LEAD-FREE PIEZOCERAMIC MATERIAL BASED ON BISMUTH SODIUM TITANATE (BST)

Abstract

The invention relates to a lead-free piezoceramic material based on bismuth sodium titanate (BST) having the following parent composition: x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-yBaTiO.sub.3-zSrTiO.sub.3 where x+y+z=1 and 0<x<1, 0<y<1, 0z0.07 or x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-yBaTiO.sub.3-zCaTiO.sub.3 where x+y+z=1 and 0<x<1, 0<y<1, 0<z0.05 or x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-y(Bi.sub.0.5K.sub.0.5)TiO.sub.3-zBaTiO.sub.3 where x+y+z=1 and 0<x<1, 0<y<1, 0z<1, characterized by addition of a phosphorus-containing material in a quantity that gives a phosphorus concentration of from 100 to 2000 ppm in the piezoceramic material.

Claims

1. A lead-free piezoceramic material based on bismuth sodium titanate (BST) of the fundamental composition TABLE-US-00011 x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3yBaTiO.sub.3zSrTiO.sub.3 with x + y + z = 1 and 0 < x < 1, 0 < y < 1, 0 z 0.07 or x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3yBaTiO.sub.3zCaTiO.sub.3 with x + y + z = 1 and 0 < x < 1, 0 < y < 1, 0 z 0.05 characterized by the addition of a phosphoric material in a quantity such that the concentration of phosphorus in the piezoceramic material is 100 to 2000 ppm, wherein the specification ppm (parts per million) relates to the mass of phosphorus in relation to the total mass of the piezoceramic composition.

2. The lead-free piezoceramic material based on bismuth sodium titante (BST) according to claim 1, wherein the fundamental composition is TABLE-US-00012 x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3yBaTiO.sub.3zSrTiO.sub.3 with y 0.1 and x + y + z = 1 or x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3yBaTiO.sub.3zCaTiO.sub.3 with y 0.1 and x + y + z = 1

3. The lead-free piezoceramic material according to claim 1, characterized in that the phosphoric compound is an inorganic phosphate, hydrogen phosphate, or dihydrogen phosphate.

4. The lead-free piezoceramic material according to claim 1, characterized in that the phosphoric compound is selected from the group which consists of KH.sub.2PO.sub.4, (NH.sub.4)H.sub.2PO.sub.4.

5. (canceled)

6. The lead-free piezoceramic material according to claim 1, characterized in that the fundamental composition contains additives in the form of oxides or complex perovskites.

7. (canceled)

8. A method for producing a lead-free piezoceramic material according to claim 1, characterized by the following steps: producing a raw material mixture of the fundamental composition, producing a calcinate of the fundamental composition, finely grinding the calcinate, producing a granulate in particular by spray granulation or producing a casting slurry for the multilayer or co-firing process, further processing in a known manner including sintering in normal atmosphere, wherein phosphoric additives are added during the fine grinding or the spray granulation and/or during the preparation of casting slurries.

9. A piezoceramic multilayer actuator based on a lead-free piezoceramic material according to claim 1.

10. A piezoceramic component, preferably having at least one piezoceramic body having at least two electrodes, more preferably in the form of a piezoelectric ultrasonic transducer, based on a lead-free piezoceramic material according to claim 1.

11. A use of a phosphoric material in a piezoceramic material based on bismuth sodium titanate (BST) of the fundamental composition
x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-yBaTiO.sub.3-zSrTiO.sub.3 with x+y+z=1 and 0<x<1,0<y<1,0z0.07
or
x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-yBaTiO.sub.3-zCaTiO.sub.3 with x+y+z=1 and 0<x<1,0<y<1,0z0.05 to reduce the giant grain growth, wherein the phosphoric material is used in a quantity such that the concentration of phosphorus in the piezoceramic material is 100 to 2000 ppm, wherein the specification ppm (parts per million) relates to the mass of phosphorus in relation to the total mass of the piezoceramic composition.

