First Principles Design of Functional Materials by Structural Mode Coupling

Abstract

Coupling between structural modes in real materials drives not only structural phase newlinetransition but also steers functional properties into the low symmetry phase. In this newlineregard, ABO3 perovskite oxides are the most studied systems owing to their functional newlineproperties such as ferroelectricity, weak ferromagnetism, linear magnetoelectricity, newlinemagneto-resistance, and insulator-metal transition (IMT), etc. In ABO3 oxides, the newlinetrilinear coupling, QTri and#8764; QT newlineN newlineQR+ newlineN newlineQAFEA , in Landau free energy expansion, newlinebetween tilt, QT (aand#8722;aand#8722;c0) , in phase rotation, QR+(a0a0c+) of BO6 octahedra and antiferroelectric newlineA-site displacement (Q AFEA ) mode is responsible for driving the system newlinefrom cubic Pm¯3m to orthorhombic Pnma phase. With the A/A and#8242; cation ordering, newlinethe trilinear coupling drives ferroelectricity in ABO3 superlattices (SLs) and double newlineperovskites (DPs). Here, rotation and tilt are two primary order parameters that drive the newlineferroelectricity into the system. Since two order parameters are involved in this technique, newlineit is called the hybrid improper ferroelectric (HIF) mechanism. This discovery opens up newlinea new avenue where coupling between various modes (not limited to trilinear coupling newlineonly) can be tailored to design novel functional materials newline