IT was first shown by W. L. Fink and E. D. Campbell (Trans. Am. Soc. Steel Treat., 9, 717; 1926), and independently by N. Seljakow, J. Kurdumoff, and N. Goodtzow ...
This is the tetragonal crystal structure of NaFe2As2, courtesy of Alexander Goncharov. Sodium (Na) is represented by the black balls, iron (Fe) by the red balls, and arsenic (As) by the yellow balls.