X-ray spectroscopic study of the electronic structure of the high-dielectric-constant materialCaCu3Ti4O12

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 ␣,␤ , Cu L ␣,␤ , 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 -and -state emission from valence-band O 2p states when in resonance with * and * conduction-band O 2p 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 3d states in determining the band gap of this material is discussed.

A novel low cost non-aqueous chemical route for giant dielectric constant CaCu3Ti4O12 ceramic

“…4(d) demonstrate Ti 2p 3/2 and Ti 2p 1/2 peaks, at 458.06 eV and 463.92 eV, respectively. As mentioned above calcium and copper were in the þ2 oxidation state, whereas titanium was in the þ4 oxidation state and the binding energy values are similar to the findings reported earlier for CCTO ceramic [44,45]. The O1s spectra shown in Fig.…”

Broadband dielectric response ofCaCu3Ti4O12: From dc to the electronic transition regime

“…Our results are compared to published results 2,9 and to model calculations of the lattice dielectric response of CCTO from first principles. [10][11][12] ͑ii͒ Within the low-frequency reflectivity spectrum, which is dominated by phonon modes, we detect an unusually large number of crossing points in the reflectivity ͑‫ץ‬R / ‫ץ‬T =0͒, which seems to be too significant to be ignored or to be explained by accidental effects. ͑iii͒ Electronic excitations for energy transfers up to 4 eV are studied via the dynamic conductivity and are compared to ab initio band structure calculations.…”

Zhang-Rice physics and anomalous copper states in A-site ordered perovskites

“…1(a)). In this structure, a surprisingly rich set of interesting physics phenomena10111213141516 have been demonstrated by replacement of the B-site 3 d transition metal ion via experiment and theory including colossal dielectric constant1718, ferrimagnetism19, charge, orbital, and spin ordering20, non-fermi liquid behavior21, enhanced electronic correlations22 and possibly the Zhang-Rice state23. In addition, previous reports hinted at the presence of a mixed-valency on Cu for B = Cr and Co2324.…”