Raman spectrum of zirconia-hafnia mixed crystals

Monoclinic crystals of Zrₓ{Hf}_{1{{-}}x}O₂ were grown by heating the layered structures Zrₓ{Hf}_{1{{-}}x}S₂ in a pure oxygen atmosphere at 800 ^∘{}C for 2 h (x=0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1.0). Their Raman spectra were recorded at 15 and 300 K. The 18 modes predicted by group theory were identified in ZrO₂ and their evolution with x was determined. At 15 K, seven phonons show distinct two-mode behavior, while others are characterized by discontinuities, either at x=0.6 or x=0.3. This latter observation is reminiscent of percolation-type phenomena.