WO2006103143A1

WO2006103143A1 - Piezoceramic, piezoelectric component containing same and method for producing the piezoceramic

Info

Publication number: WO2006103143A1
Application number: PCT/EP2006/060024
Authority: WO
Inventors: Francois Bamiere; Hermann BÖDINGER; Morgane Radanielina; Carsten Schuh
Original assignee: Siemens Aktiengesellschaft
Priority date: 2005-03-31
Filing date: 2006-02-16
Publication date: 2006-10-05
Also published as: DE102005014765A1; DE102005014765B4

Abstract

The invention concerns a piezoceramic comprising a piezoelectric phase containing a lead titanozirconate et nickel and lead niobate (PZT-PNN). The piezoceramic phase is represented by the following general empirical formula: Pb1-aDcZrxTiy (Ni1/3Nb2/3) ZO3, wherein: D represents at least one alkaline-earth metal having an alkaline-earth content c, a < 1, b > 0, c > 0 and 0.9 < (x + y + z) = 1.1 and 0.9 < (x + y + z) = 1.1. Said piezoceramic is characterized in that the piezoceramic phase represents more than 99 vol. % relative to the solids of the piezoceramic. The invention also concerns a piezoelectric component containing said piezoceramic, and a method for producing said piezoceramic, said method involving the use of mixed oxides. The method is characterized in that it consists in using starting materials of the type of piezoceramic metal oxides. The use in particular of NiO and NB2O5 causes the occurrence of intermediate pyrochlorine during the formation of the piezoceramic, which promotes the densification of the piezoceramic. A piezoceramic is thus obtained having a densification temperature less than 950 °C and a relatively high d33 coefficient. Said piezoceramic enables a monolithic piezoelectric element to be obtained wherein is used, as electrode material, silver, copper or a silver/palladium alloy with low palladium content. The inventive component comprising one or several piezoelectric elements can be in the form of a flexure transducer. It can also be in the form of an ultrasonic transducer designed to be used in medical technique. Said component can also be used as multilayer actuator for controlling a valve, in particular a motor vehicle internal combustion engine valve.

Description

description

Piezoceramic, piezoelectric component with the piezoceramic and method for producing the piezoceramic

The invention relates to a piezoceramic having a piezoceramic phase with lead zirconate titanate and lead nickel niobate (PZT-PNN). A general empirical formula of the piezo-ceramic phase is _a PBI D _c Zr _x Ti _y (Nii _{/ 3} Nb2 _{/ 3)} _Z C> _3, wherein D is at least one alkaline earth metal with a

Alkaline earth metal content c is and a <1, c> 0 and 0.9 ≤ (x + y + z) ≤ 1.1. In addition, a piezoelectric component with the piezoceramic and a method for producing the piezoceramic are specified.

A piezoceramic with perwoskit structure, the

Comprises lead zirconate titanate and lead nickel niobate, has usually a vitrification temperature (sintering temperature) of 1200 ⁰ C to 1300 ⁰ C. Due to this high vitrification temperature of the piezoceramic, only one metal will be processed as an electrode material in a common sintering (co-firing), which on has a relatively high melting temperature. Suitable metals are platinum or silver-palladium alloys with a relatively high palladium content. The metals mentioned are relatively expensive. Therefore, it is desirable to lower the sealing firing temperature of the piezoceramic.

A piezoceramic of the type mentioned above with a relatively low sealing temperature and a method for producing the piezoceramic is known for example from DE 44 16 246 C2. The piezoceramic has a glass phase in addition to the piezoceramic phase. Due to the presence of the glass phase, a sealing firing temperature of below 95O ⁰ C is reached. This can silver as

Electrode material to be processed. However, a piezoelectrically active volume of the piezoceramic is due to the Presence of the glass phase reduced. This leads to a relatively low d ₃₃ ~ coefficient.

The object of the present invention is therefore to specify a piezoceramic with lead zirconate titanate which has a relatively low sealing-fire temperature and at the same time a relatively large piezoelectrically active volume.

