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, Eg, were estimated, and it was found an Eg 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.