Phases, lattice parameters and thermal expansion of HoNi_5−xAl_x, 4 ≥x≥ 0

Abstract

The phases, lattice parameters and linear coefficient of thermal expansion were determined by X-ray powder diffraction between room temperature and 873 K for the system HoNis_xAlx (3 >_ x > 0). Alloys were hexagonal, in the space group P6/mmm; for 2 >_ x >_ 0 they were isostructural with CaCus, and for 3 >_ x _> 2 they were isostructural with YCo3Ga2. In both cases, the unit-cell parameters a and c increased as the AI content increased. The linear thermal expansion coefficient was composition dependent. Each of the investigated alloys exhibited an anisotropy in thermal expansion, the linear expansion coefficient along the a axis being larger than along the c axis.

Structural and hydrogen sorption properties of SmNi5−xAlx system – An experimental and theoretical study

“…Next, a and b phases were modelled for SmNi 4.5 Al 0.5 ÀH 2 system and enthalpy of formation for reaction analogous to (5), i.e. a þ yH 2 /b (10) reaction was calculated and compared with the value extracted from the present PCI measurements. At first, DFT calculations were performed on the SmNi 5Àx Al x (x¼0.5,1.0) intermetallic compounds with Al atoms occupying either 2c (basal layer; z ¼ 0) or 3g (equatorial layer; z ¼ 1/2) positions (type CaCu 5 ; space group P6/mmm) to determine the relative stability of the two configurations.…”