Elastic properties of tetragonal KH2PO4 by high-pressure Brillouin spectroscopy

The pressure dependence of six ratios of elastic constants to density in the Phases II and IV of potassium dihydrogen phosphate (KH2PO4) have been determined for a single crystal with tetragonal structure up to 7.5 GPa at room temperature by high-pressure Brillnuin spectroscopy. The C-11/rho, C-12/rho, C-13/rho, and C-33/rho increase in proportion to an increase in pressure, and C-44/rho and C-66/rho decrease against pressure. Acoustic velocities as a function of Euler angle phi at various pressures are calculated from the pressure dependence of the ratios of C-y/rho. At the II-IV phase transition pressure 2.7 GPa, there is no anomaly on the elastic properties.