Octahedral distortion-driven phase transition, relaxation and conduction process of Zr/Sn modified barium titanate relaxors

Abstract

This paper mainly reports the effect of Zr/Sn substitution on structural, dielectric, and electrical characteristics of pure BaTiO3 (BT). The addition of Zr4+ and Sn4+ at the Ti-site of BT has bas created compositional disordered state. The disordered state is the necessary/prerequisite for the development of the relaxor ferroelectrics. The appearance of polar nano-regions is the cause of the relaxor property of the ferroelectric. The dielectric characteristics of Ba(ZrTi)O3 (BZT) and Ba(SrTi)O3 (BST) deviate from those of traditional Curie Weiss law, and hence do not show a sharp phase transition, but little diffused as compared to that of BT. Impedance spectra is fitted to the modified Cole-Cole equation to reveal the (i) asymmetry and broadening of the dielectric/impedance dispersion curves, (ii) non-Debye type of relaxation, (iii) actual grain and grain boundary contributions and (iv) semiconductor or positive temperature coefficient of resistance (PTCR) nature of the prepared materials. The correlated barrier hopping model fits well to BT and BST, whereas overlapping polaron tunnelling and small polaron tunnelling models signify the conduction mechanism of BZT. Zr and Sn addition increases impedance, energy storage and decreases the conductivity, leakage current and loss energy of BT. The high energy efficiency, good temperature stability of energy efficiency, high recoverable energy density and high breakdown strength of BZT and BST is observed as compared to those of BT which satisfy their the energy storage applications. The relaxation phenomena and the connection of microscopic electrical grain and grain boundary with microstructure are discussed here.