An X-ray film powder profile refinement of the crystal structure of Ta₅P₃

The crystal structure of Ta₅P₃ has been refined from Guinier-Hägg X-ray powder film data [Malmros & Thomas (1977). J. Appl. Cryst. 10, 7-11] using positional parameters from its structural isomorph Nb₅P₃ as starting values. The space group is orthorhombic Pnma (No. 62), with refined cell parameters a = 25.3210 (4), b = 3.4013 (1), c = 11.4614 (2) Å, V = 987.12 (5) Å³ and Z = 4. Final R = 4.9% [comparable with the R(F) of single-crystal work]. The structure exhibits the triangular prismatic Ta coordination about the P atoms and the dense packing of the Ta atoms, both familiar in many metal-rich phases formed between transition metals and non-metals of type P, As, S and Se.