Piezoelectric crystal elements of shear mode

Abstract

Piezoelectric crystal elements are provided having preferred cut directions that optimize the shear mode piezoelectric properties. In the discovered cut directions, the crystal elements have super-high piezoelectric performance with d.sub.15, d.sub.24 and d.sub.36 shear modes at room temperature. The d.sub.15 shear mode crystal gives a maximum d value and is free from the cross-talk of d.sub.11 and d.sub.16. The d.sub.36 mode is extremely reliable compared to other shear elements due to its ready re-poling capability. The crystal elements may be beneficially used for high-sensitive acoustic transducers.

Claims

1. An acoustic transducer containing a piezoelectric single crystal product made by the process of: (a) providing a single piezoelectric crystal element with a cutting direction along zxt?45?; (i) said single piezoelectric crystal element providing a PbZ.sub.y(Mg.sub.1/3Nb.sub.2/3).sub.1-x-yTi.sub.xO.sub.3; wherein Y is defined as from 0 to at least 0.10, X is defined as 0.20 to at least 0.35, and Z is defined as at least one doped element selected from the group consisting of: Zr, Hf, Sn, In, Sc, Tm, Nb, Ta, Zn, Yb, Lu, Sb, Bi, Mn, Ga, Ce, Ni, W, Cu, Fe, K, Na, Li, and Ba; (b) mechanically finishing said single piezoelectric crystal element with cuttings along zxt?45?; (c) coating electrodes on a pair of Z surfaces; (d) poling said single piezoelectric crystal element to a first poled state in the direction along <011> cubic axis under an electrical field at room temperature and forming a poled single crystal element; and (e) providing said poled single crystal element with an operable d.sub.36 shear mode and having a d.sub.36 value up to about 2600 pC/N at room temperature.

2. The acoustic transducer of claim 1 made by a process further comprising the step of: (f) repoling said poled single crystal element in said first poled state to a second polled state.

3. A medical imaging system, containing an acoustic transducer containing a piezoelectric single crystal product made by the process of: (a) providing a single piezoelectric crystal element with a cutting direction along zxt?45?; (i) said single piezoelectric crystal element providing a PbZ.sub.y(Mg.sub.1/3Nb.sub.2/3).sub.1-x-yTi.sub.xO.sub.3; wherein Y is defined as from 0 to at least 0.10, X is defined as 0.20 to at least 0.35, and Z is defined as at least one doped element selected from the group consisting of: Zr, Hf, Sn, In, Sc, Tm, Nb, Ta, Zn, Yb, Lu, Sb, Bi, Mn, Ga, Ce, Ni, W, Cu, Fe, K, Na, Li, and Ba; (b) mechanically finishing said single piezoelectric crystal element with cuttings along zxt?45; (c) coating electrodes on a air of Z surfaces; (d) poling said single piezoelectric crystal element to a first poled state in the direction along <011> cubic axis under an electrical field at room temperature and forming a poled single crystal element; and (e) providing said poled single crystal element with an operable d.sub.36 shear mode and having a d.sub.36 value up to about 2600 pC/N at room temperature.

4. A commercial imaging system, containing an acoustic transducer containing a piezoelectric single crystal product made by the process of: (a) providing a single piezoelectric crystal element with a cutting direction along zxt?45?; (i) said single piezoelectric crystal element providing a PbZ.sub.y(Mg.sub.1/3Nb.sub.2/3).sub.1-x-yTi.sub.xO.sub.3; wherein Y is defined as from 0 to at least 0.10, X is defined as 0.20 to at least 0.35, and Z is defined as at least one doped element selected from the group consisting of: Zr, Hf, Sn, In, Sc, Tm, Nb, Ta, Zn, Yb, Lu, Sb, Bi, Mn, Ga, Ce, Ni, W, Cu, Fe, K, Na, Li, and Ba; (b) mechanically finishing said single piezoelectric crystal element with cuttings along zxt?45; (c) coating electrodes on a pair of Z surfaces; (d) poling said single piezoelectric crystal element to a first poled state in the direction-along <011> cubic axis under an electrical field at room temperature and forming a poled single crystal element; and (e) providing said poled single crystal element with an operable d.sub.36 shear mode and having a d.sub.36 value up to about 2600 pC/N at room temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A provides for a transverse shear piezoelectric coefficient, d.sub.15, a 3D plot of the piezoelectric surface of d.sub.15. Here, Z=<1,1,1>, X=<1,?1,0> and Y=<1,1,?2> and provides pseudo-cubic notation.

(2) FIG. 1B shows a 2D plot and X-cut cross section of the piezoelectric d.sub.15 surface on the (110) plane indicating the occurrence of maximum d.sub.15 and free from d.sub.16 cross talk.

