Piezoelectric component and method for producing a piezoelectric component

Abstract

A method for producing a piezoelectric component is disclosed. In an embodiment, the method includes producing a ceramic precursor material of the general formula Pb.sub.1-x-y-(2a-b)/2V.sub.(2a-b)/2Ba.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3, where RE is a rare earth metal and V is a Pb vacancy, mixing the ceramic precursor material with a sintering aid, forming a stack which includes alternating layers including the ceramic precursor material and a layer including Cu and debindering and sintering the stack thereby forming the piezoelectric component having Cu electrodes and at least one piezoelectric ceramic layer including Pb.sub.1-x-y-[(2a-b)/2]-p/2V.sub.[(2a-b)/2-p/2]Cu.sub.pBa.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3, where 0x0.035, 0y0.025, 0.42z0.5, 0.0045a0.009, 0.009b0.011, and 2a>b, p2ab.

Claims

1. A method for producing a piezoelectric component, the method comprising: producing a ceramic precursor material of the general formula Pb.sub.1-x-y-(2a-b)/2V.sub.(2a-b)/2Ba.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3, where RE is a rare earth metal and V is a Pb vacancy; mixing the ceramic precursor material with a sintering aid; forming a stack which includes alternating layers comprising the ceramic precursor material and a layer comprising Cu; and debindering and sintering the stack thereby forming the piezoelectric component having Cu electrodes and at least one piezoelectric ceramic layer comprising Pb.sub.1-x-y-[(2a-b)/2]-p/2V.sub.[(2a-b)/2-p/2]Cu.sub.pBa.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3, where 0x0.035, 0y0.025, 0.42z0.5, 0.0045a0.009, 0.009b0.011, and 2a>b, p2a-b.

2. The method according to claim 1, wherein producing the ceramic precursor material comprises: providing a mixture of starting materials, the mixture of starting materials are selected from the group consisting of Pb.sub.3O.sub.4, TiO.sub.2, ZrO.sub.2, WO.sub.3, RE.sub.2O.sub.3, BaCO.sub.3 and SrCO.sub.3; calcining the mixture at a first temperature and milling the mixture to a first average diameter; and calcining the mixture at a second temperature that is higher than the first temperature.

3. The method according to claim 2, wherein the mixture obtained by mixing the ceramic precursor material with the sintering aid is milled to a second average diameter that is smaller than the first average diameter.

4. The method according to claim 3, wherein the mixture obtained by mixing the ceramic precursor material with the sintering aid further comprises adding Cu.sub.2O with a fraction of 0.05 to 0.1 mol %.

5. The method according to claim 1, wherein mixing the ceramic precursor material comprises adding PbO or Pb.sub.3O.sub.4 as the sintering aid, a fraction selected for the sintering aid being between 0.5 and 3 mol %, based on 1 mol of ceramic precursor material.

6. The method according to claim 1, wherein forming the stack comprises applying Cu to the layer comprising the ceramic precursor material by sputter-coating with Cu or printing with a Cu paste.

7. The method according to claim 1, wherein debindering the stack takes place under steam with exclusion of oxygen.

8. The method according to claim 1, wherein sintering the stack takes place at an oxygen partial pressure which lies between an equilibrium partial pressure of PbO/Pb and an equilibrium partial pressure of Cu/Cu.sub.2O.

9. The method according to claim 8, wherein the oxygen partial pressure is set by a mixture of steam and forming gas.

10. The method according to claim 1, wherein sintering takes place at a temperature between 1000 C. and 1050 C.

11. The method according to claim 1, wherein x=0.0295, y=0.0211, z=0.475, a=0.00753, b=0.0095, and RE=Yb are selected, and wherein debindering and sintering the stack comprises producing a piezoelectric ceramic layer comprising Pb.sub.0.945V.sub.0.00128Cu.sub.0.003Ba.sub.0.0295Sr.sub.0.0211[Ti.sub.0.467Zr.sub.0.516W.sub.0.00753Yb.sub.0.0095]O.sub.3.

