Core‐Shell Structure Formation in Nb2O5‐Doped SrTiO3 by Oxygen Partial Pressure Change

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Abstract
A core‐shell structure was observed in SrTiO3 doped with 1.2 mol% of Nb2O5, after sintering in a reducing atmosphere (5H2‐95N2) and then in an oxidizing atmosphere (air). In undoped and Al2O3‐doped SrTiO3 specimens, no core‐shell structure formed after the same sintering treatments as those for SrTiO3 doped with 1.2 mol% of Nb2O5. The measured chemical compositions of the core and shell regions of 1.2‐mol%‐Nb2O5‐doped SrTiO3 grains showed that the Sr/(Ti + Nb) ratio of the shell regions grown in air was ~1% less than that of core regions grown in 5H2‐95N2, which was in good agreement with a value predicted by available defect equations. Therefore, the observed core‐shell structure is thought to result from the formation of strontium vacancies in an oxidizing atmosphere.