Preparation of Highly Crystallized Strontium Titanate Powders at Room Temperature

Highly crystallized fine powder of strontium titanate (SrTiO 3 ) was obtained at room temperature simply by leaving a vial containing the powder mixture of Sr( OH ) 2 ·8H 2 O and hydrous titania gel (TiO 2 · n H 2 O) for 10 d. Solvent and additive(s) used in the conventional low‐temperature process were not used. The crystallinity judged from the FWHM of X‐ray diffraction peak was comparable to that obtained by a solid‐state reaction. To cause the reaction at room temperature, the titania gel had to contain a considerable amount of H 2 O ( n > 0.97). The reaction is considered to be neutralization of titanic acid [H 4 TiO 4 or Ti( OH ) 4 ] and strontium hydroxide (base). Using similar process, highly crystallized BaTiO 3 powder was also obtained at 60°C. In comparison with the formation temperature of BaTiO 3 , tolerance factor in the perovskite structure was important for the room‐temperature synthesis of SrTiO 3 . SrTiO 3 was hardly obtained at room temperature by the addition of saturated strontium hydroxide solution to the hydrous TiO 2 gel ( n = 1.29). Therefore, the reaction seems to proceed in the hydrous titania gel. This process is characterized by three important points; “no solvent”, “no additional reagents”, and above all, “no heating”.