Atomistic simulations of ion migration in sodium bismuth titanate (NBT) materials: towards superior oxide-ion conductors

Abstract

Fabricating (111)-ordered NBT and avoid any A-site vacancies will yield even higher oxide-ion conductivities.

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

“…These quantify the oxygen ionic conductivity contribution to the total conductivity and are shown for characteristic compositions (see Table ) . According to recent simulations provided by Zhang et al a high level of cation conductivity can be neglected in NBT. As expected, the measured doped NBT samples (1% Fe and above) all exhibit dominating oxygen ionic conductivity.…”

Is excess faster than deficient? A molecular-dynamics study of oxygen-interstitial and oxygen-vacancy diffusion in CeO2

“…In the first set, we randomly introduced vacancies or interstitials throughout the cell and compensated the charge with a uniform background charge. We refer to these simulation cells as bgcc (background charge-compensated); they allow us to study the diffusion behaviour of the two oxygen defects, free from the interactions with compensating defects [29,[50][51][52]. The second set of simulations were performed on cells containing dopant ions to charge compensate the respective oxygen point-defects; donor dopants (Nb Ce • or Ta Ce • ) for the cells containing oxygen interstitials (  O i ) and acceptor dopants ( ¢ Gd Ce ) for the cells with oxygen vacancies (V O •• ).…”

High oxide-ion conductivity in acceptor-doped Bi-based perovskites at modest doping levels

“…The activation energy (E a ) for the oxide-ion conductivity changes on heating from B0.8 to 0.4 eV at B325-350 1C 8 and has been attributed to changes in volume fraction of co-existing R and T polymorphs. 14 Various modelling methods and studies [15][16][17] have been tried to improve understanding of structure-property relations in NBT with respect to oxide ion conductivity and some trends have emerged. For example, migration energy of oxide ions via saddle points in the lattice associated with two A-site cations and a B-site cation are lowest for Bi located on both A-sites compared to either Na or mixed Na-Bi A-site occupation.…”

“…15 Experimental E a values agree well with simulations for Na-Bi as the A-site saddle point cations, in good agreement with the (average) disordered arrangement of Na and Bi on the A-sites in NBT. The influence of polymorphism on E a 16 and ordering of Na + and Bi 3+ ions on oxygen tracer diffusion 17 have given further mechanistic insights into the oxide ion conductivity. A complete explanation is still lacking however, owing mainly to the complexity of the crystallography and polymorphism of NBT.…”

“…This insensitivity to composition was attributed to reduction in mobile ion concentration by vacancy-acceptor dopant association, thus behaving as a weak electrolyte. Zhang et al 17 performed molecular dynamics simulations to calculate the oxygen diffusion coefficient for several A-and B-site acceptor and isovalent dopants in rhombohedral BF. This study revealed significant limitations in applying widely-used, empirical crystallochemical relations to maximise oxide ion diffusivity in perovskites when the acceptor dopants are close in size to that of host cations.…”