Composition‐ and Pressure‐Induced Relaxor Ferroelectrics: First‐Principles Calculations and Landau‐Devonshire Theory
We report calculations with first‐principles density‐functional theory and Landau–Devonshire theory that provide an atomic‐scale mechanism for the composition‐ and pressure‐induced relaxor ferroelectrics. A multiphase with coexisted cubic structures (MPCCS) is found to correspond to any of the composition‐ and pressure‐induced relaxor ferroelectrics. On the other hand, a normal ferroelectric without relaxor behavior is structurally characterized by a single phase. Furthermore, the presence of the MPCCS in a composition‐ and pressure‐induced relaxor increases the degrees of freedom of relaxors and no energy barriers are involved for the rotations of the polarization direction, leading to high electromechanical coefficients.
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