Mechanochemical synthesis and characterization of Ni25Te75 nanocrystalline alloy

Autor: Carlos Eduardo Maduro de Campos, K. F. Ulbrich
Rok vydání: 2018
Předmět:
Zdroj: Journal of Materials Science. 53:13442-13450
ISSN: 1573-4803
0022-2461
DOI: 10.1007/s10853-018-2470-6
Popis: Ni25Te75 nanocrystalline alloy containing trigonal NiTe2 and Te nanocrystals was prepared through mechanochemical processing of pure elemental tellurium and nickel powders in argon atmosphere. The Ni25Te75 samples processed from 3 h to 30 h milling times were characterized by X-ray powder diffraction, transmission electron microscopy, magnetization and Raman spectroscopy. Trigonal NiTe2 crystals with average size of 16 nm can be obtained after only 3 h of processing time. For longer milling times, the trigonal NiTe2 phase becomes majority (about 70% with 30% for nanometric Te and no pure Ni was detected) and its average crystallite size slightly increases to 20 nm. Transmission electron microscopy images and electron diffraction patterns confirm the nanometric size of the crystalline domains in the agglomerated particles. The magnetic properties of the Ni25Te75 powders are dependent on synthesis time, suggesting a paramagnetic behavior mainly associated with the NiTe2 nanophase. Raman spectra showed peaks that can be associated with unreacted Te and tellurium oxides modes, but it also showed several modes that can be attributed to trigonal NiTe2 nanophase. The high-pressure experiments showed no phase transitions for NiTe2 up to 17 GPa and Te phase transitions from form I to forms II and III occurred simultaneously at 4.5 GPa, remaining up to 12 GPa; after that, only reflections of Te-III and the NiTe2 were observed. All the phase transitions observed with pressure are reversible after decompression. The bulk modulus determined from the least-squares fit of first-order Murnaghan equation of states is 110 GPa for the NiTe2 nanophase and 28 GPa for Te-I.
Databáze: OpenAIRE
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