Temperature-Dependent EXELFS of Chemically Ordered and Disordered Fe3Al

Abstract

A parallel detection system makes possible quantitative studies of extended electron energy-loss fine-stucture (EXELFS). We are studying the short-range chemical order and local thermal vibrations of chemically ordered and disordered Fe3Al foils using transmission EXELFS. The average number of Fe atoms in the first nearest-neighbor (1nn) shell surrounding the Al atoms in chemically ordered and chemically disordered materials are determined by comparing our data with ab initio EXAFS calculations. The mean-squared relative thermal displacements between the Al atoms and their 1nn shell are roughly determined by our temperature-dependent data.Chemically disordered Fe-27at%Al and Fe-25at%Al samples were prepared by piston-anvil quenching. Some samples were annealed at 300 °C for over a day to develop DO3 order. Aluminum K edge spectra were collected with a Gatan 666 parallel detection magnetic prism spectrometer attached to a Philips EM 430 electron microscope. Room temperature spectra were collected from submicron regions of the Fe-27Al samples with 300 keV electrons and a beam current of 10 nA.