Piezoelectrics and related devices from ceramics dispersed in polymers

• US 5,951,908 A
• Filed: 01/07/1998
• Issued: 09/14/1999
• Est. Priority Date: 01/07/1998
• Status: Expired due to Fees

• Current Assignee: Alliedsignal Inc.
• Original Assignee: Alliedsignal Inc.
• Inventors: Baughman, Ray Henry, Cui, Changxing, Kazmar, Theodore Robert, Dahlstrom, David Keith, Iqbal, Zafar
• Primary Examiner(s): KOSLOW, CAROL M
• Application Number:
  US09/003,625
• Time in Patent Office: 615 Days
• Field of Search: 252/62.9 R, 252/62.9 RZ, 524/413
• US Class Current: 252/62.90R
• CPC Class Codes: H10N 30/092 Forming composite materials
• CPC Class Codes: H10N 30/852 Composite materials, e.g. having 1-3 or 2-2 type connectivity

Abstract

This invention relates to compositions and processes for the fabrication of piezoelectric composites having improved figures of merit for both sensor and non-sensor applications. These composites comprise piezoelectric particles embedded in a polymer matrix. The improvements of this invention result from discoveries of the effects of polymer bulk compliance, polymer anisotropy, polymer melt index, and polymer/ceramic wettability on performance. The loss corrected figure of merit (g_h d_h /tanδ) obtained for the 0-3 composites is as high as 10.5×10^-10 m² /N, which is about four times higher than previously published for 0-3 composites of the prior art. Methods are described for the introduction of anisotropy into ceramic particle/polymer composites, so that cancellation effects that degrade the piezoelectric properties of composites can be reduced.

Claims

1. A piezoelectric composite comprising a first component that is a piezoelectric powder and a second component having three-dimensional connectivity that comprises a polymer, wherein

(a) the first component comprises substantially spherical piezoelectric particles such that at least about 90 weight percent of the particles have diameters within 20% of the weight-average of the particle diameters, and the weight-average of the particle diameters ranges from about 30 μ

m to about 200 μ

m;

(b) either (1) the polymer substantially adheres to the first component when a pellet of the polymer is fully melted and then resolidified on top of a pellet of the first component or (2) the polymer, which is formed by reaction and solidification of a fluid precursor of the polymer, substantially adheres to a pellet of the first component when said reaction and solidification is done on top of a pellet of the first component;

(c) the dielectric loss of said polymer is less than about 0.02 at 1 kHz,

(d) the melt index of said polymer exceeds 0.1 at a temperature within 40°

C. of the polymer melting temperature if said polymer has a melting temperature;

(e) the total volume of all components of the composite other than the second component ranges from about 50 volume percent to about 74 volume percent of the composite; and

(f) the elastic compliance S₃₃ of the piezoelectric composite ranges from about 1.5×

10^-10 to about 6.0×

10^-10 m² /N.

2. A composite of claim 1, wherein the second component comprises an organic polymer.

3. The composite of claim 1, wherein the second component comprises an organic polymer and wherein said piezoelectric powder comprises a ferroelectric ceramic.

4. The composite of claim 3 wherein said ferroelectric ceramic comprises a relaxor ferroelectric ceramic.

5. The composite of claim 4 wherein said relaxor ferroelectric ceramic either (1) has the form A(BΦ

_1/2 BΓ

_1/2)O₃ or A(BΦ

_1/3 BΓ

_2/3)O₃, where BΦ and

BΓ

represent atom types on B sites in a lead titanate type of structure, or (2) is a solid solution of one or more ceramics of such form A(BΦ

_1/2 BΓ

_1/2)O₃ or with another A(BΦ

_1/3 BΓ

_2/3)O₃, with another ceramic composition.

6. The composite of claim 5 wherein A is Pb;

BΦ

_1/3 is Mg_1/3, Ni_1/3 or, Zn_1/3 ;

BΓ

_2/3 is Nb_2/3 ; and

BΦ

_1/2 and BΓ

_1/2 are any two of Sc_1/2, Ta_1/2, Fe_1/2, and Nb_1/2.

7. The composite of claim 2 wherein said organic polymer comprises low density polyethylene or poly(1-butene).

8. The composite of claim 7 wherein the first component comprises Ca-modified lead titanate.

9. The composite of claim 2 wherein the second component comprises a plasticizer.

10. The composite of claim 1 which is in the form of a shaped article having anisotropic properties.

11. The composite of claim 1 which is in the form of an open cylinder having a cylindrical open core.

12. A composite of claim 1 further comprising a third component, wherein said third component is a fibrous material or a platelet or platelet-shaped material.

13. A composite of claim 12, wherein said third component comprises glass fibers or an exfoliated clay.

14. A composite of claim 13, wherein said fibers or said exfoliated clay are anisotropically oriented in said composite.

15. A composite of claim 14 that is electrically poled, wherein the direction having the highest elastic compliance is the direction of electric poling.

16. A composite of claim 1, wherein the said composite is substantially free of voids.

17. The composite of claim 3, wherein the ferroelectric ceramic comprises M_x M'"'"'_1-x NbO₃, wherein M and M'"'"' are selected from the group consisting of Na, Li, and K and x is less than unity;

Pb_x M"_v (Ti_y M_z M'"'"'_u)O₃, wherein M and M'"'"' are selected from the group consisting of Zn, Nb, Zr, Sb, and Mn;

M" is selected from the group consisting of Bi, La, and Nb, both x+v and y+z+u are about 1, and v is no more than about 0.05;

Na₀.5 Bi₀.5 TiO₃ ;

or Na₀.75 Pb₀.125 NbO₃.

18. A composite of claim 1 wherein the total volume of all components of the composite other than the second component ranges from about 60 volume percent to about 67 volume percent of the composite.

