Hydrothermal Synthesis of Nanometer‐Sized Barium Titanate Powders: Control of Barium/Titanium Ratio, Sintering, and Dielectric Properties

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Abstract
Nanometer‐sized BaTiO3 powders have been synthesized hydrothermally from Ba(OH)2 and titanium alkoxide at 150°C for 2 h, and the Ba/Ti ratio has been measured with an accuracy of ±0.003. Stoichiometric powders can be obtained by adjusting the Ba/Ti ratio of the reactants to a value of 1.018. At a lower Ba/Ti ratio, the solubility of Ba(OH)2 prevents full incorporation of barium, and barium‐deficient powders result. A higher Ba/Ti ratio leads to the incorporation of excess barium in the powder. Ks(BaTiO3,‐25°C) = 7 × 10‐8 has been calculated for the equilibrium reaction. From this result, two reproducible processes for the synthesis of stoichiometric BaTiO3 are proposed. The processes rely only on very accurate control of the chemical composition (Ba/Ti ratio) of the precursor suspension. The sintering behavior of powders having Ba/Ti ratio values between 0.965 and 1.011 is described from results of dilatometric measurements and isothermal sintering. Room‐temperature dielectric constants as high as 5600 and losses as low as 0.009 have been obtained for a stoichiometry slightly less than 1.000. It is expected that optimum sintering behavior and electrical properties are obtained in the stoichiometry range 0.995‐1.000.