CaCu3Ti4O12: Pressure dependence of electronic and vibrational structures

The effects of pressure in electronic and vibrational properties of the double perovskite CaCu3Ti4O12 have been investigated in the 0-25 GPa range by optical absorption and Raman spectroscopy. Besides a full structural characterization, we aim at unveiling whether the ambient Im3 crystal structure is stable under high pressure conditions and how its giant dielectric permitivity and electronic gap varies with pressure. Results show that there is evidence of neither structural phase transition nor metallization in CaCu3Ti4O12 in the explored pressure range. We have observed the eight Raman active modes associated with its Im3 crystal phase and obtained their corresponding frequency and pressure shift. Moreover, the direct electronic band gap (2.20 eV), which is mainly associated with the oxygen-to-copper charge transfer states, increases slightly with pressure at a rate of 13 meV GPa from 0 to 10 GPa. Above this pressure is almost constant (E-g = 2.3 eV). The results highlight the high stability of the compound in its Im3 phase against compression.