Studies on the Reorganization of Extended Defects with Increasing n in the Perovskite-Based La4Srn–4TinO3n+2 Series

Authors


  • We thank the HiT Proton Project (EU-RTN), the European Science Foundation (ESF-OSSEP), and SHEFC for financial support. One of us (J.C.-V.) thanks Filipe Figueiredo at the University of Aveiro (Portugal) for his help with the density measurements. The authors are also indebted to Myriam Aguirre at Universidad Complutense in Madrid (UCM-Spain) for her advice on TEM.

Abstract

Perovskite titanates with nominal stoichiometry ABO3+δ often exhibit quite interesting properties, but their structural characterization is not always rigorous. Herein, we demonstrate how excess oxygen can be incorporated in a titanate perovskite-based lattice. A new family of layered perovskites La4Srn–4TinO3n+2 has been investigated by means of X-ray diffraction, neutron diffraction, transmission electron microscopy, thermogravimetric analysis, and density and magnetic measurements. Such layered perovskites are known to be able to accommodate extra oxygen beyond the parental ABO3 perovskite in crystallographic shears. The structure evolves with increasing n. Firstly, the perovskite blocks become more extensive and the oxygen intergrowth layers move further apart; then the spacing between the intergrowth layers increases further and their repetition becomes more sporadic. Finally, the layered structure is lost for the n = 12 member (La2Sr4Ti6O19–δ). In this structure, excess oxygen is accommodated within the perovskite framework in randomly distributed short-range linear defects. These defects become more dilute as the cubic perovskite, that is, n = ∞, composition is approached.

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