Dielectric properties of TGBA and TGBC phases

The dielectric properties of two compounds displaying N*-TGBA-SC* or N*-TGBA-TGBC-SC* phase sequences have been studied. A simplified model based on a TGBC structure established from previous X-ray and optical works is also proposed. The observed relaxation processes are attributed to the Goldstone and the soft modes. The amplitudes (resp. frequencies) are low (resp. high), especially for the Goldstone mode. This is explained by elastic distortions due to the existence of grain boundaries, these distortions being very dependent on the block size.