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Abstract
Lead scandium niobate PbSc 1/2 Nb 1/2 O 3 undergoes a structural phase transition at about 380 K from a cubic phase (of average symmetry Pm3m to a slightly distorted polar trigonal phase (R3m). Two order parameters (polarization and ferroelastic distortion) are involved in this phase transition and some anomalies are expected in the temperature evolution of the Raman spectra of the various compounds belonging to this system (ordered lead scandium niobate, disordered, Ba-doped and Pb-vacancy).
The spectra collected between 600 K and room temperature, are analyzed and compared with group-theoretical predictions. The number of observed frequencies in the high temperature phase of the different compounds is larger than the value expected for cubic symmetry phases (Pm3m or Fm3m either). The implications of substitutional and positional disorder leading to a local symmetry breaking are discussed.