Structural, dielectric and multiferroic properties of Er and La substituted BiFeO3 ceramics

Erbium (Er) and lanthanum (La) substituted BiFeO₃ (BFO) ceramics have been prepared through conventional solid solution route. X-ray diffraction data indicated a gradual phase transition from rhombohedral to monoclinic structure in Bi_0·9?x La_0·1Er _x FeO₃ (x = 0·05, 0·07 and 0·1) (BLEFO _{x = 0·05, 0·07, 0·1}) ceramics. Differential thermal analysis (DTA) measurements of BFO samples showed a ferroelectric transition at 835°C, whereas it is shifted to 792°C for BLEFO _{x = 0·1}. The Raman spectra of BLEFO _{x = 0·05, 0·07, 0·1} samples showed the shift of Raman modes to higher wavenumbers and suppression of A₁ modes indicating decrease in ferroelectricity. The Raman spectra also indicated the structural transformation due to Er and La substitution in BFO. On subsequent erbium doping, the intrinsic dielectric constant is found to decrease from 68 (for pure BFO) to 52 for BLEFO _{x = 0·05} to 43 for BLEFO _{x = 0·07} but increased to 89 for BLEFO _{x = 0·1} when compared to pure BFO. The increase in Er content resulted in the increase in spontaneous magnetization (0·1178 emu/g at 8T for BLEFO _{x = 0·1}) due to collapse of spin cycloid structure. Ferroelectric remnant polarization of BLEFO _{x = 0·05} and BLEFO _{x = 0·07} decreases when compared to pure BFO while small remnant polarization (close to paraelectric behaviour) is evident for BLEFO _{x = 0·1}.