Vibrational Spectra of the “One-Mode” (Y1−xLax)2O3 Solid Solution Ceramics

Y₂O₃ is widely used in IR windows and optoelectronics, but its vibrational and spectral properties under La³⁺ substitutions remain unclear. This work investigates <i>x</i>La₂O₃-(1-<i>x</i>)Y₂O₃ with <i>x</i> = 0-0.2 via XRD, SEM, Raman, and IR spectroscopy to address the lack of comprehensive data on structure-property correlations. The solid solution (Y_1-<i>x</i>La<i>_x</i>)₂O₃ with 0 ≤ <i>x</i> < 0.15 was determined. The cell parameter <i>a</i> increases from 10.6113(5) Å to 10.7116(1) Å as <i>x</i> increases from 0 to 0.15 according to the Rietveld refinements. Both the Raman spectra and infrared (IR) reflection spectra show that (Y_1-<i>x</i>La<i>_x</i>)₂O₃ is a "one-mode" system, in which eight of the 22 theoretical first-order Raman modes and 12 of 16 theoretical IR modes for the (Y_1-<i>x</i>La<i>_x</i>)₂O₃ are recognized. A local vibrational mode at approximately 680 cm^-1 is observed in the Raman spectra as <i>x</i> > 0. The Raman modes and IR modes of (Y_1-<i>x</i>La<i>_x</i>)₂O₃ show red shift and obvious peak broadening as <i>x</i> increases, which is caused by the expansion of unit cell and local distortions of the crystal structure. As Y³⁺ is substituted by La³⁺, the extinction coefficient κ decreases significantly, which can lead to a lower IR absorption and should be beneficial for the IR window applications.