12. A method for producing a piezoelectric component, the method comprising: providing a mixture of starting materials, the mixture of starting materials are selected from the group consisting of Pb.sub.3O.sub.4, TiO.sub.2, ZrO.sub.2, WO.sub.3, RE.sub.2O.sub.3, BaCO.sub.3 and SrCO.sub.3; calcining the mixture at a first temperature and milling the calcinated mixture to a first average diameter; calcining the calcinated mixture at a second temperature that is higher than the first temperature and forming a green body; forming a metal layer on the green body; forming a stack of green bodies and metal layers; debindering the stack; and sintering the stack thereby forming the piezoelectric component with piezoelectric ceramic layers comprising Pb.sub.1-x-y-[(2a-b)/2]-p/2V.sub.[(2a-b)/2-p/2]Cu.sub.pBa.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3, where RE is a rare earth metal and V is a Pb vacancy, where 0x0.035, 0y0.025, 0.42z0.5, 0.0045a0.009, 0.009b0.011, 2a>b and p2a-b.

13. The method according to claim 12, wherein forming the metal layer comprises sputtering the metal layer.

14. The method according to claim 12, wherein the metal layer comprises a Cu layer.

15. The method according to claim 12, further comprising mixing the mixture calcinated at the first temperature with a sintering aid.

16. The method according to claim 15, wherein mixing the mixture calcinated at the first temperature with the sintering aid comprises adding PbO or Pb.sub.3O.sub.4.

17. The method according to claim 15, further comprising milling a mixture obtained by mixing the mixture calcinated at the first temperature with the sintering aid to a second average diameter that is smaller than the first average diameter.

18. The method according to claim 12, wherein debindering the stack comprises steaming the stack with exclusion of oxygen.

19. The method according to claim 12, wherein sintering comprises heating the stack to a temperature between 1000 C. and 1050 C.

20. The method according to claim 12, wherein debindering and sintering the stack comprises producing the piezoelectric component comprising Pb.sub.0.9451V.sub.0.00128Cu.sub.0.003Ba.sub.0.0295Sr.sub.0.0211[Ti.sub.0.467Zr.sub.0.516W.sub.0.00753Yb.sub.0.0095]O.sub.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, the specified component and the method, and their advantageous embodiments, are elucidated by means of figures, which are schematic and not true to scale, and also by a working example.

(2) FIG. 1 shows the schematic side view of a piezoelectric component;

(3) FIG. 2 shows partial pressures of differing systems;

(4) FIG. 3 shows a detail of an X-ray diffractogram; and

(5) FIGS. 4a-4c show diagrams of grain microstructures in piezoelectric ceramics.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(6) FIG. 1 shows a schematic side view of a piezoelectric component in the form of a multilayer component, as a piezoactuator. The component has a stack 1 of piezoelectric ceramic layers 10, disposed one atop another, with internal electrodes 20 between them. The internal electrodes 20 are designed as electrode layers. The piezoelectric ceramic layers 10 and the internal electrodes 20 are disposed one atop another.

(7) In the embodiment shown here, the external electrodes 30 are disposed on opposite side faces of the stack 1, and run in stripe form along the stack direction. The external electrodes 30 comprise, for example, Ag or Cu and may be applied to the stack 1 as a metal paste, and baked.

(8) The internal electrodes 20 run along the stack direction in alternation up to one of the external electrodes 30, with spacing from the second external electrode 30. In this way, the external electrodes 30 are electrically connected in alternation with the internal electrodes 20 along the stack direction. For producing the electrical connection, a connection element (not shown here) may be applied to the external electrodes 30, by soldering, for example.

(9) The internal electrodes 20 are internal Cu electrodes. The piezoelectric ceramic layers comprise Pb.sub.1-x-y-[(2a-b)/2]-p/2V.sub.[(2a-b)/2-p/2]Cu.sub.pBa.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3 material for which: 0x0.035, 0y0.025, 0.42z0.5, 0.0045a0.009, 0.009b0.0011, 2a>b, p2a-b, RE is a rare earth metal, and V is a Pb vacancy. For example, the piezoelectric ceramic layers comprise the material Pb.sub.0.9451V.sub.0.00128Cu.sub.0.003Ba.sub.0.0295Sr.sub.0.0211[Ti.sub.0.467Zr.sub.0.516W.sub.0.00753 Yb.sub.0.0095]O.sub.3.

