F. W. Lytle

Structure determination of amorphous Ge, GeO2 and GeSe by fourier analysis of extended x-ray absorption fine structure (EXAFS)☆

Abstract Fourier inversion of EXAFS data is a powerful new technique for structural investigation of non-crystalline materials with the unique capability to determine the near neighbor environment of each type of atom in a complex material. The radial structure function so obtained contains information on the number, distance, and distribution of atoms surrounding the absorbing atom. The data on Ge and GeO 2 generally agree with previous findings but with added detail. The environment of both Ge and Se in amorphous GeSe show a significant change from the crystalline material with evidence for local satisfaction of the directed bonding tendencies of each atomic species.

Structure of catalysts: Determination by EPR and Fourier analysis of the extended x‐ray absorption fine structure

An alumina‐supported CuCr catalyst was examined with the extended x‐ray absorption fine‐structure (EXAFS) technique. This is a new technique which can determine the chemical states and near‐neighbor environments of the separate Cu and Cr atomic species. Cu was found to occupy both tetrahedral and octahedral sites in the supporting alumina lattice while Cr was found only in octahedral sites. The valence state was Cr+5 in the fresh catalyst which changed to Cr+6 in the exhaust‐cycled material. Confirmation of the valence state assignment was obtained by EPR. Fourier analysis of the EXAFS produced separate radial structure functions for the Cu and Cr atoms since the experiment measures the properties of the individual atomic species rather than those of the structure as a whole. Significant differences were observed by both techniques between fresh and exhaust‐cycled material.

Calorimetric, diffraction and microscopic examination of evaporated amorphous germanium☆

Abstract Dynamic calorimetric and thermal gravimetric measurements revealed that evaporated, amorphous Ge adsorbed up to 3 wt % H2O when exposed to the atmosphere. Desiccation removed one-half; however, the remainder was removed only by heating to 450°C which also completely recrystallized the material. The heat of crystallization was found to be, ΔHc = 2.6 ± 0.4 kcal/mol. Electron microscopic examination revealed ≈100A void network as found by others with heterogeneous crystallization as samples were annealed at ≈200°C. During the annealing and crystallization, the normally forbidden (222) electron diffraction reflection was frequently observed. We interpret this as being due to (111) twinning which is evidence of wurtzite-type bonding in the original evaporated, amorphous Ge material.