Multiferroic Materials The Bifeo <sub> 3 </ Sub> Hydrothermal Synthesis And Morphology Changes

Multiferroics are multifunctional materials which exhibit simultaneously ferroelectricity (antiferroelectricity),ferromagnetism(antiferromagnetism) and ferroelasticity.As a typical single-phase multiferroic material,Bismuth ferrite(BiFeO₃,BFO) with perovskite structure has attracted increasing research interest during the past several years,because it could be widely used in micro-electronic devices such as filter,sensor,performer,executor,information storage and non-linear optical hardware.BFO had been obtained by some methods such as solid-state method,sol-gel method, coprecipitation method,flux method and hydrothermal method.The products obtained by these methods(except the hydrothermal method) need the high temperature processing,which may lead to the particles agglomeration and low property.However,pure BiFeO₃ can be synthesized by hydrothermal method at depress temperature and own better property.Seldom works have been done to prepare BFO crystallites by using the hydrothermal method and these works showed that the pure BFO was synthesized in limited experimental conditions and the morphology was not rich.Using FeCl₃·6H₂O,BiCl₃ and NH₄Cl addition as start materials,pure BFO was synthesized in wide hydrothermal conditions of 140～230℃,2～5 M NaOH,longer than 3h and 1 M NH₄Cl. This is the widest hydrothermal range to synthesize BFO and the temperature140℃is the lowest one to obtain BFO by hydrothermal method.Moreover,the morphologies of the products were rich and changed regularly.It showed that the NH₄Cl addition could make the pure BFO synthesize in a wide hydrothermal conditions and had some important effects on the reaction process.Using Fe(NO)₃·9H₂O,Bi(NO)₃·5H₂O as start materials,we synthesized pure BiFeO₃ in loose hydrothermal conditions of 180～240℃,molar ratio Fe/Bi of 1～2,and KOH concentration of 2～10 M and obtained the homogenous octahedron particles.Moreover we studied the characteristics of morphologies.We believed that the morphologies of the products were affected by three factors of the KOH concentration,temperature and molar ratio Fe/Bi.