Anab initiostudy of filled skutterudites ROs₄P₁₂(R = Sm, Eu and Gd)

Abstract

The elastic, electronic, magnetic and optical properties of filled skutterudite ROs 4 P 12 (R D Sm, Eu and Gd) have been studied by first principles calculation. The full-potential linearized augmented plane wave method based on density functional theory was employed. For the exchange-correlation potential, local spin density approximation + Coulomb repulsion (LSDA + U) is used to treat the f-electrons more effectively. The numerical values of the elastic parameters are estimated in the framework of the VoigtÀReussÀHill approximation. OsP-based filled skutterudite with localized 4f and 5d-electrons shows dense energy bands near Fermi energy originating from rare earth and Os atoms. The dense density of states near E F reveals that these compounds are suitable for thermoelectric application. Optical constants including dielectric function, optical reflectivity and refractive index are calculated for photon energy radiation up to 12 eV. The exchange-splitting of R-4f states were analyzed to explain the ferromagnetic behavior of ROs 4 P 12 . IntroductionIn recent years, the utilization of industrial waste heat into electrical energy from the thermoelectric materials has been a growing research interest.[1] The materials with dense energy band and low energy gap at E F are the key features of thermoelectric materials, which can be achieved by either doping of heavy elements or from a thin film by controlling the lattice vibration (decreasing the thermal conductivity).[2À4] This can also be achieved by the structural optimization of binary skutterudites TX 3 (T = Co, Rh or Ir; X = P, As or Sb) by rare earth elements, which gives ternary-filled skutterudites RM 4 X 12 (R = rare earth, M = Fe, Ru or Os; X = P, As or Sb).[5,6] The various interesting properties including heavy fermion behavior, superconductivity, [7,8] magnetic ordering with ferromagnetism, antiferromagnetism,[9] semi-conductivity with small hybridization gap,[10] non-fermi liquid behavior,[11] metalÀinsulator transition, [12] etc. make these compounds attractive for research purposes. To date, many researchers have investigated the variety of filled skutterudites using experimental and theoretical techniques. Full-potential linearized augmented plane wave (FP-LAPW) and full potential linearized muffin-tin orbital method (FP-LMTO) studies suggest the indirect band gap semi-conductor and