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

Abstract

Polycrystalline La and Ti co-substituted ceramics were synthesized by the\ntartaric acid modified sol-gel technique. It was observed that the\nco-substitution of La & Ti at Bi & Fe sites in BiFeO3 suppress the impurity\nphase formation which is a common problem in bismuth ferrite. The quantitative\ncrystallographic phase analysis was performed with the help of FULLPROF program\nwhich suggests the existence of compositional driven crystal structure\ntransition from rhombohederal (space group R3c) to the orthorhombic (space\ngroup Pbnm). The changes in the phonon frequencies as well as line widths of A1\nmode in Raman spectra reveal the lattice distortion which tends to modify the\ncrystal structure. The structural transition breaks the spin cycloid structure\nin co-substituted BiFeO3 nanoparticles which leads to canting of the\nantiferromagnetic spin structure. Hence, the remnant magnetization increases up\nto 10 % of co-substitution and becomes 22 times that of BiFeO3. However, it\ndecreases for higher co-substitution percentage due to significant contribution\nfrom the collinear antiferromagnetic ordering in the orthorhombic crystal\nsymmetry. The co-substitution significantly enhanced the dielectric constant\n(maximum in x = 0.100) as well as frequency independent region for dielectric\nconstant and dielectric loss.\n