Planar versus Puckered Nets in the Polar Intermetallic Series EuGaTt (Tt = Si, Ge, Sn)

Crystal Structure and Magnetism of Noncentrosymmetric Eu2Pd2Sn

The new intermetallic compound Eu₂Pd₂Sn has been investigated. A single crystal was selected from the alloy and was analyzed by single-crystal X-ray diffraction, revealing that this compound possesses the noncentrosymmetric Ca₂Pd₂Ge structure type being, so far, the only rare-earth-based representative. Bonding analysis, performed on the basis of DOS and (I)COHP, reveals the presence of strong covalent Sn–Pd bonds in addition to linear and equidistant Pd–Pd chains. The incomplete ionization of Eu leads to its participation in weaker covalent interactions. The magnetic effective moment, extracted from the magnetic susceptibility χ(T) is μ_eff = 7.87 μ_B, close to the free ion Eu²⁺ value (μ_eff = 7.94 μ_B). The maximum of χ(T) at T_N ∼ 13 K indicates an antiferromagnetic behavior below this temperature. A coincident sharp anomaly in the specific heat C_P(T) emerges from a broad anomaly centered at around 10 K. From the reduced jump in the heat capacity at T_N a scenario of a transition to an incommensurate antiferromagnetic phase below T_N followed by a commensurate configuration below 10 K is suggested.

A new intermetallic compound, Eu₂Pd₂Sn, is so far the only rare-earth representative of the Ca₂Pd₂Ge structure type. Synthesis and characterization of the structure, together with magnetic properties, are discussed.

Endohedral Cluster Superconductors in the Mo-Ga-Sn System Explored by the Joint Flux Technique

Endohedral Ga cluster compounds feature nontrivial superconducting states including the two-gap superconductivity similar in nature to MgB₂. We use the joint flux synthetic technique to introduce Sn into the Ga matrix and tune the valence electron count in the two new endohedral cluster superconductors Mo₈Ga_41-xSn_x and Mo₄Ga_21-x-δSn_x with critical temperatures of T_c = 8.7 and 5.85 K, respectively. While the former compound is a derivative of the previously known Mo₈Ga₄₁ superconductor, where Sn atoms are enclosed inside the Sn@Ga₆ octahedral clusters, the latter is a new architecture built upon Mo@Ga₉Sn clusters, Ga@Ga₁₂ cuboctahedra, and Sn₄ squares. We show that this novel Mo₄Ga_21-x-δSn_x superconductor features strong electron-phonon coupling with the large ratio of 2Δ(0)/(k_BT_c) = 4.1 similar to that of the Mo₈Ga₄₁ superconductor with the closely related crystal structure.

Zinc-lead ordering in equiatomic rare earth plumbides REZnPb (RE=La–Nd and Sm–Tb)

The plumbides REZnPb (RE=rare earth metals La–Nd and Sm–Tb) were synthesized by induction melting of the elements in sealed niobium ampoules. The samples were characterized by X-ray powder diffraction. The structures of the praseodymium and neodymium compound were refined from single-crystal X-ray diffractometer data: YPtAs type, P63/mmc, a=461.32(8), c=1658.00(3) pm, wR2=0.0588, 267 F 2 values, 12 variables for PrZnPb and a=460.12(3), c=1642.7(1), wR2=0.0617, 243 F 2 values, 12 variables for NdZnPb. The plumbides with RE=La, Ce, Sm, Gd and Tb are isotypic while the Zintl phase EuZnPb crystallizes with the orthorhombic TiNiSi type, Pnma, a=796.6(2), b=482.53(9), c=822.9(2) pm. The zinc and lead atoms build up polyanionic networks: slightly puckered Zn3Pb3 layers in AA′BB′ stacking sequence in the YPtAs type plumbides and a three-dimensional [ZnPb]2− network with distorted tetrahedral ZnPb4/4 coordination in EuZnSn. The different crystal structures are a consequence of the valence electron count, i.e. 18 for EuZnSn and 19 for the hexagonal plumbides. The crystal chemical details and bonding peculiarities are discussed.

Atomic Ordering of Two Neighboring Transition Metals-Cu and Zn from Binary CuZn to Ternary Cu3ZnSb

A new ternary compound Cu₃ZnSb was synthesized by high temperature solid state synthesis and characterized by single crystal X-ray diffraction and energy dispersive X-ray analysis. The ternary Cu₃ZnSb crystallizes in the tetragonal crystal system with the space group P4/ nmm (129), and its unit cell contains 10 atoms which are distributed over 4 independent crystallographic positions. The structure is built up with [Cu₃Sb] slabs that correspond to the unit cells of Cu₂Sb and planar 4⁴ nets of Zn atoms. The planar nets of Zn atoms are interspersed between two adjacent [Cu₃Sb] slabs. The structure can be viewed as alternating units of Cu₂Sb and CsCl type β'-brass (CuZn) structures in the [001]. An unusual atomic ordering of two neighboring transition metals Cu and Zn is observed and is confirmed by first principle calculations. The atomic ordering of Cu and Zn is retained from binary β'-brass structure (CuZn) to ternary Cu₃ZnSb. Total energy calculations confirmed the experimental model of Cu/Zn ordering to be the most stable in the structure of Cu₃ZnSb. The calculated density of states (DOS) and crystal orbital Hamiltonian population (COHP) explain the stability and bonding characteristics in the structure of Cu₃ZnSb. The implication of the persistent Cu/Zn ordering in ternary phases for materials design is emphasized.

EuSn2As2: an exfoliatable magnetic layered Zintl–Klemm phase

We synthesize EuSn₂As₂, the first exfoliatable layered magnetic Zintl–Klemm phase that features van der Waals bonding between neighboring layers.