To solve the problem, a piezoceramic is indicated, comprising a piezoceramic phase with the general

Molecular formula Pbi- _a D _c Zr _x Ti _y (Nii _{/ 3} Nb2 _{/ 3} ) _Z C> ₃ , where D is at least one alkaline earth metal with an alkaline earth metal content c and a <1, c> 0 and 0.9 <(x + y + z) <1.1. The piezoceramic is characterized in that the piezoceramic has the piezoceramic phase with a phase fraction of more than 99% by volume based on a solids content of the piezoceramic. The phase fraction of the piezoceramic phase is preferably more than 99.9% by volume and in particular more than 99.99% by volume. The solids content of the piezoceramic is formed only by solids. When specifying the

Phase portion of the piezoceramic phase, an existing porosity is not taken into account. The sum of x, y, and z does not necessarily have to be 1. This means that a non-stoichiometric composition with respect to the occupied B-sites of the perovskite is possible.

To achieve the object, a method is also specified with the following process steps: Mixing oxide starting compounds with lead, rare earth metal, alkaline earth metal, zirconium, titanium, nickel and niobium to form an oxide mixture and heat treatment of the oxide mixture. The piezoceramic is thus preferably produced by the so-called mixed-oxide method. For this purpose, powders of the oxidic starting compounds are mixed in the desired stoichiometric composition and then calcined and / or sintered. The oxidic starting compounds are in particular lead oxide (PbO), rare earth oxide (RE2O _3), alkaline earth oxide (DO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), nickel oxide (NiO), niobium oxide (Nb ₂ O ₅ ) and the mixed oxides titanium-zirconium oxide ((Ti, Zr) O ₂ ) and nickel-niobium oxide ((Nii _{/ 3} Nb _{2 / 3} ) O ₂ ). As oxidic starting compounds are also precursors of the starting materials in question, which are first converted into the actual oxidic starting compounds. Such a precursor is, for example, an alkaline earth carbonate (DCO ₃ ), which is converted by increasing the temperature in the corresponding alkaline earth metal oxide. Alternative production methods, for example the so-called sol-gel method or the emulsion method are also conceivable.

Surprisingly, it has been found that the piezoceramic with zirconium, titanium, nickel and niobium at the B sites and lead and alkaline earth metals at the A sites of the perovskite crystal structure has a relatively low sealing firing temperature. With the low bake temperature it is possible to process silver, copper or a low palladium silver-palladium alloy as the electrode material. The palladium content is less than 30 mol%, for example 10 mol% or 5 mol%. Despite low sealing temperature, the piezoceramic has a relatively high d ₃₃ ~ coefficient, so that the piezoceramic is suitable for the use of piezoceramic components in multilayer construction.

The alkaline earth metal is preferably one selected from the group consisting of calcium, strontium and / or barium. Magnesium as an alkaline earth metal is also conceivable. Likewise, mixtures of these Erkalkalimetalle are conceivable. Of the

Alkaline earth part c is selected in particular from the range of 0.01 to 0.05. The Erdalkalianteil is thus between 1 mol% and 5 mol%. For example, the alkaline earth part is 2 mol% or 4 mol%. Higher alkaline earth metal parts of up to 10 mol% are also conceivable.

In a particular embodiment, the general empirical formula of the piezoceramic phase Pb _a RE _b D _c Zr _x Ti _y (Nii _{/ 3} Nb _2/3 ) _Z O ₃ , where RE is at least one rare earth metal with a rare earth metal b. As a rare earth element, any element of the lanthanide or actinide group can be used. Preferably, the rare earth metal is one from the group europium (Eu),

Gadolinium (Gd), lanthanum (La), neodymium (Nd), praseodymium (Pr), promethium (Pm) and / or samarium (Sm) selected element. In this case, a single rare earth metal or a mixture of said rare earth metals can be used. With the rare earth metal or with the rare earth metals, the electrical or dielectric properties of the piezoceramic can be influenced targeted. At the same time, the low sintering temperature induced by the Erkalkalimetalle remains.

In a particular embodiment, the oxide starting compound with nickel from the group (Nii _{/ 3} Nb2 _{/ 3} ) O2 and NiO is selected. Preferably, a NiO content of the oxide starting compound with nickel from the range of 0.1 mol% to 10 mol% and in particular with one of the

Range of from 0.5 mol% to 5 mol% selected. The percentages do not refer to the entire piezoceramic phase, but only to the proportion that is given by oxidic starting compound with nickel. In this case, NiO can also consist entirely or partly of a precursor of NiO, for example of nickel carbonate (NiCOs) or of nickel hydroxide (Ni (OH) ₂ ).

