The dissipation mechanism in Tl 1-xC xBa 2Ca 3Cu 4O 12-δ (x = 0, 0.25, 0.5 and 0.75) superconductor under the influence of external magnetic fields have been studied. The sample with x = 0.25 have shown strong flux pinning characteristic as compared to the Tl 1-xC x-1234 (x = 0, 0.5 and 0.75) samples. The scanning electron micrographs of Tl 1-xC x-1234 shows well connected grains in x = 0 and 0.25 samples. Whereas, x = 0.5 and 0.75 samples have relatively poor grain morphology, which shows that the source of pinning in Tl 0.75C 0.25-1234 sample is intrinsic one. The transition width data was also fitted to the thermally activated flux flow model. The apical phonon modes of vibrations were studied through FTIR absorption measurements. © 2012 Elsevier B.V. All rights reserved.