Contact materials for electrostriciton actuators

Abstract

This invention provides contact materials comprising doped ceria-based materials and preparation thereof. This invention further comprises stacks and electrostriction actuators comprising the contact materials provided herein.

Description

CONTACT MATERIALS FOR ELECTROSTRICITON ACTUATORSFIELD OF THE INVENTION

[0001] This invention provides contact materials comprising doped ceria-based materials and preparation thereof. This invention further comprises stacks and electrostriction actuators comprising the contact materials provided herein.BACKGROUND OF THE INVENTION

[0002] Doped ceria is a promising replacement material for piezoelectric and classical electrostrictions, such as PMN-PT (lead magnesium niobate-lead titanate) because it has a number of advantages: (a) its electrostriction strain coefficient (or “electrostriction coefficient”) is as large as that of PMN-PT, but coexists with low dielectric permittivity 28-220 depending on doping (vs >10000 of PMN-PT); (b) elastic modulus of Zr-doped ceria is much higher than that of PMN-PT (>190 GPa vs <80 GPa); (c) ceria is non-toxic, chemically and biologically inert, while PMN-PT contains lead; (d) ceria ceramics and thin films are technologically friendly and fully compatible with Si-based microfabrication processes. Thus, ceria has potential of displacing PMN-PT and other electromechanically active materials, however, this requires development of reliable contact materials, which is currently not available. Metallic contacts form blocking layers at the interface with the ceramics, interfering with the external field and decreasing the strain for a given value of the external field.

[0003] The proposed material and preparation techniques can be used to manufacture ceria-based actuator ceramics and replace the actuators that currently are based on electrostrictive PMN-PT or piezoelectrics with the advantages mentioned above.

[0004] This invention provides doped ceria-based materials and their use as contact materials for stacks and electrostriction actuators comprising the same. The resulting contact materials prevent the formation of a blocking layer and allow application of ceria-derived materials in actuator-related applications.SUMMARY OF THE INVENTION

[0005] In one embodiment, this invention provides a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo. In another embodiment, the material is represented by the formula: Ceo.s9Zro.1Nbo.01O2. In other embodiment, the ceria-based materials are used as “contact materials” within a stack employed in actuators of electrostriction applications.

[0006] In one embodiment, this invention provides a stack comprising a multilayered structure, the multilayered structure comprises at least one active layer and at least one contact layer, wherein the active layer comprises a ceria-based material, doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti, and optionally co-doped with a metal having a lower valence than said metal M3; and the contact layer comprises a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo.

[0007] In one further embodiment, this invention provides an actuator comprising the stack as described hereinabove and a voltage source, wherein the stack is connected to the voltage source; a bias applied to the stack which produces an electrostrictive strain (or “strain”).BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

[0009] Figures 1A-1B show a stack prepared via a layer-by-layer slurry-casting technique. Figure 1A: A scheme for layer-by-layer slurry-casting preparation method. Figure IB: A SEM image of the actual stack prepared by the method depicted in Figure 1 A (layer-by-layer slurry-casting).

[0010] Figures 2A-2B show a stack prepared via co-pressing and co-firing technique. Figure 2A: A photo of the stack prepared via co-pressing and co-firing technique. Figure 2B: An impedance spectrum of the multilayered actuator stack prepared by the co-pressing and co-firing technique.

[0011] Figure 3 shows an electrostriction strain coefficient (or “electrostriction coefficient”) of an actuator comprising a stack (of Figures 2A-2B) prepared via co-pressing and co-firing technique.

[0012] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0013] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well- known methods, procedures, and components have not been described in detail so as not to obscure the present invention.Contact Materials

[0014] In one embodiment, this invention provides a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo. In another embodiment, M1is Zr or Hf. In another embodiment, M1is Zr. In another embodiment, M2is Nb or Ta. In another embodiment, M2is Nb. In one further embodiment, M1is Zr orHf andM2isNb or Ta. In one other embodiment, M1is Zr andM2isNb. Each possibility represents a separate embodiment of this invention.

[0015] In one embodiment, this invention provides a contact material comprising a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo. In another embodiment, M1is Zr or Hf. In another embodiment, M1is Zr. In another embodiment, M2is Nb or Ta. In another embodiment, M2is Nb. In one further embodiment, M1is Zr or Hf and M2is Nb or Ta. In one other embodiment, M1is Zr and M2is Nb. Each possibility represents a separate embodiment of this invention.

[0016] In some embodiments, the concentration of M1is 0.01 to 20 mol%. In some other embodiments, the concentration of M1is 0.01 to 0.1 mol%. In another embodiment, the concentration of M1is 0.1 to 0.5 mol%. In another embodiment, the concentration of M1is 0.5 to 1 mol%. In another embodiment, the concentration of M1is 1 to 5 mol%. In another embodiment, the concentration of M1is 5 to 10 mol%. In another embodiment, the concentration of M1is 10 to 20 mol%. In another embodiment, the concentration of M1is 10 mol%. Each possibility represents a separate embodiment of this invention.

[0017] In some embodiments, the concentration of M2is 0.05 to 10 mol%. In some other embodiments, the concentration of M2is 0.05 to 0.1 mol%. In another embodiment, the concentration of M2is 0.1 to 0.5 mol%. In another embodiment, the concentration of M2is 0.5 to 1 mol%. In another embodiment, the concentration of M2is 1 to 5 mol%. In another embodiment, the concentration of M2is 5 to 10 mol%. In another embodiment, the concentration of M2is 1 mol%. Each possibility represents a separate embodiment of this invention.

[0018] In one embodiment, the concentration of M1is 10 mol% and the concentration of M2is 1 mol%.

