the piezoceramic material, the sintered material can be subjected to mechanical processing (including, for example, grinding and / or cutting), contacting, polarization (e.g. by applying a DC electric field of approximately 2 to 10 kV / mm at temperatures of 20 to 150°C) and electrical measurement according to known methods.

[0063] Another embodiment of the present invention relates to a piezoelectric device comprising the above-described compound with perovskite structure or the above-described material with piezoelectric functionality.

[0064] The piezoelectric device can be a piezoelectric actuator, sensor or transformer.

[0065] Typically, the piezoelectric device comprises the compound according to the invention with a perovskite structure or the material according to the invention with piezoelectric functionality in a piezoceramic body, as well as at least two electrodes.

[0066] The piezoceramic body can be designed as a (usually mechanically hydraulically pressed) shaped body, e.g. in the form of a disc, plate, rod, hemisphere, or a ring.

[0067] The piezoelectric material and / or the electrodes can be formed as stacked layer structures. A stacked piezoelectric device can have a plurality of internal electrode layers and a plurality of piezoelectric layers, each electrode layer being alternately stacked or layered with a respective piezoelectric layer, wherein at least one of the plurality of piezoelectric layers comprises the compound with a perovskite structure according to the invention or the material with piezoelectric functionality according to the invention. Furthermore, such stacked structures can comprise additional layers as needed, such as one or more buffer layers, substrate layers, conductor sections, and / or insulating layers. The thickness and area of ​​the piezoelectric layer, as well as the number of layers, can be selected according to the intended use of the stacked piezoelectric device.

[0068] In further embodiments, the piezoelectric device may comprise, for example, a driver circuit, a current monitoring circuit, a switching means, as disclosed, for example, in DE 102015101817 A1.

[0069] The fields of application of the piezoelectric devices according to the invention are not limited in any way and include, among others, ultrasonic cleaning, ultrasonic processing, sonar technology, sensor technology, actuator technology, material testing, medical diagnostics and therapy, automotive industry, aerospace, mechanical engineering, building services, ignition systems, consumer electronics and audio applications. Examples

[0070] Following the process steps schematically shown in Fig. 1, various exemplary piezoelectric functional ceramics based on the perovskite composition Ag x BiyPb z Fe v Ti wO3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1 were manufactured as test specimen discs with dimensions of 6.5 mm x 1.0 mm (see Table 2). The individual compositions can be found in Table 1 below.

[0071] Table 1 : Example compositions and their Goldschmidt factors.

[0072] For this purpose, the raw materials Ag2<D, Bi2Os, PbTiOs, Fe2Os, und TiC> 2, and mixed and ground for 4 hours in 11 drums (in demineralized water; 4:1 mixture; ZrO2 grinding balls). The particle diameters after grinding were determined using a laser granulometer to be d = 0.7 pm, dso = 1.5 pm, and dgo = 3.5 pm. The samples were dried for 24 h at 120°C and granulated using a mesh sieve (500 pm). For calcination, the masses were filled into Al2O3 crucibles and calcined in a resistance furnace in air (60 min at 200°C, 600 min at 750°C, and 180 min at 950°C). The cooled samples were subjected to phase analysis via XRD, whereby the presence of non-perovskite foreign phases could be excluded. The calcinates were finely ground for 4 hours in 11 drums (d = 0.7 pm, dso = 1.5 pm and dgo = 3.5 pm), dried for 24 h at 120°C and sieved using a mesh sieve (500 pm) and then after addition of 0.8 wt.-% PAF granulated (bulk density dbulk = 2.5 g / cm. 3 ). By means of uniaxial dry pressing (press force 34 kN), round cylinders with a diameter of 12 mm and a height of 30 mm and a bulk density of 5.2 g / cm 3 The pellets were then sintered, ground (d = 6.5 mm), and sawn into discs (d = 6.5 mm, h = 1.0 mm) according to the conditions listed in Table 1. For the ceramographic For analysis, the sintered discs were ground, polished, and thermally treated for 2 hours at 950°C in a resistance furnace. The grain sizes in the ceramic microstructure were imaged using light microscopy and quantified using cross-section measurements and Saltykov analysis (see Table 2).

[0073] Table 2: Sintering conditions and specific grain size parameters of the ceramic microstructures of sintered ceramics.

[0074] Figures 2a and 2b show examples of the ceramographic images of sintered samples B and C.

[0075] The samples were then coated with Ag paste and fired at 850°C, and after cooling to room temperature, subjected to a polarization step (6.5 kV / mm for 15 min at 25°C in oil).

[0076] The polarized materials (cylinders with dimensions d = 6.5 mm h = 7.0 mm) were investigated for their piezoelectric and dielectric properties using an impedance analyzer. The results are summarized in Table 3.

