Electromechanical actuators

Abstract

A perovskite compound of the formula, (Na1 / 2Bi1 / 2)1-xMx(Ti1-yM′y)O3±z, where M is one or more of Ca, Sr, Ba, Pb, Y, La, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb and Lu; and M′ is one or more of Zr, Hf, Sn, Ge, Mg, Zn, Al, Sc, Ga, Nb, Mo, Sb, Ta, W, Cr, Mn, Fe, Co and Ni, and 0.01<x<0.3, and 0.01<y<0.3, and z<0.1 functions as an electromechanically active material. The material may possess electrostrictive or piezoelectric characteristics.

Description

[0001] This application is a continuation-in-part application of U.S. Ser. No. 09 / 174,981 filed Oct. 19, 1998, entitled “Piezoelectric Actuators and Methods of Making Same,” which is incorporated herein by reference. [0002] This application claims priority from and is a continuation-in-part application of U.S. Serial No. 60 / 195,835 filed Apr. 11, 2000, entitled “Electromechanical Actuators and Methods of Making Same,” and U.S. Serial No. 60 / 222,278 filed Jul. 27, 2000, entitled “Barium and Zirconium Co-Doped Sodium Bismuth Titanate,” both of which are incorporated herein by reference.[0003] This invention was made with government support under Grant Number N00014-97-0989 awarded by the Office of Naval Research. The government has certain rights in the invention.BACKGROUND OF THE INVENTION [0004] This invention relates to a class of lead-free or low lead perovskite structure oxide compounds useful as electromechanical actuators. It also relates to composite actuators utilizing these ...

AI Technical Summary

Benefits of technology

[0028] Increased doping of BaTiO3 beyond the 6% BT-MPB composition in NBT-BT continues to stabilize the ferroelectric tetragonal phase. This invention demonstrates that through simultaneous doping on the A- and B-sites in NBT with Ba2+ and Zr4+, respectively, rhombohedral and tetragonal non-ferroelectric phases can be stabilized for higher concentrations of Ba2+ (up to 26 mol % Ba2+). Within the same phases, relaxor properties are often enhanced by the introduction of greater Ba2+ doping.

Problems solved by technology

A drawback to all these lead-based perovskites is the toxicity of lead and associated difficulties in processing, crystal growth and handling.

In certain environmentally sensitive or biologically sensitive applications, they can not be used.

Another drawback is the high density and relatively low elastic modulus of the lead based perovskites.

While the intrinsic electromechanical properties of properly oriented single crystals appear to be attractive, there are numerous obstacles to their practical implementation.

Firstly, the growth, orientation, cutting and handling of large single crystals is expensive and difficult.

Secondly, ceramic ferroelectrics are mechanically brittle and weak, more so than other ceramics such as aluminum oxide, silicon nitride or silicon carbide.

Nonetheless, a conventional polycrystalline ferroelectric, electrostrictive or magnetostrictive actuator suffers in performance relative to an optimally oriented single crystal.

However, it is well-known to those skilled in the art that polycrystalline ceramics are difficult to prepare in a textured form.

While oriented polycrystalline perovskite ferroelectrics have been accomplished in the form of thin films supported by a substrate they have not been achieved in polycrystals suitable for actuation devices.

Images