High-pressure Raman and x-ray study of the spin-frustrated pyrochlore Gd_2Ti_2O_7

摘要

Pressure-dependent Raman and x-ray diffraction studies of spin-frustrated pyrochlore Gd_2Ti_2O_7 have been carried out at room temperature up to ～25 GPa and 34 GPa, respectively. A subtle distortion of the lattice at about 9 GPa is evidenced by Raman spectroscopy. X-ray results corroborate the distortion of the pyrochlore lattice at about the same pressure. Shell model lattice dynamical calculations were carried out in order to establish and understand the pressure dependence of Raman phonon frequencies. Our data may be relevant to the recent findings by Mirebeau et al. [Nature 420, 54 (2002)] who observed magnetic correlations under high pressure in Tb_2Ti_2O_7, a frustrated spin-liquid system.