High tetragonality barium titanate-based compositions and methods of forming the same

Abstract

Barium titanate-based compositions having a high tetragonality and methods of forming the same are provided, as well as devices formed from the compositions. The barium titanate-based compositions advantageously have a high tetragonality and small particle sizes. For example, in some embodiments, the barium titanate-based compositions have a tetragonality of greater than about 2.0 and an average particle size of less than about 0.3 micron. Some methods involve achieving high tetragonality by limiting the concentration of certain metals (other than barium or titanium) in the compositions and/or heat treating the compositions at relatively high temperatures. In some methods, the A/B ratio of the composition may be adjusted prior to heat treatment to ensure that a small particle size is maintained during heat treatment. The barium titanate-based compositions may be processed to form dielectric layers in electronic devices, such as MLCCs, having excellent electrical properties as a result of the high tetragonality and relatively small particle sizes.

What is claimed is:  
     
         1 . A composition comprising barium titanate-based particles having an average particle size of equal to or less than about 0.3 micron and a tetragonality of equal to or greater than about 2.0.  
     
     
         2 . The composition of  claim 1  having an average particle size of equal to or less than about 0.2 micron.  
     
     
         3 . The composition of  claim 1  having an average particle size of equal to or less than about 0.15 micron.  
     
     
         4 . The composition of  claim 1  having a tetragonality of equal to or greater than about 2.5.  
     
     
         5 . The composition of  claim 1  having a tetragonality of equal to or greater than about 3.0.  
     
     
         6 . The composition of  claim 1 , wherein the barium titanate-based particles are barium titanate particles.  
     
     
         7 . The composition of  claim 1 , wherein the barium titanate particles have a strontium and calcium concentration of less than about 200 ppm.  
     
     
         8 . The composition of  claim 1 , wherein the barium titanate-based particles are hydrothermally-produced.  
     
     
         9 . The composition of  claim 1 , wherein the barium titanate-based particles are substantially spherical.  
     
     
         10 . The composition of  claim 1 , further comprising at least one dopant metal.  
     
     
         11 . The composition of  claim 10 , wherein the barium titanate-based particles include a coating comprising the least one dopant metal.  
     
     
         12 . The composition of  claim 1 , wherein the composition has an A/B ratio of between about 1.000 and about 1.025.  
     
     
         13 . The composition of  claim 1 , wherein the composition has an A/B ratio of between about 0.975 and about 1.000.  
     
     
         14 . A composition comprising barium titanate-based particles having an average particle size of equal to or less than about 0.15 micron and a tetragonality of equal to or greater than about 1.5.  
     
     
         15 . The composition of  claim 14  having a tetragonality of equal to or greater than about 2.0.  
     
     
         16 . The composition of  claim 14 , wherein the barium titanate-based particles are barium titanate particles.  
     
     
         17 . The composition of  claim 14 , wherein the barium titanate particles have a strontium and calcium concentration of less than about 200 ppm.  
     
     
         18 . The composition of  claim 14 , wherein the barium titanate-based particles are hydrothermally-produced.  
     
     
         19 . The composition of  claim 14 , wherein the barium titanate-based particles are substantially spherical.  
     
     
         20 . The composition of  claim 14 , further comprising at least one dopant metal.  
     
     
         21 . The composition of  claim 20 , wherein the barium titanate-based particles include a coating comprising the least one dopant metal.  
     
     
         22 . The composition of  claim 14 , wherein the composition has an A/B ratio of between about 1.000 and about 1.025.  
     
     
         23 . The composition of  claim 14 , wherein the composition has an A/B ratio of between about 0.975 and about 1.000.  
     
     
         24 . A multilayer ceramic capacitor comprising: 
 an electrode layer; and    a dielectric layer formed on the electrode layer, the dielectric layer including a plurality of grains, the grains comprising a barium titanate-based material and having an average grain size of equal to or less than about 0.3 micron and a tetragonality of equal to or greater than about 2.0.    
     