[0019] In some embodiments, the contact material is represented by the formula Cei-x-yM1xM2yO2-8 wherein x ranges between 0.0001 and 0.2; and y ranges between 0.0005 and 0.1 ; and 5 ranges between 0 and 0.05. In some other embodiments, y ranges between 0.0005 and 0.001. In another embodiment, y ranges between 0.0005 and 0.001. In another embodiment, y ranges between 0.001 and 0.01. In another embodiment, y ranges between 0.01 and 0.1. In one other embodiment, y is 0.01. In some other embodiments, x ranges between 0.0001 and 0.2. In another embodiment, x ranges between0.0001 and 0.001. In another embodiment, x ranges between 0.001 and 0.01. In another embodiment, x ranges between 0.01 and 0.1. In another embodiment, x ranges between 0.1 and 0.2. In another embodiment, x is 0.1. In another embodiment, x is 0.1 and y is 0.01. In some other embodiments, 5 ranges between 0 and 0.05. In another embodiment, 5 ranges between 0 and 0.0001. In another embodiment, 5 ranges between 0.0001 and 0.001. In another embodiment, 5 ranges between 0.001 and 0.01. In another embodiment, 5 ranges between 0.01 and 0.02. In another embodiment, 5 ranges between 0.02 and 0.05. In another embodiment, 5 is 0. In another embodiment, x is 0.1 and y is 0.01 and 5 is 0. Each possibility represents a separate embodiment of this invention.

[0020] In some embodiments, the contact material of this invention has a Young’s modulus which ranges between 100 GPa and 250 GPa. In one embodiment, the Young’s modulus ranges between 100 GPa and 150 GPa. In another embodiment, the Young’s modulus ranges between 150 GPa and 200 GPa. In another embodiment, the Young’s modulus ranges between 200 GPa and 250 GPa. In another embodiment, the Young’s modulus ranges between 100 GPa and 200 GPa. In another embodiment, the Young’s modulus ranges between 150 GPa and 250 GPa. Each possibility represents a separate embodiment of this invention.

[0021] In some embodiments, the contact material of this invention has a dielectric constant which ranges between 10 and 1000. In one embodiment, the dielectric constant ranges between 10 and 50. In another embodiment, the dielectric constant ranges between 50 and 100. In another embodiment, the dielectric constant ranges between 100 and 200. In another embodiment, the dielectric constant ranges between 200 and 500. In another embodiment, the dielectric constant ranges between 500 and 1000. In another embodiment, the dielectric constant ranges between 10 and 100. In another embodiment, the dielectric constant ranges between 50 and 500. In another embodiment, the dielectric constant ranges between 100 and 500. In another embodiment, the dielectric constant ranges between 100 and 1000. In another embodiment, the dielectric constant ranges between 28 and 220. Each possibility represents a separate embodiment of this invention.

[0022] In some embodiments, the contact material of this invention has an electrical conductivity which ranges between 10'9S / m and 10'5S / m. In one embodiment, the electrical conductivity ranges between 10'9S / m and 10'8S / m. In another embodiment, the electrical conductivity ranges between 10'8S / m and 10'7S / m. In another embodiment, the electrical conductivity ranges between 10'7S / m and 10'6S / m. In another embodiment, the electrical conductivity ranges between 10'6S / m and 10'5S / m. Each possibility represents a separate embodiment of this invention.

[0023] In one specific embodiment, the contact material is represented by the formula: Ceo.89Zro.1Nbo.01O2.

[0024] In some embodiments, providing herein a contact material comprising a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo (or represented by the formula Cei-x-yM^M^Ch-s), wherein the contact material exhibits electrostriction properties. In one embodiment, the contact material is embodied within a stack which can be employed in actuators of electrostriction applications.Stacks comprising the Contact Material of this invention

[0025] In one embodiment, this invention provides a stack comprising a multilayered structure, the multilayered structure comprises at least one active layer and at least one contact layer, wherein the active layer comprises a ceria-based material, doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti, and optionally co-doped with a metal having a lower valence than said metal M3; and the contact layer comprises a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo.The active layer

[0026] In another embodiment, the ceria-based material of the active layer is represented by the formula Cei-zM3zO2-d wherein z ranges between 0.02 and 0.7 and d ranges between 0 and 0.05. In one other embodiment, M3is Zr, Hf or Ti. In another embodiment, M3is Zr or Hf. In another embodiment, M3is Zr. In some other embodiments, z ranges between 0.02 and 0.7. In another embodiment, z ranges between 0.02 and 0.05. In another embodiment, z ranges between 0.05 and 0.1. In another embodiment, z ranges between 0.1 and 0.2. In another embodiment, z ranges between 0.2 and 0.5. In another embodiment, z ranges between 0.5 and 0.7. In another embodiment, z ranges between 0.08 and 0.12. In another embodiment, z is 0.1. Each possibility represents a separate embodiment of this invention.

[0027] In some other embodiments, d ranges between 0 and 0.03. In another embodiment, d ranges between 0 and 0.05. In another embodiment, d ranges between 0 and 0.0001. In another embodiment, d ranges between 0.0001 and 0.001. In another embodiment, d ranges between 0 and 0.001. In another embodiment, d ranges between 0.001 and 0.005. In another embodiment, d ranges between 0.005 and 0.01. In another embodiment, d ranges between 0.01 and 0.03. In another embodiment, d ranges between 0.01 and 0.015. In another embodiment, d ranges between 0.015 and 0.02. In another embodiment, d ranges between 0.02 and 0.025. In another embodiment, d ranges between 0.025 and 0.03. In another embodiment, d ranges between 0.03 and 0.035. In another embodiment, d ranges between 0.035 and 0.04. In another embodiment, d ranges between 0.04 and 0.045. In another embodiment, d ranges between 0.045 and 0.05. In another embodiment, d ranges between 0.01 and 0.02. In another embodiment, d ranges between 0.02 and 0.03. In another embodiment, d rangesbetween 0.02 and 0.05. In another embodiment, d ranges between 0.01 and 0.05. In another embodiment, d ranges between 0.03 and 0.05. In another embodiment, d ranges between 0.04 and 0.05. In another embodiment, d is 0. Each possibility represents a separate embodiment of this invention.

[0028] In another embodiment, the ceria-based material of the active layer, doped by a metal M3, is co-doped with a metal having a lower valence than said metal M3. In another embodiment, the metal having a lower valence is selected from: Ca, Mg, Fe, Sc, Sn, Y, a lanthanide L and any combinations thereof. In another embodiment, the metal having a lower valence comprises a lanthanide L. In yet other embodiment, the lanthanide L is any lanthanide selected from La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and any combination thereof. In one further embodiment, the ceria-based material of the active layer, doped by a metal M3is represented by the formula Cei-q.nM3qLnO2-n / 2-d, wherein said q ranges between 0.01 and 0.7; said n ranges between 0.01 and 0.7; and said d ranges between 0 and 0.05. In one other embodiment, L is La or Yb. In one embodiment, L is La, q ranges between 0.08 and 0.12 and n ranges between 0.01 and 0.08; or L is Yb, q ranges between 0.08 and 0.12, and n ranges between 0.05 and 0.15. Each possibility represents a separate embodiment of this invention.

