Hydrothermal Synthesis and Size‐Dependent Properties of Multiferroic Bismuth Ferrite Crystallites

Abstract

A facile hydrothermal synthesis route was utilized to fabricate phase‐pure BiFeO3 (BFO) crystallites. Effects of the initial potassium hydroxide (KOH) concentration, starting materials, reaction temperature, and duration time on the crystallinity and morphologies of BFO were systematically investigated. Results show that the particle size of BFO increases with the increasing concentration of KOH, and a slight decrease of the molar ratio of Bi to Fe efficiently prohibits the presence of the secondary phase. In addition, the results of Raman measurement show that the intensity of the first normal A1 mode peak at 137.5 cm−1 decreases with the decreasing particle size. The Néel temperature, TN, decreases from 378.2° to 365.8°C as the average particle size of BFO powders decreases from 569 to 56 nm. The decrease in TN of BFO powders could be related to the decrease in spontaneous polarization and the number of antiferromagnetic interactions with decreasing particle size. The decrease of Curie temperature, TC, is attributed to the decreasing rhombohedral distortion of the unit cell with the decreasing crystallite size in BFO powders. Furthermore, the magnetic response of the BFO increases with the decreasing particle size, which is associated with the enhanced contribution of uncompensated spins at the particle surface to the overall magnetization with the increasing surface‐to‐volume ratio.