The polarized Raman spectra of ${\mathrm{CaCu}}_3{\mathrm{Ti}}_4{\mathrm{O}}_{12}$ (CCTO) single crystals were studied between 10 and 600 K. Five of the eight ${(2A}_g{+2E}_g{+4F}_g)$ Raman active modes expected for the $\mathrm{Im}3\mathrm{}¯$ structure were observed at $292{(F}_g),$ ${445(A}_g),$ ${499(E}_g),$ ${511(A}_g),$ and ${575(F}_g){\mathrm{cm}}^{-1}.$ The assignment of the Raman lines to modes of definite symmetry and eigenvector was done in close comparison with results of lattice dynamics calculations. The mode frequency vs temperature dependence exhibits no anomalies in the whole temperature range. This is consistent with earlier indications that the high value of the dielectric constants and its strong decrease below 100 K are not related to temperature-dependent atomic displacements. An additional line of $A_g$ symmetry, clearly seen at low temperatures is tentatively assigned to vibrations of distorted ${\mathrm{TiO}}_6$ octahedra, presumably at twin boundaries.

• Received 5 February 2002

DOI:https://doi.org/10.1103/PhysRevB.66.132102