Electronic structure of Mn-doped CaCu3Ti4O12: An XPS, ESR and NEXAFS study

Abstract

Mn-doped CCTO samples were synthesized using standard ceramic technology. Two series of samples of the composition CaCu3Ti4-4xMn4xO12-δ and CaCu3-3xMn3xTi4O12+δ (0.005 ≤ х≤0.06) have been investigated. According to XRD data, the samples contain copper oxide (less than 1 mol %), the largest amount of which is in CaCu3Ti4-4xMn4xO12-δ. According to XPS and NEXAFS spectroscopy, a complex mixture of Mn (II), Mn (III), Mn (IV) ions is recorded in both series of samples. In both series, Mn (II) ions are reliably determined, in large amounts in CaCu3-3xMn3xTi4O12+δ. In the ESR spectra of both series of Mn-doped CCTO samples, the exchange-narrowed line (g~2.149 at RT) broadens and rapidly degrades as the content of the doping impurity increases; a broad signal appears in the spectrum with a center in the region g = 2. In the spectra of the CaCu3Ti4-4xMn4xO12-δ series, starting from x = 0.02, a sextet of relatively narrow lines appears in the g = 2 region of the hyperfine (HF). With an increase in the Mn content from x = 0.02 to 0.06, the sextet intensity approximately doubles. The observed sextet of isolated Mn2+ ions most likely belongs to Mn2+ ions, which replace Ca2+ ions in the unit cell of perovskite (CaTiO3).