High-pressure studies of mechanical alloyed Ni75Se25 powder mixture

Extended X-ray Absorption Fine Structure and Raman studies were performed to follow the structural and vibrational behavior of mechanical alloyed Ni75Se25 mixture, containing trigonal Ni3Se2 nanocrystalline phase, when exposed to high-pressure conditions. An increase in the local structural order with pressure increasing was observed by means of Debye-Waller factor analysis. The relative Ni nearest-neighbours distances (d) were determined as a function of pressure (P). From the fitting of these d x P curves with Murnaghan's equation, the inverse linear compressibility of nanocrystalline phases (Ni3Se2 and Ni) and their derivates were determined. The high-pressure Raman experiments resulted in a poor determination of the phonons dispersion curve for Ni3Se2, phase, but they were very important to confirm the absence of nanocrystalline Se in the mechanical alloyed Ni75Se25 mixture, showing that all Se was consumed to form the Ni3Se2 phase. (c) 2005 Elsevier B.V. All rights reserved.