[0029] In some other embodiments, q ranges between 0.01 and 0.7. In another embodiment, q ranges between 0.01 and 0.05. In another embodiment, q ranges between 0.05 and 0.1. In another embodiment, q ranges between 0.1 and 0.2. In another embodiment, q ranges between 0.2 and 0.5. In another embodiment, q ranges between 0.5 and 0.7. In another embodiment, q ranges between 0.08 and 0.12. Each possibility represents a separate embodiment of this invention.In some other embodiments, n ranges between 0.01 and 0.7. In another embodiment, n ranges between 0.01 and 0.08. In another embodiment, n ranges between 0.05 and 0.15. In another embodiment, n ranges between 0.01 and 0.05. In another embodiment, n ranges between 0.05 and 0.08. In another embodiment, n ranges between 0.08 and 0.1. In another embodiment, n ranges between 0.1 and 0.2. In another embodiment, n ranges between 0.2 and 0.5. In another embodiment, n ranges between 0.5 and 0.7. Each possibility represents a separate embodiment of this invention.

[0030] In some embodiments, the active layer within the stack generates electrostrictive displacement (or “displacement”), electrostrictive stress (or “stress”), electrostrictive strain (or “strain”)or any combination thereof upon application of an electric field. In another embodiment, the active layer within the stack generates electrostrictive stress (or “stress”), electrostrictive strain (or “strain”) or both. In other embodiments, the strain resulting from the active layer of the stack disclosed herein ranges between 0.1 - 500 ppm. In one embodiment, the strain is 0.1 - 1000 ppm. In one embodiment, the strain is 0.1 - 10 ppm. In another embodiment, the strain is 10 - 50 ppm. In another embodiment, the strain is 50 - 100 ppm. In another embodiment, the strain is 100 - 200 ppm. Inanother embodiment, the strain is 200 - 500 ppm. In another embodiment, the strain is 0.1 - 100 ppm. In another embodiment, the strain is 100 ppm and 500 ppm. In one embodiment, the strain is 100- 1000 ppm. In one embodiment, the strain is 500 - 1000 ppm. In another embodiment, the strain is 1- 1000 ppm. In some other embodiments, the strain is 1-100 ppm. In another embodiment, the strain is 100-200 ppm. In another embodiment, the strain is 200-300 ppm. In another embodiment, the strain is 300-500 ppm. In another embodiment, the strain is 200-500 ppm. In another embodiment, the strain is 500-800 ppm. In another embodiment, the strain is 500-750 ppm. In another embodiment, the strain is 500-600 ppm. In another embodiment, the strain is 600-700 ppm. In another embodiment, the strain is 700-750 ppm. In another embodiment, the strain is 750-800 ppm. In another embodiment, the strain is 700-800 ppm. In another embodiment, the strain is 600-800 ppm. In another embodiment, the strain is 800-900 ppm. In another embodiment, the strain is 900-1000 ppm. In another embodiment, the strain is 800-1000 ppm. In another embodiment, the strain is 1-500 ppm. In another embodiment, the strain is 500-1000 ppm. In another embodiment, the strain is 200-1000 ppm. In another embodiment, the strain is 200-750 ppm. In another embodiment, the strain is 750-1000 ppm. In another embodiment, the strain is 200-500 ppm. In another embodiment, the strain is 500-1000 ppm. Each possibility represents a separate embodiment of this invention.

[0031] In some embodiments, the stress resulting from the active layer of the stack of this invention is at least 0.01 MPa. In one embodiment, the stress is 0.01-1 MPa. In another embodiment, the stress is 1-10 MPa. In another embodiment, the stress is 10-100 MPa. In another embodiment, the stress is 100-1000 MPa. In another embodiment, the stress is 0.01-1000 MPa. Each possibility represents a separate embodiment of this invention.

[0032] In some embodiments, the stack comprises of 2-10 layers. In another embodiment, the stack comprises 2-3 layers. In another embodiment, the stack comprises 3-5 layers. In another embodiment, the stack comprises 5-7 layers. In another embodiment, the stack comprises 2-3 layers. In another embodiment, the stack comprises 7-10 layers. In another embodiment, the stack comprises 2-5 layers. In another embodiment, the stack comprises 5-10 layers. In another embodiment, the stack comprises 3-5 layers. In some other embodiments, the stack comprises at least one active layer and at least two contact layers, wherein the first layer is a contact layer, subsequent layer or plurality of layers are active layers and the last layer is a second contact layer; and wherein both contact layers contact at least one same or different active layer. In one other embodiment, the stack has 3 layers. In some other embodiments, the stack comprises one active layer and two contact layers, wherein the first layer is a contact layer, the second layer is an active layer and the third layer is a second contact layer; and wherein the second layer (active layer) is in contact with both first and third layers (contact layers). In one embodiment, the active layer comprises a material represented by the formula Ceo.9Zro.1O2. In one other embodiment, the contact layer comprises a material represented by theformula Ceo.s9Zro.1Nbo.01O2. In one specific embodiment, the stack comprises one active layer and two contact layers, wherein the first layer is a contact layer, the second layer is an active layer and the third layer is a second contact layer; and wherein the second layer (active layer) is in contact with both first and third layers (contact layers); and wherein the active layer comprises a material represented by the formula Ceo.9Zro.1O2; and the contact layers comprises a material represented by the formula Ceo.s9Zro.1Nbo.01O2. Each possibility represents a separate embodiment of this invention.

[0033] In some embodiments, the stack comprises multilayered structure comprising between 2-10 layers. In other embodiments the multilayered structure comprises a contact layer (A) or (A’) and an active layer (B) or (B’) organized for example as follows: ABA, ABBA, ABBA’, ABBBA, ABB’BA, AB, AB’, ABB’ABB’B’A, ABBABBA, ABABA, ABA’, ABB’A’; wherein A and A’ are contact layers each of different chemical composition, and B and B’ are active layers each of different chemical composition; and “different chemical compositions” refer to compositions comprising different atoms / ions and / or different stoichiometry thereof. Each possibility represents a separate embodiment of this invention.

[0034] In some embodiments, the electrostriction coefficient (or “electrostriction strain coefficient”) of the active material of the stack of this invention is frequency independent.

