Method of preparing ferroelectric powders and ceramics

Abstract

The present invention relates methods of making a ferroelectric powder and ceramics having the steps of mixing a polymer and a metal oxide precursor mixture within a mill, milling the polymer/precursor mixture, drying the mixture, burning the dried solid, grinding the solid, and calcinating the solid to a ferroelectric powder. The present invention in particular introduces a polymeric species with a metal oxide precursor at the milling stage. The production of ceramics further involves compressing the ferroelectric powder and sintering the compression.

1 . A method of making a ferroelectric powder, comprising the steps of
 mixing a polymer with a metal oxide precursor within a mill;   milling said polymer/metal oxide precursor mixture;   drying said polymer/metal oxide precursor mixture;   burning said dried mixture;   grinding the burned solid;   and calcinating the solid.   
     
     
         2 . The method of  claim 1 , further comprising the step of adding excess lead in the range of 3 to 7 mol % following the mixing of said polymer and said metal oxide precursor. 
     
     
         3 . The method of  claim 1 , wherein said polymer has a molecular weight of 10,000 or below. 
     
     
         4 . The method of  claim 1 , wherein said polymer is selected from the group consisting of polyethylene glycol, polyethylene glycol monoethyl ether, copolymer such as polyethylene glycol/polypropylene glycol copolymers, polypropylene glycol, polyvinyl pyrolidone, and polyvinyl alcohol. 
     
     
         5 . The method of  claim 1 , wherein said polymer is used in a ratio of 0.5 to 1.5 mol to the mol amount of Pb, in the case where a Pb-oxide compound is used in said precursor mixture, or in a ratio of 0.5 to 1.5 mol to the mol amount of Bi, in the case where a Bi-oxide compound is used in said precursor mixture. 
     
     
         6 . The method of  claim 1 , wherein said polymer is polyethylene glycol with a molecular weight selected from the group consisting of 200, 2000, or 10,000. 
     
     
         7 . The method of  claim 1 , wherein said metal oxide precursor mixture is comprised of more than one metal oxide compound. 
     
     
         8 . The method of  claim 1 , wherein said metal oxide precursor mixture is comprised of one or more of the metal compounds selected from the group consisting of BaO, PbO, MgO, NiO, SrO, ZnO, La 2 O 3 , NiO 3 , Bi 2 O 3 , TiO 2 , ZrO 2 , Nb 2 O 5 , and Ta 2 O 5 . 
     
     
         9 . The method of  claim 1 , wherein said metal oxide precursor mixture is made of PbO, MgO, Nb 2 O 5 , and TiO 2 . 
     
     
         10 . The method of  claim 1 , wherein the mixing of said polymer and said precursor mixture occurs within a mill selected from the group consisting of ball mill, vibrating ball mill, rod mill, or hammer mill. 
     
     
         11 . The method of  claim 1 , wherein drying said polymer/metal oxide precursor mixture occurs between a range of about 95° C. to 115° C. for a period of between 1.5 and 3 hours. 
     
     
         12 . The method of  claim 1 , wherein burning said dried mixture occurs at a temperature of between 250° C. and 600° C. for a period of 3 to 4.5 hours. 
     
     
         13 . The method of  claim 1 , wherein grinding the burned solid comprises utilizing an organic binder during grinding. 
     
     
         14 . The method of  claim 1 , wherein calcinating said solid occurs at a temperature of between 800° C. and 1000° C. for a period of between 1.5 and 2.5 hours. 
     
     
         15 . A method of making a ceramic using a ferroelectric powder devoid of pyrochlore phase, comprising the steps of
 obtaining a ferroelectric powder   compressing said ferroelectric powder   and sintering said ferroelectric powder.   
     
     
         16 . The method of  claim 15 , wherein said ferroelectric powder is a selected from the group consisting of non-relaxor-type ferroelectric and relaxor-type ferroelectric. 
     
     
         17 . The method of  claim 15 , wherein said ferroelectric powder is selected from the group consisting of PbTiO 3 , PbZrTiO 3 , Bi 4 Ti 3 O 12 , SrBi 4 Ti 4 O 15 , BaBi 4 Ti 4 O 15 , CaBi 4 Ti 4 O 15 , Pb (Mg 1/3 Nb 2/3 )—PbTiO 3 , Pb (Ni 1/3 Nb 2/3 )—PbTiO 3 , Pb (Zn 1/3 Nb 2/3 )—PbTiO 3 , and Bi 1/2 Na 1/2 TiO 3 . 
     
     
         18 . The method of  claim 15 , wherein said ferroelectric powder possess a morphotrophic phase boundary where rhomobohedral and tetragonal phase coexist. 
     
     
         19 . The method of  claim 15 , wherein compressing said ferroelectric powders occurs with the assistance of a binder selected from the group consisting of organic binders, polymers, waxes, gums, polyvinyl alcohol, clay, silicate, and phosphate. 
     
     
         20 . The method of  claim 15 , wherein sintering comprises exposing said compressed powder to a temperature between 900° C. and 1100° C. for between 1.5 and 3 hours.