Investigations on structural, dielectric, and impedance properties of ecofriendly Ho3+ / Nb5+ co-substituted Na0.5 Bi0.5TiO3

Abstract

The lead-free, 0.5 mol% of Ho3+ substituted Na0.5 Bi0.5TiO3 (Na0.5Bi0.495Ho0.005TiO3) has been modified by Nb+5 substitution at the Ti-site to improve the relaxor nature and physical properties. Enhancement in relaxor characteristics was found through polarization loop and the bipolar strain studies. The slanted polarization loop showed slightly better recoverable energy storage density as compared to the square loop at the moderate electric field of ≈ 85 kV/cm. Maximum dielectric constant temperature (Tm) and depolarization temperature (Td) shifted towards the lower region with Nb5+ substitution along with decreased average grain size. The Cole-Cole plots portrayed the single semicircle for all the compositions at higher temperatures which confirms the Debye-type behavior due to the grain interiors. The decrement in the grain resistance with increase in temperature depicted the negative temperature coefficient of resistance (NTCR) behavior like the semiconductor materials. The 3 mol% of Nb5+ substituted composition exhibited improved insulating character at higher temperatures as compared to Na0.5Bi0.495Ho0.005TiO3. It is advantageous to use the material for high-temperature dielectric applications.