RAMAN-SPECTROSCOPY OF HIGH-TEMPERATURE SUPERCONDUCTING YBA2CU3OX SINGLE-CRYSTALS AND FILMS

Polarized Raman spectra of YBa2Cu3Ox single crystals with different oxygen content (6<x<7) have been studied. We have obtained the dependence of the frequency ν0 of the bridging oxygen O4 mode on x and Tc. The ν0(x) dependence was found to be affected by the sample preparation, while the dependence ν0(Tc) is independent of the sample history and is approximately linear. It was found that the linear-chain model was unsuccessful in reproducing the increase of the frequency ν0 with x that was found experimentally. This fact as well as an abnormally high Grüneisen constant, which was obtained from a comparison of ν0(c) and ν0(P) data, allows us to suppose the existence of an additional interaction due to appearance of the oxygen O1 chain. The O4 mode in tetragonal crystals also revealed high sensitivity to the exciting laser power density, which was considered as a photoinduced phenomenon. Finally we discuss the method of determination of a preferable crystallographic orientation of films deposited by laser ablation. © 1990.