COMPLEX OXIDE AND METHOD FOR PRODUCING THE SAME

1 . A complex oxide comprising a zirconium element, a cerium element, and optionally another rare earth metal element,

wherein D 50 and D 90 of the complex oxide measured by a laser diffraction scattering particle size distribution measurement method are 0.5 μm or less and 1 μm or less, respectively.

2 . The complex oxide according to claim 1 , wherein a specific surface area measured by a BET method after heat treatment at 1000° C. for 3 hours in an air atmosphere is 20 m 2 /g or more.

3 . The complex oxide according to claim 1 , wherein the complex oxide contains the other rare earth metal element,

wherein a percentage by mass of the other rare earth metal element in terms of oxide in a surface of the complex oxide measured by X-ray photoelectron spectroscopy is 0.80 times or more a percentage by mass of the other rare earth metal element in terms of oxide in the whole of the complex oxide.

4 . A method for producing a complex oxide, comprising:

(a) preparing for a raw material solution containing water, a zirconium salt, a cerium salt, and optionally another rare earth metal salt;

(b) adding to the raw material solution, a first precipitant selected from: an aqueous solution containing a sulfate ion; and a compound that can dissolve in water to produce a sulfate ion, to form a first precipitate containing a zirconium element, thereby obtaining a first slurry containing the first precipitate;

(c) subjecting the first slurry to a wet grinding treatment;

(d) adding to the first slurry after the wet grinding treatment, a second precipitant selected from: an aqueous solution containing a hydroxide ion; and a compound that can dissolve in water to produce a hydroxide ion, to form a second precipitate containing a zirconium element, a cerium element, and optionally another rare earth metal element, thereby obtaining a second slurry containing the second precipitate;

(e) obtaining a cake from the second slurry; and

(f) calcining the cake to produce a complex oxide containing a zirconium element, a cerium element, and optionally another rare earth metal element.

5 . The production method according to claim 4 , wherein:

in step (e), a first cake is obtained from the second slurry, and the first cake is treated with an alcohol-containing liquid to obtain a second cake having an alcohol concentration of 90 vol % or more; and

in step (f), the second cake is calcined to produce the complex oxide.

6 . The production method according to claim 4 , wherein in step (c), the wet grinding treatment is performed such that D 50 of a ground product of the first precipitate measured by a laser diffraction scattering particle size distribution measurement method is 0.5 μm or more and 1.5 μm or less.

7 . The production method according to claim 4 , wherein in step (c), the wet grinding treatment is performed such that D 90 of a ground product of the first precipitate measured by a laser diffraction scattering particle size distribution measurement method is 1 μm or more and 2.5 μm or less.

8 . The production method according to claim 4 , wherein in step (c), the wet grinding treatment is performed using beads.

9 . The production method according to claim 8 , wherein in step (c), the wet grinding treatment is performed such that acceleration applied to the beads exceeds 1 G.

10 . The production method according to claim 8 , wherein the beads have a diameter of 0.3 mm or less.

11 . The production method according to claim 8 , wherein in step (c), the wet grinding treatment is performed for 1 hour or more.

12 . The production method according to claim 4 , wherein in step (b), the first precipitate is added to the raw material solution such that a molar quantity of a sulfate ion in the raw material solution is 0.4 times or more and 2 times or less a molar quantity of a zirconium element in the raw material solution.

13 . The production method according to claim 4 , wherein in step (b), a temperature of the raw material solution when adding the first precipitant is 70° C. or more and 100° C. or less.

14 . The production method according to claim 4 , wherein in step (d), the second precipitant is added to the first slurry such that a molar quantity of a hydroxide ion in the first slurry is 2 times or more a molar quantity of an oxygen element that is required to allow each of a zirconium element, a cerium element, and another rare earth metal element in the first slurry to become oxide.

15 . The production method according to claim 4 , wherein in step (d), a temperature of the first slurry when adding the second precipitate is 35° C. or more and 60° C. or less.