WO2012000752A1

WO2012000752A1 - Lead-free piezoceramic material comprising a perovskite phase and tungsten bronze phase and method for producing a piezoceramic component with the material

Info

Publication number: WO2012000752A1
Application number: PCT/EP2011/059479
Authority: WO
Inventors: Robert Bathelt; Katrin Benkert; Carsten Schuh; Thomas Soller
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-06-30
Filing date: 2011-06-08
Publication date: 2012-01-05
Also published as: DE102010025670A1; JP2013534898A; EP2548237A1

Abstract

The invention relates to a lead-free, multi-phase piezoceramic material, comprising at least one perovskite phase having the perovskite phase composition (Li_xK_1-x-yNa_y) (Nb_1-t-uTa_tSb_u) O₃ and at least one tungsten bronze phase having the tungsten bronze phase composition (M^III _m(Li_xK_1-x-yNa_y)1_-m(Nb_1-wTa_w) ₅O₁₅ + VA'_2m, where M^III is at least one trivalent metal, VA' are a-site vacancies and the following relationships apply: 0 < m ≤ 0.05; 0 ≤ t ≤ 0.15; 0 ≤ u ≤ 0.15; 0 ≤ w ≤ 1; 0 ≤ x ≤ 0.15; 0.25 ≤ y ≤ 0.75. Also disclosed is a method for producing a piezoceramic component using the piezoceramic material, said method comprising the following steps: a) a green body having a starting piezoceramic composition of the piezoceramic material is provided, and b) said green body is subjected to a thermal treatment, wherein the piezoceramic material of the component is produced from the starting piezoceramic composition. The piezoceramic component is, for example, an ultrasonic transducer or a piezoceramic bending transducer. In particular, the piezoceramic component is a multilayer piezo actuator used for actuating a fuel valve of an internal combustion engine of a motor vehicle.

Description

description

Lead-free piezoceramic material with perovskite phase and tungsten bronze phase and method for producing a piezo-ceramic component with the material

The invention relates to a lead-free, multi-phase piezoceramic material having at least one perovskite phase and at least one tungsten bronze phase and a method for producing a piezoceramic component with the material.

Piezo ceramic materials on the basis of the binary mixing ^¬ system of lead zirconate and lead titanate, known as lead-zirconate-titanate ceramic (Pb (Ti, Zr) O3, PZT) are, because of their excellent mechanical and piezoelectric properties, for example high Curie Temperature T _c of over 300 ° C or high d33 ~ coefficient in the large and small signal range, used in many fields of technology. Piezoelectric components with these materials include bending ^{¬ converters} , multilayer actuators and ultrasonic transducers. These components are used in actuators, medical technology, ultrasound technology or automotive engineering. The ge ^¬ legally permissible content of heavy metals in electrical and electronic components within the European Union with the entry into force of the RoHS (Restriction of the use of Certain hazardous substances) -Richtline in 2006 was severely restricted (EU). This also applies to the piezoelectric components described above. The use of components with PZT as a piezoceramic material is currently only possible through a ^granted EU exemption.

With a view to improved environmental 7,101,491 B2, a more promising ^¬ the lead-free, phase-pure piezoceramic material with good piezoelectric properties, for example, known from US Pat. The material consists of a perovskite phase based on a potassium Sodium niobate (KNN). To improve the piezoelectric properties of the piezoceramic material, a plurality of dopants may be present. Particularly good piezoelectric properties are obtained with lithium, tantalum and / or antimony as dopants.

The object of the invention is to further develop the known piezoceramic material for use in piezoceramic components.

To achieve the object, a lead-free, multiphase piezoceramic material is specified, comprising at least one perovskite phase having the perovskite phase composition (Li _x K _! _X _y Na _y ) (Nbi- - _u Ta Sb _u ) O 3 and at least one tungsten bronze phase having the tungsten bronze phase composition (M ^I_

^Ix _m _(! Li _x K _ _x _ _y Na _y) i_ _m (Nbi_ _w Ta _w) 5O15 + VA _'2m, where M ¹¹¹ is a trivalent metal, at least, VA' A-site vacancies are and The following relationships apply:

- 0 <m <0.05;

- 0 <t <0.15;

- 0 <u <0.15;

- 0 <w <1;

- 0 <x <0.15;

- 0.25 <y <0.75.