[0035] In some embodiments, the ceria-based material of the active layer (the active material) has an electrostriction coefficient which ranges between 10'15m2 / V2and 10'18m2 / V2at a frequency ranging between 0.1 Hz and 105Hz. In one embodiment, the electrostriction coefficient ranges between 10'15m2 / V2and 10'16m2 / V2. In another embodiment, the electrostriction coefficient ranges between 10'16m2 / V2and 10'17m2 / V2. In another embodiment, the electrostriction coefficient ranges between 10'17m2 / V2and 10'18m2 / V2. In another embodiment, the electrostriction coefficient ranges between 10'16m2 / V2and 10'18m2 / V2. In one embodiment, the frequency ranges between 0.1 and 10Hz. In another embodiment, the frequency ranges between 10 and 100 Hz. In another embodiment, the frequency ranges between 100 and 1000 Hz. In another embodiment, the frequency ranges between 1000 and 104Hz. In another embodiment, the frequency ranges between 104and 105Hz. In another embodiment, the frequency ranges between 100 and 105Hz. In another embodiment, the frequency ranges between 1000 and 105Hz. Each possibility represents a separate embodiment of this invention.Application of the Stacks in Actuators for Electrostriction

[0036] In one embodiment, this invention provides an actuator comprising the stack as disclosed herein in the section “ Stacks comprising the Contact Materials and a voltage source, wherein the stack is connected to a voltage source; wherein when a bias is applied to the stack, it produces anelectrostrictive strain (or “strain”). In one other embodiment, the electrostriction coefficient (or “electrostriction strain coefficient”) does not change more than 1% in the course of above 90 hours of bias application; and the bias applied is 2-3 kV. In another embodiment, the bias applied is 2.6 kV. In other embodiments, an electric field applied to the actuator can be defined instead of said bias, being 2.5 - 4 kV / cm. In another embodiment, the electric field is 2.5 - 3 kV / cm. In another embodiment, the electric field is 3 - 3.5 kV / cm. In another embodiment, the electric field is 3.5 - 4 kV / cm. In another embodiment, the applied electric field is about 2.9 kV / cm. In another embodiment, the bias or electric field is applied over the course of 80-100 hours. In another embodiment, the bias or electric field is applied over the course of 80-90 hours. In another embodiment, the bias or electric field is applied over the course of 90-100 hours. In another embodiment, the bias or electric field is applied over the course of 100-150 hours. In another embodiment, the bias or electric field is applied over the course of 150-200 hours. In another embodiment, the bias or electric field is applied for 96 hours. In another embodiment, the bias is applied for 96 hours. In another embodiment, the electrostriction coefficient is bias dependent. In one embodiment, the electrostrictive strain (or “strain”) is 0.1 - 1000 ppm. In another embodiment, the strain is 1-1000 ppm. In some other embodiments, the strain is 1-100 ppm. In another embodiment, the strain is 100-200 ppm. In another embodiment, the strain is 200-300 ppm. In another embodiment, the strain is 300-500 ppm. In another embodiment, the strain is 200-500 ppm. In another embodiment, the strain is 500-800 ppm. In another embodiment, the strains is 500-750 ppm. In another embodiment, the strain is 500-600 ppm. In another embodiment, the strain is 600-700 ppm. In another embodiment, the strain is 700-750 ppm. In another embodiment, the strain is 750-800 ppm. In another embodiment, the strain is 700-800 ppm. In another embodiment, the strain is 600-800 ppm. In another embodiment, the strain is 800-900 ppm. In another embodiment, the strain is 900-1000 ppm. In another embodiment, the strain is 800-1000 ppm. In another embodiment, the strain is 1-500 ppm. In one embodiment, the strain is 0.1 - 500 ppm. In one embodiment, the strain is 0.1 - 100 ppm. In one embodiment, the strain is 100 - 500 ppm. In one embodiment, the strain is 100 - 1000 ppm. In one embodiment, the strain is 500 - 1000 ppm. In another embodiment, the strain is 500-1000 ppm. In another embodiment, the electrostriction response is 200-1000 ppm. In another embodiment, the strain is 200-750 ppm. In another embodiment, the strain is 750-1000 ppm. In another embodiment, the strain is 200-500 ppm. In another embodiment, the strain is 500-1000 ppm. In another embodiment, the strain, when the voltage is 2.6kV, is above 200 ppm. Each possibility represents a separate embodiment of this invention.Methods of preparing the Stacks

[0037] In one embodiment, this invention provides a method of preparing a stack comprising a multilayered structure, the multilayered structure comprises at least one active layer and at least onecontact layer, wherein the active layer comprises a ceria-based material, doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti and optionally co-doped with a metal having a lower valence than said metal M3; and the contact layer comprises a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo; wherein the method comprises: applying a mixture of contact material and organic material or a mixture of active material and organic material on a film having a hole, providing the film with the layer within the hole; removing any excess material of the layer which did not enter the hole; adding at the top of the film with the layer, another film having a hole; repeating the above steps as needed to provide plurality of films stacked on top of each other, each with a contact or active layer inside; at the final layer, instead of adding another film and layer, removing all films, to provide a multilayered structure; and sintering the multilayered structure, thus providing stack comprising at least one active layer and at least one contact layer.

[0038] In another embodiment, the method of preparing a stack comprising a multilayered structure of this invention as described hereinabove is considered as a slurry casting fabrication technique.

[0039] In another embodiment, the film is a cellulose acetate, a polyethylene (PE), a Polyethylene terephthalate glycol (PETG), a polypropylene (PP), a polyester, a nylon or a polyvinylchloride (PVC) film. In another embodiment, the film is a cellulose acetate. In another embodiment, the hole is circular. In another embodiment the hole is 0.1-50 mm diameter. In another embodiment the hole is 0.1-1 mm diameter. In another embodiment the hole is 0.1-10 mm diameter. In another embodiment the hole is 1-10 mm diameter. In another embodiment the hole is 10-50 mm diameter. In another embodiment the hole is 20-50 mm diameter. In another embodiment the hole is 30-50 mm diameter. In another embodiment the hole is 40-50 mm diameter. In another embodiment the hole is 10-20 mm diameter. In another embodiment the hole is 20-30 mm diameter. In another embodiment the hole is 30-40 mm diameter. In another embodiment the hole is 1-20 mm diameter. In another embodiment the hole is 6 mm diameter. In another embodiment, the (application and removal) steps are repeated twice to afford a structure having three layers - one active layer and two contact layers, wherein the first layer is a contact layer, the second layer is the active layer and the third layer is the second contact layer; and wherein the active layer contacts both contact layers. Each possibility represents a separate embodiment of this invention.

