Phonon confinement effect in mixed Sn–Ir oxide nanocrystals

Raman spectra in Sn1−xIrxO2 (x ⩽ 0.15) nanocrystals were investigated to estimate and separate the contributions of phonon confinement and composition effects. To this end, the Raman frequency of the A1g bulk-mode of pure SnO2 and Ir-mixed nanocrystals has been studied in details as a function of the size and the Iridium concentration. As an initial working hypothesis it was assumed a linear dependence of the Raman shift as a function of the Iridium molar concentration, while a quadratic expansion of the dispersion curve has been utilised in the phonon confinement effect. Comparison of predicted and experimental results is reported.