No abstract

The mineralogical status of ilmenite from a prominent modern placer deposit of India is illustrated using different techniques. Compositional, powder XRD, TGA and SEM analyses prove that consistent low temperature alteration took place in Chavara ilmenite leading to the formation of a pseudorutile-hydrated-ilmenite stage. Except for the indication of a geochemical zonation at the southern tip of the deposit, the Chavara ilmenite points to a common origin throughout its 22 km stretch along the coast. We advocate a major segregation activity by marine factors to the accumulated sediments in the shelf zone in order to originate such a huge deposit of homogeneous composition.

No abstract

The lattice dynamics of La1.85Sr0.15CuO4 are studied with a rigid-ion model that takes into account the anisotropic screening of the Coulomb field by the charge carriers. The coupling coefficients for the screened potential are obtained using a generalized Ewald transformation that incorporates the Thomas–Fermi screening function. From the calculated phonons in the long-wavelength region it can be seen that the screening considerably reduces the longitudinal optical–transverse optical splitting of the polar modes. The nonpolar modes do not exhibit any changes in their behaviour with respect to that in the unscreened Coulomb potential.