     
         25 . The multilayer ceramic capacitor of  claim 24  having an average grain size of equal to or less than about 0.2 micron.  
     
     
         26 . The multilayer ceramic capacitor of  claim 24  having an average grain size of equal to or less than about 0.15 micron.  
     
     
         27 . The multilayer ceramic capacitor of  claim 24  having a tetragonality of equal to or greater than about 2.5.  
     
     
         28 . The multilayer ceramic capacitor of  claim 24  having a tetragonality of equal to or greater than about 3.0.  
     
     
         29 . The multilayer ceramic capacitor of  claim 24 , wherein the grains comprise barium titanate.  
     
     
         30 . A method comprising: 
 mixing a barium source and a titanium source to form a reaction mixture, the barium source having a concentration of strontium and calcium of less than about 200 ppm;    maintaining the reaction mixture at an elevated temperature while the barium source reacts with the titanium source to produce barium titanate-based particles; and    heat treating the barium titanate-based particles at a temperature of between about 850° C. and about 1150°C.    
     
     
         31 . The method of  claim 30 , wherein the barium titanate-based particles have an average particle size of equal to or less than about 0.3 micron.  
     
     
         32 . The method of  claim 30 , wherein the barium titanate-based particles have a tetragonality of equal to or greater than about 2.0.  
     
     
         33 . The method of  claim 30 , comprising heat treating the barium titanate-based particles at a temperature of between about 950° C. and about 1050° C.  
     
     
         34 . The method of  claim 30 , further comprising adjusting an A/B ratio of the barium titanate-based particles prior to the heat treating step to a value between about 0.975 and 1.000 or between about 1.000 and about 1.025.  
     
     
         35 . The method of  claim 34 , comprising adjusting the A/B ratio to a value between about 0.982 and about 0.988 or between about 1.008 and about 1.012 prior to the heat treating step.  
     
     
         36 . The method of  claim 30 , further comprising processing the barium titanate-based particles to form a dielectric layer of a multilayer ceramic capacitor.  
     
     
         37 . The method of  claim 30 , wherein the barium titanate-based particles are barium titanate particles.  
     
     
         38 . The method of  claim 30 , further comprising coating the barium titanate-based particles with at least one dopant metal.  
     
     
         39 . A method comprising: 
 mixing a barium source and a titanium source to form a reaction mixture;    maintaining the reaction mixture at an elevated temperature while the barium source reacts with the titanium source to produce barium titanate-based particles;    adjusting an A/B ratio of the barium titanate-based particles; and    heat treating the barium titanate-based particles, after A/B ratio adjustment, at a temperature of between about 850° C. and about 1150° C.    
     
     
         40 . The method of  claim 39 , wherein the barium source has a concentration of strontium and calcium of less than about 200 ppm.  
     
     
         41 . The method of  claim 39 , wherein the barium titanate-based particles have an average particle size of equal to or less than about 0.3 micron.  
     
     
         42 . The method of  claim 39 , wherein the barium titanate-based particles have a tetragonality of equal to or greater than about 2.0.  
     
     
         43 . The method of  claim 39 , comprising heat treating the barium titanate-based particles at a temperature of between about 950° C. and about 1050° C.  
     
     
         44 . The method of  claim 39 , further comprising adjusting the A/B ratio of the barium titanate-based particles prior to the heat treating step to a value between about 0.975 and 1.000 or between about 1.000 and about 1.025.  
     
     
         45 . The method of  claim 39 , comprising adjusting the A/B ratio to a value between about 0.982 and about 0.988 or between about 1.008 and about 1.012 prior to the heat treating step.  
     
     
         46 . The method of  claim 39 , further comprising processing the barium titanate-based particles to form a dielectric layer of an MLCC after the heat treating step.  
     
     
         47 . The method of  claim 39 , wherein the barium titanate-based particles are barium titanate particles.  
     
     
         48 . The method of  claim 39 , further comprising coating the barium titanate-based particles with at least one dopant metal.