Chemical diffusion in complex oxides with an emphasis on BaTiO₃

Abstract

Chemical diffusion has long been studied mostly on binary oxides, but practical interest in it is increasing with more complex oxides these days, e.g., perovskite oxides that are finding a variety of electroceramic and electrochemical applications. In this paper, we compile the chemical diffusivity data of oxygen as measured on a prototype perovskite BaTiO 3 and review the connotation of their variation with oxygen activity in the light of the chemical or ambipolar diffusion theory. The chemical diffusivity of BaTiO 3 is compared with those of other perovskite oxides of mostly electrochemical concern and of typical binary transition metal oxides. The chemical diffusivity is further compared with those of the compounds such as Ag 2 S, Ag 2 Te, YSZ and Fe 3 O 4 , that have dissimilar crystal structures, but with a similar defect structure to BaTiO 3 , in order to get a further insight into the inner workings of chemical diffusivity particularly in the stoichiometric regime of complex oxides. Finally, possible complication with nonstoichiometry re-equilibration kinetics due to cation mobility is pointed out with reference to what has been observed from LiNbO 3 under an oxygen activity gradient.

Oxygen diffusion in single crystal barium titanate

“…From the former one sees that D*(N) is independent of oxygen activity. On the basis of the definition of the tracer diffusion coefficient [see eqn (12)],…”

Effects of background oxygen pressure on dielectric and ferroelectric properties of epitaxial (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.10,Sb0.06)O3 thin films on SrTiO3

“…In other words, the higher the P O 2 in the ambient, the less is the extent of volatilization of the A-site cations, resulting in a lattice expansion, which manifests itself as a macroscopic stress-free strain and is substantiated by the x-ray data. 31 The room temperature dielectric constant ͑K 33 ͒ of the films at 1 MHz deposited at various P O 2 is demonstrated in Fig. The observed surface morphology is reminiscent to what has been previously seen in NaNbO 3 films on SrTiO 3 substrates.…”

Defect chemistry of alkaline earth metal (Sr/Ba) titanates

“…The defect chemistry of acceptor-doped BaTiO 3 has been intensively investigated by Smyth [70][71][72][73] and Yoo [120][121][122][123][124][125][126][127][128][129][130][131] . All their works demonstrate that the defect chemistry of BaTiO 3 is similar to that of SrTiO 3 .…”