Method of poling ferroelectric materials

1. A method of poling a ferroelectric sample suitable for use in a fuel injector of an internal combustion engine, the method comprising:

providing a ferroelectric sample having a stack of ferroelectric layers, wherein adjacent layers are separated by internal electrodes, forming a first group and a second group of electrodes;

applying a multiaxial pressure to the ferroelectric sample; and

generating an electric field between the first and second group of electrodes while the multiaxial pressure is applied, wherein the electric field is large enough to cause permanent crystallographic realignment and dipole reorientation in regions of the ferroelectric sample;

wherein the multiaxial pressure is sufficient to prevent formation of tensile cracks in regions of the ferroelectric sample that are not exposed to sufficient electric field to undergo permanent crystallographic realignment and dipole reorientation.

2. The method of claim 1 , wherein the multiaxial pressure is applied by means of a fluid.

3. The method of claim 2 , wherein the fluid is pressurised.

4. The method of claim 2 , wherein the fluid is a dielectric fluid.

5. The method of claim 2 , wherein the fluid is a fuel.

6. The method of claim 1 , wherein the method further comprises positioning the ferroelectric sample within the fuel injector before generating the electric field between the first and second group of electrodes.

7. The method of claim 1 , further comprising removing the electric field between the first and second group of electrodes before removing the multiaxial pressure from the ferroelectric sample.

8. The method of claim 1 , wherein the electric field is generated by applying a potential difference between the first and second group of electrodes.

9. The method of claim 1 , wherein the first and second group of electrodes are interdigitated.

10. The method of claim 1 , further comprising:

providing a first electrode on a first end face of the sample;

providing a second electrode on a second end face of the sample, the second face being opposed to the first face;

generating an initial electric field between the first and second electrodes, as a first stage of a two-stage poling method;

removing the initial electric field between the first and second electrodes; and

generating the electric field between the first and second group of electrodes as a second stage of the two-stage poling method.

11. The method of claim 10 , further comprising removing the initial electric field from between the first and second electrodes prior to applying the multiaxial pressure to the ferroelectric sample.

12. The method of claim 10 , wherein the first electrode covers the surface area of the first end face and the second electrode covers the surface area of the second end face.

13. The method of claim 10 , wherein the initial electric field is generated by applying a potential difference between the first and second electrodes.

14. A method of poling a ferroelectric sample suitable for use in a fuel injector of an internal combustion engine, the method comprising:

providing a ferroelectric sample having a stack of ferroelectric layers, wherein adjacent layers are separated by internal electrodes, forming a first group and a second group of electrodes;

positioning the ferroelectric sample within the fuel injector;

applying a multiaxial pressure to the ferroelectric sample; and

generating an electric field between the first and second group of electrodes while the multiaxial pressure is applied, wherein the electric field is large enough to cause permanent crystallographic realignment and dipole reorientation in regions of the ferroelectric sample;

wherein the multiaxial pressure is sufficient to prevent formation of tensile cracks in regions of the ferroelectric sample that are not exposed to sufficient electric field to undergo permanent crystallographic realignment and dipole reorientation.

15. The method of claim 14 , wherein the multiaxial pressure is applied by means of a pressurised fluid.

16. The method of claim 15 , wherein the fluid is a fuel.

17. A method of poling a ferroelectric sample suitable for use in a fuel injector of an internal combustion engine, the method comprising:

providing a ferroelectric sample having a stack of ferroelectric layers, wherein adjacent layers are separated by internal electrodes, forming a first group and a second group of electrodes;

applying a multiaxial pressure to the ferroelectric sample;

providing a first electrode on a first end face of the ferroelectric sample;

providing a second electrode on a second end face of the ferroelectric sample, the second face being opposed to the first face;

generating an initial electric field between the first and second electrodes;

removing the initial electric field between the first and second electrodes; and

subsequently generating an electric field between the first and second group of electrodes, wherein the electric field is large enough to cause permanent crystallographic realignment and dipole reorientation in regions of the ferroelectric sample;

wherein the multiaxial pressure is sufficient to prevent formation of tensile cracks in regions of the ferroelectric sample that are not exposed to sufficient electric field to undergo permanent crystallographic realignment and dipole reorientation.

18. The method of claim 17 , further comprising removing the initial electric field from between the first and second electrodes prior to applying the multiaxial pressure to the ferroelectric sample.

19. The method of claim 17 , wherein the first electrode covers the surface area of the first end face and the second electrode covers the surface area of the second end face.

20. The method of claim 17 , wherein the initial electric field is generated by applying a potential difference between the first and second electrodes.