RAMAN-SCATTERING IN PURE AND TI-DOPED PBHFO3 ANTIFERROELECTRIC CRYSTALS

Raman scattering investigations were performed over a large temperature range from 10 to 700 K on pure and Ti-doped PbHfO3 single crystals. The modifications of the Raman spectra were precisely observed in the vicinity of two structural phase transitions occurring in the crystal: an antiferroelectric (A(1)) --> antiferroelectric (A(2)) phase transition at 436 K and antiferroelectric (A(2)) --> paraelectric (P) phase transition at 484 K. The characteristic parameters of the Raman structures were determined throughout the whole phase transition sequence. The softening of the two lowest-frequency Raman lines seems to have a dominating influence on the slight increase in dielectric permittivity at the A(1) --> A(2) phase transition in both pure and doped samples suggesting a displacive nature for this transition. For Ti-doped samples the form of the A(1) --> A(2) transition is smoother than for undoped samples while the A(1) --> P transition appears to be unaffected by doping with Ti.