Core-shell structure of nanoscaled Ba0.5Sr0.5TiO₃ self-wrapped by MgO derived from a direct solution synthesis at room temperature

A nanoscaledBa0.5Sr0.5TiO3 (BST) powder was successfully synthesized using a modified hydrothermal process at a low temperature (∼80°C). By dissolving Ba(OH)2·8H 2U and Sr(OH)2·8H2O in deionized water as a base solution, nanocrystalline BST powder can be obtained by mixing an ethanol solution of tetrabutyl titanate with a hot base solution by stirring. The grain size of BST is close to 17-20 nm, as calculated by XRD patterns and confirmed by TEM and SEM measurements. A perovskite structure core material of the nanoscaled BST was successfully self-wrapped by a non-ferroelectric oxide MgO derived from a magnesium nitrate (Mg(NO3) 2·6H2O) solution under ultrasonic dispersion. A small amount of ammonia solution was added to this mixture to adjust it to a proper level of acidity in order to form a homogeneous core-shell structure. Straightforward experimental results revealed the formation of a core-shell structure. High-resolution transmission electron microscopy (HRTEM) combined with EDX was used to confirm the composition and its variation. TEM, SEM, and XRD results showed that the average particle size of a core-shell structure was less than 150 nm up to sintering at 1100°C, depending on the core BST powder and its dispersion.