Factor group analysis of the Raman spectrum of Pb5Ge3O11

Abstract The complete Raman spectrum of Pb 5 [GeO 4 /Ge 2 O 7 ] is investigated. The results are analyzed by factor group analysis for external and librational modes taking polariton effects into account. The temperature dependence of the intensity of different modes in the depolarized spectra allows to distinguish between modes of pure E symmetry (at the Γ‐point for P3 space group) and those with mixed symmetry. The modes in the frequency region above 200 cm +1 are assigned to internal modes of the GeO 4 tetrahedron and the Ge 2 O 7 double tetrahedron. As Pb 5 Ge 3 O 11 exhibits above its ferroelectric‐paraelectric phase transformation at T c = 450 K additional anomalies of the birefringence and of the lattice constants the Raman spectrum up to 750 K is investigated.