Brillouin spectroscopy of relaxor ferroelectrics and metal hydrides

A complete set of elastic and piezoelectric constants for single-domain rhombohedral Pb(Zn1/3Nb2/3)O34.5%PbTiO3 is obtained using Brillouin scattering. The bulk modulus and elastic constants agree with the values obtained from ultrasonic methods, but the piezoelectric constants are smaller. Differences in piezoelectric constants from different techniques are due to frequency dispersion and the contributions of domain boundaries. The pressure dependence of the Brillouin shifts of amorphous BeH2 was measured from ambient pressure to 17 GPa. The equation of state is deduced from the pressure dependence of the sound velocity; the bulk modulus is 14.2 (±3.0) GPa and its pressure derivative is 5.3 (±0.5).