X-ray spectroscopic study of the electronic structure of the high-dielectric-constant material CaCu3Ti4O12 -: art. no. 195111

The element-specific valence- and conduction-band densities of states for the high-dielectric-material CaCu3Ti4O12 have been measured using soft x-ray emission and absorption spectroscopies. Ti L alpha,beta, Cu L alpha,beta, and O K soft x-ray emission spectra of CaCu3Ti4O12 were measured with monochromatic photon excitation on selected energies above the Ti and Cu L-2,L-3 and O K absorption edges, respectively. X-ray absorption spectra were recorded at the same edges, The electronic structure was also calculated using density functional theory employing the full-potential linearized augmented plane-wave method. Excellent agreement is seen between the results of these calculations and the measured x-ray emission and absorption spectra. This agreement is particularly good at the O K edge where the resonant behavior of the x-ray emission spectrum can be attributed directly to sigma- and pi-state emission from valence-band O 2p states when in resonance with pi* and sigma* conduction-band O 2p states. Resonant inelastic x-ray scattering is observed at the Ti L-2,L-3 absorption edge and is compared to previous studies of Ti containing perovskite compounds. The role of Cu 3d states in determining the band gap of this material is discussed.