The oxide starting compound with niobium is preferably selected from the group (Nii _/ 3Nb2 _/ 3) O ₂ and Nb ₂ Os. In particular, a Nb ₂ O content selected at the oxidic starting compound with niobium in the range of 0.1 mol% to 10 mol% and in particular with a mol from the range from and including 0.5% to 5 mol%. In particular, a corresponding oxide mixture of PbO, RE ₂ O ₃ , DO, ZrO ₂ , TiO ₂ , (Nii _{/ 3} Nb _2/3 ) O ₂ , NiO and Nb ₂ Os leads to a piezoceramic with the desired properties. Instead of ZrO ₂ and TiO _2, it is also possible to use a mixed oxide of zirconium and titanium ((Ti, Zr) O ₂ ) become. The addition of NiO and Nb2Üs during the heat treatment of the oxide mixture preferably leads to the formation of an intermediate pyrochlore phase. It is believed that the pyrochlore phase, which is dissolved again during the heat treatment, favors the compression of the piezoceramic so that the low sealing temperature is reached.

According to a further aspect of the invention, a piezoelectric component with at least one monolithic piezoelement is specified, comprising an electrode layer, at least one further electrode layer and at least one piezoceramic layer with the piezoceramic arranged between the electrode layers. It is conceivable, for example, that with the new piezoceramic a piezoceramic bending transducer is designed. The bending transducer has one or more such piezoelectric elements. It is also conceivable that an ultrasonic transducer, which is used in medical technology, is equipped of such piezoelectric elements with the new piezoceramic.

Preferably, a plurality of the piezo elements is arranged one above the other to form a monolithic, stape-shaped actuator body in multilayer construction (multilayer actuator). The piezoelectric component with the actuator body in multilayer construction is used to control a valve, in particular for controlling a valve of an internal combustion engine.

On the basis of several embodiments, the invention is explained in more detail below. The figures are schematic and do not represent true to scale figures.

FIG. 1 shows a piezoelectric component with a monolithic piezoelement with the piezoceramic.

FIG. 2 shows the shrinkage behavior of a PNN-PZT

Piezoceramic doped with strontium and neodymium. FIG. 3 shows the dependence of the d ₃₃ ~ coefficient of the neodymium-doped PNN-PZT piezoceramic on the level of strontium and barium doping.

Given is a piezoceramic with a piezoceramic phase, which has the general empirical formula Pbi- _a RE _b Zr _x Ti _y (Nii _{/ 3} Nb2 _{/ 3} ) _z θ ₃ . The piezoceramic consists of 99% by volume of the piezoceramic phase based on the solids content. A foreign phase as a solid content is almost not included.

The starting point of the piezoceramic is a composition in which lead with a lead content of 0.9925 (a = 0.0075) is contained. The rare earth metal is neodymium with a rare earth metal content b of 0.015. The zirconium content x is 0.294, the titanium content y is 0.38 and the fraction z of (Nii _{/ 3} Nb2 _/ 3) is 0.326.

The piezoceramic phase is characterized by an isovalent Erdalkalidotierung D with a Erdalkalianteil c. The alkaline earth metal is according to a first embodiment strontium. Strontium is contained with a strontium content c of 0.01 to 0.04.

FIG. 2 shows the change in the shrinkage behavior of the piezoceramic as a function of the strontium doping. The reference 200 with a strontium content of 0 mol% densifies at temperatures of about 1200 ⁰ C. In contrast, the piezoceramic densifies with a fraction of 1 mol%

(201), 2 mol% (202) 3 mol% (203), and 4 mol% (204) at a vitrification temperature of about 900 ⁰ C.

FIG. 3 shows the dependence of the d ₃₃ ~ coefficient of the piezoceramic on the proportion of strontium

(Reference 301): The d ₃₃ coefficients were obtained at an electric field strength of 1 kV / mm. Each piezoceramic was sintered at a temperature of 1000 ⁰ C. As the proportion of strontium increases, the d ₃₃ coefficient of the piezoceramic increases.

To prepare the piezoceramic are powdered PbO, Nd ₂ O ₃ , SrCO ₃ , ZrO ₂ , TiO ₂ in the mixed-oxide process,

(Nii _{/ 3} Nb _2/3 ) O ₃ , NiO and Nb ₂ Os mixed, possibly ground. PbO is added as usual due to the relatively high vapor pressure of PbO in excess. Subsequently, the oxide mixture is calcined or sintered. As shown above, there is already at temperatures below 1000 ⁰ C to a compression.

