Frequency dependent dielectric constant of BiFeO3, Bi0.9Sm0.1FeO3 and Bi0.85 Ho0.05 Sm0.1FeO3 at ambient temperature. Inset of Fig is the frequency-dependent dielectric loss of BiFeO3, Bi0.9Sm0.1FeO3 and Bi0.85 Ho0.05 Sm0.1FeO3 at ambient temperature.