Crystal Structure and a Giant Magnetoresistance Effect in the New Zintl Compound Eu3Ga2P4

Electron-deficient copper pnictides: A2Mg3Cu9Pn7 (A = Sr, Eu; Pn = P, As) and Eu5Mg2.39Cu16.61As12

Five pnictide Zintl compounds, A₂Mg₃Cu₉Pn₇ (A = Sr, Eu; Pn = P, As) and Eu₅Mg_2.39Cu_16.61As₁₂, were synthesized from the Pb-flux reactions. The anion structures of these compounds can be described as being composed of edge- or corner-sharing CuPn₄ tetrahedra, which construct complex 3D frameworks with cations filled into the cavities.

Eu3Ir2In15: A Mixed-Valent and Vacancy-Filled Variant of the Sc5Co4Si10 Structure Type with Anomalous Magnetic Properties

A new compound, Eu3Ir2In15, has been synthesized using indium as an active metal flux. The compound crystallizes in the tetragonal P4/mbm space group with lattice parameters a = 14.8580(4) Å, b = 14.8580(4) Å, and c = 4.3901(2) Å. It was further characterized by SEM-EDX studies. The effective magnetic moment (μeff) of this compound is 7.35 μB/Eu ion with a paramagnetic Curie temperature (θp) of -28 K, suggesting antiferromagnetic interaction. The mixed-valent nature of Eu observed in magnetic measurements was confirmed by XANES measurements. The compound undergoes demagnetization at a low magnetic field (10 Oe), which is quite unusual for Eu-based intermetallic compounds. Temperature-dependent resistivity studies reveal that the compound is metallic in nature. A comparative study was made between Eu3Ir2In15 and hypothetical vacancy-variant Eu5Ir4In10, which also crystallizes in the same crystal structure. However, our computational studies along with control experiments suggest that the latter is thermodynamically less feasible compared to the former, and hence we propose that it is highly unlikely that an RE5T4X10 would exist with X as a group 13 element.

Phase characterization, thermal stability, high-temperature transport properties, and electronic structure of rare-earth Zintl phosphides Eu3M2P4 (M = Ga, In)

Two rare-earth-containing ternary phosphides, Eu3Ga2P4 and Eu3In2P4, were synthesized by a two-step solid-state method with stoichiometric amounts of the constitutional elements. Refinements of the powder X-ray diffraction are consistent with the reported single-crystal structure with space group C2/c for Eu3Ga2P4 and Pnnm for Eu3In2P4. Thermal gravimetry and differential scanning calorimetry (TG-DSC) measurements reveal high thermal stability up to 1273 K. Thermal diffusivity measurements from room temperature to 800 K demonstrate thermal conductivity as low as 0.6 W/m·K for both compounds. Seebeck coefficient measurements from room temperature to 800 K indicate that both compounds are small band gap semiconductors. Eu3Ga2P4 shows p-type conductivity and Eu3In2P4 p-type conductivity in the temperature range 300-700 K and n-type conductivity above 700 K. Electronic structure calculations result in band gaps of 0.60 and 0.29 eV for Eu3Ga2P4 and Eu3In2P4, respectively. As expected for a valence precise Zintl phase, electrical resistivity is large, approximately 2600 and 560 mΩ·cm for Eu3Ga2P4 and Eu3In2P4 at room temperature, respectively. Measurements of transport properties suggest that these Zintl phosphides have potential for being good high-temperature thermoelectric materials with optimization of the charge carrier concentration by appropriate extrinsic dopants.