Mechanochemical synthesis of non-crystalline ZrTiO₄ precursor from inhomogeneous mixed gels

The effects of vibration ball-milling of a mixture of two gels, prepared from mixing ZrO₂ and TiO₂ sols, on crystallization processes during heating are studied in order to determine enhanced mechanochemical reactions with the aid of hydroxyl groups. Data of differential thermal analysis (DTA) and X-ray diffractometry show that TiO₂ (anatase) and ZrO₂ (tetragonal) crystallized at 698 and 712 K, respectively, when a powdered gel mixture was heated to 1023 K to 10 K min^-1 in air. No reactions between the two phases were detected. After vibro-milling a powdered gel mixture at room temperature for 3 to 30 h, a new exothermic DTA peak appeared around 950 K and ZrTiO₄ (orthorhombic) was detected on heating to 1023 K. After vibro-milling, the compositional micro-homogeneity of non-heated gels was estimated from the fluctuations of elemental compositions in local areas using energy dispersive spectrometer with a 25 nm electron beam. The fraction of ZrTiO₄ crystallized on heating the gels to 1023 K, determined by Raman spectroscopy, increased linearly with increasing the micro-homogeneity for non-heated gels. It is suggested that atomic movement and short-range ordering of ZrTiO₄ rather than crystallization of individual oxides occur when applying mechanical stress to a powdered mixture of ZrO₂ and TiO₂ gels.