Modified ferroelectricity in multiferroic Ba 4 Nd 2 Fe 2 Nb 8 O 30 ceramics via atmosphere treatment

Single-phase multiferroic Ba 4 Nd 2 Fe 2 Nb 8 O 30 ceramics with the tetragonal tungsten bronze structure were synthesized. The dielectric, ferroelectric, and magnetic properties were systematically studied at room temperature, and the room-temperature multiferroic features were certified by the polarization–electric field hysteresis loops and magnetization-field curves in Ba 4 Nd 2 Fe 2 Nb 8 O 30 ceramics. Interestingly, it was found that the ferroelectric polarization was enhanced by treating samples in non-oxidizing atmospheres, and the highest remnant polarization of 0.94 μC/cm 2 can be found in the N 2 -annealed samples. The refined neutron powder diffraction results showed that the modified ferroelectricity was originated from the displacement of Fe 3+ /Nb 5+ cations at B -sites rather than the oxygen vacancies. These results indicate that the heat treatment in controlled atmosphere is effective means to improve ferroelectricity in tetragonal tungsten bronze structure ceramics.