Although this is the $B24$ structure defined in Strukturbericht, it is not the currently accepted structure for TlF. See (Berastegui, 2000) and the TlF-II page. The current structure is a slight distortion of rock salt ($B1$).
J. A. A. Ketelaar, Die Kristallstruktur des Thallofluorids, Z. Kristallogr. 92, 30–38 (1935), doi:10.1524/zkri.1935.92.1.30.
Found in
P. Berastegui and S. Hull, The Crystal Structures of Thallium(I) Fluoride, Journal of Solid State Chemistry 150, 266–275 (2000), doi:10.1006/jssc.1999.8587.
First cited in
M. J. Mehl, D. Hicks, C. Toher, O. Levy, R. M. Hanson, G. L. W. Hart, and S. Curtarolo, The AFLOW Library of Crystallographic Prototypes: Part 1, Comp. Mat. Sci. 136, S1-S828 (2017). (doi=10.1016/j.commatsci.2017.01.017)