(3) The maximum d.sub.15, obtained:

(4) d.sub.15=5192 pC/N at ?=0?, ?=?22.5?, and ?=0?

(5) d.sub.15=?5192 pC/N at ?=0?, ?=157.5?, and ?=0?

(6) FIG. 2A shows a Z-cut plot of the piezoelectric surface of d.sub.15.

(7) FIG. 2B shows a Z-cut of a 2D plot of the piezoelectric surface of d.sub.15 indicating the independence of d.sub.15 from cut direction rotating around Z axis.

(8) FIG. 2C shows the free XY-cut (<111> poling 3 m) for d.sub.15 mode, angle Theta can be 0-360?.

(9) FIG. 3A shows a Y-cut of a 3D plot of the piezoelectric surface of d.sub.15.

(10) FIG. 3B shows a Y-cut of a 2D plot of the piezoelectric d.sub.15 which shows a d.sub.15 free of cross talk from d.sub.16.

(11) FIG. 4A shows 3D plot of the piezoelectric surface of d.sub.36. Here, Z=<0,1,1>, X=<1,0,0> and Y=<0,1,?1> and provide a pseudo-cubic notation.

(12) FIG. 4B shows A 2D plot, Z-cut cross section of the piezoelectric d.sub.3 surface on the (011) plane. The maximum d.sub.36 obtained:

(13) d.sub.36=2600 pC/N at ?=45? or 225?, ?=0?, and ?=0?.

(14) d.sub.36=?2600 pC/N at ?=135? or 315?, ?=0?, and ?=0?

(15) FIG. 5 shows the xzt-22.5? cut of d.sub.15 mode for <111> poled PMN-PT crystal.

(16) FIG. 6 shows the zxt ?45? cut of d.sub.36 mode for <011> poled PMN-PT crystal.

(17) FIG. 7 is a table with figures and data providing a comparison between experimental value and calculated data that validates the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(18) The representation surfaces of the piezoelectric strain coefficient (d) were calculated for [011], [001] and [111] poled PMN-PT crystals with ?31% PT. It was discovered that the zxt ?45? cut (rotation around z-axis ?45?) for [011] poled PMN-PT crystal gives a unique re-poleable shear piezoelectric coefficient d.sub.36 up to 2600 pC/N.

(19) The zxt 0? cut (without rotation) d.sub.31 up to ?1750 pC/N was obtained for the [011] poled crystals. It was also found that an extraordinarily high shear piezoelectric coefficient d.sub.15 up to 5190 pC/N for the single domain crystal (3 m) occurred in the xzt ?22.5? cut (22.5? clockwise rotation about x-axis). These calculated results were experimentally verified, as will be discussed.

(20) The transformation of piezoelectric coefficients by changing coordinate system is represented by the following equation:
d.sub.ijk=?a.sub.ila.sub.jma.sub.knd.sub.lmn(2)

(21) where d.sub.lmn is the piezoelectric coefficient in the original coordinate system,

(22) d.sub.ijk is the piezoelectric coefficient in the new rotated coordinate system, and

(23) a.sub.il, a.sub.jm and a.sub.kn are the components of the transformation matrix.

(24) The coordinate rotation was defined in the following way: rotation was first made by angle ? around the z-axis, then around the new x-axis by angle ?, and finally around the new z-axis by angle ?. All of the rotations were counterclockwise. The new piezoelectric coefficients after the rotation in the 3-dimensional space were derived as functions of the independent piezoelectric coefficients in the original coordinate system arid the rotated Euler angles (?, ?, ?) using tensor calculations.

(25) To obtain the independent piezoelectric coefficients, three sets of samples of PMN-31% PT crystal (3 m, mm2, and 4 mm) were prepared to cope with the scattering of the measured data within each set caused by the PT-content variation and the process history.

(26) The coordinates were selected as follows: [111] as z-axis, [110] as x-axis, and [112] as y-axis for 3 m symmetry; [011] as z-axis, [100] as x-axis, and [011] as y-axis for mm2 symmetry; and [001] as z-axis, [100] as x-axis, and [010] as y-axis for 4 mm, respectively.

(27) An electrical field strength 5 kV/cm for poling was applied along the z-axis at room temperature. As used herein, room temperature ranges roughly from 33? F. to roughly 100? F.

(28) The poling current density was limited within 10 ?A/cm.sup.2 by an automatic DC power supply unit. A complete poling can be achieved by retaining the poling E-field for one minute after setting the poling current back to zero. The independent piezoelectric coefficients of the three engineered multi-domain systems were directly measured using a modified Berlincourt meter with homemade adaptors. After repeated tries employing this setting, it was determined that the present embodiment provides a measurement error within about ?5%.

