Hydrothermal synthesis of nanometer-sized barium titanate powders: Controlof barium/titanium ratio, sintering, and dielectric properties

Nanometer-sized BaTiO3 powders have been synthesized hydrothermally from Ba (OH)(2) and titanium alkoxide at 150 degrees 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 inco rporation of barium, and barium-deficient powders result. A higher Ba/Ti ra tio leads to the incorporation of excess barium in the powder, K-s(BaTiO3, -25 degrees C) = 7 x 10(-8) has been calculated for the equilibrium reactio n. From this result, two reproducible processes for the synthesis of stoich iometric BaTiO3 are proposed, The processes rely only on very accurate cont rol of the chemical composition (Ba/Ti ratio) of the precursor suspension. The sintering behavior of powders having Ba/Ti ratio values between 0.965 a nd 1.011 is described from results of dilatometric measurements and isother mal sintering, Room-temperature dielectric constants as high as 5600 and lo sses as low as 0.009 have been obtained for a stoichiometry slightly less t han 1.000. It is expected that optimum sintering behavior and electrical pr operties are obtained in the stoichiometry range 0.995-1.000.