Zintl Phase

We have performed a detailed theoretical study of the structural, elastic, electronic and optical properties of two newly synthesized Zintl phases CaIn 2 P 2 and SrIn 2 P 2 by means of first-principles calculations based on density functional theory within the generalized gradient approximation of Wu and Cohen. The optimized lattice parameters, including the lattice constants and internal coordinates, are in good agreement with the existing experimental measurements. The relative changes of the structural parameters versus hydrostatic pressure have been investigated. The elastic properties of MIn 2 P 2 have been examined by calculating all independent single-crystal elastic constants C ij using the static finite strain technique, and the polycrystalline isotropic elastic moduli, namely bulk modulus, shear modulus, Young's modulus and Poisson's coefficient, via the Voigt–Reuss–Hill approximations. The elastic wave velocities along some crystalline directions have been evaluated. The mechanical stability of the considered materials has been examined on the light of the pressure dependence of the elastic constants. The elastic anisotropy of the two phases has been studied using three different methods. The electronic properties have been studied throughout the calculations of the band structure, density of states, charge density distributions, charge transfers, and charge-carries masses. These two materials turn out to be narrow gap semiconductors. Finally, we have predicted the basic optical properties, such as the dielectric function, refractive index, extinction coefficient, reflectivity coefficient, absorption coefficient and loss function for polarized incident radiation with electrical vector E parallel to the crystalline axes a and c. A considerable anisot-ropy is observed in the frequency dependent optical spectra.

A thorough transport and thermodynamic investigation of flux-grown single crystals of the ternary Zintl phase Yb 11 AlSb 9 , combined with first-principles density functional theory calculations, shows that this compound is a metal above T z 100 K and a semiconductor with small hybridization gap at low-T. The general behavior resembles those of Kondo lattice semiconductors, although some of the measured properties are strongly sample dependent, as often seen in hybridized f-electron materials. We thus suggest that Yb 11 AlSb 9 can be considered as a new Yb-based Kondo lattice semiconductor joining the family of strongly correlated electron systems.