Raman scattering study of the Pb(Hf _x Ti_1-x )O ₃ ceramics

Raman spectroscopy was used to study the long wavelength vibrations of tetragonal perovskite (space group P4mm) Pb(Hf _x Ti_1-x )O₃ (PHT) (0.10 = samples at room temperature and at ≈ 20 K. For x ≤ 0.40, Raman spectra collected from the PHT samples were very similar to the previous spectra collected from the PZT samples with the same value of x, except the mode at around 190 cm^-1, whose frequency was decreasing with increasing x in PHT ceramics. Correspondingly, the latter feature was taken as a sign of the 'mass effect' (Hf versus Zr) while the similarity of the remaining parts of the Raman spectra was assumed to be due to the almost identical ionic radii difference between Ti⁴⁺ and Zr⁴⁺ and between Ti⁴⁺ and Hf⁴⁺ ionic radii. The behaviour of the mode at around 280 cm^-1 revealed that a phase transition occurred once x was changing from 0.40 to 0.50.