Correlation Between Photoluminescence and Structural Defects in Ca_1+xCu_3−xTi₄O₁₂ Systems

Ca_1+xCu_3−xTi₄O₁₂ powders were synthesized by a conventional solid-state reaction. X-ray diffraction (XRD) was performed to verify the formation of cubic CaCu₃Ti₄O₁₂ (CCTO) and orthorhombic CaTiO₃ (CTO) phases at long range. Rietveld refinements indicate that excess Ca atoms added to the Ca_1−xCu_3−xTi₄O₁₂ (x = 1.0) composition segregated in a CaTiO₃ secondary phase suggesting that solubility limit of Ca atoms in the CaCu₃Ti₄O₁₂ lattice was reached for this system. The FE-SEM images show that the Ca_1+xCu_3−xTi₄O₁₂ (0 < x < 3) powders are composed of several agglomerated particles with irregular morphology. X-ray absorption near-edge structure spectroscopy (XANES) spectra indicated [TiO₅V_o^z]-[TiO₆] complex clusters in the CaCu₃Ti₄O₁₂ structure which can be associated with oxygen vacancies (V_o^z = V_o^x, V_o^•, and V_o^••) whereas in the CaTiO₃ powder, this analysis indicated [TiO₆]–[TiO₆] complex clusters in the structure. Ultraviolet-visible (UV–vis) spectra and photoluminescence (PL) measurements for the analyzed systems revealed structural defects such as oxygen vacancies, distortions, and/or strains in CaCu₃Ti₄O₁₂ and CaTiO₃ lattices, respectively.