12. The use according to claim 11, wherein the fundamental composition is TABLE-US-00013 x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3yBaTiO.sub.3zSrTiO.sub.3 with y 0.1 and x + y + z = 1 or x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3yBaTiO.sub.3zCaTiO.sub.3 with y 0.1 and x + y + z = 1

13. The use according to claim 11, characterized in that the phosphoric compound is an inorganic phosphate, hydrogen phosphate, or dihydrogen phosphate.

14. The use according to claim 11, characterized in that the phosphoric compound is selected from the group which consists of KH.sub.2PO.sub.4, (NH.sub.4)H.sub.2PO.sub.4.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS(S)

[0050] FIG. 1 is a flow chart illustrating one embodiment of the method for producing a lead-free piezoceramic material of the present invention.

[0051] FIGS. 2 and 3 are a graph showing the curve of the sintering density for the fundamental composition 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.12BaTiO.sub.3-0.03SrTiO.sub.3 in dependence on the sintering temperature and the corresponding light microscopy structure recordings, respectively.

[0052] FIG. 4 is a graph illustrating the extreme drop of the insulation resistance with the sample temperature.

[0053] FIGS. 5a and 5b are graphs showing the electrical conductivity versus electrical field strength of samples at various temperatures.

[0054] FIGS. 6A-6L (hereinafter collectively referred to as FIG. 6) are graphs which depict the curve of impedance and phase of the thickness oscillation for the samples sintered at different temperatures.

[0055] FIG. 7 is a series of light microscopy structure recordings of samples 2a to 2h.

[0056] FIG. 8 is a graph showing the curve of the sintering density in dependence on the sintering temperature of samples 2a to 2c, 2e and 2g.

[0057] FIG. 9 is a graph showing the substantial increase of the specific insulation resistance of samples 2a to 2h at higher temperatures.

[0058] FIGS. 10a-10e are graphs showing the electrical conductivity versus electrical field strength of samples containing various concentrations of phosphorous at various temperatures.

[0059] FIGS. 11A-11J (hereinafter collectively referred to as FIG. 11) are graphs which depict the characteristic resonance curves of the samples sintered at different temperatures.

[0060] FIG. 12 is a graph showing the depolarization temperature Td for different phosphorus sources and proportions.

[0061] FIGS. 13 and 14 are graphs showing the electromechanical elongation and the sample current in the temperature range from 25 to 150 C. for a composition according to the present invention.

EXAMPLES

[0062] The measurement results set forth hereafter relate to the fundamental system x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-yBaTiO.sub.3-zSrTiO.sub.3.

[0063] FIG. 1 describes the general technological sequence of the sample production. The technological steps in which the addition of phosphoric materials as described in the claims can be performed are identified with *.

[0064] The mixing of the raw materials and the fine grinding of the calcinate were each performed in an agitator bead mill.

[0065] Phosphoric additions were performed specifically during the following technological steps:

TABLE-US-00004 FM fine grinding G addition during the granulation VS addition during the organic slurrying for the film production

[0066] The structure characterization was performed according to the following classification:

TABLE-US-00005 0 material not processable 1 fine-grained, homogeneous structure 2 inhomogeneous structure, giant grain growth 3 coarse-grained structure

[0067] The sample density was determined on sintered cylinders according to the buoyancy method and is specified either as a mean value for the specified sintering temperature or as the density in g/cm.sup.3> for the lowest sintering temperature having measurable electrical values in the specified temperature range.

[0068] For the electrical measurements, metallized samples having a diameter of 12 mm, an insulation edge of 0.5 mm, and a thickness of 0.5 mm were used. The polarization was performed at 80 C., 15 minutes, 5 kV/mm.

[0069] Samples having strong variation of the measured values, disturbance of the resonance curves, or excessively low maximum phase angle in the radial or thickness oscillation are identified by S.

[0070] The coupling factors of the radio and thickness oscillation are k.sub.p and k.sub.t, respectively.

[0071] The depolarization temperature T.sub.d is generally defined as the inflection point in the temperature dependence of the dielectric constant of polarized samples.

[0072] The specific insulation resistance .sub.is is determined at 50 V on polarized samples with temperature increase from room temperature up to 200 C.