Alternatively, zirconium and titanium are used as (Ti, Zr) O ₂ . A particularly fine and thus reactive powder of this mixed oxide is accessible by hydrothermal co-precipitation.

According to a second embodiment, instead of

Strontium barium used as alkaline earth metal. The piezoceramic was also sintered at a temperature of

1000 ^° C. Also in the case of barium, as the proportion of barium increases, the d ₃₃ coefficient of the piezoceramic increases (FIG. 3, reference numeral 302).

BaCO _{3 is} used to produce the piezoceramic. The

Manufacture takes place in accordance with the method for producing the strontium-doped piezoceramic.

With the new piezoceramic, a novel piezoelectric component 1 with the piezoceramic is accessible (FIG. 1). This component has at least one monolithic piezoelement 10 with a first electrode layer 101, a second electrode layer 102 and a piezoceramic layer 103 with the piezoceramic arranged between the electrode layers 101 and 102.

The electrode layers have silver as the electrode material. Alternatively, the electrodes are made of copper or a low-silver-palladium alloy Palladium content. By electrical control of the electrodes, an electric field is coupled into the piezoceramic layer. Due to the coupled-in electric field, the piezoelectric ceramic layer and thus of the entire piezoelectric element are deflected. Due to the relatively high d ₃₃ -

Coefficients a relatively strong deflection is achieved.

According to a further, not shown embodiment, a plurality of such piezoelectric elements 10 are arranged one above the other to form a monolithic actuator body in multilayer construction. To produce the actuator body in multilayer construction, ceramic green sheets are printed with the piezoceramic or with the oxidic starting materials of the piezoceramic with the corresponding electrode material, stacked on top of one another, laminated, debinded and sintered.

Claims

claims

1 . Piezoceramic, having a piezoceramic phase with the general empirical formula Pbi- _a D _c Zr _x Ti _y (Nii _{/ 3} Nb _2/3 ) _Z C> ₃ , where

D is at least one alkaline earth metal having an alkaline earth metal content c and a <1, c> 0 and 0.9 <(x + y + z) <1.1, characterized in that - the piezoceramic phase of the piezoceramic over 99 vol% based on a solids content of the piezoceramic has.

2. piezoceramic according to claim 1, wherein the phase content is greater than 99.9% by volume and in particular more than 99.99% by volume.

3. piezoceramic according to claim 1 or 2, wherein the alkaline earth metal is selected from the group calcium, strontium and / or barium element.

4. piezoceramic according to one of claims 1 to 3, wherein the Erdalkalianteil c is selected from the range of 0.01 to 0.05.

5. piezoceramic, wherein the general empirical formula of the piezoceramic phase Pbi- _a RE _b D _c Zr _x Ti _y (Nii _{/ 3} Nb2 _{/ 3} ) _Z C> ₃ , where RE is at least one rare earth metal with a rare earth metal b.

6. piezoceramic according to claim 5, wherein the rare earth metal is selected from the group europium, gadolinium, lanthanum, neodymium, praseodymium, promethium and / or samarium element.

7. A method for producing the piezoceramic according to one of claims 1 to 6 with the following method steps: a) mixing starting oxide compounds with lead, rare earth metal, alkaline earth metal, zirconium, titanium, nickel and niobium to form an oxide mixture; and b) heat treating the oxide mixture.

8. The method of claim 7, wherein the oxide starting compound with nickel from the group (Nii _{/ 3} Nb2 _/ 3) O2 and NiO is selected.

9. The method of claim 8, wherein a NiO content of the starting oxide compound with nickel is selected in the range of 0.1 mol% to 10 mol%, and more preferably in the range of 0.5 mol% to 5 mol% becomes.

10. The method according to any one of claims 7 to 9, wherein the starting oxide compound is selected with niobium from the group (Nii _{/ 3} Nb2 _/ 3) O2 and Nb2Üs.

11. The method according to claim 10, wherein an Nb ₂ O 5 content of the oxide starting compound with niobium from the range of 0.1 mol% to 10 mol% and in particular having a range of from 0.5 mol% to 5 mol % is selected.

12. Piezoelectric component having at least one monolithic piezoelectric element (10), comprising an electrode layer (101), at least one further electrode layer (102) and - at least one between the electrode layers (101, 102) arranged piezoceramic layer (103) with the piezoceramic according to one of Claims 1 to 6.