Inelastic X-ray scattering in metallic glasses Pere Bruna a, f, * , Jorge Serrano b , Eloi Pineda c, g , María Jazmín Duarte a, d , Kun Zhao e , Wei Hua Wang e , Daniel Crespo a, g a Dpt. de Física Aplicada, Universitat Politècnica de Catalunya, EETAC, C/Esteve Terradas 5, 08860 Castelldefels, Spain b ICREA-Dpt. de Física Aplicada, Universitat Politècnica de Catalunya, EETAC, C/Esteve Terradas 5, 08860 Castelldefels, Spain c Dpt. de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, ESAB, C/Esteve Terradas 8, 08860 Castelldefels, Spain d CINVESTAV, Departamento de Materiales, Unidad Querétaro, Querétaro 76230, Mexico e Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China f Centre de Recerca en Nanoenginyeria, Universitat Politècnica de Catalunya, Spain g Centre de Recerca de l’Aeronàutica i de l’Espai, Universitat Politècnica de Catalunya, Spain article info Article history: Available online 26 April 2012 Keywords: B. Elastic properties B. Glasses, metallic F. Diffraction abstract The behavior of acoustic modes in solids can yield information on the glass dynamics at different length and frequency scales. Inelastic X-ray scattering (IXS) using Synchrotron radiation allows us to obtain detailed information on the sound speed behavior at different length scales as well as approaching the macroscopic limit. This gives an insight to the microscopic mechanisms responsible for the mechanical properties in the THz frequency domain. IXS also provides a method to investigate the fragility of glass- forming liquids via the non-ergodicity factor of the corresponding glasses. Moreover, some questions arise about how phenomena such as the polyamorphism, observed, e.g. in Ce 55 Al 44 upon application of pressure, affect the mechanical properties of a metallic glass at a microscopic level. In this article we reveal a change in the high frequency response at the mesoscopic length scale with respect to the ultrasounds limit in metallic glasses. We will also review further applications of IXS on Pd and Ce-based metallic glasses to determine elastic constants, changes in sound speed due to polyamorphism and to investigate their fragility. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Metallic glasses (MGs) are characterized by their amorphous structure, i.e. their lack of a crystalline lattice, and their metallic character that yields a simpler glassy structure due to the isotropic character of the metallic bonding. These features, offer the oppor- tunity to use bulk metallic glasses in a wide range of novel func- tional and structural applications, exploiting their magnetic, anti-corrosive or mechanical properties, such as high strength to density ratios and very high restitution coefficients during elastic deformation. Moreover, MGs are ideal systems to study some fundamental aspects of the glassy state, like the mechanisms involved in the Boson Peak and the glass transition. One way to study these materials is through the study of their collective dynamics. The collective motion of randomly distributed atoms is, at the microscopic level, governed by the interatomic forces between them. Thus, a better knowledge of this interaction leads to a better comprehension of the macroscopic properties of MGs. The collective dynamics of amorphous systems, either liquids or glasses, has been traditionally studied by means of Inelastic Neutron Scattering (INS) [1] but the kinematic limitations of this technique do not allow the study of collective excitations propa- gating with sound speeds larger than w1500 m/s [2]. Therefore, MGs, with typical longitudinal sound speeds of around 4000 m/s, have not been studied by inelastic scattering until the advent of third generation Synchrotron radiation sources that provided bril- liant X-rays beams with the necessary resolving power to perform Inelastic X-Ray Scattering experiments (IXS). IXS is free of kine- matic restrictions, and it yields other advantages with respect to INS; X-rays beams can be focused down to sizes as small as 10  10 mm 2 allowing the study of very small samples and of materials under extreme pressure and temperature conditions. IXS is the only available technique giving access to the high frequency response of metallic glasses. The energy spectrum measured by IXS is proportional to the classical atomic dynamic structure factor S(q,u), where q and Zu are the momentum and the energy transfer in the scattering process, * Corresponding author. Dpt. de Física Aplicada, Universitat Politècnica de Cata- lunya, EETAC, C/Esteve Terradas 5, 08860 Castelldefels, Spain. E-mail address: pere.bruna@upc.edu (P. Bruna). Contents lists available at SciVerse ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2012.03.013 Intermetallics 30 (2012) 148e153