Functional properties of A-site cation ordered phases derived from La2MnNiO6 double perovskites

Starting from a room temperature parent La2MnNiO6 double perovskite as a prototype example, we ventured ferroelectricity and metal-insulator transition in the AA ' BB ' O6 double perovskites. Using first-principles density functional calculations guided by symmetry, we have shown that by appropriate A-site substitution i.e., by forming AA ' combinations, La2MnNiO6 within Mn and Ni in rock-salt ordering can be transformed into both ferroelectric insulating or polar metallic phase. We found that the charge difference between the cations and the radius mismatch between A and A ' are the key factors for deciding a particular ordering. The layered ordering becomes more stable when both charge difference and radius mismatch are large. The energy gain is more pronounced when the charge difference at the A-site is large. Further, we have identified and discussed the key structural distortions responsible for driving functional properties into the system. Our proposed mechanism is valid for other similar A2BB ' O6 systems within 3d-3d double perovskites architecture with B and B ' sublattices in the rock-salt ordering.

Automated summary

Starting from a room temperature parent La2MnNiO6 double perovskite as a prototype example, the study explores the ferroelectricity and metal-insulator transition in the AA ' BB ' O6 double perovskites. Through first-principles density functional calculations guided by symmetry, it is shown that appropriate A-site substitution can transform La2MnNiO6 from rock-salt ordering to both ferroelectric insulating or polar metallic phase. The key factors for determining a specific ordering are found to be the charge difference between the cations and the radius mismatch between A and A '.