New phases in the thorium-iron-tin system: ThFe0.22Sn2 and Th4Fe13Sn5

The structures of two new phases were determined by single crystal diffractometric data. The phase ThFe0.22(2)Sn-2, orthorhombic, space group Cmcm (No. 63), Pearson symbol oS16-3.12, a = 4.479(1), b = 17.045(3), c = 4.430(1) Angstrom, V = 338.2(1) Angstrom(3), Z = 4, R = 0.038 for 260 reflections with F-0>4 sigma F-0) has a defective structure derived from the CeNiSi2 type. The phase Th4Fe13Sn5, tetragonal, space group P4/mbm (No. 127), Pearson symbol tP44, a = 8.290(1), c = 11.946(1) Angstrom, V = 821.0(2) Angstrom(3), Z = 2, R = 0.061 for 760 reflections with F-0>4 sigma(F-0) shows a structure of a new type, formed by two segments which alternate along the c-axis. One segment shows an atomic arrangement very similar to that of the Ce(Mn,Ni)(11) structure, while the other corresponds to a half-cell of the Cr5B3 type. Slabs of centered icosahedra containing only iron atoms are a characteristic feature of this structure, common also, besides the cited Ce(Mn,Ni)(11), to the Ce2Ni17Si9 and Nd6Fe13Si (or La6Co11Ga3) structures. For the phase Th4Fe13Sn5 a transition to the ferromagnetic state at 375 K was observed by differential scanning calorimetry, electrical and magnetic measurements.