[0073] The electromechanical elongation S.sub.3 is determined by means of laser interferometer at 2 kV/mm. The value at room temperature and the associated sample current I are specified in the table.

[0074] Characteristic values in the studied temperature range are shown in Table 2.

[0075] The diagrams and light microscopy structure recordings relate to the composition defined in the table under the respective sample number.

[0076] The prior art and the deficiencies to be remedied are to be described in greater detail hereafter:

TABLE-US-00006 TABLE 1 sintering Density No. x y z in ppm temperature C. in g/cm.sup.3 Structure S 1a 0.850 0.120 0.030 0 1120 5.2 1 460 1b 0.850 0.120 0.030 0 1140 5.5 1 S 570 1c 0.850 0.120 0.030 0 1160 5.6 1 530 1d 0.850 0.120 0.030 0 1180 5.7 2 590 1e 0.850 0.120 0.030 0 1200 5.7 3 S 480 1f 0.850 0.120 0.030 0 1220 5.7 3 S 480 .sub.is in m .sub.is in m RT, 2 kV/mm No. tan 10.sup.3 kp kt Td in C. (RT) (150 C.) S3 10.sup.3 I in A 1a 16 0.12 0.37 215 6.1E+08 8.0E+05 0.25 6.9E07 1b 119 0.10 0.21 210 2.0E+08 1.0E+06 0.19 3.2E06 1c 13 0.12 0.40 210 1.1E+10 1.8E+06 0.23 3.8E07 1d 16 0.13 0.41 210 1.8E+10 4.0E+06 0.27 4.1E07 1e 44 0 0 220 1.9E+09 3.6E+06 0.31 5.5E07 1f 79 0 0 230 9.1E+08 1.9E+06 0.32 3.1E07

[0077] FIG. 2, samples 1a to if from Table 1, shows the curve of the sintering density for the fundamental composition 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.12BaTiO.sub.3-0.03SrTiO.sub.3 in dependence on the sintering temperature. The low density at low sintering temperatures, the narrow sintering interval, and the drop of the density at high sintering temperatures caused by the decomposition of the samples (vaporization Bi, Na) are characteristic.

[0078] The corresponding light microscopy structure recordings (FIG. 3) show the transition from the fine-grained, insufficiently compacted material to the giant grain growth in the middle of the studied temperature range and to coarse-grained structure at higher sintering temperatures.

[0079] The extreme drop of the insulation resistance with the sample temperature has proven to be disadvantageous (FIG. 4, samples 1a to 1f). The results are insufficient or undefined polarization and excessively low or strongly varying electrical values.

[0080] The non-tolerable electrical conductivity is clearly recognizable in the depiction of the sample current at higher electrical field strengths and higher temperatures (FIG. 5a, samples 1a to 1f, 5b, sample 1d). The operating temperature of actuators is thus significantly restricted.

[0081] The depiction of the curve of impedance and phase of the thickness oscillation for the samples sintered at different temperatures (FIG. 6, samples 1a to 1f) discloses a relationship between structure and resonance behavior (3 individual samples are shown in each case). The material is characterized by [0082] strong variation of the curve profiles at the respective sintering temperature, [0083] strong variation of the curve profiles upon variation of the sintering temperature, and [0084] extremely disturbed resonance behavior at higher sintering temperatures.

[0085] The data are summarized in Table 1.

[0086] It is therefore shown that none of the applied sintering temperatures results in sufficiently good and reproducible electrical or electromechanical values and the previous technology is not suitable for large-scale industrial production.

[0087] Comparable behavior is shown by samples 2a, 5a, 9a, 10a, 14, and 15, which are listed in Table 2 but do not fall in the scope of the claims.

