Doping Effect On The Properties Of Bi₇Ti₄NbO₂₁ With The Intergrowth Layer Structure

Quantum functional materials possessing "composite" characteristics is a series of materials of which the native parameters have interaction with many kinds of applied fields(such as light,electric,magnetic,sound,and thermal field).The interaction of materials and applied fields and the coupling effects between all kinds of the native parameters provide considerably important potential application prospects.Therefore,studying on quantum functional materials has already become an important direction of material science.Although some theories and new material system have been developed in the past decades,there are still lots of unknown needed to be explored.Developing new Quantum functional materials is beneficial to making new commercial devices,and proposing new mechanisms.And therefore,developing Quantum functional materials is of extremely important significances in both theoretical and practices.As potential candidates of quantum functional intergrowth layer Aurivillius materials which have 2 independent units have drawn special attention because of their special structure,be helpful in improving the ferroelectric properties and megnetoelectric coupling.Unfortunately,researches on intergrowth layer Aurivillius materials are mainly focused on their A-site substitution effects,and few works on B-site-substitution,especially magnetic ions doped materials were rarely reported.In this work,the 2+3 Aurivillius intergrowth phases of Bi7Ti4-2xCoxNb1+xO21 were successfully synthesized via a solid reaction method.XRD and HAADF-STEM analyses clearly demonstrated that the Co substituted Bi7Ti4-2xCoxNb1+xO21 keeps the intergrowth phase structure when x<0.3.A new analysing method which maps the linear brightness in HAADF images was applied to give the clear Bi atom position,and it revealed that the lattice shrinkage in the c direction caused by the Co substitution mainly occurred at(BiTiNbO7)2-block in(B13TiNbO9)layer,which was also confirmed by the Raman spectra investigation.Polarization-electric field(P-E)investigations and pulsed polarization positive-up negative-down(PUND)measurements indicated that the Co substitution can enhance the ferroelectric properties of the samples,which was mainly intrinsic to the structure.For example,2Ec=135.23kV/cm and 2Pr=9.33?C/cm2 can be achieved when x=0.3.Especially,paramagnetic properties instead of the original nonmagnetic could be achieved in these Co substituted samples.Also with the Co substitution,Bi7Ti4NbCO2 changed from diamagnetic(?<0)to paramagnetic(??7×10-5).The calculated effective magnetic moment in Bi7Ti4-2xCoxNb1+xO21 samples have similar values,suggesting that the Cobalt atoms in the materials have almost the same efficient moment.