Effect of tuning of charge defects by K, Ba, La doping on structural and electrical behaviour of NaNbO3

Abstract

The aim of this study is to highlight the impact of monovalent, divalent and trivalent substitutions on structural, and electrical properties. Creation of defects and its impact on phase transition behaviour reflected in dielectric properties makes it more interesting. Compositions (x) in the material system Na1-xAxNbO3 (where, x = 0.0 abbreviated as S0, and x = 0.05 for K1+, Ba2+, and La3+ doped samples abbreviated as S1, S2, and S3 respectively) are prepared by the conventional solid-state reaction method. Rietveld refinement of diffraction data has confirmed single-phase formation with an orthorhombic structure having Pbcm space group symmetry. FTIR spectra show the shifting of vibrational modes towards higher wave number sides with increasing valence states of dopants. SEM images of these samples show a decrease in average grain size for S1, S2, and S3, respectively. Dielectric plots from room temperature to 773K at 1 kHz, 10 kHz, and 100 kHz for x = 0.0 have shown two prominent anomalies, one at 404K and the other one at 610K. The low-temperature anomaly has disappeared in samples S1, S2, and S3, whereas the high-temperature sharp anomaly at 610K for sample S0 has shifted to 618K for sample S1 and vanished for samples S2 and S3. Tanδ with temperature plots show two anomalies for samples S0, S1, and S2, whereas for S3, only one broad anomaly is observed. Conductivity has been found to increase with doping through the equivalent concentration of iso-valent K1+ and graded off-valent Ba2+ and La3+ cations. Impedance analysis has proposed an electronic circuit model containing two parallel equivalent RC elements.