Modified optical and magnetic properties at room-temperature across lead-free morphotropic phase boundary in (1-x)BiTi_3/8Fe_2/8Mg_3/8O₃–xCaTiO₃

Perovskite compounds of the formula (1-x)BiTi_3/8Fe_2/8Mg_3/8O₃–xCaTiO₃ ((1-x)BMFT-xCTO), a class of highly potential ferroelectric photovoltaic materials with a morphotropic phase boundary (MPB), have been synthesized by solid-state reaction and exhibit simultaneously visible-light response and ferromagnetic order at room-temperature (RT). The effects of structural phases and lattice distortions on electron transitions and orbital orderings are systematically investigated. The crystal lattice displays constriction with increasing x and Raman peaks show non-liner shift due to Bi³⁺ and Fe³⁺/Mg²⁺ replaced by Ca²⁺ and Ti⁴⁺ randomly, respectively. Microstructural characterizations illustrate the rhombohedral-orthorhombic MPB occurrence during the crystal growth. Optical spectroscopy analysis shows band-gaps of our samples are about 2.2 eV with anomalies at the point of phase transition. Furthermore, the (1-x)BMFT-xCTO displays RT ferromagnetism when x<0.15, which can be explained by an F center theory. These results reveal rich physical phenomena and open an avenue to design promising perovskites for solar-energy conversion devices and multiferroic applications.