Ionic conductivity of acceptor doped sodium bismuth titanate: influence of dopants, phase transitions and defect associates

Abstract

The temperature dependent ionic conductivity of NBT results from an interplay of defect complex formation, phase coexistence, and dopant concentration.

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

“…In the case of pure NBT, 0.1 and 0.3 mol% Fe doped NBT and pure as well as 1 mol% Fe‐doped NBT–6BT only one single semicircle and therefore a single conduction process can be detected within the measuring frequency range ( R b ~1.2 MΩcm at 500°C). This is well in line with recently reported results on Mg‐acceptor doped NBT . Low concentrations of acceptor dopant do not lead to a significant increase in conductivity and the conductivity is dominated by an intrinsic electronic contribution.…”

“…However, at higher concentrations the oxygen vacancies are responsible for the dominant ionic conductivity. This behavior has already been reported as a typical feature of NBT based B‐site acceptor doped oxygen ionic conductors and was attributed to a phase and defect dipole formation dependent concentration of mobile vacancies . The total conductivity increases by at least four orders of magnitude over the whole temperature range and saturates for doping levels above 2 mol% Fe.…”

“…This is highly detrimental for piezoelectric applications and illustrates that knowledge of the defect chemical properties of lead‐based ferroelectrics cannot be directly transferred to the lead‐free successors. However, evidence has been provided that the complex formation in NBT is highly dependent on dopant concentration, or oxygen vacancy concentration, respectively . The higher the dopant concentration, the higher the concentration of mobile oxygen vacancies.…”

“…However, the impact on conductivity is by far not as extensive and the low temperature conductivity is hardly affected. In case of NBT the conductivity changes from low intrinsic electronic conductivity to orders of magnitude higher ionically dominated conductivity with small acceptor content variations over a wide temperature range . With respect to the ferroelectric properties it could be shown that high dielectric loss and leakage current result with high oxygen vacancy content already at room temperature .…”

“…However, evidence has been provided that the complex formation in NBT is highly dependent on dopant concentration, or oxygen vacancy concentration, respectively. [9][10][11][12][13] The higher the dopant concentration, the higher the concentration of mobile oxygen vacancies. The dependence of complex formation on vacancy concentration can be expected to be nonlinear as the ionic conductivity changes by orders of magnitude with only small changes in acceptor concentration.…”