TABLE-US-00007 TABLE 2 sintering Density No. x y z P addition addition at in ppm temperature C. in g/cm.sup.3 Structure S 2a 0.850 0.120 0.030 0 1160- 5.6 2 S 1240 5a 0.850 0.120 0.030 0 1180- 5.6 2 1220 9a 0.770 0.200 0.030 0 1180- 5.6 1 1220 10a 0.970 0.030 0.000 0 1120- 5.7 2 S 1180 14 0.850 0.150 0.000 0 1160- 5.5 1 1220 15 0.850 0.150 0.000 0 1160- 5.6 3 1220 2b 0.850 0.120 0.030 PE169 FM 250 1160- 5.7 1 1240 4 0.850 0.120 0.030 PE169 FM 250 1160- 5.6 1 1220 6 0.850 0.120 0.030 PE169 FM 500 1180- 5.6 1 1220 7 0.850 0.120 0.030 PE169 FM 250 1180- 5.7 1 1220 8 0.790 0.180 0.030 PE169 FM 250 1180- 5.7 1 1220 9b 0.770 0.200 0.030 PE169 FM 250 1180- 5.6 1 1220 14a 0.850 0.150 0.000 PE169 FM 250 1160- 5.7 1 1220 2c 0.850 0.120 0.030 KDP G 115 1180- 5.7 2 1220 2d 0.850 0.120 0.030 KDP G 225 1180- 5.7 2 1220 2e 0.850 0.120 0.030 KDP G 285 1180- 5.7 1 1220 2f 0.850 0.120 0.030 KDP G 570 1180- 5.7 1 1220 2g 0.850 0.120 0.030 KDP G 1140 1180- 5.7 1 1220 2h 0.850 0.120 0.030 KDP G 1705 1180- 5.7 1 1220 2i 0.850 0.120 0.030 KDP G 2275 1180- 0 1220 3 0.850 0.120 0.030 KDP G 285 1160- 5.6 1 1220 5b 0.850 0.120 0.030 KDP G 455 1160- 5.7 1 1220 10b 0.970 0.030 0.000 KDP G 115 1120- 5.8 2 S 1180 10c 0.970 0.030 0.000 KDP G 1140 1120- 5.8 1 1180 10d 0.970 0.030 0.000 KDP G 1705 1120- 5.8 1 1180 11 0.900 0.100 0.000 KDP G 285 1160- 5.7 1 1220 12 0.880 0.120 0.000 KDP G 285 1160- 5.7 1 1220 13 0.860 0.140 0.000 KDP G 285 1160- 5.7 1 1220 15a 0.850 0.150 0.000 KDP G 285 1160- 5.7 1 1220 2j 0.850 0.120 0.030 ADP G 135 1180- 5.7 2 1220 2k 0.850 0.120 0.030 ADP G 675 1180- 5.8 1 1220 2l 0.850 0.120 0.030 ADP G 1345 1180- 5.8 1 1220 2m 0.850 0.120 0.030 ADP G 2695 1180- 0 1220 2n 0.850 0.120 0.030 PE169 VS 570 1160- 5.7 1 1220 .sub.is in m .sub.is in m RT, 2 kV/mm No. tan 10.sup.3 kp kt Td in C. (RT) (150 C.) S3 10.sup.3 I in A 2a 550 12 0 0 195 1.9E+10 5.7E+06 0.32 3.7E07 5a 540 9 0.12 0.46 205 1.5E+11 9.5E+06 0.30 3.7E07 9a 500 21 0.17 0.41 215 3.8E+10 1.1E+09 0.26 3.0E07 10a 360 11 0.20 0.40 195 2.3E+10 3.6E+06 0.18 3.0E07 14 530 19 0.14 0.40 235 9.9E+10 1.6E+08 0.26 3.0E07 15 440 9 0.11 0.46 235 1.3E+11 1.3E+07 0.25 2.0E07 2b 750 27 0.16 0.42 180 3.8E+10 3.8E+09 0.34 5.0E07 4 670 22 0.16 0.42 200 5.7E+10 19.E+09 0.34 4.4E07 6 780 25 0.16 0.42 185 1.1E+11 7.6E+09 0.35 4.9E07 7 640 24 0.16 0.40 200 5.7E+10 3.8E+09 0.30 3.7E07 8 550 24 0.16 0.40 205 9.5E+10 9.5E+09 0.25 3.0E07 9b 560 23 0.16 0.40 205 3.8E+10 3.8E+09 0.25 3.0E07 14a 630 24 0.16 0.43 210 1.4E+11 5.5E+09 0.30 4.0E07 2c 600 37 0.16 0.35 205 3.8E+09 9.5E+06 0.32 4.4E07 2d 700 25 0.16 0.41 200 1.5E+10 5.7E+07 0.32 4.4E07 2e 710 26 0.16 0.41 200 1.1E+11 3.8E+09 0.32 4.4E07 2f 740 28 0.16 0.41 195 1.1E+11 1.9E+09 0.31 4.8E07 2g 770 26 0.15 0.39 190 1.1E+11 3.8E+09 0.30 5.2E07 2h 780 27 0.15 0.37 185 7.6E+10 4.7E+09 0.30 5.2E07 2i 3 720 27 0.16 0.41 195 8.5E+10 6.5E+09 0.34 4.9E07 5b 770 28 0.16 0.41 195 3.8E+10 1.7E+09 0.35 5.4E07 10b 330 11 0.19 0.40 195 1.4E+10 2.3E+06 0.19 3.0E07 10c 440 37 0.18 0.35 185 7.2E+10 1.2E+09 0.20 6.0E07 10d 460 40 0.16 0.31 180 5.7E+10 5.7E+08 0.18 7.0E07 11 740 32 0.15 0.41 195 1.6E+10 4.4E+09 0.35 5.3E07 12 690 25 0.16 0.42 210 1.3E+10 3.4E+09 0.32 5.2E07 13 630 24 0.16 0.41 225 3.0E+10 7.0E+08 0.30 5.1E07 15a 610 23 0.16 0.42 230 7.2E+10 5.7E+09 0.30 3.0E07 2j 690 35 0.16 0.41 200 7.6E+10 3.8E+09 0.35 4.2E07 2k 820 25 0.16 0.41 175 7.6E+10 3.8E+09 0.35 5.4E07 2l 940 31 0.16 0.37 150 3.8E+10 5.7E+09 0.35 6.2E07 2m 2n 730 25 0.16 0.44 185 1.3E+11 3.0E+09 0.36 4.7E07

