Ternary rare-earth titanium antimonides: Phase equilibria in the RE–Ti–Sb (RE=La, Er) systems and crystal structures of RE2Ti7Sb12 (RE=La, Ce, Pr, Nd) and RETi3(SnxSb1–x)4 (RE=Nd, Sm)

Investigations on phase relationships and crystal structures have been conducted on several ternary rare-earth titanium antimonide systems. The isothermal cross-sections of the ternary RE–Ti–Sb systems containing a representative early (RE=La) and late rare-earth element (RE=Er) have been constructed at 800 °C. In the La–Ti–Sb system, the previously known compound La3TiSb5 was confirmed and the new compound La2Ti7Sb12 (own type, Cmmm, Z=2, a=10.5446(10) Å, b=20.768(2) Å, and c=4.4344(4) Å) was discovered. In the Er–Ti–Sb system, no ternary compounds were found. The structure of La2Ti7Sb12 consists of a complex arrangement of TiSb6 octahedra and disordered fragments of homoatomic Sb assemblies, generating a three-dimensional framework in which La atoms reside. Other early rare-earth elements (RE=Ce, Pr, Nd) can be substituted in this structure type. Attempts to prepare crystals in these systems through use of a tin flux resulted in the discovery of a new Sn-containing pseudoternary phase RETi3(SnxSb1−x)4 for RE=Nd, Sm (own type, Fmmm, Z=8; a=5.7806(4) Å, b=10.0846(7) Å, and c=24.2260(16) Å for NdTi3(Sn0.1Sb0.9)4; a=5.7590(4) Å, b=10.0686(6) Å, and c=24.1167(14) Å for SmTi3(Sn0.1Sb0.9)4). Its structure consists of double-layer slabs of Ti-centred octahedra stacked alternately with nets of the RE atoms; the Ti atoms are arranged in kagome nets.