Haiying Bie

Structure and magnetic properties of hexagonal perovskite-type rare-earth vanadium germanides REVGe3 (RE = La–Nd)

The ternary rare-earth vanadium germanides REVGe3 (RE = La–Nd) have been synthesized by arc-melting and annealing at 800 °C for 3 weeks. Their crystal structures were determined by powder X-ray diffraction and refined by the Rietveld method. The hexagonal cell parameters are a = 6.2587(3)–6.2145(2) A and c = 5.6992(3)–5.6403(2) A in the progression from LaVGe3 to NdVGe3. Like the previously known chromium-containing series RECrGe3, they adopt a hexagonal perovskite-type structure, in which chains of face-sharing VGe6 octahedra are connected by triangular Ge3 clusters. Except for Pauli paramagnetic LaVGe3, magnetic measurements revealed weak antiferromagnetic ordering at low temperatures (TN = 4–15 K) for the other RE members, in contrast to the ferromagnetic ordering found earlier in RECrGe3. An investigation of the solid solutions LaV1−xCrxGe3 (0 ≤ x ≤ 1) and LaCr1−xMnxGe3 (0 ≤ x ≤ 0.2) revealed that addition of V or Mn into LaCrGe3 tends to suppress the ferromagnetic ordering.

Ternary Rare-Earth Titanium Antimonides RE2Ti11-xSb14+x [RE = Sm, Gd, Tb, Yb)

The isostructural rare-earth titanium antimonides RE 2Ti 11 - x Sb 14 + x ( RE = Sm, Gd, Tb, Yb) have been synthesized by arc-melting reactions of the elements. Single-crystal X-ray diffraction revealed that they adopt a new structure type (Pearson symbol oP54, space group Pnma, Z = 2; a = 15.8865(6)-15.9529(9) A, b = 5.7164(2)-5.7135(3) A, c = 12.9244(5)-12.9442(7) A for RE = Sm-Yb). The structure consists of titanium-centered octahedra (CN6) and pentagonal bipyramids (CN7) connected to form a 3D framework whose cavities are filled with RE atoms. 1D linear skewers of titanium atoms, within face-sharing octahedral chains, and similar skewers of antimony atoms, associated with the titanium-centered pentagonal bipyramids, extend along the b direction. On proceeding from Sm 2Ti 11Sb 14 to Tb 2Ti 10.41(1)Sb 14.59(1) and Yb 2Ti 10.58(1)Sb 14.42(1), antimony atoms are disordered within some of the titanium sites. Resistivity measurements on the samarium and ytterbium members indicated metallic behavior.

Ge Pairs and Sb Ribbons in Rare-Earth Germanium Antimonides RE12Ge7−xSb21 (RE=La–Pr)

The ternary rare-earth germanium antimonides RE(12)Ge(7-x)Sb(21) (RE = La-Pr; x = 0.4-0.5) are synthesized by direct reactions of the elements. Single-crystal X-ray diffraction studies indicate that they adopt a new structure type (space group Immm, Z = 2, a = 4.3165(4)-4.2578(2) A, b = 15.2050(12)-14.9777(7) A, c = 34.443(3)-33.9376(16) A in the progression from RE = La to Pr), integrating complex features found in RE(6)Ge(5-x)Sb(11+x) and RE(12)Ga(4)Sb(23). A three-dimensional polyanionic framework, consisting of Ge pairs and Sb ribbons, outlines large channels occupied by columns of face-sharing RE(6) trigonal prisms. These trigonal prisms are centered by additional Ge and Sb atoms to form GeSb(3) trigonal-planar units. A bonding analysis attempted through a Zintl-Klemm approach suggests that full electron transfer from the RE atoms to the anionic substructure cannot be assumed. This is confirmed by band-structure calculations, which also reveal the importance of Ge-Sb and Sb-Sb bonding. Magnetic measurements on Ce(12)Ge(6.5)Sb(21) indicate antiferromagnetic coupling but no long-range ordering down to 2 K.