Bulk elastic properties of metals determined by Brillouin scattering and its application to RCu2Si2(R=rare earth)

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Abstract
Measurements of Brillouin scattering from surface-wave excitations of metals by means of a tandem Fabry-Perot interferometer according to Sandercock allow the reliable determination of bulk elastic moduli and elastic constants, respectively, of polycrystals and single crystals. This determination is independent of Cauchy's relation (cL=3cT, or c12=c44). The accuracy of the method of 5-10% (depending on the penetration depth of the light) has been demonstrated for cubic rare-earth (R) compounds with known elastic constants, such as CePd3 (polycrystal) and CeAl2 (single crystal). The method has been applied to determine the bulk moduli cB of polycrystalline tetragonal RCu2Si2 at 300K with an accuracy of better than 10%. The stable-valent compounds follow cB varies as Q/V (Q=valence of the R ion, V=unit cell volume). With respect to this behaviour, valence instabilities are identified by the softening of cB of EuCu2Si (32%) and YbCu2Si2 (43%). The 'heavy-fermion' superconductor CeCu2Si2 shows a 14% softening of cB with respect to the reference compounds.

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