Changes in shear elastic constant, long-range order, and lattice parameter were measured during disordering and eventual amorphization of Z^Al by ion irradiation. Large ( = 50%) elastic softening was observed during disordering, and anomalies occurred in all three measured parameters over a narrow range of ion doses. The results indicate that a first-order phase transformation triggered by an elastic instability occurs during solid-state amorphization. The changes reported here during disordering and amorphization are very similar to behavior observed previously in a large number of solids during heating to melting.
Recent Brillouin experiments on a-Si02 have shown that it undergoes an amorphous-to amorphous-phase transition as a function of pressure. Here we report Brillouin scattering results from a-GeO&, a-As&S3, a-B&03, and a polymeric glass. Irreversible effects under pressure are found for a-GeOz and a-B203 which we also interpret as due to phase transitions. The polymeric glass and a-As2S3 show no evidence of unusual behavior.
Using Brillouin scattering we have succeeded in observing the normal modes of vibration of unsupported films in a region where the dispersion relationship is quadratic. Extremely low-lying excitations were observed in thin films with thicknesses as small as 200 A. Contrary to what has been found in work on supported films, we are able to extract information on a number of the elastic moduli because the measured velocities in very thin films do not depend on the properties of the substrate. This technique should be a valuable addition to the tools which can be used in the study of materials in thin-film form.
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