Core-shell structure formation in Nb2O5-doped SrTiO3 by oxygen partial pressure change

Abstract

A core-shell structure was observed in SrTiO3 doped with 1.2 mol% of Nb2O5, after sintering in a reducing atmosphere (5H(2)-95N(2)) and then in an oxidizing atmosphere lair). 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 similar to 1% less than that of core regions grown in 5H(2)-95N(2), 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.