Evolution of the microstructure of undoped and Nb-doped SrTiO3

Electrical conductivity of Sr1−xTiO3−δ materialsmaterials

“…Strontium vacancies may also be formed in stoichiometric strontium titanate, especially at very high temperatures, and their concentration is expected to remain frozen at temperatures below 1000 ~ [8]. In these conditions, the arguments presented for Sr-deficient samples may also be used for stoichiometric samples, especially for the sample which was sintered at 1400 ~ (case A), with an activation energy of about 1.51 eV in the range 400-800 ~ The impedance spectra obtained for the sample with larger grain size (case C) shows that the overall behaviour of this sample may still be affected by the bulk conductivity, and this might be responsible for the lower value of activation energy found for this case.…”

“…For example, firing under reducing conditions yields materials with higher n-type conductivity, and lower p-type contribution relative to firing in air [8]. These effects were interpreted by combining the reactions of oxygen loss under reducing conditions (Eq.…”

“…According to some authors [8] formation of Ruddlesden-Popper phases of a generic type SrO.nSrTiO3 may act as a sink for the excess of SrO. Results reported by Moos and Hardtl [8] suggest that the concentration of ionic defects depends on the firing conditions but remains frozen-in at working temperatures as high as 1100 ~ The band gap is relatively high in strontium titanate based materials (=3 eV), and in this case the concentrations of ionic defects may be much higher than the concentrations of electronic species. Equation 3 should thus yield an approximate neutrality condition [v; j--tVol can be combined with the mass action laws of reactions 1 and 2 to obtain the expected power law dependence of the concentrations of charge carriers on the oxygen partial pressure ( P02 88 or Po2-Y4…”

Combined effects of A-site deficiency and dopant content on the transport properties of Nb-doped strontium titanate

“…A-site deficiency also improves the sinterability, except for cases when the content of Nb is similar to the value of Sr- [23] pointed out that differences in sinterability may be related to changes in defect chemistry. A 4-wire/2-electrodes method was used for electrical characterization both in air and in reducing conditions.…”

“…3A can also be used to evaluate the diffusion coefficient of the diffusing species. An approximate model for symmetrical diffusion in a plate-like sample was used for this purpose, and one thus expects the following concentration profile after suddenly changing from initial uniform concentration Ci to the surface concentration Co [23] …”