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A polarized Raman study of tetragonal monocrystalline WSi 2 is reported. The two Raman lines of WSi 2 have been assigned in terms of symmetry. Using a linear chain model, force constants of 6.64 and 3.16 N/cm for compressive Si-Si and Si-W motions along the c axis of the unit cell have been derived. The values of 3.30 and 2.30 N/cm for the shear motions perpendicular to the c axis have been obtained. Polarized Raman spectra of a thermally annealed WSi 2 film reveal a preferred orientation of the layer; this effect is confirmed by X-ray diffraction. The thermal behavior of the WSi 2 Raman lines has been analysed both for single crystal and thin firm over a wide temperature range (79–853 K). The wavenumbers, half-widths and intensities are strongly temperature dependent. The frequency shift has been related to the thermal expansion of the crystal, using the Gruneisen theory. The important broadening of the A 1g mode with temperature is explained in terms of anharmonicity and the loss of intensity of the two lines is discussed.

The commensurate-incommensurate transition of PbO, lead monoxide, was confirmed by small anomalies observed below 200 K on both heat capacity curves and Raman spectra. For Pb 0.94 Ti 0.06 O 1.06 , no transition has been detected using neutron diffraction, heat capacity measurements and Raman spectroscopy. Structural refinements show new interlayer Pb-O and Ti-O bonds. Extra oxygen atoms are located in the interlayers of the host lattice of the PbO structure; they break the interactions between the electronic lone pairs of the Pb 2+ ions and the transition no longer occurs.

Three phase transitions were found in LiNH 4 SO 4 crystals by heat capacity measurements between 10 and 310 K. One is first order at T tr = 288.7 K and the two others are of high order over a large temperature range with maximum C p,m anomalies around 248 and 37 K respectively. Raman spectroscopic studies down to 10 K show that both NH + 4 rotations and Li + translations are involved in the phase transition around 248 K. The mechanism of the transition at 37 K is essentially governed by reorientational motions of the ammonium group. All these results are discussed in the light of numerous studies previously reported on the behaviour of LiNH 4 SO 4 crystals.

The heat capacity of the layer compound [NH 3 (CH 2 ) 5 NH 3 ]MnCl 4 has been measured from 10 to 330 K by adiabatic calorimetry. The C p anomaly associated with the well-known order-disorder transition ( Pnma ↔ Imma ) has a maximum at 299.6 K and the disordering process occurs over a large temperature range (from about 200 to 400 K). The associated excess entropy was determined from experimental calorimetric data and lattice heat capacities estimated from usual models; it was interpreted in terms of the transformation from “all- trans ” into “twisted” conformations of the alkylenediammonium chains, as proposed from a recent quasielastic neutron-scattering study. The enthalpy change between the two conformations has been found equal to 19kJ mol −1 in agreement with Raman scattering results. Finally, the thermal behaviour of this compound has been compared with that of related [NH 3 (CH 2 ) n NH 3 ]MCl 4 derivatives.