Synthesis and characterization of NiTe-Ni2Te3 processed by mechanosynthesis at ambient conditions

Abstract

In this work, an analysis on the physicochemical properties of materials based on NiTe-Ni₂Te₃ synthesized through a mechanosynthesis process by using a planetary ball mill, at ambient conditions, was carried out. Pure nickel and tellurium powders with a mass ratio of 1:1 were used as precursors. The milling speed was kept constant at 500 rpm, and the effective milling time was varied, 2, 4, 6, 8 and 10 h. The structural, morphological, optical and electrical properties of NiTe-Ni₂Te₃ materials were studied. The crystallographic properties by X-ray powder diffraction (DRX) were analyzed, and it was determined that the materials present a mix of two different compounds; a hexagonal phase of NiTe and a monoclinic phase of Ni₂Te. From scanning electron microscopy (SEM) the presence of agglomerates of particles with irregular morphologies and others in disc form were evidenced. From reflectance measurements the bandgap energies, E_g, were estimated, and it was found an E_g increase with milling time. From the infrared spectroscopy analysis (FTIR), the characteristic vibrational frequencies, 425 and 672 cm⁻¹, of the NiTe-Ni₂Te₃ system were observed. The electrical properties were measured by Hall effect, using the Van Der Pauw contacts confiration, confirming the n-type conductivity in all the samples, and obtaining that sample synthesized with 8 h of milling presented the best electrical properties, resistivity of 0.77 Ωcm, electron concentration of 2.0 × 10¹⁷ cm⁻³ and mobility 53.08 cm²V⁻¹s⁻¹. The Seebeck coefficient and power factor were estimated to evaluate the thermoelectric properties of the samples. The sample synthesized with 4 h of milling presented the highest Seebeck coefficient and power factor, − 74.56 µVK⁻¹ and 4.27 µWcm⁻¹ K⁻², respectively. The obtained results showed promising properties of synthesized NiTe-Ni₂Te₃ powders and its possible application as thermoelectrical materials.