Rich antiferroelectric phase diagram of antiferroelectric-ferroelectric superlattices: internal electric field- and interface induced phase transitions

We propose a thermodynamic model to the study the antiferroelectric (AFE) phase transitions in antiferroelectric-ferroelectric (AFE-FE) superlattices in which the coupling at the interface between two layers is mediated by local polarizations. Phase diagram of the AFE layer in term of the degree of interfacial effectλand temperatureTinvolving ferrielectric (FI) and ferroelectric (FE) phases is investigated. These two phases are stabilized by the interfacial effect and internal electric field. AFE thicknessLAFEversusTphase diagram is also constructed. Intermediate regions of two-phase coexistence (IM) emerge in theλ-TandLAFE-Tphase diagrams, if certain interface propertiesλand layer thicknessLAFEcriteria are met. These IM regions are metastable states, which exist as a transition state between two phases. A tricritical point locates at the boundaries across the FI, IM and FE phases is found in theLAFE-Tphase diagram. Competition among the internal electric field due to the electrostatic coupling, the FE ordering arises from the interfacial effect and the antiferroelectric ordering within the AFE layer giving rises to the rich AFE phase diagram.