RAMAN-SCATTERING FROM Y-BA-CU-O HIGH TC-SUPERCONDUCTORS

Raman scattering experiments have been carried out on polycrystalline samples of the high temperature superconductors Y//1//. //2Ba//0//. //8CuO//4// minus //x and YBa//2Cu//3O//7// minus //y throughout the temperature range 15 K less than equivalent to T less than equivalent to 300 K. The vibrational frequencies in each compound have been measured and compared to values obtained from Raman and infrared experiments carried out on similar compounds. The appearance of two new modes in Y//1//2Ba//0//. //8CuO//4// minus //x at 170 K and 90 K and investigation of the temperature dependence of a 644 cm** minus **1 mode in YBa//2Cu//3O//7// minus //y has indicated that a structural modification occurs at approximately 170 K. This result is discussed in relation to the results of previous EXAFS experiments.