Phase transformation, dielectric and magnetic properties of Nb doped Bi_(0.8)Sr_(0.2)FeO_3 multiferroics

摘要

Bi_(0.8)Sr_(0.2)Fe_(1-x)Nb_xO_3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (ε) and dielectric loss (tan 8) values at lower frequencies. For x = 0.05 sample, both e and tan 5 are lower than for Bi_(0.8)Sr_(0.2)FeO_3 sample indicating its high resistivity. For x = 0.10 sample, the value of e is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent "s" of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in magnetization for x = 0.10 sample is due to the structural phase transition from rhombohedral to triclinic caused by Nb substitution. For this sample, values of remnant magnetization (M_r) and coercive field (H_c) are 0.155 emu/g and 2.695 kOe, respectively.