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 effect λ and temperature T involving ferrielectric (FI) and ferroelectric (FE) phases is investigated. These two phases are stabilized by the interfacial effect and internal electric field. AFE thickness LAFE versus T phase diagram is also constructed. Intermediate regions of two-phase coexistence (IM) emerge in the λ-T and LAFE-T phase diagrams, if certain interface properties λ and layer thickness LAFE criteria 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 the LAFE-T phase 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.

中文翻译：

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反铁电-铁电超晶格丰富的反铁电相图：内部电场和界面诱导相变

我们提出了一个热力学模型来研究反铁电-铁电 (AFE-FE) 超晶格中的反铁电 (AFE) 相变，其中两层之间的界面处的耦合由局部极化介导。研究了 AFE 层在界面效应程度 λ 和温度 T 方面的相图，涉及铁电 (FI) 和铁电 (FE) 相。这两个相通过界面效应和内部电场稳定。还构建了 AFE 厚度 LAFE 与 T 相图。如果满足某些界面特性 λ 和层厚度 LAFE 标准，则两相共存 (IM) 的中间区域出现在 λ-T 和 LAFE-T 相图中。这些 IM 区域是亚稳态，它们作为两相之间的过渡态存在。在 LAFE-T 相图中，三临界点位于 FI、IM 和 FE 相的边界处。由于静电耦合引起的内部电场之间的竞争，FE 有序性源于界面效应，AFE 层内的反铁电有序性产生了丰富的 AFE 相图。