  The local structure of beta-tantalum was investigated by comparing
experimental extended x-ray absorption fine structure (EXAFS) measurements with
calculated spectra of proposed models. Four possible structure candidates were
examined: a beta-Uranium based structure, a distorted A15 structure, a bcc-Ta
based superlattice structure with N interstitials and a simple hcp structure.
The local structural measurements were found to be consistent with the
beta-Uranium based model containing 30 atoms per unit cell and having the space
group P42/mnm. The thermal effect analysis on x-ray diffraction and EXAFS
spectra, which reveals that beta-Ta is highly disordered, agrees with the low
symmetry and anisotropic system of the beta-U model.
