  Polycrystalline La and Ti co-substituted ceramics were synthesized by the
tartaric acid modified sol-gel technique. It was observed that the
co-substitution of La & Ti at Bi & Fe sites in BiFeO3 suppress the impurity
phase formation which is a common problem in bismuth ferrite. The quantitative
crystallographic phase analysis was performed with the help of FULLPROF program
which suggests the existence of compositional driven crystal structure
transition from rhombohederal (space group R3c) to the orthorhombic (space
group Pbnm). The changes in the phonon frequencies as well as line widths of A1
mode in Raman spectra reveal the lattice distortion which tends to modify the
crystal structure. The structural transition breaks the spin cycloid structure
in co-substituted BiFeO3 nanoparticles which 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 BiFeO3. However, it
decreases for higher co-substitution percentage due to significant contribution
from the collinear antiferromagnetic ordering in the orthorhombic crystal
symmetry. The co-substitution significantly enhanced the dielectric constant
(maximum in x = 0.100) as well as frequency independent region for dielectric
constant and dielectric loss.
