Effect of rhombohedral to orthorhombic transition on magnetic and dielectric properties of La and Ti co-substituted BiFeO3

Polycrystalline Bi 1− x La x Fe 1− x Ti x O 3 ( x = 0.000–0.250) ceramics were synthesized by the tartaric acid modified sol–gel technique. It was observed that the co-substitution of La and Ti at Bi and Fe sites in BiFeO 3 suppresses the impurity phase formation which is a common problem in the bismuth ferrite ceramics. The quantitative crystallographic phase analysis of x-ray diffraction pattern by employing Rietveld technique was performed with the help of FULLPROF program which suggests the existence of compositional driven crystal structure transition from rhombohedral (space group R3c) to the orthorhombic (space group Pbnm) symmetry. The oxygen octahedral tilt angle was found to be ∼13.82° for BiFeO 3 (space group R3c) and decreases with the increase in co-substitution percentage. The structural transition breaks the spin cycloid structure in co-substituted BiFeO 3 nanocrystallites and leads to canting of the antiferromagnetic spin structure. Hence, the remnant magnetization increases up to 10% of co-substitution and becomes 22 times that of BiFeO 3 . However, it decreases for higher co-substitution percentage due to significant contribution from the collinear antiferromagnetic ordering in the orthorhombic crystal symmetry. The dielectric constant attains a maximum for 10% of co-substitution.