The involvement of Pna21 phase in the multiferroic characteristics of La/Lu co-substituted BiFeO3 ceramics

Rare earth ion (RE)-substitution has been recognized as an effective way for improving multiferroic properties especially for realizing the electric field-controlled magnetism in BiFeO3 ceramics, where the symmetry modulation of R3c-Pna2(1)-Pbnm and unlocking ferromagnetism by destroying the cycloidal spin structure are the key points. In Lu-substituted BiFeO3 ceramics, however, the Pna2(1) phase is not involved. In the present work, La/Lu co-substitution was investigated to involve the Pna2(1) phase in BiFeO3 ceramics. The phase transition from R3c to Pna2(1) occurred with an increase in x, and the mixed structure of R3c, Pna2(1), and Pbnm phases was determined in Bi0.82-xLaxLu0.18FeO3 ceramics. The greatly enhanced ferroelectric polarization and the switching from antiferromagnetic to the weak ferromagnetic state through the destruction of the cycloidal spin structure were achieved. Subsequently, the direct magnetoelectric coupling coefficient alpha(ME) up to 2.02 mV/cm Oe was obtained. The increased effective ionic radius of RE in the present ceramics played a key role in involving Pna2(1) phase in RE-substituted BiFeO3 ceramics, and the critical value was about 0.104 23(2) nm.

Automated summary

The study investigated the effects of La/Lu co-substitution on BiFeO3 ceramics, and found that this method can introduce the Pna2(1) phase in the ceramics, further enhancing ferroelectric polarization and achieving the transition from antiferromagnetic to weak ferromagnetic state by destroying the cycloidal spin structure.