Polarized hyper-Raman scattering study of the silent F2u mode in PbMg1/3Nb2/3O3

A single crystal of the relaxor PbMg1/3Nb2/3O3 is studied by hyper-Raman scattering. The relative scattering intensities obtained for the band near 250 cm(-1) in various polarization geometries are fully compatible with hyper-Raman spectroscopy tensor of the F-2u zone-center vibrational mode of prototype Pm(3)over barm (O-h(1)) cubic perovskite structure. The mode was investigated between room temperature and 775 K, thus covering the range around the Burns temperature T-d and the crossover temperature T-*. At variance with recent anticipations, no softening was observed.