Formation of perovskite phase mixed metal oxides via thermal decomposition of metal-organic complexes with bifunctional ligands

Abstract

Single-source metal precursors designed to form crystalline perovskite phase mixed metal oxides at low temperatures have been synthesized using α-hydroxycarboxylates and alkoxides as ligands. Divalent salts of Ba, Sr, Ca and Pb, [A(O2CCR2OH)2], R = H, Me, were formed from the reaction between ACO3 and HO2CCR2OH in which the hydroxyl group is free to react with metal alkoxide compounds B(OR′)4 where B=Ti, Zr, Sn. These compounds react to eliminate two equivalents of alcohol producing precursors with fixed stoichiometry as shown by the equation: A(O2CCR2OH)2+B(OR′)4 → A(O2CCR2O)2B(OR′)2+2HOR′. The reaction product is only slightly soluble in pyridine, however upon hydrolysis these compounds form clear solutions from which yellow powders can be isolated by removal of the solvent. Thermolysis of these powders in the temperature range 300–350°C yields perovskite ABO3. Aqueous solutions of these powders can also be used to form sub-micron sized particles of ABO3 materials via aerosol processing techniques. In control experiments it was shown that Pb(O2CCH2OPh)2 does not react with metal alkoxide compounds. As a result perovskite PbTiO3 is not formed below 550°C. Solutions for spin coating thin films can be formed by dissolution of the powder in ethanol, but the crystallization behavior is quite different compared to the bulk powders.