Oxide ion conductor, manufacturing method therefor, and fuel cell using the same

Abstract

An oxide ion conductor is manufactured having a relatively high mechanical strength while the ionic conduction thereof is maintained at a satisfactory level. The oxide ion conductor is represented by the formula Ln1 1-x A x Ga 1-y-z-w B1 y B2 z B3 w O 3-d . In the oxide ion conductor, Ln1 is at least one element selected from the group consisting of La, Ce, Pr, Nd, and Sm, A is at least one element selected from the group consisting of Sr, Ca, and Ba, B1 is at least one element selected from the group consisting of Mg, Al, and In, B2 is at least one element selected from the group consisting of Co, Fe, Ni, and Cu, and B3 is at least one element selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn, Mn, and Zr, wherein x is 0.05 to 0.3, y is 0.025 to 0.29, z is 0.01 to 0.15, w is 0.01 to 0.15, y+z+w is 0.035 to 0.3, and d is 0.04 to 0.3.

What is claimed is:  
     
         1 . An oxide ion conductor represented by the formula Ln1AGaB1B2B3O, 
 wherein Ln1 is at least one element selected from the group consisting of La, Ce, Pr, Nd, and Sm, the content thereof being 43.6 to 51.2 percent by weight,    A is at least one element selected from the group consisting of Sr, Ca, and Ba, the content thereof being 5.4 to 11.1 percent by weight,    the content of Ga is 20.0 to 23.9 percent by weight,    B1 is at least one element selected from the group consisting of Mg, Al, and In,    B2 is at least one element selected from the group consisting of Co, Fe, Ni, and Cu,    B3 is at least one element selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn, Mn, and Zr,    wherein, in the case in which B3 is an element differing from B1 or B2, the content of B1 is 1.21 to 1.76 percent by weight, the content of B2 is 0.84 to 1.26 percent by weight, and the content of B3 is 0.23 to 3.08 percent by weight, and    in the case in which B3 is an element equal to B1 or B2, the total content of B1 and B3 is 1.41 to 2.70 percent by weight, and the total content of B2 and B3 is 1.07 to 2.10 percent by weight.    
     
     
         2 . An oxide ion conductor according to  claim 1 , wherein first crystal grains composed of elements Ln1, A, and Ga and second crystal grains composed of element B1 are present between matrix crystal grains other than the first crystal grains and the second crystal grains.  
     
     
         3 . An oxide ion conductor according to  claim 1 , wherein first crystal grains composed of elements Ln1, A, and Ga and second crystal grains composed of element B1 are present in the matrix crystal grains other than the first crystal grains and the second crystal grains.  
     
     
         4 . An oxide ion conductor according to one of claims  2  and  3 , wherein the grain diameters of the first crystal grains and the second crystal grains are 0.1 to 2.0 μm.  
     
     
         5 . An oxide ion conductor according to one of claims  2  and  3 , wherein the grain diameter of the matrix crystal grains is 2.0 to 7.0 μm.  
     
     
         6 . An oxide ion conductor represented by the formula Ln1 1-x A x Ga 1-y-z-w B1 yB 2 z B3 w O 3-d , 
 wherein Ln1 is at least one element selected from the group consisting of La, Ce, Pr, Nd, and Sm,    A is at least one element selected from the group consisting of Sr, Ca, and Ba,    B1 is at least one element selected from the group consisting of Mg, Al, and In,    B2 is at least one element selected from the group consisting of Co, Fe, Ni, and Cu,    B3 is at least one element selected from the group consisting of Al, Mg, Co, Ni, Fe, Cu, Zn, Mn, and Zr, and    x is 0.05 to 0.3, y is 0.025 to 0.29, z is 0.01 to 0.15, w is 0.01 to 0.15, y+z+w is 0.035 to 0.3, and d is 0.04 to 0.3.    
     
     
         7 . An oxide ion conductor according to  claim 6 , wherein first crystal grains composed of elements Ln1, A, and Ga and second crystal grains composed of element B1 are present between matrix crystal grains other than the first crystal grains and the second crystal grains.  
     
     
         8 . An oxide ion conductor according to  claim 6 , wherein first crystal grains composed of elements Ln1, A, and Ga and second crystal grains composed of element B1 are present in the matrix crystal grains other than the first crystal grains and the second crystal grains.  
     
     
         9 . An oxide ion conductor according to one of claims  7  and  8 , wherein the grain diameters of the first crystal grains and the second crystal grains are 0.1 to 2.0 μm.  
     
     
         10 . An oxide ion conductor according to one of claims  7  and  8 , wherein the grain diameter of the matrix crystal grains is 2.0 to 7.0 μm.  
     
     
         11 . A method for manufacturing an oxide ion conductor, comprising: 
 a step of mixing individual powdered oxides composed of Ln1, A, Ga, B1, and B2 in ratios in accordance with those described in  claim 1  so as to form a first powdered mixture;    a step of calcining the first powdered mixture at 500 to 1,300° C. for 1 to 10 hours so as to form calcined powder;    a step of mixing a powdered oxide composed of B3 in a ratio in accordance with that described in  claim 1  with the calcined powder so as to form a second powdered mixture;    a step of molding the second powdered mixture into a molded body having a predetermined shape; and    a step of baking the molded body for sintering at 1,200 to 1,600° C. for 0.5 to 20 hours.    
     
     
         12 . A solid oxide fuel cell provided with an electrolyte comprising an oxide ion conductor according to one of claims  1  and  6 .  
     
     
         13 . A gas sensor comprising an oxide ion conductor according to one of claims  1  and  6 .  
     
     
         14 . An oxygen separation membrane for use in an electrochemical oxygen pump, comprising an oxide ion conductor according to one of claims  1  and  6 .