“…While the properties of the IR-active phonon modes are indeed well known for the Y123 system [8,9,10,11], the situation is not that clear for the bilayer high-T c compounds of the type A 2 Sr 2 CaCu 2 O 8 (A2212; A = Tl, Bi). Despite of experimental [5,6,12,13] and theoretical [14,15,16] efforts, the assignment of the c axis IR phonon modes in Bi2212 and Tl2212 remains contradictory, as discussed in [13].…”