Crystal structure and electrical conductivity correlation in CaTi1−xFexO3−δ system

Abstract

Abstract. The structural refinements of CaTil.xFexO3_ ~ (x = 0 -0.4) were performed by means of the X-ray data full-profile analysis method on the basis of the orthorhombic perovskite structure (space group Pbnm). The lattice parameters, atomic coordinates, occupancies and equivalent isotropic temperature factors were refined. The characteristic Debye temperature value was determined for the composition x = 0.25 by analysis of the temperature dependence of X-ray reflections intensity. Using the structural refinement results, the model of oxygen vacancy formation, ordering and transport under acceptor doping was proposed. The dependence of the ionic conductivity on the iron concentration in CaTil_xFexO3_ ~ calculated in the frame of proposed model describes well the experimental data.

High-temperature electrical transport in Al-doped calcium and strontium titanates

“…These data are similar to those on the dependence of ionic conductivity on substitute concentration in CaTil_xFexO3_ s [6,7]. It was supposed [6] that in substituted calcium titanate, formation of complexes of substitution defects (FeTi) and oxygen vacancy complexes starts near x = 0.2 and this is a reason of ionic conductivity decrease. This scheme of defect formation is applicable to CaTil_xAlxO3_ 5 as long as it has the same crystal symmetry.…”

“…Recent studies show that in alkali earth titanates CaTit_xFexO3~ (A = Ca, St, Ba), Fe-substitution leads to a considerable rise in conductivity, however the dependence of ionic conductivity on the dopant concentration is nonmonotone: increase in ionic conductivity at low iron contents (x < 0.2) is followed by decrease at higher x [6,7]. It will be interesting to investigate ionic conduction in the perovskite-type oxides doped with other cations of valence lower than that of Ti.…”

Influence of acceptor doping on ionic conductivity in alkali earth titanate perovskites

“…X-ray diffraction does not show long-range ordering of the oxygen vacancies in the region of x = 0.05 -0.38 in CaTil_xFexO3.x/2 system, which was confirmed by transmission electron microscopy measurements [13]. According to the refined X-ray powder diffraction data for CaTil_xFexO3.8 (x = 0 -0.4) presented in [14], the symmetry of the samples is orthorhombic and there is no evidence of ordering of oxygen vacancies. Summarizing the results of [12][13][14], one can conclude that for the CaTil.xFexO3.…”

“…According to the refined X-ray powder diffraction data for CaTil_xFexO3.8 (x = 0 -0.4) presented in [14], the symmetry of the samples is orthorhombic and there is no evidence of ordering of oxygen vacancies. Summarizing the results of [12][13][14], one can conclude that for the CaTil.xFexO3. ~ system disordered substitutional solid solutions are formed within the Fe concentration range of x < 0.4.…”

“…A few studies of crystal structure evolution under Fesubstitution in CaTiO3 system have been performed by means of electron microscopy, transmission electron microscopy and X-ray diffraction [12][13][14]. According to the results of electron microscope investigations and Xray diffraction of Ca2Ti2.2xFe2xO6.…”