To achieve the object, a method for producing a piezoceramic component with the piezoceramic material is also specified with the following method steps: a) providing a green body with a piezoceramic starting composition of the piezoceramic material and b) heat treating the green body, wherein the piezoceramic starting composition of the piezoceramic Material of the component is created. The piezoceramic material is lead-free. Lead-free means that very small, detectable impurities can be present on lead, for example in the ppm range. The piezoceramic material has a lead-free, at least two-phase system which has a perovskite phase based on an alkali metal niobate and a tungsten bronze phase based on an alkali metal niobate and / or on the basis of an alkali tantalate. The alkali niobate of the perovskite phase is doped with tantalum and / or with antimony. Is preferably ^¬ least one of these metals are present (u + t + 0). For the tungsten bronze phase, in addition to the pure alkali niobates or alkali tantalates, in particular mixed forms of these two oxidic alkali compounds are conceivable. The mixed form contains both niobium and tantalum (alkali niobate tantalate). In addition, the tungsten bronze phase on the A sites is doped with trivalent (trivalent) metal M ¹¹¹ . Any trivalent metals are suitable. Different metals can also be used in the same piezoceramic material. The perovskite phase is doped on the A sites with ^different metals.

The composition is a multi-phase system that has a high elongation (eg, high d33 coefficient) and a high Curie temperature ( _Tc ). It has ^¬ ge shows that the piezoceramic material then has very good pie ^¬ zoelektrische properties when, as it is not from the state of the art, single-phase (phase-in), but two or more phases. At least one tungsten bronze phase is present in addition to at least one perovskite phase. In addition, other (fixed) phases may be present. Also, the particular composition of the perovskite phase and the tungsten bronze phase has a great influence on the piezoelectric properties of the material. Namely, the two phases of the piezoceramic material are in the vicinity of a phase transformation from the ortho rhombic crystal system to the tetragonal crystal system. In the vicinity of such a phase transformation very good piezoelectric properties of a material result. This concerns both the elongation and the coupling factor and the lectric properties. As a result, the necessary for the actuators high strains can be achieved.

Preferably, the trivalent metal M ^{111 is} a rare earth metal RE. In particular, the rare earth element RE is neodymium

(Nd ³⁺ ). Based on the A-space doping with trivalent neodymium very good piezoelectric properties can be achieved. Due to the A-space doping with a trivalent metal, there is a corresponding number of A-space vacancies. It is believed that this is the cause of the reduction of the phase transition temperature from the ortho rhombic to the tetragonal phase of the tungsten bronze phase, and as a result, the cause of the improved electrical and piezoelectric properties of the material is.

For tailoring the piezoceramic material, for example the custom cutting of the phase transition temperature of the perovskite phase and / or the tungsten bronze phase, B-site dopants may be present. Such B-site dopants are, for example, Ti, Zr, Si, Ge, Y or Sc. The B-sites of the perovskite phase and / or the B-sites of the tungsten bronze phase are partly occupied by one type of metal or by different types of metals.

The proportions of the two phases on the piezoceramic material can be very different. With regard to good piezoelectric properties, it is particularly advantageous if a proportion of the tungsten bronze phase on the piezoceramic material is in the range of from 0.01% by volume to 25% by volume inclusive, and in particular from the range of 0 inclusive , Is selected from 05% by volume up to and including 15% by volume. Preferably, the proportion of the tungsten bronze phase is selected up to and including 10% by volume. The proportions refer to the solid of the material. For a material consisting only of the two specified phases, the value of the perovskite phase on the piezoceramic material is in the range of 99.99 inclusive Vol .-% up to and including 75.0 vol .-% and in particular a value in the range of 99.95 vol .-% inclusive up to and including 85 vol .-% and 90 vol .-%. With regard to the method for producing the piezoceramic material, the following should be noted: The green body is a shaped body which, for example, consists of homogeneously mixed, pressed-together oxides of the stated metals. Likewise, the green body may have an organic additive, which is processed with the oxides of the metals to a slurry. The organic additive is, for example, a binder or a dispersant. From the slurry, a green body is produced in a molding process. The green body is ^¬ example, a green sheet, which is produced by the forming process (film drawing). The green body with the piezoceramic starting composition produced in the shaping process is subjected to a heat treatment. The heat treatment of the green body includes calcination and / or sintering. It comes to the formation and compression of the forming piezoceramic material.