[0040] In some other embodiments, the sintering is done at a sintering temperature which ranges between 700°C and 1400°C. In another embodiment, the sintering temperature ranges between 700°Cand 800°C. In another embodiment, the sintering temperature ranges between 800°C and 900°C. In another embodiment, the sintering temperature ranges between 900°C and 1000°C. In another embodiment, the sintering temperature ranges between 1000°C and 1100°C. In another embodiment, the sintering temperature ranges between 1100°C and 1200°C. In another embodiment, the sintering temperature ranges between 1200°C and 1300°C. In another embodiment, the sintering temperature ranges between 1300°C and 1400°C. In another embodiment, the sintering temperature ranges between 700°C and 1000°C. In another embodiment, the sintering temperature ranges between 700°C and 900°C. In another embodiment, the sintering temperature ranges between 1000°C and 1400°C. In another embodiment, the sintering temperature ranges between 1200°C and 1400°C. Each possibility represents a separate embodiment of this invention.

[0041] In some other embodiments, the sintering is performed for a duration ranging between 1 minute and 10 hours. In another embodiment, the sintering is performed for a duration ranging between 1 minute and 10 minutes. In another embodiment, the sintering is performed for a duration ranging between 10 minutes and 30 minutes. In another embodiment, the sintering is performed for a duration ranging between 30 minutes and 1 hour. In another embodiment, the sintering is performed for a duration ranging between 1 hour and 2 hours. In another embodiment, the sintering is performed for a duration ranging between 2 hours and 5 hours. In another embodiment, the sintering is performed for a duration ranging between 5 hours and 10 hours. In another embodiment, the sintering is performed for a duration ranging between 1 hour and 5 hours. In another embodiment, the sintering is performed for a duration ranging between 2 hours and 10 hours. In another embodiment, the sintering is performed for a duration ranging between 10 minutes and 60 minutes. Each possibility represents a separate embodiment of this invention.

[0042] In some embodiment, the sintering is done at a sintering temperature which ranges between 700°C and 1400°C; and it is performed for a duration ranging between 1 minute and 10 hours.

[0043] In some embodiment, the removal of the films (in order to arrive at the multilayered structure and before sintering) is done by mechanical means. In one embodiment, the removal is performed by lifting the films.

[0044] Without being bound by any mechanism or theory, it is herein contemplated that the sintering conditions (including temperature and duration thereof) provide good and robust contact between all layers (contact / active) and also removes the organic materials from the active and contact layers. Thus, the sintering affords a robust and stable stack having the specific electro-mechanical properties as described herein. Without the contact materials, previously metallic contacts have been utilized and formed blocking layers at the interface with the ceramics, which interfered with the external field and decreased the strain for a given value of the external field. Once the stack is prepared and comprises the active and contact layers disclosed herein, the resulting contact (layer) prevents theformation of a blocking layer and allows application of ceria-derived materials in actuator-related applications. The sintering also gives rise to relaxation at the atomic level of the lattices of the ceramics, hence good chemo / physical interaction between all layers (active and contact) is achieved, resulting in robust contact between them. Prior to sintering, the role of the organic material is to provide a mobile phase in which the active and / or contact materials are suspended or dispersed. This mobility is required in order to provide a good ability of said contact / active materials to be spread, before becoming a layer in the multilayered actuator, i.e. to get eventually a layer with a good local concentration distribution of the active / contact materials. This ability to be spread; and concentration distribution - result in a robust and smooth layer, once the mobile phase is sintered or fired. Viscosity of said mobile phase is controlled via various materials, e.g. terpineol or polyvinyl alcohol (PVA).

[0045] In some embodiments, the sintering step in the method of preparing the stacks of this invention removes the organic material from the contact and / or active layers. In one embodiment, the sintering step bums completely (100%) the organic material of the contact and / or active layers. In one other embodiment, low amount of organic residues and / or carbon materials (e.g. charcoal) is present following the sintering. In another embodiment, the low amount of organic residues and / or carbon materials (e.g. charcoal) is lower than 10, lower than 3 or lower than 1% w / w, compared to initial amount of the organic material. Each possibility represents a separate embodiment of this invention.

[0046] In some embodiments, the mixture of the active material with an organic material is homogeneous. In another embodiment, the mixture layer is in a form of a paste or suspension. In other embodiment, the form is a paste. In other embodiment, the form is a suspension. In some embodiments, the mixture of the active material with an organic material comprises a ceria-based material in a concentration of 50-80 wt.% and an organic material in a concentration of 20-50 wt.%. wherein the ceria-based material is doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti and optionally co-doped with a metal having a lower valence than said metal M3. In some embodiments, the “active material” refers to the ceria-based material which is doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti and is optionally co-doped with a metal having a lower valence than said metal M3.In some other embodiments, the mixture of the active material with an organic material comprises the active material in a concentration of 50-60 wt.%. In another embodiment, the mixture of the active material with an organic material comprises the active material in a concentration of 60-70 wt.%. In another embodiment, the mixture of the active material with an organic material comprises the active material in a concentration of 70-80 wt.%. In one embodiment, the mixture of the active material with an organic material comprises the active material in a concentration of 70 wt.%. In some other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 20-30 wt.%. In other embodiments, the mixture of the active material with an organic material comprises the organicmaterial in a concentration of 30-40 wt.%. In other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 40-50 wt.%. In one embodiment, the mixture of the active material with an organic material comprises the organic material in a concentration of 30 wt.%. In one specific embodiment, the mixture of the active material with an organic material comprises the active material in a concentration of 70 wt.%, and the organic material in a concentration of 30 wt.%. Each possibility represents a separate embodiment of this invention.

