Effects of A-site nonstoichiometry on oxide ion conduction in 0.94Bi0.5Na0.5TiO₃–0.06BaTiO₃ ceramics

Abstract

Lead free 0.94(Bi 0:5 Na 0:5 ÞTiO 3 -0.06BaTiO 3 ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by $3-4 orders of magnitude and an associated activation energy of 1.57 eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities ( $ 10 3 -cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi 0:5 Na 0:5 ÞTiO 3 . Long term annealing studies were also conducted at 800 C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi 0:5 Na 0:5 ÞTiO 3 -0.06BaTiO 3 ceramics are very sensitive to Bi/Na stoichiometry.

The effect of Fe‐acceptor doping on the electrical properties of Na1/2Bi1/2TiO3 and 0.94 (Na1/2Bi1/2)TiO3–0.06 BaTiO3

“…The NBT–6BT becomes less sensitive toward increasing vacancy concentration. This explains why reports on extraordinarily high conductivity in NBT–6BT are so rare . The bismuth nonstoichiometry in NBT–6BT investigated for example by Seo et al is not high enough to induce high ionic conductivity.…”

“…This explains why reports on extraordinarily high conductivity in NBT-6BT are so rare. 23 The bismuth nonstoichiometry in NBT-6BT investigated for example by Seo et al 22 is not high enough to induce high ionic conductivity. Similarly, it was possible for Sapper et al 24 to investigate ferroelectric hardening in 1 mol% Fe doped NBT-6BT.…”

“…Thus, this could also explain a rather large spread of reported properties of NBT–BT in literature. However, Prasertpalichat et al provided evidence of high ionic conductivity in off‐stoichiometric NBT–BT. Nevertheless, Sapper et al even reported that ferroelectric hardening in NBT–6BT is possible by a B‐site Fe acceptor doping.…”

Dielectric behaviors and relaxor characteristics in Bi0.5Na0.5TiO3-BaTiO3 ceramics

“…The local structural heterogeneities and the relative stability of its R3c and Cc phases make the BNT-based ceramics as multi-functional materials with good small signal piezoelectric response, high strain activity and enhanced energy storage performance. 10,[30][31][32][33][34][35] Especially, BNT-based ceramics were observed to have several dielectric anomalies distinguished from canonical relaxors. [36][37][38][39] Simultaneously, the peculiar ferroelectric or relaxor properties depend on its mechanical or thermal treatment.…”

Composition-sensitive electrical properties of charge nonstoichiometric 0.94Bi0.5+xNa0.5−xTiO3–0.06BaTiO3 ceramics

“…It is noticed that composition nonstoichiometry can provide charge nonstoichiometry (electrons or holes doped) and lattice site nonstoichiometry (certain atoms in excess or deficiency). It has been confirmed that composition nonstoichiometric BNT-based ceramics have changed electrical properties [20][21][22][23][24][25][26][27] and even conductivity. [28][29][30][31][32] However, one must notice that such composition nonstoichiometric BNT-based materials are not the most proper objects for investigating the relationship between charge and electrical property.…”