Investigation of semiconductive Lu1-xScxNiSb solid solution

Abstract

The electrokinetic and energetic characteristics of the semiconductor solid solution Lu 1- x Sc x NiSb were investigated in the ranges Т =80–400 K, х =0–0.10 . Samples were prepared using an electric arc furnace by direct arc melting of the constituent elements under a purified argon atmosphere (porous Ti was used as a getter). The alloys were annealed at 1 073 K for 720 hours and quenched in cold water. Phase analysis was performed using X-ray powder diffraction patterns of the synthesized samples. The elemental and phase compositions of the synthesized samples were examined by Scanning Electron Microscopy (SEM) using Tescan Vega 3 LMU scanning microscope. Microprobe analysis of the concentration of atoms on the surface of Lu 1- x Sc x NiSb samples, including x = 0–0.10, established their correspondence to the initial compositions of the alloys, and X-ray phase and structural analyzes showed no traces of extraneous phases on the diffractograms except for the main phase indexed in the MgAgAs structure type. The temperature dependencies of electrical resistivity ( r ( T )) were measured employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 80–400 K. Thermopower coefficient ( α ) was measured in relation to the pure copper in the temperature range 80–400 K. It has been experimentally established that in the Lu 1‑ x Sc x NiSb solid solution both structural defects of neutral and donor nature are simultaneously generated, the concentration of which increases with increasing content of Sc atoms. The observed high-temperature activation parts on the temperature dependences of the resistivity ln( ρ (1/ T )) for all Lu 1- x Sc x NiSb samples indicates the location of the Fermi level ε F in the band gap of the semiconductor, and positive values of the thermopower coefficient α ( T ) specify its position near the valence band. The main carriers of electric conductivity are free holes. From the high-temperature parts of the dependence α (1/ T ) the values of the activation energy ε 1 α are calculated, which are proportional to the amplitude of large-scale fluctuations of continuous energy bands. The calculated from the low-temperature parts values of activation energy ε 3 α are proportional to the modulation amplitude of small-scale fluctuations of strongly doped and compensated semiconductor. It was shown that the investigated semiconductor solid solution Lu 1- x Sc x NiSb is a promising thermoelectric material. Keywords : electric conductivity, thermopower coefficient, Fermi level, structural defect.