Effect of oleic acid on morphologies of BaTi5O11 nanocrystals synthesized by hydrothermal method

Abstract BaTi5O11 nanocrystals were synthesized by a hydrothermal method, and the effect of oleic acid (OA) in the Ba–Ti precursors on morphologies of BaTi5O11 nanocrystals was investigated. As the OA/(Ba2+ + Ti4+) molar ratio ranged from 0 to 8, single-phase BaTi5O11 nanocrystals were synthesized at 260 °C for 20 h. When OA reagent was not added to the precursors, rice-like BaTi5O11 nanocrystals were obtained. As the OA/(Ba2+ + Ti4+) molar ratio was 1, elongated lath-like BaTi5O11 nanocrystals were synthesized with the width of about 130 nm, thickness of about 50 nm and length of about 400 nm. With increasing the OA/(Ba2+ + Ti4+) molar ratio from 1 to 6, the grain size of elongated lath-like BaTi5O11 nanocrystals gradually decreased. As the OA content increased, the amount of adsorbed OA molecules on the surface of Ti(OH) x nucleus increased and hindered the reaction of Ba2+ ions with Ti(OH) x nucleus, which caused the decrease of grain size of lath-like BaTi5O11 nanocrystals. When the BaTi5O11 nanocrystals were synthesized at OA/(Ba2+ + Ti4+) molar ratio of 1, they had the largest dielectric constant (εr) of 40.9 at 5 GHz.