As we have been unable to find a copy of (Karlsson, 1951), we obtained the value a = 4.44Å from (Pearson, 1958). The ICSD entry uses a = 3.14Å, referencing the original publication. For now we will continue to use the value from (Pearson, 1958).
This structure has the same AFLOW designation, AB_tP2_123_a_d, as CuAu ($L1_{0}$). The only difference in the structures is the c/a ratio. $L1_{0}$ has $c/a ≈ \sqrt{2}$, characteristic of face-centered cubic ordering, while $L2_{a}$ has $c/a ≈ 1$, a body-centered cubic-like system.
N. Karlsson, An X-Ray Study of the Phases in the Copper-Titanium System, J. Inst. Met. 79, 391–405 (1951).
Found in
W. B. Pearson, A Handbook of Lattice Spacings and Structures of Metals and Alloys, International Series of Monographs on Metal Physics and Physical Metallurgy, vol. 4 (Pergamon Press, Oxford, London, Edinburgh, New York, Paris, Frankfort, 1958), 1964 reprint with corrections edn.
First cited in
D. Hicks, M.J. Mehl, M. Esters, C. Oses, O. Levy, G.L.W. Hart, C. Toher, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 3, Comp. Mat. Sci. 199, 110450 (2021). (doi=10.1016/j.commatsci.2021.110450)