(10) The aim of the working example below is to elucidate the production of the component comprising the material Pb.sub.0.9451V.sub.0.00128Cu.sub.0.003Ba.sub.0.0295Sr.sub.0.0211[Ti.sub.0.467Zr.sub.0.516W.sub.0.00753 Yb.sub.0.0095]O.sub.3.

(11) In accordance with the general formula Pb.sub.1-x-y-(2a-b)/2V.sub.(2a-b)/2Ba.sub.xSr.sub.y[(Ti.sub.zZr.sub.1-z).sub.1-a-bW.sub.aRE.sub.b]O.sub.3, the parameters x=0.0295, y=0.0211, z=0.475, a=0.00753, b=0.0095, and RE=Yb are selected, resulting in Pb.sub.0.9466V.sub.0.00278Ba.sub.0.295Sr.sub.0.0211[Ti.sub.0.467Zr.sub.0.516W.sub.0.00753Yb.sub.0.0095]O.sub.3. First of all, the raw materials Pb.sub.3O.sub.4, TiO.sub.2, ZrO.sub.2, WO.sub.3, Yb.sub.2O.sub.3, BaCO.sub.3, and SrCO.sub.3, whose impurities content has been checked and whose metal content determined separately in each case, are weighed out in the corresponding molar ratio and subjected to rotary mixing with ZrO.sub.2 grinding media in an aqueous slip for 24 hours (method step A1). Following evaporation and sieving, reaction takes place at 925 C., with a hold time of 2 hours, in a ZrO.sub.2 capsule, and the reaction product is subjected to milling in an eccentric mill with addition of water, using ZrO.sub.2 beads (diameter 2 mm) (method step A). At 300 cycl/min, a first average diameter d.sub.50 of 0.66 m (corresponding to d.sub.90=1.64 m) is obtained after just 30 minutes. The slip is evaporated down, the residue is passed through a sieve, and reaction takes place a second time, with a 2 h hold time at 950 C., in order to complete the reaction (method step A3).

(12) FIG. 3 shows as a detail of an X-ray diffractogram, in which the angle in is plotted against the intensity Int, the comparison between the first and second calcination steps, in other words between the products after method step A2) and after method step A3). After the first reaction (plot I) there are still relatively Ti-rich tetragonal particles present alongside relatively Zr-rich rhombohedral crystallites, as evident from a splitting of the 200/002 reflection. After the second reaction (plot II), the splitting can no longer be resolved, evidencing the improved uniform distribution of Ti and Zr in the lattice of the PZT perovskite structure.

(13) Following the addition of 2.5 mol % of PbO in the form of Pb.sub.3)O.sub.4, the reaction powder obtained at 950 C. is subjected to fine milling to 0.3 to 0.35 m in an eccentric mill in water or ethanol, using ZrO.sub.2 beads (diameter 0.8 mm) (method step B). This requires about 2 hours at 300 cycl/min. The dispersing medium is evaporated off, and the residue is passed through a sieve and, following addition of a PEG binder (polyethylene glycol), granules are prepared, from which slices with a diameter of 15.5 mm and a thickness of 1.4 to 1.5 mm are compression-molded.

(14) Prior to sintering, these green bodies are provided with Cu electrodes by sputtering (method step C).

(15) The compression moldings in slice form are first of all debindered by heating to 500 C. in air, and then sintered with a heating ramp of 6 K/min at 1000 C. and with a hold time of 3 h (method step D, comparative sample 1). Further compression moldings are sintered with the same debindering and heating ramp at 950 C. with a hold time of 4 h (comparison sample 2). Further compression moldings are sintered in an atmosphere with reduced oxygen partial pressure, set temperature-dependently through the ratio of steam to forming gas on heating at 3 K/min, with a hold time at 1010 C. of 4 h (working example).