(29) A single domain PMN-PT crystal (3 m) can be obtained by completely poling along the [111] direction. The single domain crystal has four independent piezoelectric coefficients: d.sub.15 (=d.sub.24), d.sub.16 (=2d.sub.21=?2d.sub.22), d.sub.31 (=d.sub.32) and d.sub.33. The representation surface of the shear piezoelectric coefficient d.sub.is was then calculated, and is represented in FIG. 1. As shown, the amplitude of the surfaces represents the absolute value of the piezoelectric coefficient in that orientation.

(30) The maximum value of d.sub.15 of 5190 pC/N is in the direction of ? of 337.5? and ? of 0? (xzt ?22.5?). The maximum amplitude of d.sub.15 (?5190 pC/N) was found at ? of 157.5? and ? of 0? (xzt 157.5?). The maximum d.sub.15 value in the rotated coordinate is approximately 1.1 times the original d.sub.15. Particularly, the cross talk from d.sub.16 is eliminated for the rotated coordinate. In contrast, strong cross talk between d.sub.15 (4800 pC/N) and d.sub.16 (1975 pC/N) exists before the rotation.

(31) The shear piezoelectric coefficient d.sub.36 is a dependent tensor and is zero in original coordinate circumstances. To explore the maximum value of d.sub.36 in a rotated coordinate system, the representation surface of the shear piezoelectric coefficient d.sub.36 was calculated and this is shown as FIG. 4.

(32) The maximum d.sub.36 (+2600 pC/N) was obtained in the direction of ? of 0? and ? of ?45? (zxt ?45?) or ?225?.

(33) In an effort to verify the above maximum values from theoretical calculation, four groups of samples were prepared by cutting in the rotation angle where the maximum d values had occurred. The measured maximum d values confirmed the calculation results, which are summarized in Table 1 in context with the four types of vibration modes. The calculation on 4 mm multi-domains was not presented in this work, as it has been initially described in a limited manner. described in references hereinabove and is incorporated here fully by reference.

(34) It can be seen from the good consistency between the calculated results and the measured data in FIG. 7, that the present invention is easily verified as valid.

(35) Referring now to FIG. 5, a process for preparation of the single crystal element of the present invention comprises at least the steps: (a) poling a single crystal with a selected composition, in the direction along the <111> cubic axis under 500V/mm electrical field at room temperature; (b) mechanically finishing of the single crystal elements with cuttings such as xzt-22.5?, ?5?; and (c) coating working electrodes on both X surfaces and removing the poling electrodes-on both Z surfaces.

(36) Referring now to FIG. 6, an alternative is provided for preparation of the single crystal elements described herein which comprises the steps: (a) mechanically finishing of the single crystal elements with cuttings such as zxt ?45? (?50); (b) coating electrodes on a pair of Z surfaces; and (c) poling the single crystal in the direction along the <011> cubic axis under 500V/mm electrical field at room temperature.

(37) A variety of experiments were conducted to test the above considerations. These experiments are discussed below.

Experiment 1

(38) A plate crystal element, similar to that shown in FIG. 5, was created and measured data of d.sub.15 as high as 6,000 pC/N, and d.sub.16 less than 100 pC/N, and d.sub.11 less than 90 pC/N.

Experiment 2

(39) A plate crystal element, constructed as shown in FIG. 6, was measured and provided measured data of d.sub.36 as high as 2,000 pC/N and d.sub.34/d.sub.35 less than 50 pC/N. The d.sub.3 shear mode crystal elements was easily be re-poled, if any de-poling occurred or was necessary.

Experiment 3

(40) The plate crystal element as FIG. 2, was provided wherein the rotation angle theta was taken from 0 to 330? in increments of 30?. The measured data of d.sub.15 are listed in Table 2.

(41) TABLE-US-00002 TABLE 2 Experiment data for free X-Y cut (<111> poling 3 m) d.sub.15 shear mode crystals Theta ? 0? 30? 60? 90? 120? 150? d.sub.15 pC/N 3940 3720 4050 3870 4100 4220 Theta ? 180? 210? 240? 270? 300? 330? d.sub.15 pC/N 4190 3788 4240 3870 4301 3904

Experiment 4

(42) In this experiment, a plate crystal element, as shown in FIGS. 3A and 3B provided measured data of d.sub.15 as high as 4400 pC/N and d.sub.16 less than 100 pC/N.

(43) Those of skill in the art should understand, that crystal cutting orientation are described with IRE notation. Those of skill in the crystal forming arts should additionally understand that the d.sub.ij parameters were measured on a Berlincout type meter with an adapter and dielectric constant measured on a HP-4294A Impedance Analyzer.

(44) Having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes, modifications, and adaptations may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.