Process for the synthesis of crystalline powders of perovskite compounds

• US 5,900,223 A
• Filed: 11/14/1996
• Issued: 05/04/1999
• Est. Priority Date: 09/03/1993
• Status: Expired due to Term

• Current Assignee: CHON International Company Limited
• Original Assignee: CHON International Company Limited
• Inventors: Matijevic, Egon, Her, Yie-Shein
• Primary Examiner(s): BOS, STEVEN J
• Application Number:
  US08/748,719
• Time in Patent Office: 901 Days
• Field of Search: 423/598, 423/593, 423/263, 423/71, 423/179.5, 423/184, 423/158, 423/65, 423/92, 423/21.1, 423/160, 423/161
• US Class Current: 423/263
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01B 13/363 Mixtures of oxides or hydroxides by precipitation
• CPC Class Codes: C01G 23/006 Alkaline earth titanates
• CPC Class Codes: C01G 33/00 Compounds of niobium
• CPC Class Codes: C01P 2002/34 perovskite-type (ABO3)
• CPC Class Codes: C01P 2002/54 one element only
• CPC Class Codes: C01P 2002/72 by d-values or two theta-values, e.g. as X-ray diagram
• CPC Class Codes: C01P 2004/03 obtained by SEM
• CPC Class Codes: C01P 2004/32 Spheres
• CPC Class Codes: C01P 2004/52 highly monodisperse size distribution
• CPC Class Codes: C01P 2004/61 Micrometer sized, i.e. from 1-100 micrometer
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/20 Powder free flowing behaviour
• CPC Class Codes: C01P 2006/32 Thermal properties
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: Y10S 977/776 Ceramic powder or flake

Abstract

A process for the preparation of crystalline perovskite powders consisting essentially of primary particles uniform in nanometer or micrometer size and uniform and near spherical shape and of narrow size distribution, of the general formula A_x (BO₃)_y, wherein cation A is at least one metal selected from the group comprising Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺ and La³⁺ and B in the anion (BO₃) is at least one metal selected from the group consisting of Ti⁴⁺, Zr⁴⁺, Sn⁴⁺, Hf⁴⁺, Nb⁵⁺ and Ta⁵⁺, x is equal to the valence of the anion (BO₃) and y is equal to the valence of cation (A), comprising contacting, under stirring, an aqueous solution (I) containing inorganic or organic salts or organometallic compounds of at least one metal A and of at least one metal B, the ratio (A)/(B) being around the stoichiometric value corresponding to the above general formula, with an aqueous basic solution (II) containing an inorganic or organic base in an amount at least above the stoichiometric amount corresponding to the above general formula, preheated to 70°-100° C., and performing the process at temperatures of from 70° to 100° C. while maintaining the reaction mixture at constant OH^- concentration.

Claims

1. A process for the preparation of crystalline perovskite powders of the general formula A_x (BO₃)_y, wherein cation A is at least one metal selected from the group consisting of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, and La³⁺, and B in the anion (BO₃) is at least one metal selected from the group consisting of Ti⁴⁺, Zr⁴⁺, Sn⁴⁺, Hf⁴⁺, Nb⁵⁺, and Ta⁵⁺, x is equal to the valence of the anion (BO₃), and y is equal to the valence of the cation A, the general formula of the crystalline perovskite powders having an A/B molar ratio value, said process comprising:

separately and simultaneously injecting two solutions into a reactor containing a stirred aqueous base solution having a pH of about 14 and preheated to 70-100°

C., one of said two solutions being an aqueous solution (I) containing salts or organometallic compounds of at least one metal A as defined above and of at least one metal B as defined above, the molar ratio A/B in the salts or organometallic compounds being approximately equal to the value of the ratio A/B of the general formula of the crystalline perovskite powders, and the other of said two solutions being an aqueous basic solution (II) containing a base in an amount from 0.4 to 6 mol/dm³ ; and

maintaining the flow rate of solution (I) constant and injecting the base solution (II) to form a reaction mixture, the base solution(II) being injected at a flow rate sufficient to maintain the pH of the reaction mixture constant at about 14 while the process is performed at 70°

C.-100°

C. with a reaction time of 30 minutes or less, said flow rates of solutions (I) and (II) varying from 5 to 40 cm³ /min, thereby causing crystalline perovskite powders to precipitate.

2. A process according to claim 1, in which the total concentration of metal ions in solution (I) ranges from 0.1 to 2.0 mol dm^-3, the molar ratio of A/B ranges from 0.8 to 1.2 and the base concentration in solution (II) ranges from 0.4 to 6 mol dm^-3.

3. A process according to claim 1, in which the salts are selected from halides, nitrates, acetates, perchlorates, oxalates and alkoxides and the base is selected from alkaline or alkaline-earth metal hydroxides and ammonium hydroxide.

4. A process according to claim 1, in which the salts are chlorides and the base is NaOH or KOH.

5. A process according to claim 1, in which A is selected from Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ optionally substituted with from 0 to 50% of at least one dopant D of the group Ca²⁺, Mg²⁺, Sr²⁺ and La³⁺ and B is selected from Ti⁴⁺, and Nb⁵⁺ optionally substituted with at least one dopant D'"'"' of the group Zr⁴⁺, Sn⁴⁺, Hf⁴⁺, Nb⁵⁺ and Ta⁵⁺, with the condition that D is different from A, and D'"'"' is different from B.

6. A process according to claim 1 in which besides solutions (I) and (II) there is used a solution (III) containing a salt of the same element B contained in solution (I) and a salt of a dopant D or a salt of the same element A contained in solution (I) and a salt of a dopant D'"'"', D being selected from Ca²⁺, Mg²⁺, Sr²⁺ and La³⁺, D'"'"' being selected from Zr⁴⁺, Sn⁴⁺, Hf⁴⁺, Nb⁵⁺, and Ta⁵⁺, D being different from A and D'"'"' being different from B, wherein solutions I, II, and III are simultaneously injected into a reactor or a combination of two of the said solutions are injected into a reactor followed by a simultaneous injection of a second combination of two of the said solutions.

7. A process according to claim 2 in which the total concentration of metal ions in solution (I) ranges from 0.5 to 1.2 mol/dm^-3.

8. A process according to claim 1 wherein the powders consist essentially of spherical primary particles having an average size from 0.15 to 0.4 micrometers.