Intrinsic and tunable ferromagnetism in Bi(0.5)Na(0.5)TiO(3) through CaFeO(3-δ) modification

New (1-x)Bi(0.5)Na(0.5)TiO(3) + xCaFeO(3-δ) solid solution compounds were fabricated using a sol–gel method. The CaFeO(3-δ) materials were mixed into host Bi(0.5)Na(0.5)TiO(3) materials to form a solid solution that exhibited similar crystal symmetry to those of Bi(0.5)Na(0.5)TiO(3) phases. The random distribution of Ca and Fe cations in the Bi(0.5)Na(0.5)TiO(3) crystals resulted in a distorted structure. The optical band gaps decreased from 3.11 eV for the pure Bi(0.5)Na(0.5)TiO(3) samples to 2.34 eV for the 9 mol% CaFeO(3-δ)-modified Bi(0.5)Na(0.5)TiO(3) samples. Moreover, the Bi(0.5)Na(0.5)TiO(3) samples exhibited weak photoluminescence because of the intrinsic defects and suppressed photoluminescence with increasing CaFeO(3-δ) concentration. Experimental and theoretical studies via density functional theory calculations showed that pure Bi(0.5)Na(0.5)TiO(3) exhibited intrinsic ferromagnetism, which is associated with the possible presence of Bi, Na, and Ti vacancies and Ti(3+)-defect states. Further studies showed that such an induced magnetism by intrinsic defects can also be enhanced effectively with CaFeO(3-δ) addition. This study provides a basis for understanding the role of secondary phase as a solid solution in Bi(0.5)Na(0.5)TiO(3) to facilitate the development of lead-free ferroelectric materials.