A LATTICE DYNAMICAL STUDY OF THE ROLE OF PRESSURE ON RAMAN MODES IN HIGH-T-C HGBA2CUO4

A lattice dynamical study has been carried out to investigate the Rama n frequencies and the effect of pressure on the apical-oxygen (O-A) vi bration (Raman Active) in the Hg-O-A-Cu bond in HgBa2CuO4 high-T-C sup erconductor by using an unscreened rigid ion model. The calculated Ram an frequencies are, in general, in fair agreement with experimental va lues. The calculated values of the O-A A(1g) Raman mode agree reasonab ly well with the experimental Raman data up to 7.5 GPa and show that t he O-A A(1g) vibrational mode increases linearly as the pressure is in creased, suggesting phonons to play a dominant role in this system.