[0047] In some embodiments, the mixture of the active material with an organic material comprises the Cei-zM3zO2-d material (as the active material) in a concentration of 50-80 wt.%, and an organic material in a concentration of 20-50 wt.%. In some other embodiments, the mixture of the active material with an organic material comprises Cei-zM3zO2-d material in a concentration of 50-60 wt.%. In another embodiment, the mixture of the active material with an organic material comprises Cei- zM3zO2-d material in a concentration of 60-70 wt.%. In another embodiment, the mixture of the active material with an organic material comprises Cei-zM3zO2-d material in a concentration of 70-80 wt.%. In one embodiment, the mixture of the active material with an organic material comprises the Cei- zM3zO2-d material in a concentration of 70 wt.%. In some other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 20-30 wt.%. In other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 30-40 wt.%. In other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 40-50 wt.%. In one embodiment, the mixture of the active material with an organic material comprises the organic material in a concentration of 30 wt.%. In one specific embodiment, the mixture of the active material with an organic material comprises the Cei-zM3zO2-d material in a concentration of 70 wt.%, and the organic material in a concentration of 30 wt.%. Each possibility represents a separate embodiment of this invention.

[0048] In some embodiments, the mixture of the active material with an organic material comprises the Cei-q.nM3qLnO2-n / 2-d material (as the active material) in a concentration of 50-80 wt.%, and an organic material in a concentration of 20-50 wt.%. In some other embodiments, the mixture of the active material with an organic material comprises the Cei-q.nM3qLnO2-n / 2-d material in a concentration of 50-60 wt.%. In another embodiment, the mixture of the active material with an organic material comprises the Cei-q.nM3qLnO2-n / 2-d material in a concentration of 60-70 wt.%. In another embodiment, the mixture of the active material with an organic material comprises the Cei-q.nM3qLnO2-n / 2-d material in a concentration of 70-80 wt.%. In one embodiment, the mixture of the active material with an organic material comprises the Cei-q.nM3qLnO2-n / 2-d material in a concentration of 70 wt.%. In some other embodiments, the mixture of the active material with an organic material comprises the organicmaterial in a concentration of 20-30 wt.%. In other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 30-40 wt.%. In other embodiments, the mixture of the active material with an organic material comprises the organic material in a concentration of 40-50 wt.%. In one embodiment, the mixture of the active material with an organic material comprises the organic material in a concentration of 30 wt.%. In one specific embodiment, the mixture of the active material with an organic material comprises the Cei-q.nM3qLnO2-n / 2-d material in a concentration of 70 wt.%, and the organic material in a concentration of 30 wt.%. Each possibility represents a separate embodiment of this invention.

[0049] In some embodiments, the mixture of the contact material and the organic material is homogeneous. In another embodiment, the mixture layer is in a form of a paste or suspension. In other embodiment, the form is a paste. In other embodiment, the form is a suspension. In some embodiments, the mixture of the contact material and the organic material comprises a ceria-based material, in a concentration of 50-80 wt.%, and the organic material in a concentration of 20-50 wt.%, wherein the ceria-based material is doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo. In some embodiments, the “contact material” refers to the ceria-based material, which is doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo. In some other embodiments, the mixture of the contact material and the organic material comprises the contact material in a concentration of 50-60 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the contact material in a concentration of 60-70 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the contact material in a concentration of 70-80 wt.%. In one embodiment, the mixture of the contact material and the organic material comprises the contact material in a concentration of 70 wt.%. In some other embodiments, the mixture of the contact material and the organic material comprises the organic material in a concentration of 20-30 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the organic material in a concentration of 30-40 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the organic material in a concentration of 40-50 wt.%. In one embodiment, the mixture of the contact material and the organic material comprises the organic material in a concentration of 30 wt.%. In one specific embodiment, the mixture of the contact material and the organic material comprises the contact material in a concentration of 70 wt.%, and the organic material in a concentration of 30 wt.%. Each possibility represents a separate embodiment of this invention.

[0050] In some embodiments, the mixture of the contact material and the organic material comprises the Cei-x.yM1xM2yO2-5 material (as the contact material) in a concentration of 50-80 wt.%, and the organic material in a concentration of 20-50 wt.%. In some other embodiments, the mixture of thecontact material and the organic material comprises the Cei-x.yM1xM2yO2-8 material in a concentration of 50-60 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the Cei-x.yM1xM2yO2-8 material in a concentration of 60-70 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the Cei-x.yM1xM2yO2-5 material in a concentration of 70-80 wt.%. In one embodiment, the mixture of the contact material and the organic material comprises the Cei-x.yM1xM2yO2-5 material in a concentration of 70 wt.%. In some other embodiments, the mixture of the contact material and the organic material comprises the organic material in a concentration of 20-30 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the organic material in a concentration of 30-40 wt.%. In another embodiment, the mixture of the contact material and the organic material comprises the organic material in a concentration of 40-50 wt.%. In one embodiment, the mixture of the contact material and the organic material comprises the organic material in a concentration of 30 wt.%. In one specific embodiment, the mixture of the contact material and the organic material comprises the Cei-X.yM1xM2yO2-5 material in a concentration of 70 wt.%, and the organic material in a concentration of 30 wt.%. Each possibility represents a separate embodiment of this invention.

[0051] In some embodiments, the organic material within the mixture of the contact material and the organic material and / or the mixture of the active material and the organic material is terpineol, butyl carbitol, ethyl cellulose, polyivinyl alcohol (PVA), acrylics (e.g. polyurethane acrylate, Poly(methyl methacrylate)), methanol, ethanol, n-propanol, isopropanol or any alcohol until including C6 (hexanol); or any combination thereof; or any combination of said listed herein materials (“terpineol . . . C6 (hexanol)”) with water. In one embodiment, the organic material is a mixture of terpineol and ethyl cellulose. In another embodiment, the organic material is a mixture of ethanol and water. In another embodiment, the organic material is PVA dissolved in ethanol and / or water. In one other embodiment, the organic material is a mixture of terpineol, having a concentration of 80-99.9 wt.%, and ethyl cellulose, having a concentration of 0.1-20 wt.%.

[0052] In some other embodiments, the terpineol has a concentration of 80-90 wt.%. In another embodiment, the terpineol has a concentration of 90-99 wt.%. In another embodiment, the terpineol has a concentration of 99-99.9 wt.%. In one embodiment, the terpineol has a concentration of 97 wt.%. In some other embodiments, the ethyl cellulose has a concentration of 0.1-1 wt.%. In another embodiment, the ethyl cellulose has a concentration of 1-10 wt.%. In another embodiment, the ethyl cellulose has a concentration of 10-20 wt.%. In one embodiment, the ethyl cellulose has a concentration of 3 wt.%. In one specific embodiment, the organic material is a mixture of terpineol, having a concentration of 97 wt.%, and ethyl cellulose, having a concentration of 3 wt.%. Each possibility represents a separate embodiment of this invention.

