Phonons in CaCuO2

CaCuO2 is the infinite number of Cu-O planes limit of most of the high-temperature superconductors. From infrared reflectivity of ceramic (Ca0.86Sr0.14)CuO2, we have measured all five of the group-theoretically allowed phonons. Also, group theory predicts no Raman-allowed phonons, in agreement with our observations. We compare the observed phonons with those reported in other high-temperature superconductors and, in particular, with Nd2CuO4 (T structure) because of the similar Cu-O plane structural element. © 1989 The American Physical Society.