[0088] The following exemplary embodiments show the behavior of compositions produced according to the invention.

Exemplary Embodiment 1

[0089] The fundamental composition 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.12BaTiO.sub.3-0.03SrTiO.sub.3 was processed according to the flow chart (FIG. 1) and [0090] either a phosphoric dispersing agent was added during the fine grinding (PE169, producer Akzo Nobel) [0091] or potassium dihydrogen phosphate was introduced during the granulation by addition to the binder.

[0092] Samples 2i with 2275 ppm P (TP) and 2m with 2695 ppm P (ADP) were not processable in this manner.

[0093] As may be seen from the light microscopy structure recordings (FIG. 7, samples 2a to 2h), an addition according to the invention of phosphorus 250 ppm causes the creation of a homogeneous, fine-grained structure.

[0094] FIG. 8 (samples 2a, 2b, 2c, 2e, and 2g) shows a significant improvement of the compaction upon addition of quantities according to the invention of phosphorus 250 ppm.

[0095] In addition, a substantial increase of the specific insulation resistance is surprisingly shown at higher temperatures, by multiple orders of magnitude (FIG. 9, samples 2a to 2h). Sufficiently good, reproducible polarization of the samples is thus ensured from 250 ppm.

[0096] FIGS. 10a to 10e make it clear that with phosphorus proportions according to the invention 250 ppm, a substantial reduction of the sample current is to be noted even at higher temperatures. The operation of actuators is thus also possible at higher operating temperatures.

[0097] The variation of the sample properties is substantially reduced. If one observes characteristic resonance curves of the samples sintered at different temperatures it is thus noticeable that with phosphorus proportions according to the invention 250 ppm, the differences between the samples sintered at different temperatures are substantially reduced and therefore the sintering interval may surprisingly be broadened to a technologically usable, easily implementable temperature range (Tables 3a, 3b, FIG. 11).

