Propriétés thermodynamiques et optiques des oxydes alcalino‐terreux

Abstract

Propriet6s thermodynamiques et optiques des oxydes alcnlino-terreux Par M. GALTIER et A. MONTANERUn modMe dynamique ditcrivant les forces B long rayon d'action sous forme d'interactions dip61es-dipales, et les forces B court rayon d'action B I'aide d'intkractions B trois corps, est appliquk aux oxydes alcalino-terreux de structure NaCl. Les r h l t a t s expitrimentaux existants (chaleurs spkcifiques, absorption infrarouge, diffusion Raman e t diffraction des neutrons) sont ensuite comparks aux prkvisions thkoriques ditduites des densitks d'ktat B un e t deux phonons. L'accord assez satisfaisant permet de conclure sur la validitit du modble et d'interprkter les spectres optiques.A dynamical model is used for alkaline earth oxides with rock salt structure. Long range forces are described by dipole-dipole interaction while short range forces are derived from a three-body potential. The available experimental data (specific heat, infrared absorption, Raman and neutron scattering) are then compared with theoretical values, deduced from the one and two phonon densities of state. The fairly good agreement suggests the validity of the model and gives an interpretation of optical spectra.

Shedding light onto the spectra of lime: Raman and luminescence bands of CaO, Ca(OH)2 and CaCO3

“…680 cm −1 is in good agreement with the measurements by Galvan‐Ruiz et al , who assign all bands to CaO . Contrarily, other studies claim that CaO, like other minerals with halite structure (e.g. MgO and NaCl; compare, for example, Refs .…”

“…653 cm −1 and a weak contribution at 1073 cm −1 . Contrarily, other authors claim that calcium oxide does not have any Raman‐active modes, except for weak second‐order contributions observed in some spectra . The theoretical and experimental data presented by Padanyi shows that the Raman spectrum of Ca(OH) 2 consists of sharp bands at 260 cm −1 , 359 cm −1 , and 3620 cm −1 together with a broad band at 684 cm −1 .…”

X-ray study of the atomic charge densities in MgO, CaO, SrO and BaO

“…The increasing ionicity with increasing atomic number of the cation is noticed in the measurements of elastic constants by Son & Bartels (1972) and by Bartels & Vetter (1973) and in infrared spectroscopy by Galtier (1973) and Montaner (1974). It might be possible to relate the slightly stronger deformation of oxygen together with the lack of negative deformation of the cation in MgO, as compared to CaO, to the occurrence of covalency.…”

“…The values obtained for the Debye-Waller factors should be compared with the mean square amplitudes obtained from lattice-dynamical calculations (Galtier & Montaner, 1975). For MgO, other experimental determinations can be compared (Lawrence, 1973;Togawa, 1965).…”

“…Furthermore, theoretical models in lattice dynamics seem not to give a satisfactory explanation of spectroscopic results, especially in the c~ise of SrO and BaO (Galtier, 1973;Montaner, 1974;Rieder, Weinstein, Cardona & Bilz, 1973).…”