H. Brusset

Normal coordinate analysis for CaNb2O6 of columbite structure

The Raman and infrared spectra of CaNb2O6 are assigned by normal coordinate analysis according to Shimanouchi’s method. The Raman spectroscopy results enabled us to refine the force field, which was then checked by the infrared spectroscopy results. The obtained force constants show that there are three different types of Nb–O bonds in the columbite structure and that the Ca–O bonds are of electrostatic nature. The potential energy distribution calculation gives us a precise assignment for all the observed frequencies.

Spectres de vibration et calcul du champ de force des antimoniates et des tantalates de structure trirutile

Abstract The i.r. and Raman spectra of antimonates M II Sb 2 O 6 and tantalates M II Ta 2 O 6 belonging to the trirutile structure are studied. The vibrational assignment is obtained by means of the comparison of the spectra, the use of the correlation method and normal coordinate calculations. A force field characteristic of this type of compounds is proposed.

Characterization of different bondings in some divalent metal niobates of columbite structure

Abstract The structural characteristics of the columbite niobates MNb 2 O 6 (M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) from their X ray diffraction powder patterns and indexed according to the Pbcn space group are given. Cell parameters are refined for each compound. Previous spectroscopic studies by normal coordinate analysis provide the basis for a discussion of the precise nature of the NbO and MO bonds. Force constants and bond order are given and the influence of the electronegativity of the M 2+ cations upon these bonds is shown.

Etude par spectrophotométries d'absorption infrarouge et de diffusion Raman des niobates de structure columbite

Resume Infrared and Raman spectra of the niobates of columbite structure M Nb 2 O 6 ( M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) were recorded in the region 1100-50 cm −1 . All of them are similar at the shorter wavelengths (> 400 cm −1 ) but depend on the cation at lower frequencies. By comparison of i.r. and Raman spectra, the main vibration frequencies have been assigned.

Etude par spectroscopies d'absorption i.r. et de diffusion Raman des composés AIIBV2O6 de structure de type “blocs 1 × 2” —I. Etude du niobate de baryum BaNb2O6

The i.r. and Raman spectra of the niobate and tantalate of “1 × 2 block” type structure AIIBV2O6 (AII = Ca, Sr, Ba, Pb) are presented and analyzed. The complete vibrational analysis of BaNb2O6 is presented and a force field is proposed for this type of compounds, the potential energy distribution is given and some characteristic normal modes are drawn in comparison with the normal modes of the double octahedron B2O10 which is the basic motif of the “1 × 2 block” type structure.

Normal coordinate analysis of the MNb2O6 series of columbite structure (M=Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd)

Normal coordinate analysis of the MNb2O6 series of columbite structure (M=Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) was carried out and the results obtained permitted the assignment of all the observed vibrational bands of the columbite series. It is also shown that the force fields of the columbite series are very similar when cations are changed. The variations are interpreted as due to the mass, the electronegativity, and the positions of the cations in the periodic table. The order of the bonds is also given.

Etude vibrationnelle d'aluminates et de gallates de terres rares—I. Alluminates de structure pérovskite

Abstract The i.r. spectra of some aluminates of rhomboedral and orthorhombic perovskite types are presented and analysed. The complete vibrational analysis of NdAlO 3 is presented and a force field is proposed for this type of compounds; the potential energy distribution is given and the normal modes are drawn using ORTEP program.

Etude par spectroscopies d'absorption i.r. et de diffusion Raman des composés AIIBv2O6 de structure de type “blocs 1×2”—II. Etude du niobate de strontium SrNb2O6 et des tantalates de calcium CaTa2O6 et de baryum BaTa2O6(II)

Abstract The normal coordinate analysis of CaTa 2 O 6 , BaTa 2 O 6 (II) and SrNb 2 O 6 compounds (type II) of “1×2 block” structural type was performed in order to define more precisely the assignment of the observed i.r. and Raman vibration frequencies. The results obtained showed that the I and II types of “1×2 block” type structure (I: BaNb 2 O 6 , BaTa 2 O 6 (I) and the values of the force constants agreed with the nature of the Nb(Ta)O bridge.

An estimation of the film-penetration model parameters

Abstract It it shown in this paper that the process of evaporation of liquids into a turbulent gas flow in a wetted-wall column can be represented by the film-penetration model. The numerical values of the two parameters S and L of this model, estimated from mass transfer data, appear to be well defined functions of flow conditions. The surface renewal mechanism used in the considered mass transfer model was shown to be consistent with the momentum transfer concept. The results may be used to predict mass transfer processes with chemical reactions in similar flow systems, by applying the theoretical developments using the film-penetration theory [7–10]. The same procedure may be used to estimate the film-penetration parameters in other flow systems, such as the flow of liquid films in a wetted-wall column, or other complicated system such as stirred tanks, bubble columns, packed columns etc.

Etude par spectroscopies d'absorption i.r. et de diffusion Raman des composés AIIB2VO6 de structure de type “blocs 1 × 2”—III. Etude des niobate et tantalate de plomb rhomboèdriques PbNb2O6 et PbTa2O6

Abstract The normal coordinate analysis of PbNb 2 O 6 and PbTa 2 O 6 compounds of “1 × 2 block” structural type has been carried out using a crown model unit corresponding to the pseudo-cell unit of the crystal structure. The results permitted the assignment of the observed i.r. and Raman frequencies and the force fields obtained have been compared to the “1 × 2 block” homologues, i.e. BaNb 2 O 6 , CaTa 2 O 6 , BaTa 2 O 6 (II), SrNb 2 O 6 whose force fields have been previously determined.