Characterization of ytterbium-yttrium mixed oxides using Raman spectroscopy and x-ray powder diffraction

Ytterbium–yttrium mixed oxides, which are potential emitter materials for thermophotovoltaic energy converters, were prepared using two different synthesis methods. The results of a characterization using Raman spectroscopy and x-ray powder diffraction (XRD) are presented. The purpose of this study was to confirm whether the materials prepared are indeed substitutional solid solutions of ytterbium oxide and yttrium oxide. Both XRD and Raman spectroscopy are established techniques for the analysis of solid solutions. Linear relationships between the Raman band position and the composition of mixed crystals are known for solid solutions with one active Raman mode. An aspect of this study was the investigation of the relationship between composition and band position and linewidth of vibrational modes when applying Raman techniques to a system with several vibrational modes. A linear relationship between the band position of a vibrational mode at about 600 cm⁻¹, which is assigned to a stretching vibration, and the ytterbium content of the material was observed. Using an empirical fit to the most intense band around 370 cm⁻¹, even a substitution of 2 mol% Yb may be detected using non-linear least-squares data analysis. In addition, a discussion of additional features observed in the Raman spectra at Raman shifts >650 cm⁻¹ is presented.