Ti-rich and Cu-poor grain-boundary layers of CaCu3Ti4O12 detected by x-ray photoelectron spectroscopy

Cleaved and polished surfaces of CaCu3Ti4O12 ceramics have been investigated by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX), respectively. While EDX technique shows the identical CaCu3Ti4O12 stoichiometry for the two surfaces, XPS indicates that the cleaved surface with grain-boundary layers is remarkably Ti-rich and Cu-poor. The core-level spectrum of Cu 2p unambiguously shows the existence of monovalent copper only for the cleaved surface. Possible grain-boundary structure and its formation are discussed.