The effect of Fe‐acceptor doping on the electrical properties of Na_1/2Bi_1/2TiO₃ and 0.94 (Na_1/2Bi_1/2)TiO₃–0.06 BaTiO₃

Abstract

Na1/2Bi1/2TiO3 (NBT) based ceramics are amongst the most promising lead‐free ferroelectric materials. It was expected that the defect chemistry and the effect of doping of NBT would be similar to that observed for lead based materials, however, acceptor doping does not lead to ferroelectric hardening. Instead, high oxygen ionic conductivity is induced. Nevertheless, for solid solutions with BaTiO3 (BT), which are more relevant with respect to ferroelectric applications, such a drastic change of electrical properties has not been observed so far. To rationalize the difference in defect chemistry between NBT and its solid solution 94(Na1/2Bi1/2TiO3)–0.06 BaTiO3 (NBT–6BT) compositions with different concentrations of Fe‐dopant were investigated. The study illustrates that the materials exhibit very similar behavior to NBT, and extraordinarily high oxygen ionic conductivity could also be induced in NBT–6BT. The key difference between NBT–6BT and NBT is the range of the dependence of ionic conductivity with dopant concentration. Previous studies of NBT–6BT have not reached sufficiently high dopant concentrations to observe high conductivity. In consequence, the same defect chemical model can be applied to both NBT and its solid solutions. This will help to rationalize the effect of doping on ferroelectric properties of NBT‐ceramics and defect chemistry related degradation and fatigue.

Dramatic impact of the TiO2 polymorph on the electrical properties of ‘stoichiometric’ Na0.5Bi0.5TiO3 ceramics prepared by solid-state reaction

“…Previous studies 4,5 have revealed the significant change in σ b induced by low levels of Na or Bi non-stoichiometry (<1 at.%) as being related to a switch between electronic and oxide-ion conduction. Similar behavior can be observed using varying concentrations of acceptor dopants 9,14 . The presence of a small number of oxygen vacancies can change the predominant intrinsic electronic conduction behavior of NBT based on a d 0 insulator to predominant oxide-ion conduction due to the high mobility of oxygen ions in the NBT lattice 15 .…”

“…Previous studies 9,14,15,26,27 show low levels of acceptor-doping, such as Na + , Li + , K + , Ca 2+ , Sr 2+ , Ba 2+ to replace Bi 3+ on A-site, and Mg 2+ , Zn 2+ , Sc 3+ , Al 3+ , Fe 3+ , and Ga 3+ to replace Ti 4+ on B-site, can create oxygen vacancies in NBT by an ionic compensation mechanism, and consequently introduce high-levels of oxide-ion conductivity into NBT. On the contrary, low levels of donor-type dopants such as Nb 5+ , Ta 5+ can fill oxygen vacancies to suppress oxide-ion conduction.…”

An overview of oxygen vacancy dynamics in (1 − x)(Bi1/2Na1/2)TiO3–xBaTiO3 solid solution

“…Nevertheless, in the BNT-7%BT doped with acceptor dopants, the ionic conduction becomes predominant while the impedance data is qualitatively identical to that of pure BNT. 14 In those compositions, a plateau appears in the final stage of degradation. This will be discussed in more details in a separate paper.…”

“…6 Unless being doped with acceptors, common binary/ternary solid solutions are always claimed to be type III, where the single semicircle in Impedance Spectroscopy (IS) is interpreted as electronic conduction. 14 However, the interconnection of type I to III transition is not appreciated with respect to the phase diagram of a solid solution.…”

Probing Oxide Ion Conductivity in Na0.5Bi0.5TiO3–BiFeO3–BaTiO3-Based Ferroelectric Materials

“…However, it has been observed that Al 3+ and Nb 5+ doping at the B-site show a mixed conductivity with t ion ∼ 0.57. 2,46,48,49 Bi deficiency and acceptor doping are two methods that have been used largely for creating oxygen vacancies in NBTbased materials. An oxygen vacancy can be created during sample processing due to the loss of Bi 2 O 3 , and this can be represented using Kroger−Vink eq 1…”