Temperature-dependent resonant Raman scattering of yttria doped zirconia phases in thermal barrier coatings

To understand the strong Raman scattering intensity of metastable t'-YSZ thermal barrier coatings, about three times than other phases of yttria doped zirconia, a careful investigation of high temperature phase is performed by ultraviolet Raman scattering at 355 nm up to 1500 degrees C. The studied specimens are thermal barrier coating as well as single crystals of monoclinic zirconia and cubic yttria stabilized zirconia. The ultraviolet Raman scattering efficiency of cubic and metastable zirconia indicate a crossover between the laser line and the band gap of these phases that are well explained by Loudon's resonant Raman scattering model. In the case of pure zirconia, the Raman scattering intensity presents a tetragonal martensitic phase transition at around 1050-1200 degrees C with a small anomaly of Raman intensity. From this study, one can infer that the strong Raman scattering intensity of t'YSZ may originate from the photoelasticity effect of the ferroelastic phase.