CaCu₃Ti₄O₁₂: pressure dependece of electronic and vibrational structures.

E. Jara¹, J. González¹, F. Aguado¹, R. Valiente² and F. Rodríguez¹*.

MALTA Team, DCITIMAC¹ and Applied Physics Dpt.², Facultad de Ciencias, University of Cantabria, 39005 Santander, Spain

*fernando.rodriguez@unican.es

CaCu₃Ti₄O₁₂ (CCTO) displays a cubic double-perovkite structure Im3 at ambient pressure and it is better known for having the largest dielectric constant (16000-18000) ever measured [1],  being almost constant over a wide temperature (100-700 K) and frequency (0-10⁶ kHz) ranges. These properties make it attractive for device implementation. The variation of the crystal structure under pressure has been investigated by x-ray diffraction in the 0-57 GPa range [2], and no evidence of structural phase transition was detected.

In this work, we present optical absorption and Raman spectroscopy measurements under pressure in the 0 – 25 GPa range. CCTO presents a challenging optical behaviour under pressure associated with the square planar Cu²⁺ absorption (D_4h CuO₄ center). We have investigated the variation of the charge-transfer band gap with pressure, which continously redshifts with pressure from its ambient pressure value E_g = 2.2 eV [3]. The Raman spectra show the eight Raman active modes expected for the Im3 space group (2A_g+2E_g+4F_g) following results of lattice dynamics calculations given elsewhere [4].

A detailed correlation analysis between vibrational and electronic structures as a function of pressure with will be presented at the conferece.

[1] M. A. Subramanian, Dong Li, N. Duan, B. A. Reisner, and A. W. Sleight, J. Solid State Chem. 151, 323 (2000).

[2] Y. Ma, J. Liu, C. Gao, W. N. Mei, A. D. White, and J. Rasty, Appl. Phys. Lett. 88, 191903 (2006).

[3] C. C. Homes, T. Vogt, S. M Shapiro, S. Wakimoto and A. P. Ramirez, Science 293, 673 (2001).

[4] N. Kolev, R. P. Bontchev, A. J. Jacobson, V. N. Popov, V. G. Hadjiev, A. P. Litvinchuk, and M. N. Iliev, Phys. Rev. B 66, 132102 (2002).