Sensitivity of the Kβ″ X-ray Emission Line to Coordination Changes in GeO2 and TiO2.

The hard X-ray Kβ″ emission line shows sensitivity with respect to a wide range of cation-ligand coordination, which we investigate in the cases of GeO2 and TiO2 on the basis of ab initio spectral calculations on amorphous and crystalline structures. In compressed amorphous GeO2, the sampling of a large number of instantaneous coordination polyhedra from an ab initio molecular dynamics trajectory reveals that the functional relation between the Kβ″ shift and coordination is close to linear between 4-fold and 7-fold coordination. A similar sensitivity of the Kβ″ emission line exists in the coordination range between six and nine of crystalline high-pressure TiO2 polymorphs. Our results demonstrate the potential of the Kβ″ emission line in research on the structure of amorphous oxide material.