Transport phenomena of TiCoSb: defect induced modification in the structure and density of states

Abstract

TiCoSb_1+x (x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.06) samples have been synthesized, employing solid state reaction method followed by arc melting. Theoretical calculations, using density functional theory (DFT), have been performed to estimate the band structure and density of states (DOS). Further, energetic calculations using first principles have been carried out to reveal the formation energy for vacancy, interstitial and anti-site defects. A detailed structural calculation, employing Rietveld refinement, reveals the presence of embedded phases, vacancies, and interstitial atoms, which is also supported by theoretical calculations. Lattice strain, crystalline size, and dislocation density have been estimated by Williamson–Hall and modified Williamson–Hall methods. Thermal variation of resistivity [ρ(T)] and thermopower [S(T)] have been explained using the Mott equation and density of states (DOS) modification near the Fermi surface due to a Co vacancy and embedded phases. Figure of merit (ZT) has been calculated and a ZT for TiCoSb 4 to 5 times higher than earlier reported values was obtained at room temperature.