Sensitivity of the Kβ″ X-ray Emission Line to Coordination Changes in GeO 2 and TiO 2 .

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 GeO 2 and TiO 2 on the basis of ab initio spectral calculations on amorphous and crystalline structures. In compressed amorphous GeO 2 , 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 TiO 2 polymorphs. Our results demonstrate the potential of the Kβ″ emission line in research on the structure of amorphous oxide material.