Multiferroic properties of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18)(R=Eu,Sm,Nd,Bi and La)ceramics

An improved technique was used to prepare the ceramic samples of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18)(BRFNT,R=Eu,Sm,Nd,Bi,and La).The five-layer Aurivillius phase of the samples was confirmed by X-ray diffraction(XRD)without detectable impurities.BRFNT samples exhibit the pseudo-tetragonal except the orthorhombic BSmFNT samples.The characteristic plate-like morphology was revealed by field emission transmission electron microscopy(FETEM)images.At ambient tempe rature,all the samples present both ferroelectric and magnetic properties and BEuFNT shows the best ferroelectric behavior with its remanent polarization as high as 14.9μC/cm^(2)under 155 kV/cm,which is three times higher than that of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18).Moreover,the remanent magnetization of BEuFNT is increased up to 1.20 emu/g compared to that of Bi_(5.75)R_(0.25)Fe_(1.4)Ni_(0.6)Ti_(3)O_(18)which is only 0.53 emu/g.With increasing radius of the introduced A-site ions,the ferroelectric phase transition temperature(T_(CE))is decreased while the magnetic phase transition temperature(T_(CM))fluctuates.The decrease in both T_(CE)and T_(CM) corresponds to the upward shift of the related Raman modes and vice versa,indicating that the T_(CE)and the T_(CM) depend not only on the t factor,but also on the strength of the covalent bonds.