[0077] Table 3: Dielectric and piezoelectric properties of the exemplary compositions. f s : resonance frequency; tanö: dielectric loss factor; G: permittivity, kerr: effective coupling factor

[0078] The data demonstrate that the materials according to the invention have an advantageously high piezo constant d33 (higher than 70 pC / N) in conjunction with high Curie temperatures T c(550°C to 650°C).

[0079] To estimate the maximum application temperature, the thermal aging stability of exemplary ceramics was tested in a further series of tests. For this purpose, the samples were aged at various temperature levels, starting at 300°C, for 20 hours each. It was determined up to which aging temperature TA the piezo constant d33 of the samples (cylinders with dimensions d = 6.5 mm and h = 7.0 mm) was at least 60% of the initial value (determined at room temperature). The results of these aging tests are listed in Table 4.

[0080] Table 4: Determination of the aging temperature (min. 60 h thermal treatment) depending on the piezo coefficient d33.

[0081] The obtained data demonstrate that the perovskite compounds according to the present invention enable the provision of functional ceramics with excellent piezoelectric and dielectric properties at high temperatures.

Claims

PATENT CLAIMS 1. Compound with perovskite structure, characterized by the fact that it has the basic composition Ag x BiyM z Fe v N w O3 with x + y + z = 0.9 to 1.1 and v + w = ​​0.9 to 1.1, wherein M is selected from Pb and / or Ba, and wherein N is selected from Ti and / or Zr.

2. Compound with perovskite structure according to claim 1 , wherein x, y, z, v and w are: 0.01 < x < 0.20 0.50 < y < 0.80 0.05 < z < 0.50 0.50 < v < 0.70 0.30 < w < 0.

50.

3. Compound with perovskite structure according to one of claims 1 or 2, wherein x, y, z, v and w are: 0.02 < x < 0.14 0.56 < y < 0.76 0.10 < z < 0.42 0.54 < v < 0.62 0.38 < w < 0.

46.

4. Compound with perovskite structure according to one of claims 1 to 3, wherein the compound has a perovskite structure tolerance factor according to Goldschmidt t in the range of 0.820 to 0.880, preferably in the range of 0.840 to 0.

860.

5. Compound with perovskite structure according to any one of claims 1 to 4, wherein Ag + and Bi 3+ occupy position A in the underlying perovskite basic structure ABO3.

6. Compound with perovskite structure according to any one of claims 1 to 5, wherein Fe 3+ and Ti 4+ occupy position B in the underlying perovskite basic structure ABO3.

7. Material with piezoelectric functionality, characterized in that the material comprises perovskite material containing the compound according to one of claims 1 to 6.

8. Material according to claim 7, wherein the material consists of radiographically pure perovskite material without radiographically detectable non-perovskite foreign phases.

9. Material according to one of claims 7 or 8, wherein the perovskite material does not contain a perovskite phase with the formula (Bi a Ki. a)TiO3 comprising 0.4 < a < 0.6, and wherein the perovskite material preferably does not include potassium ions.

10. Material according to any one of claims 7 to 9, wherein the perovskite material is doped with manganese (Mn).

11. Material according to one of claims 7 to 10, wherein the material exhibits piezoelectric functionality at operating temperatures up to 500°C, and preferably has a piezo constant d33 (with a field and a change in length along the polarity axis (longitudinal effect)) of greater than 50 pC / N, and more preferably greater than 60 pC / N, at operating temperatures up to 500°C.

12. Method for producing a material with piezoelectric functionality according to any one of claims 7 to 11, comprising: (1) the mixing of a raw material combination comprising Ag, Bi, Pb and / or Ba, Fe, Ti and / or Zr, and O and, where appropriate, the grinding of the raw material combination; (2) the heat treatment of the mixed and, if necessary, ground raw material combination to provide the perovskite material with the composition Ag x BiyM z Fe v N w O3 with x + y + z = 0.9 to 1, 1 and v + w = ​​0.9 to 1, 1 , where M is selected from Pb and / or Ba, and where N is selected from Ti and / or Zr.

13. Method according to claim 12, wherein in step (1) an aqueous medium and preferably water is used as the mixing and / or grinding medium.

14. A method according to one of claims 12 or 13, wherein the raw material combination comprises Bi2C>3, Fe2C>3, TiC>2 and / or ZrC>2, and PbTiCh and / or BaTiCh, as well as one or more compounds selected from Ag2 <d, agf, agci, agbr, agl, agnch, agcno, agns, ag2s und agoh, vorzugsweise eine oder mehrere verbindungen ausgewählt aus ag2<d, besonders bevorzugt ag2ü.

15. Piezoelectric device, preferably comprising a piezoceramic body with at least two electrodes, comprising a compound with a perovskite structure according to any one of claims 1 to 6 or a material with piezoelectric functionality according to any one of claims 7 to 11.< / d,>

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