Pressure dependence of light scattering spectra of kdp

Abstract

Low frequency Raman scattering spectra of the B2 mode of KDP has been observed under a hydrostatic pressure in a range 0-52.0 kbar using a diamond-anvil cell. The overdamped central component of z(yx)z +δ and x(yx)y spectra at atmospheric pressure becomes gradually underdamped spectra up to 27.5 kbar revealing Peercy's result well. Numerical analysis of both spectra based on the coupled phonon model gives an unreasonable wave vector dependence of the soft mode frequency near Γ point of the Brillouin zone. In the pressure region above 27.5 kbar, the change of the spectral shape suggests existence of the pressure induced phase transition reported recently by the X-ray study. Also in the high pressure phase, a new central component grows drastically with increasing pressure corresponding to an excitation activated by pressure.