[0053] In some other embodiments, this invention provides additional methods of preparing a stack comprising a multilayered structure, the multilayered structure comprises at least one active layer and at least one contact layer, wherein the active layer comprises a ceria-based material, doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti and optionally co-doped with a metal having a lower valence than said metal M3; and the contact layer comprises a ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo; wherein the methods comprise:1. co-sintering the contact material with the active material during its preparation;2. applying the contact material to a surface of a formed active material as a paste, slurry and or paint and then sintering at the sintering temperatures and times as described hereinabove, to create a good, robust contact;3. vacuum deposition of the contact material on the surface of a formed active material and then sintering as mentioned above. The deposition can be from a stoichiometric material or as a metal containing the correct concentration of metals (e.g. to reactive deposition of Ceo.89Zro.1Nbo.01O2 from a metallic target containing in mol% Ceo.89Zro.1Nbo.o1). The deposition can be in vacuum with subsequent oxidation and formation of the contact material or deposition in presence of oxygen, which oxidizes the alloy during the deposition, forming the contact material during deposition;4. application of the contact material via screen-printing or extrusion simultaneously with the screen printing of the active material, or screen-printing or extrusion on the surface of the active material;5. Sol -gel deposition of the contact materials on the surface of a formed active material, with subsequent sintering as mentioned above; and / or6. Loading the active and contact layers sequentially into a die and compacting them together with an isostatic press (co-pressing and co-firing technique).

[0054] In one embodiment, the stack was prepared via the co-pressing and co-firing technique (see point 6 above): the stack was prepared by loading the active material (e.g. Ceo.9Zro.1O2) and the contact material (e.g. Ceo.89Zro.1Nbo.01O2) powders sequentially into a die and compacting them together with an isostatic press to form layers. In one embodiment, each layer consisted of enough powder to cover the previous layer, and at least 3 mm (3-10, 3-20 or 3-50 mm) high. Between each addition of powder, a low amount of pressure was applied (0.5 - 10, 10-20, 0.5 - 20, 10-20, 1-10 or 1 MPa). The resulting green body was compacted by cold isostatic pressing (20-500, 20-100, 100-200, 200-300, 300-400, 400-500, 100-500, 200-400 or 300 MPa). Resulting stacks were polished and top and bottom faces were made parallel with silicon carbide polishing papers (up to 1000-2000, up to 1000-1500, up to1500-2000 or up to 1600 mesh). Silicon carbide residue was removed by 0.5-200 (e.g. 30) minutes washing with ethanol (e.g. absolute or 100%) in an ultrasonic bath. Figure 2A depicts a photo of the resulting exemplary stack. Each possibility represents a separate embodiment of this invention.

[0055] In some other embodiments, stacks of this invention which are fabricated using co-pressing, co-firing, or slurry-casting techniques can be oxidized to reduce surface and bulk conductivity. In one embodiment, the oxidation can be achieved by four methods: (i) heating to 300-700, 300-500, 300- 400, 400-600 or 400-700 °C under oxygen gas flow (100-1000, 500-1000, 200-1000, 400-1000, 700- 1000, 500-800 or 900-1000 ccm) , (ii) heating to 300-700, 300-500, 300-400, 400-600 or 400-700°C under CO2 gas flow, (iii) heating to 700-1000, 700-800, 800-900, 900-1000 or 800-1000 °C under CO gas flow, and (iv) by submerging the stack in a (Na,K)NOs melt, and applying positive voltage on the stack.

[0056] In one embodiment, the term “a” or “one” or “an” refers to at least one. In one embodiment the phrase “two or more” may be of any denomination, which will suit a particular purpose. In one embodiment, “about” or "approximately" may comprise a deviance from the indicated term of + 1 %, or in some embodiments, - 1 %, or in some embodiments, ± 2.5 %, or in some embodiments, ± 5 %, or in some embodiments, ± 7.5 %, or in some embodiments, ± 10 %.

[0057] The following examples are presented in order to more fully illustrate the preferred embodiments of the invention. They should in no way be construed, however, as limiting the broad scope of the invention.EXAMPLESEXAMPLE 1Contact material (Ceo.s9Zro.1Nbo.01O2) preparation and characterization

[0058] An aqueous solution of (NH4)2CO3(Acros Organics, extra pure, 99%) was added drop-wise to an aqueous solution containing Ce(NO3)3‘6H2O (Strem 99.5-.9% purity). Cerium nitrate was coprecipitated with NbCh (Alfa Aesar, 99.9) and ZrO(NO3)2‘6H2O (Arcos 99.5%). The resulting mixture was kept at 80°C under continuous stirring for 1 hour. Precipitates were washed with deionized water and then ethanol, and the powder was ground and calcined at 500°C for 3 hours.EXAMPLE 2Active material (Ceo.9Zro.1O2) preparation and characterization

[0059] An aqueous solution of (NH4)2CO3(Acros Organics, extra pure, 99%) was added drop-wise to an aqueous solution containing Ce(NO3)3‘6H2O (Strem 99.5-.9 % purity). Doped ceria was prepared by co-precipitating cerium nitrate with ZrO(NO3)2‘6H2O. Co-doped ceria was prepared by co-precipitating cerium nitrate with the appropriate nitrate and ZrO(NO3)2‘6H2O,. The resulting mixture was kept at 80°C under continuous stirring for 1 hour. Precipitates were washed with deionized water and then ethanol, and the powder was ground and calcined at 500°C for 3 hours.EXAMPLE 3Stack fabrication using a layer-by-layer slurry-casting technique

[0060] A stack was prepared via layer-by-layer slurry-casting technique (Figure 1 A). Each layer was made from a paste containing 70wt% a solid powder of the corresponding composition and 30 wt % of liquid medium (97 wt % terpineol, 3 wt % ethyl cellulose). Each layer was applied on a cellulose acetate film with a 6 mm diameter hole, with enough material to fill the hole, by using a silicone squeegee and stacked on top of each other. The cellulose acetate film was lifted, and the stack was sintered at between 700°C and 1400°C; for a duration ranging between 1 minute and 10 hours, resulting in the triple-layered structure represented in the SEM image of Figure IB. From the SEM image, it is clear that (a) even without composition and sintering protocol optimization, the slurry casting produced a body without large air bubbles; (b) there is no interpenetration between the layers (there is no electrical shorting between the top and the bottom).EXAMPLE 4Stack fabrication using a co-pressing and co-firing technique

