Département de chimie moléculaire

Elastic properties are an important issue in explaining the behavior of seisms and to ascertain the mineralogical compn. of the Earth's shells through which seismic waves pass. Computational methods can yield an addnl., detailed, free-of-heterogeneity model knowledge of the mineral series of interest. Therefore, a computational study on the influence of the interlayer cation in the muscovite-paragonite (Ms-Pg) series on the crystal cell, internal geometry, and the elastic properties was made to shed light on the mineralogical, geophys., and geochem. properties of the series. These properties have been calcd. by means of D. Functional Theory (SIESTA2.0.2 code). The crystal structure and internal geometry agreed with the range of exptl. values in the literature. In general, elastic stiffness consts. (EC) agreed with the known exptl. values. ECs of different interlayer cation configurations for the middle concn. sample showed very similar values, except for C33, The majority of ECs, with the exception of C33 and C66, decreased as a function of Na' [Na/(Na + K)], many of which showed ideal cryst. soln. behavior, and some showed mixing terms. The polycryst. bulk modulus registered similar values for the end-members of the series and a min. at Na' = 0.5, although an est. of the value at room temp. made the Pg stiffer than Ms; while the shear modulus showed a decreasing trend as a function of the Na'. Velocities of the sound waves lowered as a function of Na'. Local deformabilities were also studied, where the highest deformability was found for the interlayer space. The results are discussed in the framework of the mineralogical, geochem., and geophys. knowledge of the series. [on SciFinder(R)]