First-principles Study On Coupled Behavior Of Strain And Optoelectronic Properties In Superlattice

Compared with the sigle characteristics of monomer material, ferroelectricsuperlattices constituted by a variety of different cycle growth components havesuperior performance, such as piezoelectric, polarization, optical and dielectricproperties. Numerous studies show that the impact factors of superlatticeperformance include superlattice components, strain induced by different latticeconstants of substrates and supperlattices, the electrostatic field and the interfacesbetween the components. According to first principles, BiAlO3/PbTiO3ferroelectricsuperlattice containing polar discontinuity polarization is simulated and analyzed byVASP software in this subject, influencing factors strain and component interfaceare considered; another major part of this project is the effects of strain to theoptical and polarization properties of tetragonal BiFeO3superlattice.The equilibrium lattice parameters of BiAlO3/PbTiO3superlattic weredetermined as a=3.82, c=7.69according to the relationship curve betweenenergy and lattice constant. The relationship between polarization, piezoelectric andlattice parameter a was studied through calculating the relationship of atomicdisplacement, the born effective charge and in-place parameter a. With the icreaseof a, the born effective charge of Ti increased, while the born effective charge of O6decreased. Since the Ti-O bond was very sensitive to strain, it could be inferred thata dynamic charge transfer had been occurred between Ti and O6atoms. Thepolarization and piezoelectric coefficient of BAO/PTO superlattice decreased withthe increasing of in-plane lattice parameter.Then the relationship of the performance of cycle stacking superlattice（BiAlO3）n/（PbTiO3）nand the layers of cycle n was studied. Polarization, latticedistortion degree and radiate energy band gap had a trend of decrease as n increased.The local layer polarization curve of （BiAlO3）n/（PbTiO3）nsuperlattice showedthat the （BiAlO3）n/（PbTiO3）nsuperlattice was a typical film containingdiscontinuous polar.Finally, the relationship beteewn polarization, optical properties and strain inBiFeO3superlattices was considered. The polarization value of BiFeO3superlattice decreased with the decreasing compressive strain. In strain equilibrium state, theoptical properties of BiFeO3superlattices mainly generated from the transitionsfrom valence band O2p orbital electrons to the conduction band Fe3d orbitalelectrons. In strain states, the band gap decreased, while dielectric function,absorptivity, energy loss factor and extinction coefficient increased. Therefore,appropriately strain can be used to improve optical properties of films.