THE A-B ANISOTROPY IN BI2SR2CACU2O8 SUPERCONDUCTOR - AN INVESTIGATION BY RAMAN-SPECTROSCOPY

In the present paper, we report a study of the Raman active phonons of Bi2Sr2CaCu2O8 for frequencies extending down to 20 cm-1 and temperatures ranging from 77 to 673 K. In spite of important changes in the spectra occurring under heating, we show that the a-b anisotropy, exemplified by Raman spectroscopy in Bi2Sr2CaCU2O8 and obvious on the macroscopic scale through the crystal morphology, still persists at 673 K. These changes are interpreted in terms of disordering effects in the BiO planes and speak in favor of an order-disorder transition around 500 K.