Nanosized tetragonal β-FeSe phase obtained by mechanical alloying: structural, microstructural, magnetic and electrical characterization

Abstract

Nanocrystalline tetragonal b-FeSe phase was prepared mechanochemically using ball milling procedures in an inert atmosphere, starting from Fe x Se powder mixtures with x ¼ 1.00, 1.25 and 1.50, with x ¼ 1.25 and 1.50 leading to more than 93% of pure phase after annealing at 400 C for 1 hour under vacuum. X-ray powder diffraction provides information on phase formation and phase transitions with milling time and temperature. The Rietveld method was used to refine the crystal structure, including the z coordinate of Se and occupancies, to determine the microstructure and to assess the amount of contaminant phases observed. Lattice contraction is found in the ab-plane more than along the c-axis, the small average size of crystalline domains (<22 nm) and the high microstrain (>1%) indicate the formation of highly strained nanoparticles. Magnetic and electrical characterization showed a poor superconductivity at 4 K and semiconducting properties only for thermally treated samples. These observations are explained by the presence of ferromagnetic impurity phases (residual Fe, hexagonal d-FeSe phase and monoclinic Fe 3 Se 4 ), but other effects caused by the mechanochemical synthesis must be considered, such as small average size, large/non-uniform size distribution and high microstrain of the nanosized tetragonal b-FeSe phase.The increase of the b-FeSe phase content with increasing storage time (ageing) above a few days to months in air, at RT and in the dark was observed for all as-milled samples. Preliminary data on the ageing effect are shown while a systematic study on this is in progress and will be presented elsewhere.

Synthesis of electron- and hole-doped bulk BaFe2As2 superconductors by mechanical alloying

“…To date, MA has been used in synthesising a variety of equilibrium and non-equilibrium alloy phases from precursor powders [1]. The mechanical alloying method has been successfully used in the preparation of superconductors such as Nb 3 Al [2], MgB 2 [3,4], DyBa 2 Cu 3 O 6+δ [5], Bi − Sr − Ca − Cu − O system [6], Y Ba 2 Cu 3 O 7−d [7,8], FeSe 1−x [9,10], SmFeAsO [11], SmFe 1−x Co x AsO [12], SmFe 1−x Co x AsO 1−x F x [13], Ba 0.6 K 0.4 Fe 2 As 2 [14,15]. Therefore, mechanical alloying may become the main method to form a high-quality homogeneous precursor or parent superconducting compound.…”

Structural, microstructural and magnetic characterization of the β-CoTe nanophase synthesized by a novel mechanochemical method

“…For every 3 h of milling time, about 0.100 mg of the material was shed out and stored in microtubes of 2 mL each for further characterization procedures. These are the standard parameters and procedures when dealing with TMCs in our lab, as can be seen in our recent publications, [24][25][26] hence they are used for this synthesis as well.…”

Structure, microstructure and magnetic investigation of the hexagonal δ-FeSe nanophase produced by mechanochemical synthesis

“…More synthesis details are found in the earlier work. 21 In the synthesis, we assume that the stoichiometry of d-FeSe (nal product aer milling) is based on starting ratio powders prior to mechanochemical synthesis.…”