AMORPHOUS ALLOY Fe_-P : STRUCTURAL MODEL, VIBRATIONAL SPECTRA AND ELECTRONIC STATES

Abstract
The relaxed structural models of amorphous metallic alloy Fe_100-x P_x have been constructed and analyzed . The pair atomic potentials of Morse-type are used for relaxing the DRPHS system consisted of two types of spheres. The analysis of Voronoi poly-hedra can be understood in terms of the tightly captured P-atoms in the framework of Fe-atoms and the change of alloy composition. The analysis of the geometrical configuration of the near neighbor Fe shell around P-atoms shows that the symmetry of the local atomic arrangement around P-atoms is very similar to that in the crystalline Fe₃P, i.e. about 80% P-atoms are located inside the trigonal prism formed by Fe-atoms. The vibrational spectra and the electronic states have been calculated by the recursion method in the present model. We have found the acoustic and optical branch, which correspond to Fe-Fe and P-Fe vibration respectively. The longitudinal and transverse vibrations can not be seen as separated peaks in the density of states but in the wavevector dependent spectra. The first moment and the sound velocity in amorphous systems are reduced by about 10% in comparison with those in crystal. Electronic structure is calculated by using the atomic sphere approximation to the KKR method. The secular equation of the KKR method contains the structure constant depending upon the one-electron energy. The choice of vanishing kinetic energy outside the muffin-tin spheres greatly simplifies the structure constant. The associated error can be substantially reduced by allowing the sphere slightly overlap and the starting equation is just the separate form of the structure and the potential dependent terms. The potential function can be linearized in the neighborhood of an appropriate energy. The resulting secular equation can easily be manipulated by the recursion method. The potential parameters are determined by superposing the charge density of neutral atoms. The strong hybridization of Fe-3d and P-3p band is observed and the electron energy stabilization is attributed to the charge transfer from P to Fe and hybridization.