The electronic and electrochemical properties of the TiFe-based alloys

• Published in: Journal of alloys and compounds 2003-01, Vol.348 (1), p.285-292
• Main Authors: Szajek, A, Jurczyk, M, Jankowska, E
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electrochemical properties; Electrode materials; Electron states; Electronic band structure; Exact sciences and technology; Materials science; Materials synthesis; materials processing; Mechanical alloying; Nanoscale materials and structures: fabrication and characterization; Physics; Plane-wave methods (including augmented plane-wave method); Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation; Theories and models of many electron systems; Transition metal alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/S0925-8388(02)00802-2

Ti(Fe,M)-based alloys (M=Ni, Mo, Cr, Co) were mechanically alloyed (MA) under an argon atmosphere to synthesize nanostructured materials. XRD analysis showed that, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase. Following the annealing in high purity argon at 750 °C for 0.5 h, XRD confirmed the formation of CsCl-type structures with crystallite sizes of about 30 nm. These materials were used as negative electrodes for a Ni–MH x battery. The alloying elements of the 3d transition metals, Ni, Mo, Cr and Co, were substituted for iron atoms, and the structural, electronic and electrochemical properties were studied. With increasing nickel content in TiFe 1− x Ni x , the material showed an increase in discharge capacity which passed through a maximum for x=3/4. In the nanocrystalline TiNi 0.6Fe 0.1Mo 0.1Cr 0.1Co 0.1 powder, a discharge capacity of up to 135 mA h g −1 (at 40 mA g −1 discharge current) was measured. For this composition the capacity degraded much more slowly with cycling in comparison to other studied compositions. The electronic structure was studied by the tight-binding version of the linear muffin-tin method in the atomic sphere approximation (TB-LMTO ASA). In the TiFe 1− x Ni x alloys, increasing the content of the Ni impurities extended the valence bands and increased the density of states at the Fermi level. Similar effects were observed for the TiNi 1/2Fe 1/8Mo 1/8Cr 1/8Co 1/8 system. Mechanical alloying proved to be a suitable procedure for obtaining TiFe-based alloy electrodes for Ni–MH x batteries.