To provide the green body, a mixing of pulverulent, oxidic metal compounds of the metals of the perovskite phase and the tungsten bronze phase is carried out according to a particular embodiment. In addition to oxides of Me ^¬ metals, for example antimony oxide (Sb ₂ 0 ₅₎ may, niobium oxide (B ₂ 0 ₅₎ and tantalum oxide (a ₂ 0 _5), and precursors of the oxides of the metals, for example, carbonates (Li ₂ C0 _3, K ₂ C0 ₃ ) or oxalates are ^¬ set. Both types of metal compounds, ie the precursors of the oxides and the oxides themselves, can be referred to as oxidi ^¬ cal metal compounds.

The powders of the oxidic metal compounds can be prepared by known processes, for example by the sol-gel, citrate, hydrothermal or oxalate process. In this case, oxidic metal compounds can be produced with only one kind of metal. It is also conceivable, in particular, that oxidic metal compounds with more types of Metals are used (mixed oxides). Therefore, according to a Customized ^¬ ren embodiment, a piezoceramic out put ^¬ composition is used with at least one metal oxide compound with at least two of the metals. Examples of these are lithium niobate (LiNbOs) or lithium tantalate (Li-TaOs). The oxide metal compound having at least two of the metals may also be the perovskite phase or the tungsten bronze phase itself. To provide these mixed oxides can also be resorted to the above-mentioned precipitation reactions. Also conceivable is a mixed-oxide process. In this case, powdery oxides of the metals are mixed together and calcined at higher temperatures. Calcination results in mixed oxides.

The workup of the metal oxides with the conversion into the piezoceramic material can be done in various ways. It is conceivable, for example, that first the powders of the oxidic metal compounds are homogeneously mixed. The piezoceramic starting composition is formed in the form of a homogeneous mixture of the metal oxides. Subsequently, the piezoceramic starting ^{composition is} treated by heat ^¬ treat, for example, by calcination, in the piezoceramic material. The piezoceramic material is ground to a fine piezoceramic powder. Subsequently, a ceramic green body with an organic binder and further organic additives is produced from the fine piezoceramic powder in the shaping process. This ceramic green body is debinded and sintered. In this case, the pie ^¬ zokeramische component forms with the piezoceramic material.

As an alternative to the procedure described, the powders of the oxidic metal compounds can be homogeneously mixed and processed in the shaping process into a ceramic green body with organic binder. This green body also has the piezoceramic starting composition. Subsequent sintering leads to the piezoceramic component with the piezoceramic material. According to a particular embodiment, a piezoceramic component having at least one piezoelectric element is produced which has an electrode layer with electrode material, at least one further electrode layer with a further electrode material and at least one piezoceramic layer arranged between the electrode layers with the piezoceramic material. A single piezoelectric element represents the smallest unit of the piezoceramic component. To produce the piezoelectric element, for example, a ceramic green sheet with the piezoceramic starting composition is printed on both sides with the electrode materials. The Elect ^¬ clear materials can thereby be the same or different. Subsequent debindering and sintering results in the piezoelectric element.

According to a particular embodiment, a piezoelectric element is used, in which the electrode material and / or the wider ^¬ re electrode material at least one element selected from the group consisting of silver, copper and palladium elemental metal. The piezoceramic material or the piezoelectric element is produced in particular by co-sintering the piezoceramic starting composition and the electrode material (cofiring). The electrode material may consist of the pure metals, for example, only of silver or only of copper. An alloy of said metals is also possible, for example an alloy of silver and palladium.

The sintering to the piezoceramic material can be carried out both in reducing or oxidizing sintering atmosphere. In a reducing sintering atmosphere, almost no oxygen is present. An oxygen partial pressure is less than 1-10 ^-2 mbar, and preferably less than 1-10 ^-3 mbar. By sintering in a reducing sintering atmosphere inexpensive copper is possible as an electrode material.

