High‐pressure High‐temperature Synthesis, Magnetic Properties and X‐ray Absorption Spectroscopy of Phases RE 3 Sn 7 and hp‐ RE Sn 3– x ( RE = Tb, Ho, Er)

The high‐temperature high‐pressure syntheses of binary phases hp‐ RE Sn 3– x ( RE = Tb, Ho, Er) was reinvestigated showing good agreement with previously determined stability fields concerning pressure and temperature conditions. Phases hp‐ RE Sn 3– x adopt a cubic Cu 3 Au arrangement ( a = 466.52(6) pm for hp‐TbSn 3– x ; a = 465.44(8) pm for hp‐HoSn 3– x and a = 464.98(9) pm for hp‐ErSn 3– x ). Superstructure reflections observed in experiments with synchrotron radiation indicate an ordered arrangement for HoSn 3– x prepared at 8.4(8) GPa and 1270 K (space group Pm $\bar3$ m ). hp‐HoSn 3– x transforms exothermally at 460 K and ambient pressure into the low‐pressure modification HoSn 3– x indicating that the ordered Cu 3 Au‐type arrangement is a metastable high‐pressure phase., A second set of phases is identified as compounds RE 3 Sn 7 ( RE = Ho, Er) being isotypic to the ambient pressure modifications Gd 3 Sn 7 and Tb 3 Sn 7 (space group Cmmm ; lattice parameters a = 434.95(7) pm, b = 2615.6(6) pm, c = 442.09(7) pm for Ho 3 Sn 7 and a = 434.29(5) pm, b = 2607.2(4) pm, c = 441.49(5) pm) for Er 3 Sn 7 ). The crystal structure of compounds RE 3 Sn 7 is interpreted as an intergrowth of AlB 2 ‐, CaF 2 ‐ and AuCu 3 ‐like segments. Analysis of the chemical bonding in Er 3 Sn 7 by means of the electron localizability approach reveals two‐center Sn–Sn bonding in the AlB 2 ‐like segment and multi‐center bonding in the AuCu 3 ‐ and CaF 2 ‐like motifs., The electrical resistivity of ρ ≈ 31 μΩ cm at 300 K reveals that hp‐HoSn 3– x is a metallic conductor. The phases hp‐ RE Sn 3– x and RE 3 Sn 7 ( RE = Ho, Er) show paramagnetic Curie–Weiss behavior of the rare earth metal ions Ho 3+ and Er 3+ , respectively. Ho 3 Sn 7 and Er 3 Sn 7 order antiferromagnetically at 10.0 K and 8.2 K, respectively. The high‐pressure phases RE Sn 3– x show no magnetic order above 2 K. XAS measurements on the compounds Tb 3 Sn 7 and hp‐TbSn 3– x indicate a 4 f 8 configuration evidencing the oxidation state +3 for terbium.