Powder neutron diffraction studies for the L21 phase of Co2YGa (Y=Ti, V, Cr, Mn and Fe) Heusler alloys

Site occupancies of Co, Y(Y=Ti, V, Cr, Mn and Fe) and Ga atoms for the L2(1) phase in Co2YGa alloys annealed at 773 K were precisely investigated by powder neutron diffraction measurement. While Co atoms in all the five alloys almost perfectly occupy the x (2a) site, the occupancy of the z(4b) site by Ga atoms depends on the kind of Y atom, and it decreases with increasing number of valence electrons except for Co2CrGa alloy. Degrees of long-range order on the z site occupancy of Ga atoms experimentally determined for all the alloys are in good agreement with those thermodynamically estimated from their order-disorder transition temperatures using the Bragg-Williams-Gorsky approximation. (C) 2010 Elsevier B.V. All rights reserved.