In principle, by means of the piezoceramic out put ^¬ composition any piezoceramic component with the piezoceramic material are produced. The piezoceramic component mainly comprises at least one top ^¬ be signed piezo element. Preferably, the piezoceramic component with the piezoelement is selected from the group of piezoceramic bending transducers, piezoceramic multilayer actuator, piezoceramic transformer, piezoceramic motor and piezoceramic ultrasonic transducer. The piezoelectric element is for example part of a piezoelectric bending transducer. By stacking a variety of one-sided or two-sided printed with electrode material

Green films, subsequent debinding and sintering creates a monolithic stack of piezo elements. With suitable dimensioning and shape results in a monolithic piezoceramic multilayer actuator. This piezoceramic Rather schichtaktor is preferably used for driving a motor ^¬ injection valve of an internal combustion engine. Due to the stack-shaped arrangement of the piezoelectric elements, a piezoceramic ultrasonic transducer is also accessible, with suitable dimensioning and shape. The ultrasonic transducer is used for example in medical technology or for material testing.

With reference to several embodiments and the associated figures, the invention will be described in more detail below. The figures are schematic and are not true ^¬ dimensioning true to scale images.

FIG. 1 shows a ceramic piezoelectric element in a lateral cross section.

Figure 2 shows a piezoelectric component having a plurality of piezoelectric elements in a lateral cross section. Figure 3 shows the d33 ~ coefficient of the at different

Temperatures sintered piezoceramic material with different Nd doping at a field strength of 2 kV / mm. FIG. 4 shows the permittivities of the exemplary embodiments.

Given is a two-phase, lead-free piezoceramic material. The material has a perovskite phase with a ^subsequent perovskite phase composition: (Li _x K _! _{X x} _y Na _y ) (Nbi_t-uTa _t Sb _u ) 0 ₃ .

In addition to the perovskite phase, a tungsten bronze-phase with the following tungsten bronze-phase composition (M ¹¹ ^ (Li _x _K! _ _X _ Yna _y)! _ _M (Nb! _ _W Ta _w) ₅ 0 ₁₅ + VA _'2m The trivalent metal M ¹¹¹ is Ne ^¬ odym (Nd ³⁺ ).

The proportion of the tungsten bronze phase in the piezoceramic material is 10% by volume. The proportion of perovskite phase be ^¬ contributes 90 vol .-%.

The embodiments include the following effective compositions:

Due to the A-site doping with Nd, twice the number of vacancies on the A sites results in each case. The Nd doping of 0 mol% is not covered by the invention and functions merely as a reference. Sintered at a temperature of 1140 ° C, 1150 ° C or 1160 ° C. Since ^¬ at each resulted in a sintered density of about 4.95 g / cm ^3.

To characterize the dielectric properties of the piezoceramic materials, a sample in the form of a

Tablet made of piezoceramic material. For this purpose, pulverulent, oxidic starting materials are pressed together to form a ceramic green body in the form of a tablet and sintered at temperatures of 1140.degree. C., 1150.degree. C. or 1160.degree. On the main surfaces of each resulting tablet electrode layers of silver are applied, via which an electric field is coupled into the ceramic. The result is a piezoelectric element with electrode layers of Sil ^¬ over and arranged therebetween piezoceramic layer with the respective piezoceramic material.

At the sintering temperatures of 1140 ° C., 1150 ° C. and 1160 ° C., the d33 coefficients of the piezoceramic materials with dopings of less than 1.0 mol% are increased compared with the undoped piezoceramics (FIG. 3). In contrast, the values at% egg ^¬ ner Nd doping of 1.0 mol are. Lowered.

