Temperature and hydrostatic pressure dependence of vibrational modes in PbTi_1–xZr_xO₃

The room temperature Raman spectra of PbTi_0.1Zr_0.9O₃ at hydrostatic pressures up to 68.5 kbar indicate three phase transitions. At 5.71 kbar a new phase appears, most probably the rhombo‐hedral high‐temperature phase, F_R(HT) which is in coexistence with the rhombohedral low‐temperature phase F_R(HT). Between 8 and 9.1 kbar the relative intensities of all lines change and two additional structures appear. It is likely that this change is due to a transition into the orthorhombic antiferroelectric phase. A further transition between 39.7 and 42 kbar cannot be positively interpreted on the basis of the present data. The temperature dependence of the Raman spectra gives evidence that the additional structure in the F_R(LT) phase is due to the doubling of the unit cell, i.e. PbTi_1–xZr_xO₃ seems to show one‐mode behaviour.