Pseudobinary intermetallic compounds in Hf2M '-Hf2M '' (M ', M '' = Mn, Fe, Ni, Cu) systems and their interaction with hydrogen at high pressures

Ternary alloys in the Hf2Ni-Hf2Mn, Hf2Ni-Hf2Fe, Hf2Ni-Hf2Cu and Hf2Fe-Hf2Cu systems have been prepared and characterised by X-ray diffraction and pres sure-composition isotherm measurements. Single phase compounds have been ob tained for all Ni-containing alloys with a general composition of Hf2Ni0.5M 0.5. These compounds retained the structure type of parent Hf2M intermetall ics: cubic Ti2Ni type for Hf2Ni0.5Fe0.5 and Hf2Ni0.5Mn0.5 and tetragonal Mo Si2 type for Hf2Ni0.5Cu0.5. The new hydrides obtained from ternary intermet allics had the composition of Hf2Ni0.5M0.5Hx where x=3.1 (M=Cu) and 4.9-5.0 (M=Mn, Fe). Formation of hydride phases from cubic Mn- or Fe-containing co mpounds occurred without any change in structure type but was accompanied b y unit cell volume expansion of 23-24%. In the case of Cu, there was a tetr agonal to orthorhombic transformation. An absence of phase transformations in high pressure range of 100 to 2000 atm for new compounds unlike the earl ier studied Hf2M-H-2 systems has to be noted. (C) 1999 Elsevier Science S.A . All rights reserved.