Raman spectroscopy needs a change in polarizability associated with a vibration. Metal oxides often have that on a pretty low level which makes their Raman activity quite often pretty low, so maybe ATR-IR spectroscopy would be the better option.
On of the materials I work on, Yttria stabilized Zirconia, has exactly one peak with considerable Raman intensity and even that one can be hard to see occasionally. Its position is primarily determined by the Y/Zr mixture ratio, defect analysis needs to be done by other methods here.