Subtle local structural variations in oxygen deficient niobium germanate thin film glasses as revealed by x-ray absorption spectroscopy

The local electronic and crystal structure of niobium-lead-germanate, Nb₂O₅-PbO- GeO₂ (NPG), glass thin films on silicon substrates were probed by XANES and EXAFS. NPG glasses are promising candidates for applications in nonlinear optical devices because they exhibit interesting optical characteristics such as high nonlinear third order optical susceptibility. In this work NPG glasses were prepared with pulsed laser deposition method with varying oxygen partial pressure to induce thin films with different oxygen stoichiometry. Previously, it was shown that oxygen stoichiometry has a very important effect to produce unusual high optical susceptibility. Detailed EXAFS and XANES analyses in a series of NPG thin films revealed the subtle variations in the local environment around Nb atoms and the Nb oxidation states caused by oxygen deficiencies. (paper)