Method of making mixed metal oxide ceramics
A method of making dielectric ceramics containing mixed metal oxides is provided. The method comprises the steps of at least partially coating a metal oxide powder with a metal hydroxide or metal oxide, compacting the coated powder with one or more additional metal compounds or metal compound precursors, and directly sintering the compact in a single step. The method of the invention may be used to avoid occurrence of significant quantities of one or more undesired but thermodynamically or kinetically favored side products. The method of the invention may also be used to synthesize perovskites, in particular lead-magnesium-niobium (PMN), lead-magnesium-niobium-lead-titanium (PMN-PT) perovskites, or lead zirconate titanate (PZT).
1. A method of making a ceramic composition comprising a mixed metal compound, said method comprising the steps of:
a. providing a coated metal oxide powder, wherein the coating comprises a metal hydroxide compound containing a first metal;
b. compacting said coated metal oxide powder with one or more metal compounds or metal compound precursors selected from the group consisting of PbO, 3Pb(NO 3 ) 2 .7PbO, Pb(NO 3 ) 2 , PbCO 3 , (PbCO 3 ) 2 Pb(OH) 2 , Pb(OH) 2 and PbTiO 3 , to form a body; and
c. heating said body from step (b) comprising said coated metal oxide powder and said one or more metal compounds or metal compound precursors selected from the group consisting of PbO, 3Pb(NO 3 ) 2 .7PbO, Pb(NO 3 ) 2 , PbCO 3 , (PbCO 3 ) 2 Pb(OH) 2 , Pb(OH) 2 and PbTiO 3 , to form a ceramic composition comprising a substantially pure perovskite phase of a mixed metal compound.
2. The method of claim 1 , wherein said coated metal oxide powder is compacted with one or more compounds selected from the group consisting of metal compounds and metal compound precursors, without calcining a mixture of said coated metal oxide powder and said one or more compounds selected from the group consisting of metal compounds and metal compound precursors prior to said compacting step.
3. The method of claim 1 , wherein the mixed metal compound comprises at least one mixed metal compound selected from the group consisting of lead magnesium niobate, lead magnesium tantalite, lead nickel niobate, lead scandium tantalite, lead indium niobate, barium titanate and lead zirconate titanate.
4. The method of claim 3 , wherein the mixed metal compound comprises lead magnesium niobate.
5. The method of claim 1 , wherein the metal oxide powder is Nb 2 O 5 .
6. The method of claim 1 , wherein the first metal is magnesium.
7. The method of claim 6 , wherein the one or more compounds selected from the group consisting of metal compounds and metal compound precursors comprise PbO.
8. The method of claim 7 , wherein the one or more compounds selected from the group consisting of metal compounds and metal compound precursors further comprises PbTiO 3 .
9. The method claim 1 , wherein the heating step is carried out at a temperature of about 800° C. to about 1100° C.
10. The method of claim 1 , wherein the ceramic composition is substantially free of a pyrochlore phase.
11. The method of claim 1 , wherein the metal oxide powder comprises Nb 2 O 5 , the metal hydroxide comprises Mg(OH) 2 , and the second metal is Pb.
12. The method of claim 1 , wherein the said mixed metal compound comprises barium titanate.
13. The method of claim 1 , wherein the step of providing the coated metal oxide powder comprises the steps of:
(i) providing a composition comprising water, the metal oxide powder and a compound selected from the group consisting of metal hydroxides and metal hydroxide precursors;
(ii) if the pH of the suspension is below a pH of 8.9, adjusting a pH of the suspension to a pH level exceeding 8.9; and
(iii) forming said coating of said metal hydroxide on a surface of the metal oxide powder.
14. The method of claim 13 , wherein the pH is adjusted to a pH of about 9 to about 11.
15. The method of claim 13 , wherein the pH is adjusted to a pH of about 9.5 to about 10.5.
16. The method of claim 1 , wherein the step of providing the coated metal oxide powder comprises the steps of:
(i) providing a composition comprising water, the metal oxide powder and a metal hydroxide precursor;
(ii) if the pH of the suspension is below a pH of 8.9, adjusting a pH of the suspension to a pH level exceeding 8.9; and
(iii) forming said coating of said metal hydroxide in situ on a surface of the metal oxide powder.
17. The method of claim 16 , wherein the precursor of said metal hydroxide is dissolved in said water in step (i) to form a solution and said metal hydroxide is precipitated from said solution in step (iii).
18. The method of claim 17 , wherein the metal oxide powder comprises Nb 2 O 5 , the metal hydroxide comprises Mg(OH) 2 , and the second metal is Pb.
19. The method of claim 18 , wherein the ceramic composition is substantially free of a pyrochlore phase.