19. A process for forming an article which comprises

i) forming a piezoelectric composite comprising a first component that is a piezoelectric powder and a second component having three-dimensional connectivity that comprises a polymer, wherein

(a) the first component comprises substantially spherical piezoelectric particles such that at least about 90 weight percent of the particles have diameters within 20% of the weight-average of the particle diameters, and the weight-average of the particle diameters ranges from about 30 μ

m to about 200 μ

m;

(b) either (1) the polymer substantially adheres to the first component when a pellet of the polymer is fully melted and then resolidified on top of a pellet of the first component or (2) the polymer, which is formed by reaction and solidification of a fluid precursor of the polymer, substantially adheres to a pellet of the first component when said reaction and solidification is done on top of a pellet of the first component;

(c) the dielectric loss of said polymer is less than about 0.02 at 1 kHz,

(d) the melt index of said polymer exceeds 0.1 at a temperature within 40°

C. of the polymer melting temperature if said polymer has a melting temperature;

(e) the total volume of all components of the composite other than the second component ranges from about 50 volume percent to about 74 volume percent of the composite; and

(f) the elastic compliance S₃₃ of the piezoelectric composite ranges from about 1.5×

10^-10 to about 6.0×

10^-10 m² /N; and

ii) forming a shaped article from said composite and imparting anisotropic properties to the shaped article by subjecting it to one or more treatments selected from the group consisting of uniaxially draw, uniaxial compression, biaxial draw, biaxial compression, and shear deformation.

20. The process of claim 19 wherein said shear deformation is done by shearing the shaped article between oppositely rotating cylinders.

21. A process of forming a composite comprising a first component that is a piezoelectric powder, a second component having three-dimensional connectivity that comprises a polymer, and a third component comprising a fibrous material or a plate-like material wherein

(a) the first component comprises substantially spherical piezoelectric particles such that at least about 90 weight percent of the particles have diameters within 20% of the weight-average of the particle diameters, and the weight-average of the particle diameters ranges from about 30 μ

m to about 200 μ

m;

(b) either (1) the polymer substantially adheres to the first component when a pellet of the polymer is fully melted and then resolidified on top of a pellet of the first component or (2) the polymer, which is formed by reaction and solidification of a fluid precursor of the polymer, substantially adheres to a pellet of the first component when said reaction and solidification is done on top of a pellet of the first component;

(c) the dielectric loss of said polymer is less than about 0.02 at 1 kHz,

(d) the melt index of said polymer exceeds 0.1 at a temperature within 40°

C. of the polymer melting temperature if said polymer has a melting temperature;

(e) the total volume of all components of the composite other than the second component ranges from about 50 volume percent to about 74 volume percent of the composite; and

(f) the elastic compliance S₃₃ of the piezoelectric composite ranges from about 1.5×

10^-10 to about 6.0×

10^-10 m² /N;

the process comprising commingling the second component and third component to form an intimate mixture and then commingling the intimate mixture with the first component.

22. A process of forming a piezoelectric composite comprising a first component that is a piezoelectric powder and a second component having three-dimensional connectivity that comprises a polymer, wherein

(a) the first component comprises substantially spherical piezoelectric particles such that at least about 90 weight percent of the particles have diameters within 20% of the weight-average of the particle diameters, and the weight-average of the particle diameters ranges from about 30 μ

m to about 200 μ

m;

(b) either (1) the polymer substantially adheres to the first component when a pellet of the polymer is fully melted and then resolidified on top of a pellet of the first component or (2) the polymer, which is formed by reaction and solidification of a fluid precursor of the polymer, substantially adheres to a pellet of the first component when said reaction and solidification is done on top of a pellet of the first component;

(c) the dielectric loss of said polymer is less than about 0.02 at 1 kHz,

(d) the melt index of said polymer exceeds 0.1 at a temperature within 40°

C. of the polymer melting temperature if said polymer has a melting temperature;

(e) the total volume of all components of the composite other than the second component ranges from about 50 volume percent to about 74 volume percent of the composite; and

(f) the elastic compliance S₃₃ of the piezoelectric composite ranges from about 1.5×

10^-10 to about 6.0×

10^-10 m² /N;

the process comprising mixing the first component and second component either as dry powders or as dry powders in combination with substantially a non-solvent for the first component and second component to form a free-flowing mixture and then forming this free-flowing mixture into a shaped composite by melting the second component.

23. A process of forming a piezoelectric composite comprising a first component that is a piezoelectric powder and a second component having three-dimensional connectivity that comprises a polymer, wherein

(a) the first component comprises substantially spherical piezoelectric particles such that at least about 90 weight percent of the particles have diameters within 20% of the weight-average of the particle diameters, and the weight-average of the particle diameters ranges from about 30 μ

m to about 200 μ

m;

(b) either (1) the polymer substantially adheres to the first component when a pellet of the polymer is fully melted and then resolidified on top of a pellet of the first component or (2) the polymer, which is formed by reaction and solidification of a fluid precursor of the polymer, substantially adheres to a pellet of the first component when said reaction and solidification is done on top of a pellet of the first component;

(c) the dielectric loss of said polymer is less than about 0.02 at 1 kHz,

(d) the melt index of said polymer exceeds 0.1 at a temperature within 40°

C. of the polymer melting temperature if said polymer has a melting temperature;

(e) the total volume of all components of the composite other than the second component ranges from about 50 volume percent to about 74 volume percent of the composite; and

(f) the elastic compliance S₃₃ of the piezoelectric composite ranges from about 1.5×

10^-10 to about 6.0×

10^-10 m² /N;

the process comprising forming a mixture of the first component and a monomer or prepolymer, followed by reaction of said monomer or prepolymer under conditions sufficient to produce the second component.