Preparation By Solid State Reaction Method And Physical Properties Of Hybrid Improper Ferroelectric (Ca_1-xLi_x)₃Ti₂O₇?x=0,0.01,0.03? Ceramics

The multiferroic material refers to a material simultaneously exhibiting ferroelectricity and ferromagnetism.It has recently been found that the electric polarization is induced by a complex distortion pattern consisting of octahedral rotation mode and octahedral tilt mode in Ca3Ti2O7(CTO).The discovery paves an avenue for the research of room-temperature multiferroic materials,which become one of the research hotspots in the word.Hybrid improper ferroelectric CTO ceramics were synthesized by a solid-state reaction method.Their polarization switching currents,dynamic processes of polarization-switching,and leakage current properties were investigated.It was found that the dynamic polarization curves of CTO ceramics exhibit obvious dependence on the frequency of the driving electric fields.The increasing rounded shape and the remnant polarization in P-E loops with decreasing measuring frequency is a result of the contribution from the leakage current.Moreover,CTO ceramics show a switchable diode effect.The underlying mechanism for the observed effects were proposed based on the interplaying between mobile charged defects and bound charges.The charged defects also lead to a decrease of the band gap of the CTO ceramic,as revealed by absorption spectrum analysisIn addition,Li-doped(Ca1-xLix)3Ti2O7(x=0,0.01,0.03)ceramic samples were prepared by solid state reaction.By analyzing the dynamic hysteresis loop of the sample,we found that the Li doped sample has a smaller remnant polarization and an increased coercive field than the undoped sample.This is mainly because the particle size of the doped sample becomes larger so that the coercive field increased.The UV-visible absorption spectrum of the sample showed that with Li substitution,the optical band gap of the sample increased,this is mainly the effect of the oxygen vacancy concentration and the degree of the oxygen octahedral rotations.In addition,we also found that the leakage current value of the 1%Li sample is smaller than that of the.When further doped to 3%Li,the leakage current value is larger than the undoped sample.The behavior could be ascribed to the change of oxygen vacancies and Ti4+ concentration in samples.In samples with different Li different compositions,we can observe that there is polarization current in the sample,and the smaller the leakage current,the more obvious the polarization current can be observed in the I-E curve.