TABLE-US-00008 TABLE 3a Sample .sub.is in m .sub.is in m 2b tan 10.sup.3 kp kt (RT) (150 C.) S3 10.sup.3 I in A 1160 750 29 0.16 0.40 2.0E+10 3.4E+09 0.36 6.3E07 1180 730 27 0.17 0.42 3.8E+10 3.8E+09 0.34 5.0E07 1200 750 27 0.17 0.41 2.0E+10 3.4E+09 0.34 5.4E07 1220 770 27 0.16 0.42 2.6E+10 3.7E+09 0.32 5.9E07 1240 730 27 0.16 0.42 2.0E+10 3.4E+09 0.32 5.9E07

TABLE-US-00009 TABLE 3b Sample .sub.is in m .sub.is in m 2e tan 10.sup.3 kp kt (RT) (150 C.) S3 10.sup.3 I in A 1180 710 27 0.16 0.43 1.7E+11 5.1E+09 0.32 4.4E07 1200 710 26 0.16 0.41 3.4E+10 1.3E+09 0.33 4.8E07 1220 700 25 0.17 0.42 1.1E+11 3.8E+09 0.34 4.6E07

[0098] Surprisingly, the depolarization temperature may be set in a broad range by selection of the phosphoric material. FIG. 12 (samples 2a, 2c to 2h, 2j to 2l) displays the depolarization temperature Td, for different phosphorus sources and proportions. The possibility is therefore opened up of varying the depolarization temperature specifically for the application.

Exemplary Embodiment 2

[0099] Samples 3, 4, 5b, 6, and 2n according to Table 2 are further examples of the modification according to the invention, which is applicable in large-scale industrial processes, of the fundamental composition 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.12BaTiO.sub.3-0.03SrTiO.sub.3.

[0100] It can be seen as an essential technological advantage that in examples 3 and 5b, the material was processed without phosphorus up to the fine grinding and the phosphorus was first added during the slurrying for the spray granulation.

[0101] In examples 4, 6, the phosphorus addition was performed during the fine grinding, in example 2n during the organic slurrying for the film casting.

[0102] It is advantageous that the large-scale industrial material processing is performed uniformly up to the fine grinding independently of the primary shaping process (compression or film casting) and therefore the type and quantity of the phosphorus addition can be optimally adapted to the respective shaping process.

[0103] However, the possible combination of viscosity-determining phosphoric dispersing agents or binders and substantially viscosity-neutral additives such as KDP or ADP can also be advantageous.

[0104] FIGS. 13 and 14, sample 3, show the electromechanical elongation and the sample current in the temperature range from 25 to 150 C. for a composition according to the invention.

Exemplary Embodiment 3

[0105] Table 2 contains, as further examples according to the invention, variations of the fundamental composition x(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-yBaTiO.sub.3-zSrTiO.sub.3 with respect to the BaTiO.sub.3 and SrTiO.sub.3

TABLE-US-00010 No. x y z P addition addition at in ppm 7 0.850 0.120 0.030 PE169 FM 250 8 0.790 0.180 0.030 PE169 FM 250 9a 0.770 0.200 0.030 0 9b 0.770 0.200 0.030 PE169 FM 250 10a 0.970 0.030 0.000 0 10b 0.970 0.030 0.000 KDP G 115 10c 0.970 0.030 0.000 KDP G 1140 10d 0.970 0.030 0.000 KDP G 1705 11 0.900 0.100 0.000 KDP G 285 12 0.880 0.120 0.000 KDP G 285 13 0.860 0.140 0.000 KDP G 285 14 0.850 0.150 0.000 0 14a 0.850 0.150 0.000 PE169 FM 250 15 0.850 0.150 0.000 15a 0.850 0.150 0.000 KDP G 285
Excerpt from Table 2

[0106] In the range y0.10, the material system behaves similarly with respect to the phosphorus modification as the fundamental composition 0.85(Bi.sub.0.5Na.sub.0.5)TiO.sub.3-0.12BaTiO.sub.3-0.03SrTiO.sub.3.

[0107] The range y<0.10 requires phosphorus proportions in the upper claimed value range.