X-ray spectroscopic study of the electronic structure of the high-dielectric-constant material CaCu3Ti4O12

Abstract

The element-specific valence- and conduction-band densities of states for the high-dielectric-material CaCu 3 Ti 4 O 12 have been measured using soft x-ray emission and absorption spectroscopies. Ti L a , b ,Cu L a , b , and O K soft x-ray emission spectra of CaCu 3 Ti 4 O 12 were measured with monochromatic photon excitation on selected energies above the Ti and Cu L 2,3 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 s - and p -state emission from valence-band O 2 p states when in resonance with p * and s * conduction-band O 2 p states. Resonant inelastic x-ray scattering is observed at the Ti L 2,3 absorption edge and is compared to previous studies of Ti containing perovskite compounds. The role of Cu 3 d states in determin- ing the band gap of this material is discussed