[0061] A stack was prepared via co-pressing and co-firing technique. The stack was prepared by loading the Ceo.9Zro.1O2 and Ceo.s9Zro.1Nbo.01O2 powders sequentially into a die and compacting them together with an isostatic press. Each layer consisted of enough powder to cover the previous layer, and 3 mm high. Between each addition of powder, a low amount of pressure was applied (1 MPa). The resulting green body was compacted by cold isostatic pressing (300 MPa). Resulting stacks were polished and top and bottom faces were made parallel with silicon carbide polishing papers (up to 1600 mesh). Silicon carbide residue was removed by 30 min washing with 100% ethanol in an ultrasonic bath. Figure 2A depicts a photo of the resulting stack.EXAMPLE 5Stack Electrical Tests

[0062] Experiments with the stack of Example 4 showed an insignificant decrease in the electrostriction coefficient (or “electrostriction strain coefficient”) while reducing the resistivity by more than three orders of magnitude. No measurable decrease in the actuating abilities was observed after > 100 hrs of continuous actuation resulting in strain >200 ppm.

[0063] The electrostriction coefficient of the stack of Example 4 was tested for 96 hours at the bias of 2.6 kV (field ~2.9 kV / cm). No degradation was found in the electrostriction coefficient (±1%). The electrostriction coefficient of the stack shows an insignificant change up to 1 Hz. Above 1Hz, the electrostriction coefficient drops to 10'17m2 / V2, as observed in Figure 3.

[0064] These results implied that a) the contact material did not degrade electrically and b) the contact material did not degrade mechanically. Also, Figure 2B depicts an impedance spectra of the actuator comprising the stack presented in Example 4, indicating that a non-blocking contact was formed.

[0065] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims

CLAIMSWhat is claimed is:

1. A ceria-based material, doped by a metal M1and co-doped with M2, wherein the metal M1comprises Hf, Zr, or Ti and M2comprises Nb, Ta, W, V, or Mo.

2. The material of claim 1, wherein the concentration of M1is 0.01 to 20 mol%.

3. The material of claim 1, wherein the concentration of M2is 0.05 to 10 mol%.

4. The material of claim 3, wherein the material is represented by the formula Cei-X- yM1xM2yO2-5 wherein x ranges between 0.0001 and 0.2; and y ranges between 0.0005 and 0.1; and 5 ranges between 0 and 0.05.

5. The material of claim 1, wherein M1is Zr.

6. The material of claim 1, wherein M2is Nb.

7. The material of claim 4, wherein 6 is 0.

8. The material of claim 4, wherein x is 0.

19. The material of claim 4, wherein y is 0.01.

10. The material of claim 1, wherein the material is represented by the formula: Ceo.89Zro.1Nbo.01O2.

11. A stack comprising a multilayered structure, the multilayered structure comprises at least one active layer and at least one contact layer, wherein the active layer comprises a ceriabased material, doped by a metal M3, wherein said metal M3is selected from Hf, Zr and Ti; and optionally co-doped with a metal having a lower valence than said metal M3; and the contact layer comprises the ceria based material according to claim 1.

12. The stack of claim 11, wherein the ceria-based material of the active layer has an electrostriction coefficient which ranges between 10'15m2 / V2and 10'18m2 / V2at a frequency ranging between 0.1 Hz and 105Hz.

13. The stack of claim 11, wherein the ceria-based material of the active layer doped by the metal M3is represented by the formula Cei-zM3zO2-d wherein z ranges between 0.02 and 0.7 and d ranges between 0 and 0.05.

14. The stack of claim 13, wherein z is 0.1.

15. The stack of claim 11, wherein the ceria-based material of the active layer, doped by a metal M3is co-doped with a metal having a lower valence than said metal M3.

16. The stack of claim 15, wherein said metal having a lower valence is selected from: Ca, Mg, Fe, Sc, Sn, Y, a lanthanide L and any combinations thereof.

17. The stack of claim 15, wherein said metal having a lower valence comprises a lanthanide L.

18. The stack of claim 17, wherein said lanthanide L is any lanthanide selected from La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu or any combination thereof.

19. The stack of claim 18, wherein the ceria-based material, doped by a metal M3is represented by the formula Cei-q.nM3qLnO2-n / 2-d, wherein said q ranges between 0.01 and 0.7; said n range between 0.01 and 0.7; and said d ranges between 0 and 0.05.

20. The stack of claim 18, wherein L is La or Yb.

21. The stack of claim 19, wherein L is La, q ranges between 0.08 and 0.12 and n ranges between 0.01 and 0.08, or wherein L is Yb, q ranges between 0.08 and 0.12, and n ranges between 0.05 and 0.15.

22. The stack of claim 11, wherein the active layer within the stack generates strain, stress or both upon application of an electric field.

23. The stack of claim 22, wherein said strain ranges between 0.1 ppm and 1000 ppm.

24. The stack of claim 22, wherein said stress is at least 0.01 MPa.

25. The stack of claim 11 , comprising one active layer and two contact layers, wherein the first layer is a contact layer, the second layer is an active layer and the third layer is a second contact layer; and wherein the active layer is in contact with both contact layers.

26. The stack of claim 25, wherein the active layer comprises the ceria-based material, doped by the metal M3, represented by the formula Ceo.9Zro.1O2.

27. The stack of claim 25, wherein the contact layer comprises a ceria-based material represented by the formula Ceo.s9Zro.1Nbo.01O2.

28. An actuator comprising the stack according to claim 11 and a voltage source, wherein the stack is connected to the voltage source; wherein when a bias is applied to the stack it produces an electrostriction response.

29. The actuator of claim 28, wherein the electrostriction response does not change more than 1% in the course of above 90 hours of bias application; and the bias applied is 2-3 kV.

30. The actuator of claim 28, wherein the bias applied is 2.6 kV.

31. The actuator of claim 28, wherein the bias is applied for 96 hours.

32. The actuator of claim 28, wherein the strain is 0.1-1000 ppm strain.

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