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The elastic behavior has been studied of a bulk metallic glass of composition Pd~i40Pio, prepared by the recently developed technique of slow cooling from a dehydrated flux of boric oxide in an ultraclean environment.A large ratio (8 jp=4. 56) of the bulk to shear moduli and a large Poisson's ratio (0.40) at room temperature indicate intrinsic softening of transverse acoustic phonons. Pulse-echo-overlap measurements have been made of both ultrasonic modes between 4.2 and 293 K. Both Cll and C~decrease with temperature and show enhanced stiffening at low temperatures which can be associated with two-level systems. To examine nonlinear acoustic properties of a metallic glass the hydrostatic pressure dependence of the ultrasonic wave velocities has been measured. Both d8 /dP (=7.52) and dC~/dI' (=1.0) are positive, showing that the modes stiffen under hydrostatic pressure in the normal way. The results are used to examine quantitatively the vibrational anharmonicity of a metallic glass by recourse to the mode Gruneisen parameters {y~= 3.20, y, =2 23). The mean long wavelength acoustic mode Griineisen parameter p H( =2 59) at room temperature is comparable with the thermal Griineisen parameter yH (=2.24). In general, the temperature and pressure dependences of the elastic constants show that metallic glasses, unlike many Si02-based insulating glasses, have elastic and anharmonic properties similar in kind to the crystalline state (in this case to the component transition metals nickel and palladium). An equation of state for a metallic glass is presented for the first time: The compression is found to be small, being similar to that of nickel.

The hydrostatic pressure and temperature dependence of velocities of ultrasonic modes propagated in natural crystals of iron pyrites FeS2 have been measured. It is confirmed that C12 is positive; the Poisson ratio shows the usual positive sign; it becomes more positive under pressure and remains positive down to low temperatures. Vibrational anharmonicity of iron pyrites is discussed in the Gruneisen parameter approach.

Detailed measurements are presented of ultrasonic wave velocity and attenuation in the orthorhombic, superconducting and the tetragonal, non-superconducting forms of GdBa2Cu30,-,. Theorthorhombicstate datadisplay asharpelastictransition at about 240 K which is absent from that of the tetragonal state; however, x-ray diffraction measurements show no evidence of a structural phase transition. The lattice thermal expansion is found to be fairly isotropic. The elastic response in the superconducting state is found to be dominated by conventional anharmonic and anelastic phenomena: no effects that can be specifically attributed to the formation of the superconducting state have been detected. The ultrasonic velocity and attenuation data are explained by the presence in the tetragonal state of one and in the orthorhombic state of two thermally activated anelastic relaxation mechanisms which are attributed to various oxygen vacancy hopping processes.