INFRARED STUDIES OF THE BI CUPRATES

The infrared reflectivity of the bismuth-based high-T-c superconductor s Bi2.07Sr1.8CuO6+delta (2201) with T-c = 7 K, Bi2.1Sr1.9CaCu2O8+delta (2212) with T-c = 85 K, and Bi1.8Pb0.3Sr2Ca2Cu3O10+delta (2223) with T-c = 108 K have been measured between 25 and 8000 cm(-1) at temperatu res between 5 and 300 K. The temperature- and frequency-dependent far- infrared part of the spectrum is analysed. The Kramers-Kronig analysis was used to determine the optical conductivity and a tentative mode a ssignment was investigated for all three phases. The softening of phon on modes in Cu-O and Bi-O layers was also observed.