A-site non-stoichiometry and defect complexes in Nd-substituted CaTiO3 perovskite oxide

This is the authors' abstract. We don't add key points for this paper.

: A-site non-stoichiometric perovskite oxides have attracted growing interest as electrocatalysts and photocatalysts, since A-site vacancies can activate lattice oxygen and enhance catalytic performance in reactions such as pollutant degradation and hydrogen production. In this context, the A-site deficient perovskite oxide was synthesized by solid-state reaction and characterized by a combination of X-ray diffraction (XRD), transmission electron microscopy (TEM/HRTEM), and electron paramagnetic resonance (EPR) spectroscopy. Rietveld refinement confirms that the compound adopts an orthorhombic Pnma structure over the entire temperature range investigated (25–1200 °C), with no evidence of a phase transition toward higher symmetry. The lattice parameters are in good agreement with theoretical predictions based on an effective vacancy radius model, suggesting that A-site vacancies contribute to lattice expansion. Selected-area electron diffraction (SAED) patterns are in agreement with the Pnma symmetry and the a - b + a - octahedral tilt system, while HRTEM imaging reveals linear defects consistent with local strain accommodation associated with cation non-stoichiometry. EPR spectroscopy identifies two distinct Nd 3+ environments: a regular A-site center ( ) and an associated defect center ( ), consistent with the presence of oxygen vacancy related defect centres. The absence of any Ti 3+ signal suggests that charge compensation is mainly associated with defect related mechanisms rather than Ti reduction. These results provide complementary information on the average and local structures of the A-site deficient perovskite and contribute to a better understanding of the relationship between site A non-stoichiometry, local structural distortions and defect chemistry in CaTiO 3 -based perovskites.