(16) FIG. 2 additionally shows different partial pressures according to which the appropriate oxygen partial pressure can be selected as a function of temperature. In the graph, the temperature T in K is plotted against the logarithmic oxygen partial pressure log (p(O.sub.2)). The equilibrium partial pressure of the Cu/Cu.sub.2O system, P.sub.Cu/Cu2O, and of the PbO/Pb system, P.sub.PbO/Pb, are shown. The oxygen partial pressure P.sub.O2 is allowed to vary between these equilibrium partial pressures if oxidation of Cu to Cu.sub.2O and reduction of PbO to Pb (or of PbTiO.sub.3 to Pb and TiO.sub.2) are to be avoided. FIG. 2 shows one possible profile of the oxygen partial pressure, which throughout the sintering operation lies between the equilibrium partial pressures P.sub.Cu/Cu2O and P.sub.PbO/Pb. This profile has discontinuities at 940 K and at 1170 K. The discontinuities are situated between three lines, likewise shown in FIG. 2, which correspond to different amounts of forming gas (line with small dots, line with small squares, line with gaps). If the amounts of N.sub.2 and of the H.sub.2O vapor remain constant, the oxygen partial pressure during sintering can be adjusted by adjusting the amount of forming gas.

(17) Even under the defined operating conditions of the working example, sintering is accompanied by contamination of Cu from the electrodes, in the range of about 600 ppm. The Cu cations in the I oxidation state are incorporated as Cu acceptors, with elimination of an equivalent amount of 0.0015 mol of PbO, thus giving the following formula for the final composition of a piezoceramic produced under these conditions: Pb.sub.0.9451V.sub.0.00128Cu.sub.0.003Ba.sub.0.0295Sr.sub.0.0211[Ti.sub.0.467Zr.sub.0.516W.sub.0.00753 Yb.sub.0.0095]O.sub.3.

(18) The sintered density of the samples in slice form is determined by weighing and ascertaining the geometric dimensions on five individual samples in each case, and the relative density .sub.rel is calculated by comparison with the X-ray density of the PZT perovskite phase, at .sub.th=8.03 g/cm.sup.3. For the samples provided with 2.5 mol % of PbO as sintering aid, after sintering at 1000 C., a density =7.830.04 g/cm.sup.3 is found, corresponding to 97.5% of the theoretical density, and even on sintering at 950 C. a comparable value =8.810.04 g/cm.sup.3 is obtained, corresponding to 97.3% of the theoretical density. The sinter density obtained under defined operating conditions is 7.7 to 7.9 g/cm.sup.3. In the absence of addition of PbO in the form of Pb.sub.3O.sub.4, the value .sub.rel found for the relative density of the sintering at 1000 C. is only 84.9%.

(19) Accordingly, the free specific surface energy introduced by fine milling, and the formation of sinter-promoting defects induced by donor-acceptor doping at the B sites, are not sufficient to allow high sinter densification at just 1000 C. The addition of 2.5 mol % of PbO in the form of Pb.sub.3O.sub.4 as a sintering aid proves necessary in order to obtain a sufficiently dense piezoceramic.

(20) FIG. 4 shows diagrams of grain microstructures of piezoelectric ceramics. FIG. 4a) shows the microstructure obtained on sintering at 1010 C. when the oxygen partial pressure corresponds, on a temperature-dependent basis, during the hold time of 4 h, to the profile shown in FIG. 2. The effect of the as a result of the additional incorporation of the Cu acceptor centers on grain growth is clearly apparent. The average grain diameter is 2 to 3 m. In contrast, the grain microstructures shown in FIGS. 4 b) and 4 c) for comparative samples 1 and 2 (sintering in air at 1000 C. for 3 h and sintering in air at 950 C. for 4 h, respectively) show smaller average grain diameters of 1 to 2.5 m (FIG. 4b) and 0.5 to 2 m (FIG. 4c).

(21) Other characteristic variables of the compression molding according to the working example, provided with Cu electrodes, are indicated hereinafter: The deflection parameter d.sub.33, which corresponds to the piezoelectric charge constant, can be defined by the relation S.sub.3=d.sub.33*E.sub.3, with the relative extension S=l/l and the electric field strength E. The measurement performed after polarization at about 3 kV/mm gives a d.sub.33 of 520 pm/V. From a measurement of capacity, the value found for the dielectric constant is 2100. For the planar coupling factor, the value k.sub.p=0.65 was ascertained in accordance with the following relation:

(22) $k_p{\left[2.51\frac{f_a-f_g}{f_a}-{\left(\frac{f_a-f_g}{f_a}\right)}^2\right]}^{1\text{/}2}.$

(23) The invention is not restricted by the description with reference to the working examples; instead, the invention encompasses every new feature and every combination of features, including more particularly every combination of features in the claims, even if this feature or this combination itself is not explicitly stated in the claims or working examples.