Concerning the transformations of Ti3Ir alloy during high-energy ball-milling

Thermodynamically stable Ti3Ir with the Cr3Si (A15)-type crystal structure can gradually be transformed into a metastable Ti3Ir alloy with a bce cryst al structure by high-energy ball-milling for 12.5 h. The long-term ball-mil ling for up to 112 h, however, is accompanied by a solid-state reaction bet ween Ti3Ir and the vial material leading to the formation of a nano-crystal line or amorphous MgZn2-type phase with the Ti(Fe1.85Ir0.15) stoichiometry and a micro-crystalline thermodynamically stable CsCl-type phase. Both the CsCl- and MgZn2-type phases were obtained in the crystalline form after ann ealing ball-milled Ti3Ir. Properties of the A15 Ti3Ir alloy changed conside rably after ball-milling. The superconducting transition observed in the or iginal A15 alloy at similar to 4.3 K no longer exists in the ball-milled ma terial. The electrochemically determined hydrogen storage capacity of the b all-milled alloy also decreases in comparison to the A15 material from 269 to 104 mAh/g. On the contrary, the electrochemical discharge capacity of Ti 3Ir increases From 45 to 104 mAh/g after ball-milling. (C) 2000 Elsevier Sc ience S.A. All rights reserved.