Raman spectra of tetragonal zirconia: powder to zircaloy oxide frequency shift

The shifts of the two main characteristic Raman active bands of t-ZrO2 in oxide films developed on zirconium alloy relatively to their position in nanopowder (267, 456 cm-1) are discussed. The origin of the shifts is analyzed within the lattice dynamical treatment according to which neither hydrostatic compression nor biaxial one can be responsible for this shift. It is put in evidence that only an abnormal high value of the internal tetragonality (Δz=Lz/c) can provide this effect. Additionally, the symmetry assignment of the two bands are determined which, in particular, argues for the identification of the band near 267 cm-1 as a totally symmetric A1g soft mode