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 (ε _r) of 40.9 at 5 GHz.