Freestanding Films With Electric Field-Enhanced Piezoelectric Coefficients

Abstract

A method to produce low-temperature sinterable powders which are then subsequently used to fabricate freestanding piezoelectric films with very large electric-field-enhanced piezoelectric response is provided. The −d 31 coefficient for PMN-PT layers can be as high as 2000 pm/V, larger than that of commercial single crystalline PMN-PT bulk materials, at 10 kV/cm (or 20 V over the 20-micron film thickness). In contrast to single crystals, the polycrystalline freestanding films are easy to fabricate and can be made into any size. The films are also easily miniaturized. The method can be applied to nearly any piezoelectric material.

1 - 5 . (canceled) 
     
     
         6 . A polycrystalline ceramic freestanding film made by a method comprising the steps of:
 dispersing coated particles in a solution of a material reactive with the coating of said coated particles to form a dispersion,   drying the dispersion to form a powder;   calcining the powder to form a calcined product wherein the coating of the coated particles has at least partially reacted,   suspending the calcined product in a precursor solution for a material reactive with the calcined product,   forming a powder of the calcined product and the material reactive with the calcined product from said precursor solution,   tape casting a slurry of said powder of the calcined product and the material reactive with the calcined product, a binder, a dispersing resin and a solvent,   separating the layer of the calcined product and the material reactive with the calcined product from the carrier tape to provide a freestanding film of the calcined product and the material reactive with the calcined product, and   reactive sintering the freestanding film of the calcined product and the material reactive with the calcined product, under conditions whereby the calcined product reacts with the material reactive with the calcined product to provide a sintered freestanding polycrystalline ceramic film.   
     
     
         7 . A polycrystalline ceramic freestanding film as claimed in  claim 6 , wherein said coated particles are selected from the group consisting of: Mg(OH) 2 -coated Nb 2 O 5  powders and ZrO 2 -coated TiO 2  powders. 
     
     
         8 . A polycrystalline ceramic freestanding film as claimed in  claim 7 , wherein said powder of the calcined product and the material reactive with the calcined product is selected from the group consisting of: lead-free piezoelectrics/dielectrics/ferroelectrics. 
     
     
         9 . A polycrystalline ceramic freestanding film as claimed in  claim 8 , wherein the coated particle is a Mg(OH) 2 -coated Nb 2 O 5  powder and the material reactive with the coated particles comprises lead. 
     
     
         10 . A polycrystalline ceramic freestanding film as claimed in  claim 9 , wherein the material reactive with the calcined product comprises lead titanate. 
     
     
         11 . A polycrystalline ceramic freestanding film as claimed in  claim 10 , wherein the sintering step is carried out at a temperature below about  900  degrees Celsius. 
     
     
         12 . A polycrystalline ceramic freestanding film as claimed in  claim 11 , wherein the precursor comprises lead acetate and titanium isopropoxide. 
     
     
         13 . A polycrystalline ceramic freestanding film as claimed in  claim 6 , wherein the binder is selected from the group consisting of acrylic resins. 
     
     
         14 . A polycrystalline ceramic freestanding film as claimed in  claim 13 , wherein the binder is selected from the group consisting of: acrylic acid esters and methacrylic acid esters made from monomers containing 4-12 carbon atoms. 
     
     
         15 . A polycrystalline ceramic freestanding film claimed in  claim 14 , wherein the binder is selected from the group consisting of: methyl methacrylate, ethyl methacrylate, iso-butyl methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, heptyl acrylate, heptyl methacrylate, octyl acrylate, octyl methacrylate, nonyl acrylate, nonyl methacrylate, decyl acrylate, decyl methacrylate, undecyl acrylate, undecyl methacrylate, dodecyl acrylate, and dodecyl methacrylate. 
     
     
         16 . A polycrystalline ceramic freestanding film as claimed in  claim 13 , wherein the dispersing resin is a blend of a low molecular weight dispersing resin having a molecular weight in the range of about 1,000-10,000, and a high molecular weight dispersing resin having a molecular weight in the range of about 40,000-80,000. 
     
     
         17 . A polycrystalline ceramic freestanding film as claimed in  claim 16 , wherein the low molecular weight dispersing resin comprises methyl methacrylate and iso-bornyl methacrylate. 
     
     
         18 . A polycrystalline ceramic freestanding film as claimed in  claim 17 , wherein the high molecular weight dispersing resin comprises iso-butyl methacrylate polymer. 
     
     
         19 . A polycrystalline ceramic freestanding film as claimed in  claim 6 , wherein the calcined product comprises lead magnesium niobate and the material reactive with the calcined product comprises lead titanate. 
     
     
         20 . A multi-layer actuator made using the polycrystalline ceramic freestanding film as claimed in  claim 6 . 
     
     
         21 . A multi-layer actuator made using the polycrystalline ceramic freestanding film as claimed in  claim 10 . 
     
     
         22 . A multi-layer actuator made using the polycrystalline ceramic freestanding film as claimed in  claim 12 . 
     
     
         23 . A multi-layer actuator made using the polycrystalline ceramic freestanding film as claimed in  claim 15 . 
     
     
         24 . A multi-layer actuator made using the polycrystalline ceramic freestanding film as claimed in  claim 18 . 
     
     
         25 . A multi-layer actuator made using the polycrystalline ceramic freestanding film as claimed in  claim 19 .