Raman scattering and infrared transmittance techniques were used to investigate the room-temperature phonon spectra of the polycrystalline Ba 3 In 2 UO 9 , Sr 3 In 2 UO 9 , Ba 3 In 2 WO 9 and Sr 3 In 2 WO 9 double perovskites. Although X-ray diffraction has shown that both Ba 3 In 2 UO 9 and Ba 3 In 2 WO 9 crystallize in a disordered cubic (Pm3m−O h 1 ) structure with one formula unit per unit cell (Z = 1), Raman measurements revealed that both Ba 3 In 2 UO 9 and Ba 3 In 2 WO 9 compounds should exhibit a 1 : 1 ordered domains with Fm3m symmetry, embedded in the Pm3m matrix. Observation of a ν 1 -like vibration of the InO 6 octahedron reflects the occurrence of a two-phonon-like behavior due to the intrinsic occupational disorder at octahedral symmetry sites. Assignment of most of the Raman and infrared phonons is also given.
In this work we investigate the room-temperature Raman spectra of several rare-earth [RE(HCOO) 3 ; RE = La, Pr, Nd, Gd, Tb and Y] formates. Polarized measurements were carried out for La(HCOO) 3 yielding the observation of most of the Ramanactive phonons predicted by group theory analysis. The respective assignment is given based on the formate vibrations and correlations with previous results in other RE(HCOO) 3 systems. The wavenumber 'softening' observed when RE goes from Y to La is accounted for the lattice expansion.
Raman spectroscopy, polarized microscopy and thermal measurements were used to investigate the sequence of phase transition in the lead oxide salts Pb 8 O 5 (XO 4 ) 2 (where X = As and V). For Pb 8 O 5 (AsO 4 ) 2 , a second-order phase transition is observed at 500 K. For Pb 8 O 5 (VO 4 ) 2 , a second-order and a first-order structural phase transitions are observed at 425 and 525 K, respectively. The ferroelastic character of Pb 8 O 5 (VO 4 ) 2 is also discussed.
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