In comparison to the permittivity of the undoped ceramic, the permittivity of the piezoceramic materials with Nd doping is consistently increased. However, the permittivity decreases again when going to higher Nd dopings (over 0.75 mol.%). The electrical insulation resistance of the embodiments is increased compared to the undoped KNN ceramic. Based on the described method for producing the samples, a piezoelectric component 1 is produced with the pie ^¬ zokeramischen material. The piezoelectric component 1 is according to a first embodiment, a piezoelectric actuator 1 in monolithic multilayer construction (Figure 2). The piezoactuator 1 consists of a multiplicity of piezoelements 10 arranged one above the other in a stack (FIG. 1). Each of the piezoelectric elements 10 has an electrode layer 11, a further electrode layer 12 and an electrode layer between the electrodes. denschichten 11 and 12 arranged piezoceramic layer 13. The adjacent in the stack piezo elements 10 each have ^¬ weils on a common electrode layer. The electrode ^¬ layers 11 and 12 consist of (approximately) pure silver. In an alternative embodiment, the electrode layers 11 and 12 comprise an electrode material of a silver-palladium alloy in which palladium is contained in a proportion of 5% by weight. The green sheets are dried, printed with a paste containing the electrode material stacked lami ^¬ defined, binder removal and sintered to the piezoelectric actuator 1 (as the electrode material silver or silver-palladium alloy) under an oxidizing sintering atmosphere.

The resulting monolithic piezoceramic multi-layer actuator is used to actuate a fuel injection valve of an internal combustion engine of a motor vehicle. Other, not shown embodiments, such as piezokera ^¬ mixing bending transducer, piezoceramic transformer or piezoceramic ultrasonic transducer with the new piezokera mixing material are also accessible.

Claims

claims

1. Lead-free, multi-phase piezoceramic material, comprising

- At least one perovskite phase with the perovskite phase composition (Li _x K _! _ _x _ _y Na _y ) (Nbi- _t - _u Ta _t Sb _u ) 0 ₃ and

- At least one tungsten bronze phase with the tungsten bronze phase composition (M ¹¹ ^ (Li _x K _! _ _x _ _y Na _y ) i_ _m (Nbi_ _w Ta _w ) ₅ 0i ₅ +

VA '2m, where

- M ^{111 is} at least one trivalent metal, VA 'A space vacancies are and the following relationships apply:

- 0 <m <0.05;

- 0 <t <0.15;

- 0 <u <0.15;

- 0 <w <1;

- 0 <x <0.15;

- 0.25 <y <0.75.

2. Material according to claim 1, wherein the trivalent metal M ^{111 is} a rare earth element RE

3. Material according to claim 1 or 2, wherein the rare earth ^¬ tall RE neodymium is.

4. Material according to any one of claims 1 to 3, wherein an on ^¬ part of the tungsten bronze phase on piezoceramic material from the range of 0.01% by volume inclusive up to and including 25 vol .-% and in particular from the range of 0 inclusive , 05 Vol .-% up to and including 15 Vol .-% is selected.

5. A method for producing a piezoceramic component (1) with a piezoceramic material according to one of claims 1 to 4 with the following method steps:

a) providing a green body with a piezoceramic starting composition of the piezoceramic material and b) heat treating the green body, wherein the piezoceramic material of the piezoceramic material of the component (1) is formed.

6. The method of claim 5, wherein for providing the green body, a mixing powdered, oxidic metal compounds of the metals of the perovskite phase and the tungsten bronze phase is performed.

7. The method of claim 6, wherein a piezoceramic starting ^¬ starting composition is used with at least one mixed oxide with at least two of the metals.

8. The method according to any one of claims 5 to 7, wherein a piezoceramic component (1) with at least one piezoelectric element (10) is produced, the one electrode layer (11) with electrode material, at least one further electrode layer (12) with a further electrode material and at least egg ^¬ ne between the electrode layers (11, 12) arranged piezo zokeramikschicht (13) to the piezo-ceramic material on ^¬ has.

9. The method according to any one of claims 8, wherein a piezoelectric element (10) is used, in which the electrode material and / or the further electrode material at least one selected from the group consisting of silver, copper and palladium elemen- tares metal.

10. The method according to any one of claims 5 to 9, wherein the piezoceramic component (1) with the piezoelectric element (10) from the group piezoceramic bending transducer, piezoceramic multilayer actuator, piezoceramic transformer, piezoceramic motor and piezoceramic ultrasonic transducer is selected.

11. Use of a piezoceramic multilayer actuator produced by the method according to claim 10 for controlling a fuel injection valve of an internal combustion engine.